[TCP]: Merge exit paths in tcp_v4_conn_request.
[linux-2.6] / net / ipv4 / tcp_input.c
1 /*
2  * INET         An implementation of the TCP/IP protocol suite for the LINUX
3  *              operating system.  INET is implemented using the  BSD Socket
4  *              interface as the means of communication with the user level.
5  *
6  *              Implementation of the Transmission Control Protocol(TCP).
7  *
8  * Version:     $Id: tcp_input.c,v 1.243 2002/02/01 22:01:04 davem Exp $
9  *
10  * Authors:     Ross Biro
11  *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
12  *              Mark Evans, <evansmp@uhura.aston.ac.uk>
13  *              Corey Minyard <wf-rch!minyard@relay.EU.net>
14  *              Florian La Roche, <flla@stud.uni-sb.de>
15  *              Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
16  *              Linus Torvalds, <torvalds@cs.helsinki.fi>
17  *              Alan Cox, <gw4pts@gw4pts.ampr.org>
18  *              Matthew Dillon, <dillon@apollo.west.oic.com>
19  *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
20  *              Jorge Cwik, <jorge@laser.satlink.net>
21  */
22
23 /*
24  * Changes:
25  *              Pedro Roque     :       Fast Retransmit/Recovery.
26  *                                      Two receive queues.
27  *                                      Retransmit queue handled by TCP.
28  *                                      Better retransmit timer handling.
29  *                                      New congestion avoidance.
30  *                                      Header prediction.
31  *                                      Variable renaming.
32  *
33  *              Eric            :       Fast Retransmit.
34  *              Randy Scott     :       MSS option defines.
35  *              Eric Schenk     :       Fixes to slow start algorithm.
36  *              Eric Schenk     :       Yet another double ACK bug.
37  *              Eric Schenk     :       Delayed ACK bug fixes.
38  *              Eric Schenk     :       Floyd style fast retrans war avoidance.
39  *              David S. Miller :       Don't allow zero congestion window.
40  *              Eric Schenk     :       Fix retransmitter so that it sends
41  *                                      next packet on ack of previous packet.
42  *              Andi Kleen      :       Moved open_request checking here
43  *                                      and process RSTs for open_requests.
44  *              Andi Kleen      :       Better prune_queue, and other fixes.
45  *              Andrey Savochkin:       Fix RTT measurements in the presence of
46  *                                      timestamps.
47  *              Andrey Savochkin:       Check sequence numbers correctly when
48  *                                      removing SACKs due to in sequence incoming
49  *                                      data segments.
50  *              Andi Kleen:             Make sure we never ack data there is not
51  *                                      enough room for. Also make this condition
52  *                                      a fatal error if it might still happen.
53  *              Andi Kleen:             Add tcp_measure_rcv_mss to make
54  *                                      connections with MSS<min(MTU,ann. MSS)
55  *                                      work without delayed acks.
56  *              Andi Kleen:             Process packets with PSH set in the
57  *                                      fast path.
58  *              J Hadi Salim:           ECN support
59  *              Andrei Gurtov,
60  *              Pasi Sarolahti,
61  *              Panu Kuhlberg:          Experimental audit of TCP (re)transmission
62  *                                      engine. Lots of bugs are found.
63  *              Pasi Sarolahti:         F-RTO for dealing with spurious RTOs
64  */
65
66 #include <linux/mm.h>
67 #include <linux/module.h>
68 #include <linux/sysctl.h>
69 #include <net/tcp.h>
70 #include <net/inet_common.h>
71 #include <linux/ipsec.h>
72 #include <asm/unaligned.h>
73 #include <net/netdma.h>
74
75 int sysctl_tcp_timestamps __read_mostly = 1;
76 int sysctl_tcp_window_scaling __read_mostly = 1;
77 int sysctl_tcp_sack __read_mostly = 1;
78 int sysctl_tcp_fack __read_mostly = 1;
79 int sysctl_tcp_reordering __read_mostly = TCP_FASTRETRANS_THRESH;
80 int sysctl_tcp_ecn __read_mostly;
81 int sysctl_tcp_dsack __read_mostly = 1;
82 int sysctl_tcp_app_win __read_mostly = 31;
83 int sysctl_tcp_adv_win_scale __read_mostly = 2;
84
85 int sysctl_tcp_stdurg __read_mostly;
86 int sysctl_tcp_rfc1337 __read_mostly;
87 int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
88 int sysctl_tcp_frto __read_mostly = 2;
89 int sysctl_tcp_frto_response __read_mostly;
90 int sysctl_tcp_nometrics_save __read_mostly;
91
92 int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
93 int sysctl_tcp_abc __read_mostly;
94
95 #define FLAG_DATA               0x01 /* Incoming frame contained data.          */
96 #define FLAG_WIN_UPDATE         0x02 /* Incoming ACK was a window update.       */
97 #define FLAG_DATA_ACKED         0x04 /* This ACK acknowledged new data.         */
98 #define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted.  */
99 #define FLAG_SYN_ACKED          0x10 /* This ACK acknowledged SYN.              */
100 #define FLAG_DATA_SACKED        0x20 /* New SACK.                               */
101 #define FLAG_ECE                0x40 /* ECE in this ACK                         */
102 #define FLAG_DATA_LOST          0x80 /* SACK detected data lossage.             */
103 #define FLAG_SLOWPATH           0x100 /* Do not skip RFC checks for window update.*/
104 #define FLAG_ONLY_ORIG_SACKED   0x200 /* SACKs only non-rexmit sent before RTO */
105 #define FLAG_SND_UNA_ADVANCED   0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
106 #define FLAG_DSACKING_ACK       0x800 /* SACK blocks contained D-SACK info */
107 #define FLAG_NONHEAD_RETRANS_ACKED      0x1000 /* Non-head rexmitted data was ACKed */
108 #define FLAG_SACK_RENEGING      0x2000 /* snd_una advanced to a sacked seq */
109
110 #define FLAG_ACKED              (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
111 #define FLAG_NOT_DUP            (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
112 #define FLAG_CA_ALERT           (FLAG_DATA_SACKED|FLAG_ECE)
113 #define FLAG_FORWARD_PROGRESS   (FLAG_ACKED|FLAG_DATA_SACKED)
114 #define FLAG_ANY_PROGRESS       (FLAG_FORWARD_PROGRESS|FLAG_SND_UNA_ADVANCED)
115
116 #define IsSackFrto() (sysctl_tcp_frto == 0x2)
117
118 #define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
119 #define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
120
121 /* Adapt the MSS value used to make delayed ack decision to the
122  * real world.
123  */
124 static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
125 {
126         struct inet_connection_sock *icsk = inet_csk(sk);
127         const unsigned int lss = icsk->icsk_ack.last_seg_size;
128         unsigned int len;
129
130         icsk->icsk_ack.last_seg_size = 0;
131
132         /* skb->len may jitter because of SACKs, even if peer
133          * sends good full-sized frames.
134          */
135         len = skb_shinfo(skb)->gso_size ? : skb->len;
136         if (len >= icsk->icsk_ack.rcv_mss) {
137                 icsk->icsk_ack.rcv_mss = len;
138         } else {
139                 /* Otherwise, we make more careful check taking into account,
140                  * that SACKs block is variable.
141                  *
142                  * "len" is invariant segment length, including TCP header.
143                  */
144                 len += skb->data - skb_transport_header(skb);
145                 if (len >= TCP_MIN_RCVMSS + sizeof(struct tcphdr) ||
146                     /* If PSH is not set, packet should be
147                      * full sized, provided peer TCP is not badly broken.
148                      * This observation (if it is correct 8)) allows
149                      * to handle super-low mtu links fairly.
150                      */
151                     (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
152                      !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
153                         /* Subtract also invariant (if peer is RFC compliant),
154                          * tcp header plus fixed timestamp option length.
155                          * Resulting "len" is MSS free of SACK jitter.
156                          */
157                         len -= tcp_sk(sk)->tcp_header_len;
158                         icsk->icsk_ack.last_seg_size = len;
159                         if (len == lss) {
160                                 icsk->icsk_ack.rcv_mss = len;
161                                 return;
162                         }
163                 }
164                 if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
165                         icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
166                 icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
167         }
168 }
169
170 static void tcp_incr_quickack(struct sock *sk)
171 {
172         struct inet_connection_sock *icsk = inet_csk(sk);
173         unsigned quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
174
175         if (quickacks == 0)
176                 quickacks = 2;
177         if (quickacks > icsk->icsk_ack.quick)
178                 icsk->icsk_ack.quick = min(quickacks, TCP_MAX_QUICKACKS);
179 }
180
181 void tcp_enter_quickack_mode(struct sock *sk)
182 {
183         struct inet_connection_sock *icsk = inet_csk(sk);
184         tcp_incr_quickack(sk);
185         icsk->icsk_ack.pingpong = 0;
186         icsk->icsk_ack.ato = TCP_ATO_MIN;
187 }
188
189 /* Send ACKs quickly, if "quick" count is not exhausted
190  * and the session is not interactive.
191  */
192
193 static inline int tcp_in_quickack_mode(const struct sock *sk)
194 {
195         const struct inet_connection_sock *icsk = inet_csk(sk);
196         return icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong;
197 }
198
199 static inline void TCP_ECN_queue_cwr(struct tcp_sock *tp)
200 {
201         if (tp->ecn_flags & TCP_ECN_OK)
202                 tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
203 }
204
205 static inline void TCP_ECN_accept_cwr(struct tcp_sock *tp, struct sk_buff *skb)
206 {
207         if (tcp_hdr(skb)->cwr)
208                 tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
209 }
210
211 static inline void TCP_ECN_withdraw_cwr(struct tcp_sock *tp)
212 {
213         tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
214 }
215
216 static inline void TCP_ECN_check_ce(struct tcp_sock *tp, struct sk_buff *skb)
217 {
218         if (tp->ecn_flags & TCP_ECN_OK) {
219                 if (INET_ECN_is_ce(TCP_SKB_CB(skb)->flags))
220                         tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
221                 /* Funny extension: if ECT is not set on a segment,
222                  * it is surely retransmit. It is not in ECN RFC,
223                  * but Linux follows this rule. */
224                 else if (INET_ECN_is_not_ect((TCP_SKB_CB(skb)->flags)))
225                         tcp_enter_quickack_mode((struct sock *)tp);
226         }
227 }
228
229 static inline void TCP_ECN_rcv_synack(struct tcp_sock *tp, struct tcphdr *th)
230 {
231         if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr))
232                 tp->ecn_flags &= ~TCP_ECN_OK;
233 }
234
235 static inline void TCP_ECN_rcv_syn(struct tcp_sock *tp, struct tcphdr *th)
236 {
237         if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr))
238                 tp->ecn_flags &= ~TCP_ECN_OK;
239 }
240
241 static inline int TCP_ECN_rcv_ecn_echo(struct tcp_sock *tp, struct tcphdr *th)
242 {
243         if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK))
244                 return 1;
245         return 0;
246 }
247
248 /* Buffer size and advertised window tuning.
249  *
250  * 1. Tuning sk->sk_sndbuf, when connection enters established state.
251  */
252
253 static void tcp_fixup_sndbuf(struct sock *sk)
254 {
255         int sndmem = tcp_sk(sk)->rx_opt.mss_clamp + MAX_TCP_HEADER + 16 +
256                      sizeof(struct sk_buff);
257
258         if (sk->sk_sndbuf < 3 * sndmem)
259                 sk->sk_sndbuf = min(3 * sndmem, sysctl_tcp_wmem[2]);
260 }
261
262 /* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
263  *
264  * All tcp_full_space() is split to two parts: "network" buffer, allocated
265  * forward and advertised in receiver window (tp->rcv_wnd) and
266  * "application buffer", required to isolate scheduling/application
267  * latencies from network.
268  * window_clamp is maximal advertised window. It can be less than
269  * tcp_full_space(), in this case tcp_full_space() - window_clamp
270  * is reserved for "application" buffer. The less window_clamp is
271  * the smoother our behaviour from viewpoint of network, but the lower
272  * throughput and the higher sensitivity of the connection to losses. 8)
273  *
274  * rcv_ssthresh is more strict window_clamp used at "slow start"
275  * phase to predict further behaviour of this connection.
276  * It is used for two goals:
277  * - to enforce header prediction at sender, even when application
278  *   requires some significant "application buffer". It is check #1.
279  * - to prevent pruning of receive queue because of misprediction
280  *   of receiver window. Check #2.
281  *
282  * The scheme does not work when sender sends good segments opening
283  * window and then starts to feed us spaghetti. But it should work
284  * in common situations. Otherwise, we have to rely on queue collapsing.
285  */
286
287 /* Slow part of check#2. */
288 static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb)
289 {
290         struct tcp_sock *tp = tcp_sk(sk);
291         /* Optimize this! */
292         int truesize = tcp_win_from_space(skb->truesize) >> 1;
293         int window = tcp_win_from_space(sysctl_tcp_rmem[2]) >> 1;
294
295         while (tp->rcv_ssthresh <= window) {
296                 if (truesize <= skb->len)
297                         return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
298
299                 truesize >>= 1;
300                 window >>= 1;
301         }
302         return 0;
303 }
304
305 static void tcp_grow_window(struct sock *sk, struct sk_buff *skb)
306 {
307         struct tcp_sock *tp = tcp_sk(sk);
308
309         /* Check #1 */
310         if (tp->rcv_ssthresh < tp->window_clamp &&
311             (int)tp->rcv_ssthresh < tcp_space(sk) &&
312             !tcp_memory_pressure) {
313                 int incr;
314
315                 /* Check #2. Increase window, if skb with such overhead
316                  * will fit to rcvbuf in future.
317                  */
318                 if (tcp_win_from_space(skb->truesize) <= skb->len)
319                         incr = 2 * tp->advmss;
320                 else
321                         incr = __tcp_grow_window(sk, skb);
322
323                 if (incr) {
324                         tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr,
325                                                tp->window_clamp);
326                         inet_csk(sk)->icsk_ack.quick |= 1;
327                 }
328         }
329 }
330
331 /* 3. Tuning rcvbuf, when connection enters established state. */
332
333 static void tcp_fixup_rcvbuf(struct sock *sk)
334 {
335         struct tcp_sock *tp = tcp_sk(sk);
336         int rcvmem = tp->advmss + MAX_TCP_HEADER + 16 + sizeof(struct sk_buff);
337
338         /* Try to select rcvbuf so that 4 mss-sized segments
339          * will fit to window and corresponding skbs will fit to our rcvbuf.
340          * (was 3; 4 is minimum to allow fast retransmit to work.)
341          */
342         while (tcp_win_from_space(rcvmem) < tp->advmss)
343                 rcvmem += 128;
344         if (sk->sk_rcvbuf < 4 * rcvmem)
345                 sk->sk_rcvbuf = min(4 * rcvmem, sysctl_tcp_rmem[2]);
346 }
347
348 /* 4. Try to fixup all. It is made immediately after connection enters
349  *    established state.
350  */
351 static void tcp_init_buffer_space(struct sock *sk)
352 {
353         struct tcp_sock *tp = tcp_sk(sk);
354         int maxwin;
355
356         if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
357                 tcp_fixup_rcvbuf(sk);
358         if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
359                 tcp_fixup_sndbuf(sk);
360
361         tp->rcvq_space.space = tp->rcv_wnd;
362
363         maxwin = tcp_full_space(sk);
364
365         if (tp->window_clamp >= maxwin) {
366                 tp->window_clamp = maxwin;
367
368                 if (sysctl_tcp_app_win && maxwin > 4 * tp->advmss)
369                         tp->window_clamp = max(maxwin -
370                                                (maxwin >> sysctl_tcp_app_win),
371                                                4 * tp->advmss);
372         }
373
374         /* Force reservation of one segment. */
375         if (sysctl_tcp_app_win &&
376             tp->window_clamp > 2 * tp->advmss &&
377             tp->window_clamp + tp->advmss > maxwin)
378                 tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
379
380         tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
381         tp->snd_cwnd_stamp = tcp_time_stamp;
382 }
383
384 /* 5. Recalculate window clamp after socket hit its memory bounds. */
385 static void tcp_clamp_window(struct sock *sk)
386 {
387         struct tcp_sock *tp = tcp_sk(sk);
388         struct inet_connection_sock *icsk = inet_csk(sk);
389
390         icsk->icsk_ack.quick = 0;
391
392         if (sk->sk_rcvbuf < sysctl_tcp_rmem[2] &&
393             !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
394             !tcp_memory_pressure &&
395             atomic_read(&tcp_memory_allocated) < sysctl_tcp_mem[0]) {
396                 sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
397                                     sysctl_tcp_rmem[2]);
398         }
399         if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
400                 tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss);
401 }
402
403 /* Initialize RCV_MSS value.
404  * RCV_MSS is an our guess about MSS used by the peer.
405  * We haven't any direct information about the MSS.
406  * It's better to underestimate the RCV_MSS rather than overestimate.
407  * Overestimations make us ACKing less frequently than needed.
408  * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
409  */
410 void tcp_initialize_rcv_mss(struct sock *sk)
411 {
412         struct tcp_sock *tp = tcp_sk(sk);
413         unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
414
415         hint = min(hint, tp->rcv_wnd / 2);
416         hint = min(hint, TCP_MIN_RCVMSS);
417         hint = max(hint, TCP_MIN_MSS);
418
419         inet_csk(sk)->icsk_ack.rcv_mss = hint;
420 }
421
422 /* Receiver "autotuning" code.
423  *
424  * The algorithm for RTT estimation w/o timestamps is based on
425  * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
426  * <http://www.lanl.gov/radiant/website/pubs/drs/lacsi2001.ps>
427  *
428  * More detail on this code can be found at
429  * <http://www.psc.edu/~jheffner/senior_thesis.ps>,
430  * though this reference is out of date.  A new paper
431  * is pending.
432  */
433 static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
434 {
435         u32 new_sample = tp->rcv_rtt_est.rtt;
436         long m = sample;
437
438         if (m == 0)
439                 m = 1;
440
441         if (new_sample != 0) {
442                 /* If we sample in larger samples in the non-timestamp
443                  * case, we could grossly overestimate the RTT especially
444                  * with chatty applications or bulk transfer apps which
445                  * are stalled on filesystem I/O.
446                  *
447                  * Also, since we are only going for a minimum in the
448                  * non-timestamp case, we do not smooth things out
449                  * else with timestamps disabled convergence takes too
450                  * long.
451                  */
452                 if (!win_dep) {
453                         m -= (new_sample >> 3);
454                         new_sample += m;
455                 } else if (m < new_sample)
456                         new_sample = m << 3;
457         } else {
458                 /* No previous measure. */
459                 new_sample = m << 3;
460         }
461
462         if (tp->rcv_rtt_est.rtt != new_sample)
463                 tp->rcv_rtt_est.rtt = new_sample;
464 }
465
466 static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
467 {
468         if (tp->rcv_rtt_est.time == 0)
469                 goto new_measure;
470         if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
471                 return;
472         tcp_rcv_rtt_update(tp, jiffies - tp->rcv_rtt_est.time, 1);
473
474 new_measure:
475         tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
476         tp->rcv_rtt_est.time = tcp_time_stamp;
477 }
478
479 static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
480                                           const struct sk_buff *skb)
481 {
482         struct tcp_sock *tp = tcp_sk(sk);
483         if (tp->rx_opt.rcv_tsecr &&
484             (TCP_SKB_CB(skb)->end_seq -
485              TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss))
486                 tcp_rcv_rtt_update(tp, tcp_time_stamp - tp->rx_opt.rcv_tsecr, 0);
487 }
488
489 /*
490  * This function should be called every time data is copied to user space.
491  * It calculates the appropriate TCP receive buffer space.
492  */
493 void tcp_rcv_space_adjust(struct sock *sk)
494 {
495         struct tcp_sock *tp = tcp_sk(sk);
496         int time;
497         int space;
498
499         if (tp->rcvq_space.time == 0)
500                 goto new_measure;
501
502         time = tcp_time_stamp - tp->rcvq_space.time;
503         if (time < (tp->rcv_rtt_est.rtt >> 3) || tp->rcv_rtt_est.rtt == 0)
504                 return;
505
506         space = 2 * (tp->copied_seq - tp->rcvq_space.seq);
507
508         space = max(tp->rcvq_space.space, space);
509
510         if (tp->rcvq_space.space != space) {
511                 int rcvmem;
512
513                 tp->rcvq_space.space = space;
514
515                 if (sysctl_tcp_moderate_rcvbuf &&
516                     !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
517                         int new_clamp = space;
518
519                         /* Receive space grows, normalize in order to
520                          * take into account packet headers and sk_buff
521                          * structure overhead.
522                          */
523                         space /= tp->advmss;
524                         if (!space)
525                                 space = 1;
526                         rcvmem = (tp->advmss + MAX_TCP_HEADER +
527                                   16 + sizeof(struct sk_buff));
528                         while (tcp_win_from_space(rcvmem) < tp->advmss)
529                                 rcvmem += 128;
530                         space *= rcvmem;
531                         space = min(space, sysctl_tcp_rmem[2]);
532                         if (space > sk->sk_rcvbuf) {
533                                 sk->sk_rcvbuf = space;
534
535                                 /* Make the window clamp follow along.  */
536                                 tp->window_clamp = new_clamp;
537                         }
538                 }
539         }
540
541 new_measure:
542         tp->rcvq_space.seq = tp->copied_seq;
543         tp->rcvq_space.time = tcp_time_stamp;
544 }
545
546 /* There is something which you must keep in mind when you analyze the
547  * behavior of the tp->ato delayed ack timeout interval.  When a
548  * connection starts up, we want to ack as quickly as possible.  The
549  * problem is that "good" TCP's do slow start at the beginning of data
550  * transmission.  The means that until we send the first few ACK's the
551  * sender will sit on his end and only queue most of his data, because
552  * he can only send snd_cwnd unacked packets at any given time.  For
553  * each ACK we send, he increments snd_cwnd and transmits more of his
554  * queue.  -DaveM
555  */
556 static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
557 {
558         struct tcp_sock *tp = tcp_sk(sk);
559         struct inet_connection_sock *icsk = inet_csk(sk);
560         u32 now;
561
562         inet_csk_schedule_ack(sk);
563
564         tcp_measure_rcv_mss(sk, skb);
565
566         tcp_rcv_rtt_measure(tp);
567
568         now = tcp_time_stamp;
569
570         if (!icsk->icsk_ack.ato) {
571                 /* The _first_ data packet received, initialize
572                  * delayed ACK engine.
573                  */
574                 tcp_incr_quickack(sk);
575                 icsk->icsk_ack.ato = TCP_ATO_MIN;
576         } else {
577                 int m = now - icsk->icsk_ack.lrcvtime;
578
579                 if (m <= TCP_ATO_MIN / 2) {
580                         /* The fastest case is the first. */
581                         icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
582                 } else if (m < icsk->icsk_ack.ato) {
583                         icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
584                         if (icsk->icsk_ack.ato > icsk->icsk_rto)
585                                 icsk->icsk_ack.ato = icsk->icsk_rto;
586                 } else if (m > icsk->icsk_rto) {
587                         /* Too long gap. Apparently sender failed to
588                          * restart window, so that we send ACKs quickly.
589                          */
590                         tcp_incr_quickack(sk);
591                         sk_mem_reclaim(sk);
592                 }
593         }
594         icsk->icsk_ack.lrcvtime = now;
595
596         TCP_ECN_check_ce(tp, skb);
597
598         if (skb->len >= 128)
599                 tcp_grow_window(sk, skb);
600 }
601
602 static u32 tcp_rto_min(struct sock *sk)
603 {
604         struct dst_entry *dst = __sk_dst_get(sk);
605         u32 rto_min = TCP_RTO_MIN;
606
607         if (dst && dst_metric_locked(dst, RTAX_RTO_MIN))
608                 rto_min = dst->metrics[RTAX_RTO_MIN - 1];
609         return rto_min;
610 }
611
612 /* Called to compute a smoothed rtt estimate. The data fed to this
613  * routine either comes from timestamps, or from segments that were
614  * known _not_ to have been retransmitted [see Karn/Partridge
615  * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
616  * piece by Van Jacobson.
617  * NOTE: the next three routines used to be one big routine.
618  * To save cycles in the RFC 1323 implementation it was better to break
619  * it up into three procedures. -- erics
620  */
621 static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt)
622 {
623         struct tcp_sock *tp = tcp_sk(sk);
624         long m = mrtt; /* RTT */
625
626         /*      The following amusing code comes from Jacobson's
627          *      article in SIGCOMM '88.  Note that rtt and mdev
628          *      are scaled versions of rtt and mean deviation.
629          *      This is designed to be as fast as possible
630          *      m stands for "measurement".
631          *
632          *      On a 1990 paper the rto value is changed to:
633          *      RTO = rtt + 4 * mdev
634          *
635          * Funny. This algorithm seems to be very broken.
636          * These formulae increase RTO, when it should be decreased, increase
637          * too slowly, when it should be increased quickly, decrease too quickly
638          * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
639          * does not matter how to _calculate_ it. Seems, it was trap
640          * that VJ failed to avoid. 8)
641          */
642         if (m == 0)
643                 m = 1;
644         if (tp->srtt != 0) {
645                 m -= (tp->srtt >> 3);   /* m is now error in rtt est */
646                 tp->srtt += m;          /* rtt = 7/8 rtt + 1/8 new */
647                 if (m < 0) {
648                         m = -m;         /* m is now abs(error) */
649                         m -= (tp->mdev >> 2);   /* similar update on mdev */
650                         /* This is similar to one of Eifel findings.
651                          * Eifel blocks mdev updates when rtt decreases.
652                          * This solution is a bit different: we use finer gain
653                          * for mdev in this case (alpha*beta).
654                          * Like Eifel it also prevents growth of rto,
655                          * but also it limits too fast rto decreases,
656                          * happening in pure Eifel.
657                          */
658                         if (m > 0)
659                                 m >>= 3;
660                 } else {
661                         m -= (tp->mdev >> 2);   /* similar update on mdev */
662                 }
663                 tp->mdev += m;          /* mdev = 3/4 mdev + 1/4 new */
664                 if (tp->mdev > tp->mdev_max) {
665                         tp->mdev_max = tp->mdev;
666                         if (tp->mdev_max > tp->rttvar)
667                                 tp->rttvar = tp->mdev_max;
668                 }
669                 if (after(tp->snd_una, tp->rtt_seq)) {
670                         if (tp->mdev_max < tp->rttvar)
671                                 tp->rttvar -= (tp->rttvar - tp->mdev_max) >> 2;
672                         tp->rtt_seq = tp->snd_nxt;
673                         tp->mdev_max = tcp_rto_min(sk);
674                 }
675         } else {
676                 /* no previous measure. */
677                 tp->srtt = m << 3;      /* take the measured time to be rtt */
678                 tp->mdev = m << 1;      /* make sure rto = 3*rtt */
679                 tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk));
680                 tp->rtt_seq = tp->snd_nxt;
681         }
682 }
683
684 /* Calculate rto without backoff.  This is the second half of Van Jacobson's
685  * routine referred to above.
686  */
687 static inline void tcp_set_rto(struct sock *sk)
688 {
689         const struct tcp_sock *tp = tcp_sk(sk);
690         /* Old crap is replaced with new one. 8)
691          *
692          * More seriously:
693          * 1. If rtt variance happened to be less 50msec, it is hallucination.
694          *    It cannot be less due to utterly erratic ACK generation made
695          *    at least by solaris and freebsd. "Erratic ACKs" has _nothing_
696          *    to do with delayed acks, because at cwnd>2 true delack timeout
697          *    is invisible. Actually, Linux-2.4 also generates erratic
698          *    ACKs in some circumstances.
699          */
700         inet_csk(sk)->icsk_rto = (tp->srtt >> 3) + tp->rttvar;
701
702         /* 2. Fixups made earlier cannot be right.
703          *    If we do not estimate RTO correctly without them,
704          *    all the algo is pure shit and should be replaced
705          *    with correct one. It is exactly, which we pretend to do.
706          */
707 }
708
709 /* NOTE: clamping at TCP_RTO_MIN is not required, current algo
710  * guarantees that rto is higher.
711  */
712 static inline void tcp_bound_rto(struct sock *sk)
713 {
714         if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX)
715                 inet_csk(sk)->icsk_rto = TCP_RTO_MAX;
716 }
717
718 /* Save metrics learned by this TCP session.
719    This function is called only, when TCP finishes successfully
720    i.e. when it enters TIME-WAIT or goes from LAST-ACK to CLOSE.
721  */
722 void tcp_update_metrics(struct sock *sk)
723 {
724         struct tcp_sock *tp = tcp_sk(sk);
725         struct dst_entry *dst = __sk_dst_get(sk);
726
727         if (sysctl_tcp_nometrics_save)
728                 return;
729
730         dst_confirm(dst);
731
732         if (dst && (dst->flags & DST_HOST)) {
733                 const struct inet_connection_sock *icsk = inet_csk(sk);
734                 int m;
735
736                 if (icsk->icsk_backoff || !tp->srtt) {
737                         /* This session failed to estimate rtt. Why?
738                          * Probably, no packets returned in time.
739                          * Reset our results.
740                          */
741                         if (!(dst_metric_locked(dst, RTAX_RTT)))
742                                 dst->metrics[RTAX_RTT - 1] = 0;
743                         return;
744                 }
745
746                 m = dst_metric(dst, RTAX_RTT) - tp->srtt;
747
748                 /* If newly calculated rtt larger than stored one,
749                  * store new one. Otherwise, use EWMA. Remember,
750                  * rtt overestimation is always better than underestimation.
751                  */
752                 if (!(dst_metric_locked(dst, RTAX_RTT))) {
753                         if (m <= 0)
754                                 dst->metrics[RTAX_RTT - 1] = tp->srtt;
755                         else
756                                 dst->metrics[RTAX_RTT - 1] -= (m >> 3);
757                 }
758
759                 if (!(dst_metric_locked(dst, RTAX_RTTVAR))) {
760                         if (m < 0)
761                                 m = -m;
762
763                         /* Scale deviation to rttvar fixed point */
764                         m >>= 1;
765                         if (m < tp->mdev)
766                                 m = tp->mdev;
767
768                         if (m >= dst_metric(dst, RTAX_RTTVAR))
769                                 dst->metrics[RTAX_RTTVAR - 1] = m;
770                         else
771                                 dst->metrics[RTAX_RTTVAR-1] -=
772                                         (dst->metrics[RTAX_RTTVAR-1] - m)>>2;
773                 }
774
775                 if (tp->snd_ssthresh >= 0xFFFF) {
776                         /* Slow start still did not finish. */
777                         if (dst_metric(dst, RTAX_SSTHRESH) &&
778                             !dst_metric_locked(dst, RTAX_SSTHRESH) &&
779                             (tp->snd_cwnd >> 1) > dst_metric(dst, RTAX_SSTHRESH))
780                                 dst->metrics[RTAX_SSTHRESH-1] = tp->snd_cwnd >> 1;
781                         if (!dst_metric_locked(dst, RTAX_CWND) &&
782                             tp->snd_cwnd > dst_metric(dst, RTAX_CWND))
783                                 dst->metrics[RTAX_CWND - 1] = tp->snd_cwnd;
784                 } else if (tp->snd_cwnd > tp->snd_ssthresh &&
785                            icsk->icsk_ca_state == TCP_CA_Open) {
786                         /* Cong. avoidance phase, cwnd is reliable. */
787                         if (!dst_metric_locked(dst, RTAX_SSTHRESH))
788                                 dst->metrics[RTAX_SSTHRESH-1] =
789                                         max(tp->snd_cwnd >> 1, tp->snd_ssthresh);
790                         if (!dst_metric_locked(dst, RTAX_CWND))
791                                 dst->metrics[RTAX_CWND-1] = (dst->metrics[RTAX_CWND-1] + tp->snd_cwnd) >> 1;
792                 } else {
793                         /* Else slow start did not finish, cwnd is non-sense,
794                            ssthresh may be also invalid.
795                          */
796                         if (!dst_metric_locked(dst, RTAX_CWND))
797                                 dst->metrics[RTAX_CWND-1] = (dst->metrics[RTAX_CWND-1] + tp->snd_ssthresh) >> 1;
798                         if (dst->metrics[RTAX_SSTHRESH-1] &&
799                             !dst_metric_locked(dst, RTAX_SSTHRESH) &&
800                             tp->snd_ssthresh > dst->metrics[RTAX_SSTHRESH-1])
801                                 dst->metrics[RTAX_SSTHRESH-1] = tp->snd_ssthresh;
802                 }
803
804                 if (!dst_metric_locked(dst, RTAX_REORDERING)) {
805                         if (dst->metrics[RTAX_REORDERING-1] < tp->reordering &&
806                             tp->reordering != sysctl_tcp_reordering)
807                                 dst->metrics[RTAX_REORDERING-1] = tp->reordering;
808                 }
809         }
810 }
811
812 /* Numbers are taken from RFC3390.
813  *
814  * John Heffner states:
815  *
816  *      The RFC specifies a window of no more than 4380 bytes
817  *      unless 2*MSS > 4380.  Reading the pseudocode in the RFC
818  *      is a bit misleading because they use a clamp at 4380 bytes
819  *      rather than use a multiplier in the relevant range.
820  */
821 __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst)
822 {
823         __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
824
825         if (!cwnd) {
826                 if (tp->mss_cache > 1460)
827                         cwnd = 2;
828                 else
829                         cwnd = (tp->mss_cache > 1095) ? 3 : 4;
830         }
831         return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
832 }
833
834 /* Set slow start threshold and cwnd not falling to slow start */
835 void tcp_enter_cwr(struct sock *sk, const int set_ssthresh)
836 {
837         struct tcp_sock *tp = tcp_sk(sk);
838         const struct inet_connection_sock *icsk = inet_csk(sk);
839
840         tp->prior_ssthresh = 0;
841         tp->bytes_acked = 0;
842         if (icsk->icsk_ca_state < TCP_CA_CWR) {
843                 tp->undo_marker = 0;
844                 if (set_ssthresh)
845                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
846                 tp->snd_cwnd = min(tp->snd_cwnd,
847                                    tcp_packets_in_flight(tp) + 1U);
848                 tp->snd_cwnd_cnt = 0;
849                 tp->high_seq = tp->snd_nxt;
850                 tp->snd_cwnd_stamp = tcp_time_stamp;
851                 TCP_ECN_queue_cwr(tp);
852
853                 tcp_set_ca_state(sk, TCP_CA_CWR);
854         }
855 }
856
857 /*
858  * Packet counting of FACK is based on in-order assumptions, therefore TCP
859  * disables it when reordering is detected
860  */
861 static void tcp_disable_fack(struct tcp_sock *tp)
862 {
863         /* RFC3517 uses different metric in lost marker => reset on change */
864         if (tcp_is_fack(tp))
865                 tp->lost_skb_hint = NULL;
866         tp->rx_opt.sack_ok &= ~2;
867 }
868
869 /* Take a notice that peer is sending D-SACKs */
870 static void tcp_dsack_seen(struct tcp_sock *tp)
871 {
872         tp->rx_opt.sack_ok |= 4;
873 }
874
875 /* Initialize metrics on socket. */
876
877 static void tcp_init_metrics(struct sock *sk)
878 {
879         struct tcp_sock *tp = tcp_sk(sk);
880         struct dst_entry *dst = __sk_dst_get(sk);
881
882         if (dst == NULL)
883                 goto reset;
884
885         dst_confirm(dst);
886
887         if (dst_metric_locked(dst, RTAX_CWND))
888                 tp->snd_cwnd_clamp = dst_metric(dst, RTAX_CWND);
889         if (dst_metric(dst, RTAX_SSTHRESH)) {
890                 tp->snd_ssthresh = dst_metric(dst, RTAX_SSTHRESH);
891                 if (tp->snd_ssthresh > tp->snd_cwnd_clamp)
892                         tp->snd_ssthresh = tp->snd_cwnd_clamp;
893         }
894         if (dst_metric(dst, RTAX_REORDERING) &&
895             tp->reordering != dst_metric(dst, RTAX_REORDERING)) {
896                 tcp_disable_fack(tp);
897                 tp->reordering = dst_metric(dst, RTAX_REORDERING);
898         }
899
900         if (dst_metric(dst, RTAX_RTT) == 0)
901                 goto reset;
902
903         if (!tp->srtt && dst_metric(dst, RTAX_RTT) < (TCP_TIMEOUT_INIT << 3))
904                 goto reset;
905
906         /* Initial rtt is determined from SYN,SYN-ACK.
907          * The segment is small and rtt may appear much
908          * less than real one. Use per-dst memory
909          * to make it more realistic.
910          *
911          * A bit of theory. RTT is time passed after "normal" sized packet
912          * is sent until it is ACKed. In normal circumstances sending small
913          * packets force peer to delay ACKs and calculation is correct too.
914          * The algorithm is adaptive and, provided we follow specs, it
915          * NEVER underestimate RTT. BUT! If peer tries to make some clever
916          * tricks sort of "quick acks" for time long enough to decrease RTT
917          * to low value, and then abruptly stops to do it and starts to delay
918          * ACKs, wait for troubles.
919          */
920         if (dst_metric(dst, RTAX_RTT) > tp->srtt) {
921                 tp->srtt = dst_metric(dst, RTAX_RTT);
922                 tp->rtt_seq = tp->snd_nxt;
923         }
924         if (dst_metric(dst, RTAX_RTTVAR) > tp->mdev) {
925                 tp->mdev = dst_metric(dst, RTAX_RTTVAR);
926                 tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk));
927         }
928         tcp_set_rto(sk);
929         tcp_bound_rto(sk);
930         if (inet_csk(sk)->icsk_rto < TCP_TIMEOUT_INIT && !tp->rx_opt.saw_tstamp)
931                 goto reset;
932         tp->snd_cwnd = tcp_init_cwnd(tp, dst);
933         tp->snd_cwnd_stamp = tcp_time_stamp;
934         return;
935
936 reset:
937         /* Play conservative. If timestamps are not
938          * supported, TCP will fail to recalculate correct
939          * rtt, if initial rto is too small. FORGET ALL AND RESET!
940          */
941         if (!tp->rx_opt.saw_tstamp && tp->srtt) {
942                 tp->srtt = 0;
943                 tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_INIT;
944                 inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
945         }
946 }
947
948 static void tcp_update_reordering(struct sock *sk, const int metric,
949                                   const int ts)
950 {
951         struct tcp_sock *tp = tcp_sk(sk);
952         if (metric > tp->reordering) {
953                 tp->reordering = min(TCP_MAX_REORDERING, metric);
954
955                 /* This exciting event is worth to be remembered. 8) */
956                 if (ts)
957                         NET_INC_STATS_BH(LINUX_MIB_TCPTSREORDER);
958                 else if (tcp_is_reno(tp))
959                         NET_INC_STATS_BH(LINUX_MIB_TCPRENOREORDER);
960                 else if (tcp_is_fack(tp))
961                         NET_INC_STATS_BH(LINUX_MIB_TCPFACKREORDER);
962                 else
963                         NET_INC_STATS_BH(LINUX_MIB_TCPSACKREORDER);
964 #if FASTRETRANS_DEBUG > 1
965                 printk(KERN_DEBUG "Disorder%d %d %u f%u s%u rr%d\n",
966                        tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
967                        tp->reordering,
968                        tp->fackets_out,
969                        tp->sacked_out,
970                        tp->undo_marker ? tp->undo_retrans : 0);
971 #endif
972                 tcp_disable_fack(tp);
973         }
974 }
975
976 /* This procedure tags the retransmission queue when SACKs arrive.
977  *
978  * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
979  * Packets in queue with these bits set are counted in variables
980  * sacked_out, retrans_out and lost_out, correspondingly.
981  *
982  * Valid combinations are:
983  * Tag  InFlight        Description
984  * 0    1               - orig segment is in flight.
985  * S    0               - nothing flies, orig reached receiver.
986  * L    0               - nothing flies, orig lost by net.
987  * R    2               - both orig and retransmit are in flight.
988  * L|R  1               - orig is lost, retransmit is in flight.
989  * S|R  1               - orig reached receiver, retrans is still in flight.
990  * (L|S|R is logically valid, it could occur when L|R is sacked,
991  *  but it is equivalent to plain S and code short-curcuits it to S.
992  *  L|S is logically invalid, it would mean -1 packet in flight 8))
993  *
994  * These 6 states form finite state machine, controlled by the following events:
995  * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
996  * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
997  * 3. Loss detection event of one of three flavors:
998  *      A. Scoreboard estimator decided the packet is lost.
999  *         A'. Reno "three dupacks" marks head of queue lost.
1000  *         A''. Its FACK modfication, head until snd.fack is lost.
1001  *      B. SACK arrives sacking data transmitted after never retransmitted
1002  *         hole was sent out.
1003  *      C. SACK arrives sacking SND.NXT at the moment, when the
1004  *         segment was retransmitted.
1005  * 4. D-SACK added new rule: D-SACK changes any tag to S.
1006  *
1007  * It is pleasant to note, that state diagram turns out to be commutative,
1008  * so that we are allowed not to be bothered by order of our actions,
1009  * when multiple events arrive simultaneously. (see the function below).
1010  *
1011  * Reordering detection.
1012  * --------------------
1013  * Reordering metric is maximal distance, which a packet can be displaced
1014  * in packet stream. With SACKs we can estimate it:
1015  *
1016  * 1. SACK fills old hole and the corresponding segment was not
1017  *    ever retransmitted -> reordering. Alas, we cannot use it
1018  *    when segment was retransmitted.
1019  * 2. The last flaw is solved with D-SACK. D-SACK arrives
1020  *    for retransmitted and already SACKed segment -> reordering..
1021  * Both of these heuristics are not used in Loss state, when we cannot
1022  * account for retransmits accurately.
1023  *
1024  * SACK block validation.
1025  * ----------------------
1026  *
1027  * SACK block range validation checks that the received SACK block fits to
1028  * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
1029  * Note that SND.UNA is not included to the range though being valid because
1030  * it means that the receiver is rather inconsistent with itself reporting
1031  * SACK reneging when it should advance SND.UNA. Such SACK block this is
1032  * perfectly valid, however, in light of RFC2018 which explicitly states
1033  * that "SACK block MUST reflect the newest segment.  Even if the newest
1034  * segment is going to be discarded ...", not that it looks very clever
1035  * in case of head skb. Due to potentional receiver driven attacks, we
1036  * choose to avoid immediate execution of a walk in write queue due to
1037  * reneging and defer head skb's loss recovery to standard loss recovery
1038  * procedure that will eventually trigger (nothing forbids us doing this).
1039  *
1040  * Implements also blockage to start_seq wrap-around. Problem lies in the
1041  * fact that though start_seq (s) is before end_seq (i.e., not reversed),
1042  * there's no guarantee that it will be before snd_nxt (n). The problem
1043  * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
1044  * wrap (s_w):
1045  *
1046  *         <- outs wnd ->                          <- wrapzone ->
1047  *         u     e      n                         u_w   e_w  s n_w
1048  *         |     |      |                          |     |   |  |
1049  * |<------------+------+----- TCP seqno space --------------+---------->|
1050  * ...-- <2^31 ->|                                           |<--------...
1051  * ...---- >2^31 ------>|                                    |<--------...
1052  *
1053  * Current code wouldn't be vulnerable but it's better still to discard such
1054  * crazy SACK blocks. Doing this check for start_seq alone closes somewhat
1055  * similar case (end_seq after snd_nxt wrap) as earlier reversed check in
1056  * snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
1057  * equal to the ideal case (infinite seqno space without wrap caused issues).
1058  *
1059  * With D-SACK the lower bound is extended to cover sequence space below
1060  * SND.UNA down to undo_marker, which is the last point of interest. Yet
1061  * again, D-SACK block must not to go across snd_una (for the same reason as
1062  * for the normal SACK blocks, explained above). But there all simplicity
1063  * ends, TCP might receive valid D-SACKs below that. As long as they reside
1064  * fully below undo_marker they do not affect behavior in anyway and can
1065  * therefore be safely ignored. In rare cases (which are more or less
1066  * theoretical ones), the D-SACK will nicely cross that boundary due to skb
1067  * fragmentation and packet reordering past skb's retransmission. To consider
1068  * them correctly, the acceptable range must be extended even more though
1069  * the exact amount is rather hard to quantify. However, tp->max_window can
1070  * be used as an exaggerated estimate.
1071  */
1072 static int tcp_is_sackblock_valid(struct tcp_sock *tp, int is_dsack,
1073                                   u32 start_seq, u32 end_seq)
1074 {
1075         /* Too far in future, or reversed (interpretation is ambiguous) */
1076         if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
1077                 return 0;
1078
1079         /* Nasty start_seq wrap-around check (see comments above) */
1080         if (!before(start_seq, tp->snd_nxt))
1081                 return 0;
1082
1083         /* In outstanding window? ...This is valid exit for D-SACKs too.
1084          * start_seq == snd_una is non-sensical (see comments above)
1085          */
1086         if (after(start_seq, tp->snd_una))
1087                 return 1;
1088
1089         if (!is_dsack || !tp->undo_marker)
1090                 return 0;
1091
1092         /* ...Then it's D-SACK, and must reside below snd_una completely */
1093         if (!after(end_seq, tp->snd_una))
1094                 return 0;
1095
1096         if (!before(start_seq, tp->undo_marker))
1097                 return 1;
1098
1099         /* Too old */
1100         if (!after(end_seq, tp->undo_marker))
1101                 return 0;
1102
1103         /* Undo_marker boundary crossing (overestimates a lot). Known already:
1104          *   start_seq < undo_marker and end_seq >= undo_marker.
1105          */
1106         return !before(start_seq, end_seq - tp->max_window);
1107 }
1108
1109 /* Check for lost retransmit. This superb idea is borrowed from "ratehalving".
1110  * Event "C". Later note: FACK people cheated me again 8), we have to account
1111  * for reordering! Ugly, but should help.
1112  *
1113  * Search retransmitted skbs from write_queue that were sent when snd_nxt was
1114  * less than what is now known to be received by the other end (derived from
1115  * highest SACK block). Also calculate the lowest snd_nxt among the remaining
1116  * retransmitted skbs to avoid some costly processing per ACKs.
1117  */
1118 static void tcp_mark_lost_retrans(struct sock *sk)
1119 {
1120         const struct inet_connection_sock *icsk = inet_csk(sk);
1121         struct tcp_sock *tp = tcp_sk(sk);
1122         struct sk_buff *skb;
1123         int cnt = 0;
1124         u32 new_low_seq = tp->snd_nxt;
1125         u32 received_upto = tcp_highest_sack_seq(tp);
1126
1127         if (!tcp_is_fack(tp) || !tp->retrans_out ||
1128             !after(received_upto, tp->lost_retrans_low) ||
1129             icsk->icsk_ca_state != TCP_CA_Recovery)
1130                 return;
1131
1132         tcp_for_write_queue(skb, sk) {
1133                 u32 ack_seq = TCP_SKB_CB(skb)->ack_seq;
1134
1135                 if (skb == tcp_send_head(sk))
1136                         break;
1137                 if (cnt == tp->retrans_out)
1138                         break;
1139                 if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1140                         continue;
1141
1142                 if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS))
1143                         continue;
1144
1145                 if (after(received_upto, ack_seq) &&
1146                     (tcp_is_fack(tp) ||
1147                      !before(received_upto,
1148                              ack_seq + tp->reordering * tp->mss_cache))) {
1149                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1150                         tp->retrans_out -= tcp_skb_pcount(skb);
1151
1152                         /* clear lost hint */
1153                         tp->retransmit_skb_hint = NULL;
1154
1155                         if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
1156                                 tp->lost_out += tcp_skb_pcount(skb);
1157                                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1158                         }
1159                         NET_INC_STATS_BH(LINUX_MIB_TCPLOSTRETRANSMIT);
1160                 } else {
1161                         if (before(ack_seq, new_low_seq))
1162                                 new_low_seq = ack_seq;
1163                         cnt += tcp_skb_pcount(skb);
1164                 }
1165         }
1166
1167         if (tp->retrans_out)
1168                 tp->lost_retrans_low = new_low_seq;
1169 }
1170
1171 static int tcp_check_dsack(struct tcp_sock *tp, struct sk_buff *ack_skb,
1172                            struct tcp_sack_block_wire *sp, int num_sacks,
1173                            u32 prior_snd_una)
1174 {
1175         u32 start_seq_0 = ntohl(get_unaligned(&sp[0].start_seq));
1176         u32 end_seq_0 = ntohl(get_unaligned(&sp[0].end_seq));
1177         int dup_sack = 0;
1178
1179         if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
1180                 dup_sack = 1;
1181                 tcp_dsack_seen(tp);
1182                 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKRECV);
1183         } else if (num_sacks > 1) {
1184                 u32 end_seq_1 = ntohl(get_unaligned(&sp[1].end_seq));
1185                 u32 start_seq_1 = ntohl(get_unaligned(&sp[1].start_seq));
1186
1187                 if (!after(end_seq_0, end_seq_1) &&
1188                     !before(start_seq_0, start_seq_1)) {
1189                         dup_sack = 1;
1190                         tcp_dsack_seen(tp);
1191                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFORECV);
1192                 }
1193         }
1194
1195         /* D-SACK for already forgotten data... Do dumb counting. */
1196         if (dup_sack &&
1197             !after(end_seq_0, prior_snd_una) &&
1198             after(end_seq_0, tp->undo_marker))
1199                 tp->undo_retrans--;
1200
1201         return dup_sack;
1202 }
1203
1204 /* Check if skb is fully within the SACK block. In presence of GSO skbs,
1205  * the incoming SACK may not exactly match but we can find smaller MSS
1206  * aligned portion of it that matches. Therefore we might need to fragment
1207  * which may fail and creates some hassle (caller must handle error case
1208  * returns).
1209  */
1210 static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
1211                                  u32 start_seq, u32 end_seq)
1212 {
1213         int in_sack, err;
1214         unsigned int pkt_len;
1215
1216         in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
1217                   !before(end_seq, TCP_SKB_CB(skb)->end_seq);
1218
1219         if (tcp_skb_pcount(skb) > 1 && !in_sack &&
1220             after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
1221
1222                 in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
1223
1224                 if (!in_sack)
1225                         pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
1226                 else
1227                         pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
1228                 err = tcp_fragment(sk, skb, pkt_len, skb_shinfo(skb)->gso_size);
1229                 if (err < 0)
1230                         return err;
1231         }
1232
1233         return in_sack;
1234 }
1235
1236 static int tcp_sacktag_one(struct sk_buff *skb, struct sock *sk,
1237                            int *reord, int dup_sack, int fack_count)
1238 {
1239         struct tcp_sock *tp = tcp_sk(sk);
1240         u8 sacked = TCP_SKB_CB(skb)->sacked;
1241         int flag = 0;
1242
1243         /* Account D-SACK for retransmitted packet. */
1244         if (dup_sack && (sacked & TCPCB_RETRANS)) {
1245                 if (after(TCP_SKB_CB(skb)->end_seq, tp->undo_marker))
1246                         tp->undo_retrans--;
1247                 if (sacked & TCPCB_SACKED_ACKED)
1248                         *reord = min(fack_count, *reord);
1249         }
1250
1251         /* Nothing to do; acked frame is about to be dropped (was ACKed). */
1252         if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
1253                 return flag;
1254
1255         if (!(sacked & TCPCB_SACKED_ACKED)) {
1256                 if (sacked & TCPCB_SACKED_RETRANS) {
1257                         /* If the segment is not tagged as lost,
1258                          * we do not clear RETRANS, believing
1259                          * that retransmission is still in flight.
1260                          */
1261                         if (sacked & TCPCB_LOST) {
1262                                 TCP_SKB_CB(skb)->sacked &=
1263                                         ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
1264                                 tp->lost_out -= tcp_skb_pcount(skb);
1265                                 tp->retrans_out -= tcp_skb_pcount(skb);
1266
1267                                 /* clear lost hint */
1268                                 tp->retransmit_skb_hint = NULL;
1269                         }
1270                 } else {
1271                         if (!(sacked & TCPCB_RETRANS)) {
1272                                 /* New sack for not retransmitted frame,
1273                                  * which was in hole. It is reordering.
1274                                  */
1275                                 if (before(TCP_SKB_CB(skb)->seq,
1276                                            tcp_highest_sack_seq(tp)))
1277                                         *reord = min(fack_count, *reord);
1278
1279                                 /* SACK enhanced F-RTO (RFC4138; Appendix B) */
1280                                 if (!after(TCP_SKB_CB(skb)->end_seq, tp->frto_highmark))
1281                                         flag |= FLAG_ONLY_ORIG_SACKED;
1282                         }
1283
1284                         if (sacked & TCPCB_LOST) {
1285                                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
1286                                 tp->lost_out -= tcp_skb_pcount(skb);
1287
1288                                 /* clear lost hint */
1289                                 tp->retransmit_skb_hint = NULL;
1290                         }
1291                 }
1292
1293                 TCP_SKB_CB(skb)->sacked |= TCPCB_SACKED_ACKED;
1294                 flag |= FLAG_DATA_SACKED;
1295                 tp->sacked_out += tcp_skb_pcount(skb);
1296
1297                 fack_count += tcp_skb_pcount(skb);
1298
1299                 /* Lost marker hint past SACKed? Tweak RFC3517 cnt */
1300                 if (!tcp_is_fack(tp) && (tp->lost_skb_hint != NULL) &&
1301                     before(TCP_SKB_CB(skb)->seq,
1302                            TCP_SKB_CB(tp->lost_skb_hint)->seq))
1303                         tp->lost_cnt_hint += tcp_skb_pcount(skb);
1304
1305                 if (fack_count > tp->fackets_out)
1306                         tp->fackets_out = fack_count;
1307
1308                 if (!before(TCP_SKB_CB(skb)->seq, tcp_highest_sack_seq(tp)))
1309                         tcp_advance_highest_sack(sk, skb);
1310         }
1311
1312         /* D-SACK. We can detect redundant retransmission in S|R and plain R
1313          * frames and clear it. undo_retrans is decreased above, L|R frames
1314          * are accounted above as well.
1315          */
1316         if (dup_sack && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)) {
1317                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1318                 tp->retrans_out -= tcp_skb_pcount(skb);
1319                 tp->retransmit_skb_hint = NULL;
1320         }
1321
1322         return flag;
1323 }
1324
1325 static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
1326                                         struct tcp_sack_block *next_dup,
1327                                         u32 start_seq, u32 end_seq,
1328                                         int dup_sack_in, int *fack_count,
1329                                         int *reord, int *flag)
1330 {
1331         tcp_for_write_queue_from(skb, sk) {
1332                 int in_sack = 0;
1333                 int dup_sack = dup_sack_in;
1334
1335                 if (skb == tcp_send_head(sk))
1336                         break;
1337
1338                 /* queue is in-order => we can short-circuit the walk early */
1339                 if (!before(TCP_SKB_CB(skb)->seq, end_seq))
1340                         break;
1341
1342                 if ((next_dup != NULL) &&
1343                     before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) {
1344                         in_sack = tcp_match_skb_to_sack(sk, skb,
1345                                                         next_dup->start_seq,
1346                                                         next_dup->end_seq);
1347                         if (in_sack > 0)
1348                                 dup_sack = 1;
1349                 }
1350
1351                 if (in_sack <= 0)
1352                         in_sack = tcp_match_skb_to_sack(sk, skb, start_seq,
1353                                                         end_seq);
1354                 if (unlikely(in_sack < 0))
1355                         break;
1356
1357                 if (in_sack)
1358                         *flag |= tcp_sacktag_one(skb, sk, reord, dup_sack,
1359                                                  *fack_count);
1360
1361                 *fack_count += tcp_skb_pcount(skb);
1362         }
1363         return skb;
1364 }
1365
1366 /* Avoid all extra work that is being done by sacktag while walking in
1367  * a normal way
1368  */
1369 static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
1370                                         u32 skip_to_seq)
1371 {
1372         tcp_for_write_queue_from(skb, sk) {
1373                 if (skb == tcp_send_head(sk))
1374                         break;
1375
1376                 if (!before(TCP_SKB_CB(skb)->end_seq, skip_to_seq))
1377                         break;
1378         }
1379         return skb;
1380 }
1381
1382 static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
1383                                                 struct sock *sk,
1384                                                 struct tcp_sack_block *next_dup,
1385                                                 u32 skip_to_seq,
1386                                                 int *fack_count, int *reord,
1387                                                 int *flag)
1388 {
1389         if (next_dup == NULL)
1390                 return skb;
1391
1392         if (before(next_dup->start_seq, skip_to_seq)) {
1393                 skb = tcp_sacktag_skip(skb, sk, next_dup->start_seq);
1394                 tcp_sacktag_walk(skb, sk, NULL,
1395                                  next_dup->start_seq, next_dup->end_seq,
1396                                  1, fack_count, reord, flag);
1397         }
1398
1399         return skb;
1400 }
1401
1402 static int tcp_sack_cache_ok(struct tcp_sock *tp, struct tcp_sack_block *cache)
1403 {
1404         return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1405 }
1406
1407 static int
1408 tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb,
1409                         u32 prior_snd_una)
1410 {
1411         const struct inet_connection_sock *icsk = inet_csk(sk);
1412         struct tcp_sock *tp = tcp_sk(sk);
1413         unsigned char *ptr = (skb_transport_header(ack_skb) +
1414                               TCP_SKB_CB(ack_skb)->sacked);
1415         struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
1416         struct tcp_sack_block sp[4];
1417         struct tcp_sack_block *cache;
1418         struct sk_buff *skb;
1419         int num_sacks = (ptr[1] - TCPOLEN_SACK_BASE) >> 3;
1420         int used_sacks;
1421         int reord = tp->packets_out;
1422         int flag = 0;
1423         int found_dup_sack = 0;
1424         int fack_count;
1425         int i, j;
1426         int first_sack_index;
1427
1428         if (!tp->sacked_out) {
1429                 if (WARN_ON(tp->fackets_out))
1430                         tp->fackets_out = 0;
1431                 tcp_highest_sack_reset(sk);
1432         }
1433
1434         found_dup_sack = tcp_check_dsack(tp, ack_skb, sp_wire,
1435                                          num_sacks, prior_snd_una);
1436         if (found_dup_sack)
1437                 flag |= FLAG_DSACKING_ACK;
1438
1439         /* Eliminate too old ACKs, but take into
1440          * account more or less fresh ones, they can
1441          * contain valid SACK info.
1442          */
1443         if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
1444                 return 0;
1445
1446         if (!tp->packets_out)
1447                 goto out;
1448
1449         used_sacks = 0;
1450         first_sack_index = 0;
1451         for (i = 0; i < num_sacks; i++) {
1452                 int dup_sack = !i && found_dup_sack;
1453
1454                 sp[used_sacks].start_seq = ntohl(get_unaligned(&sp_wire[i].start_seq));
1455                 sp[used_sacks].end_seq = ntohl(get_unaligned(&sp_wire[i].end_seq));
1456
1457                 if (!tcp_is_sackblock_valid(tp, dup_sack,
1458                                             sp[used_sacks].start_seq,
1459                                             sp[used_sacks].end_seq)) {
1460                         if (dup_sack) {
1461                                 if (!tp->undo_marker)
1462                                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKIGNOREDNOUNDO);
1463                                 else
1464                                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKIGNOREDOLD);
1465                         } else {
1466                                 /* Don't count olds caused by ACK reordering */
1467                                 if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
1468                                     !after(sp[used_sacks].end_seq, tp->snd_una))
1469                                         continue;
1470                                 NET_INC_STATS_BH(LINUX_MIB_TCPSACKDISCARD);
1471                         }
1472                         if (i == 0)
1473                                 first_sack_index = -1;
1474                         continue;
1475                 }
1476
1477                 /* Ignore very old stuff early */
1478                 if (!after(sp[used_sacks].end_seq, prior_snd_una))
1479                         continue;
1480
1481                 used_sacks++;
1482         }
1483
1484         /* order SACK blocks to allow in order walk of the retrans queue */
1485         for (i = used_sacks - 1; i > 0; i--) {
1486                 for (j = 0; j < i; j++) {
1487                         if (after(sp[j].start_seq, sp[j + 1].start_seq)) {
1488                                 struct tcp_sack_block tmp;
1489
1490                                 tmp = sp[j];
1491                                 sp[j] = sp[j + 1];
1492                                 sp[j + 1] = tmp;
1493
1494                                 /* Track where the first SACK block goes to */
1495                                 if (j == first_sack_index)
1496                                         first_sack_index = j + 1;
1497                         }
1498                 }
1499         }
1500
1501         skb = tcp_write_queue_head(sk);
1502         fack_count = 0;
1503         i = 0;
1504
1505         if (!tp->sacked_out) {
1506                 /* It's already past, so skip checking against it */
1507                 cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
1508         } else {
1509                 cache = tp->recv_sack_cache;
1510                 /* Skip empty blocks in at head of the cache */
1511                 while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq &&
1512                        !cache->end_seq)
1513                         cache++;
1514         }
1515
1516         while (i < used_sacks) {
1517                 u32 start_seq = sp[i].start_seq;
1518                 u32 end_seq = sp[i].end_seq;
1519                 int dup_sack = (found_dup_sack && (i == first_sack_index));
1520                 struct tcp_sack_block *next_dup = NULL;
1521
1522                 if (found_dup_sack && ((i + 1) == first_sack_index))
1523                         next_dup = &sp[i + 1];
1524
1525                 /* Event "B" in the comment above. */
1526                 if (after(end_seq, tp->high_seq))
1527                         flag |= FLAG_DATA_LOST;
1528
1529                 /* Skip too early cached blocks */
1530                 while (tcp_sack_cache_ok(tp, cache) &&
1531                        !before(start_seq, cache->end_seq))
1532                         cache++;
1533
1534                 /* Can skip some work by looking recv_sack_cache? */
1535                 if (tcp_sack_cache_ok(tp, cache) && !dup_sack &&
1536                     after(end_seq, cache->start_seq)) {
1537
1538                         /* Head todo? */
1539                         if (before(start_seq, cache->start_seq)) {
1540                                 skb = tcp_sacktag_skip(skb, sk, start_seq);
1541                                 skb = tcp_sacktag_walk(skb, sk, next_dup,
1542                                                        start_seq,
1543                                                        cache->start_seq,
1544                                                        dup_sack, &fack_count,
1545                                                        &reord, &flag);
1546                         }
1547
1548                         /* Rest of the block already fully processed? */
1549                         if (!after(end_seq, cache->end_seq))
1550                                 goto advance_sp;
1551
1552                         skb = tcp_maybe_skipping_dsack(skb, sk, next_dup,
1553                                                        cache->end_seq,
1554                                                        &fack_count, &reord,
1555                                                        &flag);
1556
1557                         /* ...tail remains todo... */
1558                         if (tcp_highest_sack_seq(tp) == cache->end_seq) {
1559                                 /* ...but better entrypoint exists! */
1560                                 skb = tcp_highest_sack(sk);
1561                                 if (skb == NULL)
1562                                         break;
1563                                 fack_count = tp->fackets_out;
1564                                 cache++;
1565                                 goto walk;
1566                         }
1567
1568                         skb = tcp_sacktag_skip(skb, sk, cache->end_seq);
1569                         /* Check overlap against next cached too (past this one already) */
1570                         cache++;
1571                         continue;
1572                 }
1573
1574                 if (!before(start_seq, tcp_highest_sack_seq(tp))) {
1575                         skb = tcp_highest_sack(sk);
1576                         if (skb == NULL)
1577                                 break;
1578                         fack_count = tp->fackets_out;
1579                 }
1580                 skb = tcp_sacktag_skip(skb, sk, start_seq);
1581
1582 walk:
1583                 skb = tcp_sacktag_walk(skb, sk, next_dup, start_seq, end_seq,
1584                                        dup_sack, &fack_count, &reord, &flag);
1585
1586 advance_sp:
1587                 /* SACK enhanced FRTO (RFC4138, Appendix B): Clearing correct
1588                  * due to in-order walk
1589                  */
1590                 if (after(end_seq, tp->frto_highmark))
1591                         flag &= ~FLAG_ONLY_ORIG_SACKED;
1592
1593                 i++;
1594         }
1595
1596         /* Clear the head of the cache sack blocks so we can skip it next time */
1597         for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) {
1598                 tp->recv_sack_cache[i].start_seq = 0;
1599                 tp->recv_sack_cache[i].end_seq = 0;
1600         }
1601         for (j = 0; j < used_sacks; j++)
1602                 tp->recv_sack_cache[i++] = sp[j];
1603
1604         tcp_mark_lost_retrans(sk);
1605
1606         tcp_verify_left_out(tp);
1607
1608         if ((reord < tp->fackets_out) &&
1609             ((icsk->icsk_ca_state != TCP_CA_Loss) || tp->undo_marker) &&
1610             (!tp->frto_highmark || after(tp->snd_una, tp->frto_highmark)))
1611                 tcp_update_reordering(sk, tp->fackets_out - reord, 0);
1612
1613 out:
1614
1615 #if FASTRETRANS_DEBUG > 0
1616         BUG_TRAP((int)tp->sacked_out >= 0);
1617         BUG_TRAP((int)tp->lost_out >= 0);
1618         BUG_TRAP((int)tp->retrans_out >= 0);
1619         BUG_TRAP((int)tcp_packets_in_flight(tp) >= 0);
1620 #endif
1621         return flag;
1622 }
1623
1624 /* If we receive more dupacks than we expected counting segments
1625  * in assumption of absent reordering, interpret this as reordering.
1626  * The only another reason could be bug in receiver TCP.
1627  */
1628 static void tcp_check_reno_reordering(struct sock *sk, const int addend)
1629 {
1630         struct tcp_sock *tp = tcp_sk(sk);
1631         u32 holes;
1632
1633         holes = max(tp->lost_out, 1U);
1634         holes = min(holes, tp->packets_out);
1635
1636         if ((tp->sacked_out + holes) > tp->packets_out) {
1637                 tp->sacked_out = tp->packets_out - holes;
1638                 tcp_update_reordering(sk, tp->packets_out + addend, 0);
1639         }
1640 }
1641
1642 /* Emulate SACKs for SACKless connection: account for a new dupack. */
1643
1644 static void tcp_add_reno_sack(struct sock *sk)
1645 {
1646         struct tcp_sock *tp = tcp_sk(sk);
1647         tp->sacked_out++;
1648         tcp_check_reno_reordering(sk, 0);
1649         tcp_verify_left_out(tp);
1650 }
1651
1652 /* Account for ACK, ACKing some data in Reno Recovery phase. */
1653
1654 static void tcp_remove_reno_sacks(struct sock *sk, int acked)
1655 {
1656         struct tcp_sock *tp = tcp_sk(sk);
1657
1658         if (acked > 0) {
1659                 /* One ACK acked hole. The rest eat duplicate ACKs. */
1660                 if (acked - 1 >= tp->sacked_out)
1661                         tp->sacked_out = 0;
1662                 else
1663                         tp->sacked_out -= acked - 1;
1664         }
1665         tcp_check_reno_reordering(sk, acked);
1666         tcp_verify_left_out(tp);
1667 }
1668
1669 static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
1670 {
1671         tp->sacked_out = 0;
1672 }
1673
1674 /* F-RTO can only be used if TCP has never retransmitted anything other than
1675  * head (SACK enhanced variant from Appendix B of RFC4138 is more robust here)
1676  */
1677 int tcp_use_frto(struct sock *sk)
1678 {
1679         const struct tcp_sock *tp = tcp_sk(sk);
1680         struct sk_buff *skb;
1681
1682         if (!sysctl_tcp_frto)
1683                 return 0;
1684
1685         if (IsSackFrto())
1686                 return 1;
1687
1688         /* Avoid expensive walking of rexmit queue if possible */
1689         if (tp->retrans_out > 1)
1690                 return 0;
1691
1692         skb = tcp_write_queue_head(sk);
1693         skb = tcp_write_queue_next(sk, skb);    /* Skips head */
1694         tcp_for_write_queue_from(skb, sk) {
1695                 if (skb == tcp_send_head(sk))
1696                         break;
1697                 if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
1698                         return 0;
1699                 /* Short-circuit when first non-SACKed skb has been checked */
1700                 if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
1701                         break;
1702         }
1703         return 1;
1704 }
1705
1706 /* RTO occurred, but do not yet enter Loss state. Instead, defer RTO
1707  * recovery a bit and use heuristics in tcp_process_frto() to detect if
1708  * the RTO was spurious. Only clear SACKED_RETRANS of the head here to
1709  * keep retrans_out counting accurate (with SACK F-RTO, other than head
1710  * may still have that bit set); TCPCB_LOST and remaining SACKED_RETRANS
1711  * bits are handled if the Loss state is really to be entered (in
1712  * tcp_enter_frto_loss).
1713  *
1714  * Do like tcp_enter_loss() would; when RTO expires the second time it
1715  * does:
1716  *  "Reduce ssthresh if it has not yet been made inside this window."
1717  */
1718 void tcp_enter_frto(struct sock *sk)
1719 {
1720         const struct inet_connection_sock *icsk = inet_csk(sk);
1721         struct tcp_sock *tp = tcp_sk(sk);
1722         struct sk_buff *skb;
1723
1724         if ((!tp->frto_counter && icsk->icsk_ca_state <= TCP_CA_Disorder) ||
1725             tp->snd_una == tp->high_seq ||
1726             ((icsk->icsk_ca_state == TCP_CA_Loss || tp->frto_counter) &&
1727              !icsk->icsk_retransmits)) {
1728                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
1729                 /* Our state is too optimistic in ssthresh() call because cwnd
1730                  * is not reduced until tcp_enter_frto_loss() when previous F-RTO
1731                  * recovery has not yet completed. Pattern would be this: RTO,
1732                  * Cumulative ACK, RTO (2xRTO for the same segment does not end
1733                  * up here twice).
1734                  * RFC4138 should be more specific on what to do, even though
1735                  * RTO is quite unlikely to occur after the first Cumulative ACK
1736                  * due to back-off and complexity of triggering events ...
1737                  */
1738                 if (tp->frto_counter) {
1739                         u32 stored_cwnd;
1740                         stored_cwnd = tp->snd_cwnd;
1741                         tp->snd_cwnd = 2;
1742                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1743                         tp->snd_cwnd = stored_cwnd;
1744                 } else {
1745                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1746                 }
1747                 /* ... in theory, cong.control module could do "any tricks" in
1748                  * ssthresh(), which means that ca_state, lost bits and lost_out
1749                  * counter would have to be faked before the call occurs. We
1750                  * consider that too expensive, unlikely and hacky, so modules
1751                  * using these in ssthresh() must deal these incompatibility
1752                  * issues if they receives CA_EVENT_FRTO and frto_counter != 0
1753                  */
1754                 tcp_ca_event(sk, CA_EVENT_FRTO);
1755         }
1756
1757         tp->undo_marker = tp->snd_una;
1758         tp->undo_retrans = 0;
1759
1760         skb = tcp_write_queue_head(sk);
1761         if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
1762                 tp->undo_marker = 0;
1763         if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
1764                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1765                 tp->retrans_out -= tcp_skb_pcount(skb);
1766         }
1767         tcp_verify_left_out(tp);
1768
1769         /* Too bad if TCP was application limited */
1770         tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp) + 1);
1771
1772         /* Earlier loss recovery underway (see RFC4138; Appendix B).
1773          * The last condition is necessary at least in tp->frto_counter case.
1774          */
1775         if (IsSackFrto() && (tp->frto_counter ||
1776             ((1 << icsk->icsk_ca_state) & (TCPF_CA_Recovery|TCPF_CA_Loss))) &&
1777             after(tp->high_seq, tp->snd_una)) {
1778                 tp->frto_highmark = tp->high_seq;
1779         } else {
1780                 tp->frto_highmark = tp->snd_nxt;
1781         }
1782         tcp_set_ca_state(sk, TCP_CA_Disorder);
1783         tp->high_seq = tp->snd_nxt;
1784         tp->frto_counter = 1;
1785 }
1786
1787 /* Enter Loss state after F-RTO was applied. Dupack arrived after RTO,
1788  * which indicates that we should follow the traditional RTO recovery,
1789  * i.e. mark everything lost and do go-back-N retransmission.
1790  */
1791 static void tcp_enter_frto_loss(struct sock *sk, int allowed_segments, int flag)
1792 {
1793         struct tcp_sock *tp = tcp_sk(sk);
1794         struct sk_buff *skb;
1795
1796         tp->lost_out = 0;
1797         tp->retrans_out = 0;
1798         if (tcp_is_reno(tp))
1799                 tcp_reset_reno_sack(tp);
1800
1801         tcp_for_write_queue(skb, sk) {
1802                 if (skb == tcp_send_head(sk))
1803                         break;
1804
1805                 TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
1806                 /*
1807                  * Count the retransmission made on RTO correctly (only when
1808                  * waiting for the first ACK and did not get it)...
1809                  */
1810                 if ((tp->frto_counter == 1) && !(flag & FLAG_DATA_ACKED)) {
1811                         /* For some reason this R-bit might get cleared? */
1812                         if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
1813                                 tp->retrans_out += tcp_skb_pcount(skb);
1814                         /* ...enter this if branch just for the first segment */
1815                         flag |= FLAG_DATA_ACKED;
1816                 } else {
1817                         if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
1818                                 tp->undo_marker = 0;
1819                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
1820                 }
1821
1822                 /* Don't lost mark skbs that were fwd transmitted after RTO */
1823                 if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) &&
1824                     !after(TCP_SKB_CB(skb)->end_seq, tp->frto_highmark)) {
1825                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1826                         tp->lost_out += tcp_skb_pcount(skb);
1827                 }
1828         }
1829         tcp_verify_left_out(tp);
1830
1831         tp->snd_cwnd = tcp_packets_in_flight(tp) + allowed_segments;
1832         tp->snd_cwnd_cnt = 0;
1833         tp->snd_cwnd_stamp = tcp_time_stamp;
1834         tp->frto_counter = 0;
1835         tp->bytes_acked = 0;
1836
1837         tp->reordering = min_t(unsigned int, tp->reordering,
1838                                sysctl_tcp_reordering);
1839         tcp_set_ca_state(sk, TCP_CA_Loss);
1840         tp->high_seq = tp->frto_highmark;
1841         TCP_ECN_queue_cwr(tp);
1842
1843         tcp_clear_retrans_hints_partial(tp);
1844 }
1845
1846 static void tcp_clear_retrans_partial(struct tcp_sock *tp)
1847 {
1848         tp->retrans_out = 0;
1849         tp->lost_out = 0;
1850
1851         tp->undo_marker = 0;
1852         tp->undo_retrans = 0;
1853 }
1854
1855 void tcp_clear_retrans(struct tcp_sock *tp)
1856 {
1857         tcp_clear_retrans_partial(tp);
1858
1859         tp->fackets_out = 0;
1860         tp->sacked_out = 0;
1861 }
1862
1863 /* Enter Loss state. If "how" is not zero, forget all SACK information
1864  * and reset tags completely, otherwise preserve SACKs. If receiver
1865  * dropped its ofo queue, we will know this due to reneging detection.
1866  */
1867 void tcp_enter_loss(struct sock *sk, int how)
1868 {
1869         const struct inet_connection_sock *icsk = inet_csk(sk);
1870         struct tcp_sock *tp = tcp_sk(sk);
1871         struct sk_buff *skb;
1872
1873         /* Reduce ssthresh if it has not yet been made inside this window. */
1874         if (icsk->icsk_ca_state <= TCP_CA_Disorder || tp->snd_una == tp->high_seq ||
1875             (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
1876                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
1877                 tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
1878                 tcp_ca_event(sk, CA_EVENT_LOSS);
1879         }
1880         tp->snd_cwnd       = 1;
1881         tp->snd_cwnd_cnt   = 0;
1882         tp->snd_cwnd_stamp = tcp_time_stamp;
1883
1884         tp->bytes_acked = 0;
1885         tcp_clear_retrans_partial(tp);
1886
1887         if (tcp_is_reno(tp))
1888                 tcp_reset_reno_sack(tp);
1889
1890         if (!how) {
1891                 /* Push undo marker, if it was plain RTO and nothing
1892                  * was retransmitted. */
1893                 tp->undo_marker = tp->snd_una;
1894                 tcp_clear_retrans_hints_partial(tp);
1895         } else {
1896                 tp->sacked_out = 0;
1897                 tp->fackets_out = 0;
1898                 tcp_clear_all_retrans_hints(tp);
1899         }
1900
1901         tcp_for_write_queue(skb, sk) {
1902                 if (skb == tcp_send_head(sk))
1903                         break;
1904
1905                 if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
1906                         tp->undo_marker = 0;
1907                 TCP_SKB_CB(skb)->sacked &= (~TCPCB_TAGBITS)|TCPCB_SACKED_ACKED;
1908                 if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED) || how) {
1909                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
1910                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
1911                         tp->lost_out += tcp_skb_pcount(skb);
1912                 }
1913         }
1914         tcp_verify_left_out(tp);
1915
1916         tp->reordering = min_t(unsigned int, tp->reordering,
1917                                sysctl_tcp_reordering);
1918         tcp_set_ca_state(sk, TCP_CA_Loss);
1919         tp->high_seq = tp->snd_nxt;
1920         TCP_ECN_queue_cwr(tp);
1921         /* Abort F-RTO algorithm if one is in progress */
1922         tp->frto_counter = 0;
1923 }
1924
1925 /* If ACK arrived pointing to a remembered SACK, it means that our
1926  * remembered SACKs do not reflect real state of receiver i.e.
1927  * receiver _host_ is heavily congested (or buggy).
1928  *
1929  * Do processing similar to RTO timeout.
1930  */
1931 static int tcp_check_sack_reneging(struct sock *sk, int flag)
1932 {
1933         if (flag & FLAG_SACK_RENEGING) {
1934                 struct inet_connection_sock *icsk = inet_csk(sk);
1935                 NET_INC_STATS_BH(LINUX_MIB_TCPSACKRENEGING);
1936
1937                 tcp_enter_loss(sk, 1);
1938                 icsk->icsk_retransmits++;
1939                 tcp_retransmit_skb(sk, tcp_write_queue_head(sk));
1940                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
1941                                           icsk->icsk_rto, TCP_RTO_MAX);
1942                 return 1;
1943         }
1944         return 0;
1945 }
1946
1947 static inline int tcp_fackets_out(struct tcp_sock *tp)
1948 {
1949         return tcp_is_reno(tp) ? tp->sacked_out + 1 : tp->fackets_out;
1950 }
1951
1952 /* Heurestics to calculate number of duplicate ACKs. There's no dupACKs
1953  * counter when SACK is enabled (without SACK, sacked_out is used for
1954  * that purpose).
1955  *
1956  * Instead, with FACK TCP uses fackets_out that includes both SACKed
1957  * segments up to the highest received SACK block so far and holes in
1958  * between them.
1959  *
1960  * With reordering, holes may still be in flight, so RFC3517 recovery
1961  * uses pure sacked_out (total number of SACKed segments) even though
1962  * it violates the RFC that uses duplicate ACKs, often these are equal
1963  * but when e.g. out-of-window ACKs or packet duplication occurs,
1964  * they differ. Since neither occurs due to loss, TCP should really
1965  * ignore them.
1966  */
1967 static inline int tcp_dupack_heurestics(struct tcp_sock *tp)
1968 {
1969         return tcp_is_fack(tp) ? tp->fackets_out : tp->sacked_out + 1;
1970 }
1971
1972 static inline int tcp_skb_timedout(struct sock *sk, struct sk_buff *skb)
1973 {
1974         return (tcp_time_stamp - TCP_SKB_CB(skb)->when > inet_csk(sk)->icsk_rto);
1975 }
1976
1977 static inline int tcp_head_timedout(struct sock *sk)
1978 {
1979         struct tcp_sock *tp = tcp_sk(sk);
1980
1981         return tp->packets_out &&
1982                tcp_skb_timedout(sk, tcp_write_queue_head(sk));
1983 }
1984
1985 /* Linux NewReno/SACK/FACK/ECN state machine.
1986  * --------------------------------------
1987  *
1988  * "Open"       Normal state, no dubious events, fast path.
1989  * "Disorder"   In all the respects it is "Open",
1990  *              but requires a bit more attention. It is entered when
1991  *              we see some SACKs or dupacks. It is split of "Open"
1992  *              mainly to move some processing from fast path to slow one.
1993  * "CWR"        CWND was reduced due to some Congestion Notification event.
1994  *              It can be ECN, ICMP source quench, local device congestion.
1995  * "Recovery"   CWND was reduced, we are fast-retransmitting.
1996  * "Loss"       CWND was reduced due to RTO timeout or SACK reneging.
1997  *
1998  * tcp_fastretrans_alert() is entered:
1999  * - each incoming ACK, if state is not "Open"
2000  * - when arrived ACK is unusual, namely:
2001  *      * SACK
2002  *      * Duplicate ACK.
2003  *      * ECN ECE.
2004  *
2005  * Counting packets in flight is pretty simple.
2006  *
2007  *      in_flight = packets_out - left_out + retrans_out
2008  *
2009  *      packets_out is SND.NXT-SND.UNA counted in packets.
2010  *
2011  *      retrans_out is number of retransmitted segments.
2012  *
2013  *      left_out is number of segments left network, but not ACKed yet.
2014  *
2015  *              left_out = sacked_out + lost_out
2016  *
2017  *     sacked_out: Packets, which arrived to receiver out of order
2018  *                 and hence not ACKed. With SACKs this number is simply
2019  *                 amount of SACKed data. Even without SACKs
2020  *                 it is easy to give pretty reliable estimate of this number,
2021  *                 counting duplicate ACKs.
2022  *
2023  *       lost_out: Packets lost by network. TCP has no explicit
2024  *                 "loss notification" feedback from network (for now).
2025  *                 It means that this number can be only _guessed_.
2026  *                 Actually, it is the heuristics to predict lossage that
2027  *                 distinguishes different algorithms.
2028  *
2029  *      F.e. after RTO, when all the queue is considered as lost,
2030  *      lost_out = packets_out and in_flight = retrans_out.
2031  *
2032  *              Essentially, we have now two algorithms counting
2033  *              lost packets.
2034  *
2035  *              FACK: It is the simplest heuristics. As soon as we decided
2036  *              that something is lost, we decide that _all_ not SACKed
2037  *              packets until the most forward SACK are lost. I.e.
2038  *              lost_out = fackets_out - sacked_out and left_out = fackets_out.
2039  *              It is absolutely correct estimate, if network does not reorder
2040  *              packets. And it loses any connection to reality when reordering
2041  *              takes place. We use FACK by default until reordering
2042  *              is suspected on the path to this destination.
2043  *
2044  *              NewReno: when Recovery is entered, we assume that one segment
2045  *              is lost (classic Reno). While we are in Recovery and
2046  *              a partial ACK arrives, we assume that one more packet
2047  *              is lost (NewReno). This heuristics are the same in NewReno
2048  *              and SACK.
2049  *
2050  *  Imagine, that's all! Forget about all this shamanism about CWND inflation
2051  *  deflation etc. CWND is real congestion window, never inflated, changes
2052  *  only according to classic VJ rules.
2053  *
2054  * Really tricky (and requiring careful tuning) part of algorithm
2055  * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
2056  * The first determines the moment _when_ we should reduce CWND and,
2057  * hence, slow down forward transmission. In fact, it determines the moment
2058  * when we decide that hole is caused by loss, rather than by a reorder.
2059  *
2060  * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
2061  * holes, caused by lost packets.
2062  *
2063  * And the most logically complicated part of algorithm is undo
2064  * heuristics. We detect false retransmits due to both too early
2065  * fast retransmit (reordering) and underestimated RTO, analyzing
2066  * timestamps and D-SACKs. When we detect that some segments were
2067  * retransmitted by mistake and CWND reduction was wrong, we undo
2068  * window reduction and abort recovery phase. This logic is hidden
2069  * inside several functions named tcp_try_undo_<something>.
2070  */
2071
2072 /* This function decides, when we should leave Disordered state
2073  * and enter Recovery phase, reducing congestion window.
2074  *
2075  * Main question: may we further continue forward transmission
2076  * with the same cwnd?
2077  */
2078 static int tcp_time_to_recover(struct sock *sk)
2079 {
2080         struct tcp_sock *tp = tcp_sk(sk);
2081         __u32 packets_out;
2082
2083         /* Do not perform any recovery during F-RTO algorithm */
2084         if (tp->frto_counter)
2085                 return 0;
2086
2087         /* Trick#1: The loss is proven. */
2088         if (tp->lost_out)
2089                 return 1;
2090
2091         /* Not-A-Trick#2 : Classic rule... */
2092         if (tcp_dupack_heurestics(tp) > tp->reordering)
2093                 return 1;
2094
2095         /* Trick#3 : when we use RFC2988 timer restart, fast
2096          * retransmit can be triggered by timeout of queue head.
2097          */
2098         if (tcp_is_fack(tp) && tcp_head_timedout(sk))
2099                 return 1;
2100
2101         /* Trick#4: It is still not OK... But will it be useful to delay
2102          * recovery more?
2103          */
2104         packets_out = tp->packets_out;
2105         if (packets_out <= tp->reordering &&
2106             tp->sacked_out >= max_t(__u32, packets_out/2, sysctl_tcp_reordering) &&
2107             !tcp_may_send_now(sk)) {
2108                 /* We have nothing to send. This connection is limited
2109                  * either by receiver window or by application.
2110                  */
2111                 return 1;
2112         }
2113
2114         return 0;
2115 }
2116
2117 /* RFC: This is from the original, I doubt that this is necessary at all:
2118  * clear xmit_retrans hint if seq of this skb is beyond hint. How could we
2119  * retransmitted past LOST markings in the first place? I'm not fully sure
2120  * about undo and end of connection cases, which can cause R without L?
2121  */
2122 static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
2123 {
2124         if ((tp->retransmit_skb_hint != NULL) &&
2125             before(TCP_SKB_CB(skb)->seq,
2126                    TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
2127                 tp->retransmit_skb_hint = NULL;
2128 }
2129
2130 /* Mark head of queue up as lost. With RFC3517 SACK, the packets is
2131  * is against sacked "cnt", otherwise it's against facked "cnt"
2132  */
2133 static void tcp_mark_head_lost(struct sock *sk, int packets, int fast_rexmit)
2134 {
2135         struct tcp_sock *tp = tcp_sk(sk);
2136         struct sk_buff *skb;
2137         int cnt;
2138
2139         BUG_TRAP(packets <= tp->packets_out);
2140         if (tp->lost_skb_hint) {
2141                 skb = tp->lost_skb_hint;
2142                 cnt = tp->lost_cnt_hint;
2143         } else {
2144                 skb = tcp_write_queue_head(sk);
2145                 cnt = 0;
2146         }
2147
2148         tcp_for_write_queue_from(skb, sk) {
2149                 if (skb == tcp_send_head(sk))
2150                         break;
2151                 /* TODO: do this better */
2152                 /* this is not the most efficient way to do this... */
2153                 tp->lost_skb_hint = skb;
2154                 tp->lost_cnt_hint = cnt;
2155
2156                 if (tcp_is_fack(tp) || tcp_is_reno(tp) ||
2157                     (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
2158                         cnt += tcp_skb_pcount(skb);
2159
2160                 if (((!fast_rexmit || (tp->lost_out > 0)) && (cnt > packets)) ||
2161                     after(TCP_SKB_CB(skb)->end_seq, tp->high_seq))
2162                         break;
2163                 if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_SACKED_ACKED|TCPCB_LOST))) {
2164                         TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
2165                         tp->lost_out += tcp_skb_pcount(skb);
2166                         tcp_verify_retransmit_hint(tp, skb);
2167                 }
2168         }
2169         tcp_verify_left_out(tp);
2170 }
2171
2172 /* Account newly detected lost packet(s) */
2173
2174 static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
2175 {
2176         struct tcp_sock *tp = tcp_sk(sk);
2177
2178         if (tcp_is_reno(tp)) {
2179                 tcp_mark_head_lost(sk, 1, fast_rexmit);
2180         } else if (tcp_is_fack(tp)) {
2181                 int lost = tp->fackets_out - tp->reordering;
2182                 if (lost <= 0)
2183                         lost = 1;
2184                 tcp_mark_head_lost(sk, lost, fast_rexmit);
2185         } else {
2186                 int sacked_upto = tp->sacked_out - tp->reordering;
2187                 if (sacked_upto < 0)
2188                         sacked_upto = 0;
2189                 tcp_mark_head_lost(sk, sacked_upto, fast_rexmit);
2190         }
2191
2192         /* New heuristics: it is possible only after we switched
2193          * to restart timer each time when something is ACKed.
2194          * Hence, we can detect timed out packets during fast
2195          * retransmit without falling to slow start.
2196          */
2197         if (tcp_is_fack(tp) && tcp_head_timedout(sk)) {
2198                 struct sk_buff *skb;
2199
2200                 skb = tp->scoreboard_skb_hint ? tp->scoreboard_skb_hint
2201                         : tcp_write_queue_head(sk);
2202
2203                 tcp_for_write_queue_from(skb, sk) {
2204                         if (skb == tcp_send_head(sk))
2205                                 break;
2206                         if (!tcp_skb_timedout(sk, skb))
2207                                 break;
2208
2209                         if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_SACKED_ACKED|TCPCB_LOST))) {
2210                                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
2211                                 tp->lost_out += tcp_skb_pcount(skb);
2212                                 tcp_verify_retransmit_hint(tp, skb);
2213                         }
2214                 }
2215
2216                 tp->scoreboard_skb_hint = skb;
2217
2218                 tcp_verify_left_out(tp);
2219         }
2220 }
2221
2222 /* CWND moderation, preventing bursts due to too big ACKs
2223  * in dubious situations.
2224  */
2225 static inline void tcp_moderate_cwnd(struct tcp_sock *tp)
2226 {
2227         tp->snd_cwnd = min(tp->snd_cwnd,
2228                            tcp_packets_in_flight(tp) + tcp_max_burst(tp));
2229         tp->snd_cwnd_stamp = tcp_time_stamp;
2230 }
2231
2232 /* Lower bound on congestion window is slow start threshold
2233  * unless congestion avoidance choice decides to overide it.
2234  */
2235 static inline u32 tcp_cwnd_min(const struct sock *sk)
2236 {
2237         const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
2238
2239         return ca_ops->min_cwnd ? ca_ops->min_cwnd(sk) : tcp_sk(sk)->snd_ssthresh;
2240 }
2241
2242 /* Decrease cwnd each second ack. */
2243 static void tcp_cwnd_down(struct sock *sk, int flag)
2244 {
2245         struct tcp_sock *tp = tcp_sk(sk);
2246         int decr = tp->snd_cwnd_cnt + 1;
2247
2248         if ((flag & (FLAG_ANY_PROGRESS | FLAG_DSACKING_ACK)) ||
2249             (tcp_is_reno(tp) && !(flag & FLAG_NOT_DUP))) {
2250                 tp->snd_cwnd_cnt = decr & 1;
2251                 decr >>= 1;
2252
2253                 if (decr && tp->snd_cwnd > tcp_cwnd_min(sk))
2254                         tp->snd_cwnd -= decr;
2255
2256                 tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp) + 1);
2257                 tp->snd_cwnd_stamp = tcp_time_stamp;
2258         }
2259 }
2260
2261 /* Nothing was retransmitted or returned timestamp is less
2262  * than timestamp of the first retransmission.
2263  */
2264 static inline int tcp_packet_delayed(struct tcp_sock *tp)
2265 {
2266         return !tp->retrans_stamp ||
2267                 (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
2268                  (__s32)(tp->rx_opt.rcv_tsecr - tp->retrans_stamp) < 0);
2269 }
2270
2271 /* Undo procedures. */
2272
2273 #if FASTRETRANS_DEBUG > 1
2274 static void DBGUNDO(struct sock *sk, const char *msg)
2275 {
2276         struct tcp_sock *tp = tcp_sk(sk);
2277         struct inet_sock *inet = inet_sk(sk);
2278
2279         printk(KERN_DEBUG "Undo %s %u.%u.%u.%u/%u c%u l%u ss%u/%u p%u\n",
2280                msg,
2281                NIPQUAD(inet->daddr), ntohs(inet->dport),
2282                tp->snd_cwnd, tcp_left_out(tp),
2283                tp->snd_ssthresh, tp->prior_ssthresh,
2284                tp->packets_out);
2285 }
2286 #else
2287 #define DBGUNDO(x...) do { } while (0)
2288 #endif
2289
2290 static void tcp_undo_cwr(struct sock *sk, const int undo)
2291 {
2292         struct tcp_sock *tp = tcp_sk(sk);
2293
2294         if (tp->prior_ssthresh) {
2295                 const struct inet_connection_sock *icsk = inet_csk(sk);
2296
2297                 if (icsk->icsk_ca_ops->undo_cwnd)
2298                         tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
2299                 else
2300                         tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh << 1);
2301
2302                 if (undo && tp->prior_ssthresh > tp->snd_ssthresh) {
2303                         tp->snd_ssthresh = tp->prior_ssthresh;
2304                         TCP_ECN_withdraw_cwr(tp);
2305                 }
2306         } else {
2307                 tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
2308         }
2309         tcp_moderate_cwnd(tp);
2310         tp->snd_cwnd_stamp = tcp_time_stamp;
2311
2312         /* There is something screwy going on with the retrans hints after
2313            an undo */
2314         tcp_clear_all_retrans_hints(tp);
2315 }
2316
2317 static inline int tcp_may_undo(struct tcp_sock *tp)
2318 {
2319         return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
2320 }
2321
2322 /* People celebrate: "We love our President!" */
2323 static int tcp_try_undo_recovery(struct sock *sk)
2324 {
2325         struct tcp_sock *tp = tcp_sk(sk);
2326
2327         if (tcp_may_undo(tp)) {
2328                 /* Happy end! We did not retransmit anything
2329                  * or our original transmission succeeded.
2330                  */
2331                 DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
2332                 tcp_undo_cwr(sk, 1);
2333                 if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
2334                         NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO);
2335                 else
2336                         NET_INC_STATS_BH(LINUX_MIB_TCPFULLUNDO);
2337                 tp->undo_marker = 0;
2338         }
2339         if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
2340                 /* Hold old state until something *above* high_seq
2341                  * is ACKed. For Reno it is MUST to prevent false
2342                  * fast retransmits (RFC2582). SACK TCP is safe. */
2343                 tcp_moderate_cwnd(tp);
2344                 return 1;
2345         }
2346         tcp_set_ca_state(sk, TCP_CA_Open);
2347         return 0;
2348 }
2349
2350 /* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
2351 static void tcp_try_undo_dsack(struct sock *sk)
2352 {
2353         struct tcp_sock *tp = tcp_sk(sk);
2354
2355         if (tp->undo_marker && !tp->undo_retrans) {
2356                 DBGUNDO(sk, "D-SACK");
2357                 tcp_undo_cwr(sk, 1);
2358                 tp->undo_marker = 0;
2359                 NET_INC_STATS_BH(LINUX_MIB_TCPDSACKUNDO);
2360         }
2361 }
2362
2363 /* Undo during fast recovery after partial ACK. */
2364
2365 static int tcp_try_undo_partial(struct sock *sk, int acked)
2366 {
2367         struct tcp_sock *tp = tcp_sk(sk);
2368         /* Partial ACK arrived. Force Hoe's retransmit. */
2369         int failed = tcp_is_reno(tp) || (tcp_fackets_out(tp) > tp->reordering);
2370
2371         if (tcp_may_undo(tp)) {
2372                 /* Plain luck! Hole if filled with delayed
2373                  * packet, rather than with a retransmit.
2374                  */
2375                 if (tp->retrans_out == 0)
2376                         tp->retrans_stamp = 0;
2377
2378                 tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
2379
2380                 DBGUNDO(sk, "Hoe");
2381                 tcp_undo_cwr(sk, 0);
2382                 NET_INC_STATS_BH(LINUX_MIB_TCPPARTIALUNDO);
2383
2384                 /* So... Do not make Hoe's retransmit yet.
2385                  * If the first packet was delayed, the rest
2386                  * ones are most probably delayed as well.
2387                  */
2388                 failed = 0;
2389         }
2390         return failed;
2391 }
2392
2393 /* Undo during loss recovery after partial ACK. */
2394 static int tcp_try_undo_loss(struct sock *sk)
2395 {
2396         struct tcp_sock *tp = tcp_sk(sk);
2397
2398         if (tcp_may_undo(tp)) {
2399                 struct sk_buff *skb;
2400                 tcp_for_write_queue(skb, sk) {
2401                         if (skb == tcp_send_head(sk))
2402                                 break;
2403                         TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
2404                 }
2405
2406                 tcp_clear_all_retrans_hints(tp);
2407
2408                 DBGUNDO(sk, "partial loss");
2409                 tp->lost_out = 0;
2410                 tcp_undo_cwr(sk, 1);
2411                 NET_INC_STATS_BH(LINUX_MIB_TCPLOSSUNDO);
2412                 inet_csk(sk)->icsk_retransmits = 0;
2413                 tp->undo_marker = 0;
2414                 if (tcp_is_sack(tp))
2415                         tcp_set_ca_state(sk, TCP_CA_Open);
2416                 return 1;
2417         }
2418         return 0;
2419 }
2420
2421 static inline void tcp_complete_cwr(struct sock *sk)
2422 {
2423         struct tcp_sock *tp = tcp_sk(sk);
2424         tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
2425         tp->snd_cwnd_stamp = tcp_time_stamp;
2426         tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
2427 }
2428
2429 static void tcp_try_to_open(struct sock *sk, int flag)
2430 {
2431         struct tcp_sock *tp = tcp_sk(sk);
2432
2433         tcp_verify_left_out(tp);
2434
2435         if (tp->retrans_out == 0)
2436                 tp->retrans_stamp = 0;
2437
2438         if (flag & FLAG_ECE)
2439                 tcp_enter_cwr(sk, 1);
2440
2441         if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
2442                 int state = TCP_CA_Open;
2443
2444                 if (tcp_left_out(tp) || tp->retrans_out || tp->undo_marker)
2445                         state = TCP_CA_Disorder;
2446
2447                 if (inet_csk(sk)->icsk_ca_state != state) {
2448                         tcp_set_ca_state(sk, state);
2449                         tp->high_seq = tp->snd_nxt;
2450                 }
2451                 tcp_moderate_cwnd(tp);
2452         } else {
2453                 tcp_cwnd_down(sk, flag);
2454         }
2455 }
2456
2457 static void tcp_mtup_probe_failed(struct sock *sk)
2458 {
2459         struct inet_connection_sock *icsk = inet_csk(sk);
2460
2461         icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
2462         icsk->icsk_mtup.probe_size = 0;
2463 }
2464
2465 static void tcp_mtup_probe_success(struct sock *sk, struct sk_buff *skb)
2466 {
2467         struct tcp_sock *tp = tcp_sk(sk);
2468         struct inet_connection_sock *icsk = inet_csk(sk);
2469
2470         /* FIXME: breaks with very large cwnd */
2471         tp->prior_ssthresh = tcp_current_ssthresh(sk);
2472         tp->snd_cwnd = tp->snd_cwnd *
2473                        tcp_mss_to_mtu(sk, tp->mss_cache) /
2474                        icsk->icsk_mtup.probe_size;
2475         tp->snd_cwnd_cnt = 0;
2476         tp->snd_cwnd_stamp = tcp_time_stamp;
2477         tp->rcv_ssthresh = tcp_current_ssthresh(sk);
2478
2479         icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
2480         icsk->icsk_mtup.probe_size = 0;
2481         tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
2482 }
2483
2484 /* Process an event, which can update packets-in-flight not trivially.
2485  * Main goal of this function is to calculate new estimate for left_out,
2486  * taking into account both packets sitting in receiver's buffer and
2487  * packets lost by network.
2488  *
2489  * Besides that it does CWND reduction, when packet loss is detected
2490  * and changes state of machine.
2491  *
2492  * It does _not_ decide what to send, it is made in function
2493  * tcp_xmit_retransmit_queue().
2494  */
2495 static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked, int flag)
2496 {
2497         struct inet_connection_sock *icsk = inet_csk(sk);
2498         struct tcp_sock *tp = tcp_sk(sk);
2499         int is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
2500         int do_lost = is_dupack || ((flag & FLAG_DATA_SACKED) &&
2501                                     (tcp_fackets_out(tp) > tp->reordering));
2502         int fast_rexmit = 0;
2503
2504         if (WARN_ON(!tp->packets_out && tp->sacked_out))
2505                 tp->sacked_out = 0;
2506         if (WARN_ON(!tp->sacked_out && tp->fackets_out))
2507                 tp->fackets_out = 0;
2508
2509         /* Now state machine starts.
2510          * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
2511         if (flag & FLAG_ECE)
2512                 tp->prior_ssthresh = 0;
2513
2514         /* B. In all the states check for reneging SACKs. */
2515         if (tcp_check_sack_reneging(sk, flag))
2516                 return;
2517
2518         /* C. Process data loss notification, provided it is valid. */
2519         if (tcp_is_fack(tp) && (flag & FLAG_DATA_LOST) &&
2520             before(tp->snd_una, tp->high_seq) &&
2521             icsk->icsk_ca_state != TCP_CA_Open &&
2522             tp->fackets_out > tp->reordering) {
2523                 tcp_mark_head_lost(sk, tp->fackets_out - tp->reordering, 0);
2524                 NET_INC_STATS_BH(LINUX_MIB_TCPLOSS);
2525         }
2526
2527         /* D. Check consistency of the current state. */
2528         tcp_verify_left_out(tp);
2529
2530         /* E. Check state exit conditions. State can be terminated
2531          *    when high_seq is ACKed. */
2532         if (icsk->icsk_ca_state == TCP_CA_Open) {
2533                 BUG_TRAP(tp->retrans_out == 0);
2534                 tp->retrans_stamp = 0;
2535         } else if (!before(tp->snd_una, tp->high_seq)) {
2536                 switch (icsk->icsk_ca_state) {
2537                 case TCP_CA_Loss:
2538                         icsk->icsk_retransmits = 0;
2539                         if (tcp_try_undo_recovery(sk))
2540                                 return;
2541                         break;
2542
2543                 case TCP_CA_CWR:
2544                         /* CWR is to be held something *above* high_seq
2545                          * is ACKed for CWR bit to reach receiver. */
2546                         if (tp->snd_una != tp->high_seq) {
2547                                 tcp_complete_cwr(sk);
2548                                 tcp_set_ca_state(sk, TCP_CA_Open);
2549                         }
2550                         break;
2551
2552                 case TCP_CA_Disorder:
2553                         tcp_try_undo_dsack(sk);
2554                         if (!tp->undo_marker ||
2555                             /* For SACK case do not Open to allow to undo
2556                              * catching for all duplicate ACKs. */
2557                             tcp_is_reno(tp) || tp->snd_una != tp->high_seq) {
2558                                 tp->undo_marker = 0;
2559                                 tcp_set_ca_state(sk, TCP_CA_Open);
2560                         }
2561                         break;
2562
2563                 case TCP_CA_Recovery:
2564                         if (tcp_is_reno(tp))
2565                                 tcp_reset_reno_sack(tp);
2566                         if (tcp_try_undo_recovery(sk))
2567                                 return;
2568                         tcp_complete_cwr(sk);
2569                         break;
2570                 }
2571         }
2572
2573         /* F. Process state. */
2574         switch (icsk->icsk_ca_state) {
2575         case TCP_CA_Recovery:
2576                 if (!(flag & FLAG_SND_UNA_ADVANCED)) {
2577                         if (tcp_is_reno(tp) && is_dupack)
2578                                 tcp_add_reno_sack(sk);
2579                 } else
2580                         do_lost = tcp_try_undo_partial(sk, pkts_acked);
2581                 break;
2582         case TCP_CA_Loss:
2583                 if (flag & FLAG_DATA_ACKED)
2584                         icsk->icsk_retransmits = 0;
2585                 if (!tcp_try_undo_loss(sk)) {
2586                         tcp_moderate_cwnd(tp);
2587                         tcp_xmit_retransmit_queue(sk);
2588                         return;
2589                 }
2590                 if (icsk->icsk_ca_state != TCP_CA_Open)
2591                         return;
2592                 /* Loss is undone; fall through to processing in Open state. */
2593         default:
2594                 if (tcp_is_reno(tp)) {
2595                         if (flag & FLAG_SND_UNA_ADVANCED)
2596                                 tcp_reset_reno_sack(tp);
2597                         if (is_dupack)
2598                                 tcp_add_reno_sack(sk);
2599                 }
2600
2601                 if (icsk->icsk_ca_state == TCP_CA_Disorder)
2602                         tcp_try_undo_dsack(sk);
2603
2604                 if (!tcp_time_to_recover(sk)) {
2605                         tcp_try_to_open(sk, flag);
2606                         return;
2607                 }
2608
2609                 /* MTU probe failure: don't reduce cwnd */
2610                 if (icsk->icsk_ca_state < TCP_CA_CWR &&
2611                     icsk->icsk_mtup.probe_size &&
2612                     tp->snd_una == tp->mtu_probe.probe_seq_start) {
2613                         tcp_mtup_probe_failed(sk);
2614                         /* Restores the reduction we did in tcp_mtup_probe() */
2615                         tp->snd_cwnd++;
2616                         tcp_simple_retransmit(sk);
2617                         return;
2618                 }
2619
2620                 /* Otherwise enter Recovery state */
2621
2622                 if (tcp_is_reno(tp))
2623                         NET_INC_STATS_BH(LINUX_MIB_TCPRENORECOVERY);
2624                 else
2625                         NET_INC_STATS_BH(LINUX_MIB_TCPSACKRECOVERY);
2626
2627                 tp->high_seq = tp->snd_nxt;
2628                 tp->prior_ssthresh = 0;
2629                 tp->undo_marker = tp->snd_una;
2630                 tp->undo_retrans = tp->retrans_out;
2631
2632                 if (icsk->icsk_ca_state < TCP_CA_CWR) {
2633                         if (!(flag & FLAG_ECE))
2634                                 tp->prior_ssthresh = tcp_current_ssthresh(sk);
2635                         tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
2636                         TCP_ECN_queue_cwr(tp);
2637                 }
2638
2639                 tp->bytes_acked = 0;
2640                 tp->snd_cwnd_cnt = 0;
2641                 tcp_set_ca_state(sk, TCP_CA_Recovery);
2642                 fast_rexmit = 1;
2643         }
2644
2645         if (do_lost || (tcp_is_fack(tp) && tcp_head_timedout(sk)))
2646                 tcp_update_scoreboard(sk, fast_rexmit);
2647         tcp_cwnd_down(sk, flag);
2648         tcp_xmit_retransmit_queue(sk);
2649 }
2650
2651 /* Read draft-ietf-tcplw-high-performance before mucking
2652  * with this code. (Supersedes RFC1323)
2653  */
2654 static void tcp_ack_saw_tstamp(struct sock *sk, int flag)
2655 {
2656         /* RTTM Rule: A TSecr value received in a segment is used to
2657          * update the averaged RTT measurement only if the segment
2658          * acknowledges some new data, i.e., only if it advances the
2659          * left edge of the send window.
2660          *
2661          * See draft-ietf-tcplw-high-performance-00, section 3.3.
2662          * 1998/04/10 Andrey V. Savochkin <saw@msu.ru>
2663          *
2664          * Changed: reset backoff as soon as we see the first valid sample.
2665          * If we do not, we get strongly overestimated rto. With timestamps
2666          * samples are accepted even from very old segments: f.e., when rtt=1
2667          * increases to 8, we retransmit 5 times and after 8 seconds delayed
2668          * answer arrives rto becomes 120 seconds! If at least one of segments
2669          * in window is lost... Voila.                          --ANK (010210)
2670          */
2671         struct tcp_sock *tp = tcp_sk(sk);
2672         const __u32 seq_rtt = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
2673         tcp_rtt_estimator(sk, seq_rtt);
2674         tcp_set_rto(sk);
2675         inet_csk(sk)->icsk_backoff = 0;
2676         tcp_bound_rto(sk);
2677 }
2678
2679 static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, int flag)
2680 {
2681         /* We don't have a timestamp. Can only use
2682          * packets that are not retransmitted to determine
2683          * rtt estimates. Also, we must not reset the
2684          * backoff for rto until we get a non-retransmitted
2685          * packet. This allows us to deal with a situation
2686          * where the network delay has increased suddenly.
2687          * I.e. Karn's algorithm. (SIGCOMM '87, p5.)
2688          */
2689
2690         if (flag & FLAG_RETRANS_DATA_ACKED)
2691                 return;
2692
2693         tcp_rtt_estimator(sk, seq_rtt);
2694         tcp_set_rto(sk);
2695         inet_csk(sk)->icsk_backoff = 0;
2696         tcp_bound_rto(sk);
2697 }
2698
2699 static inline void tcp_ack_update_rtt(struct sock *sk, const int flag,
2700                                       const s32 seq_rtt)
2701 {
2702         const struct tcp_sock *tp = tcp_sk(sk);
2703         /* Note that peer MAY send zero echo. In this case it is ignored. (rfc1323) */
2704         if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
2705                 tcp_ack_saw_tstamp(sk, flag);
2706         else if (seq_rtt >= 0)
2707                 tcp_ack_no_tstamp(sk, seq_rtt, flag);
2708 }
2709
2710 static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
2711 {
2712         const struct inet_connection_sock *icsk = inet_csk(sk);
2713         icsk->icsk_ca_ops->cong_avoid(sk, ack, in_flight);
2714         tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
2715 }
2716
2717 /* Restart timer after forward progress on connection.
2718  * RFC2988 recommends to restart timer to now+rto.
2719  */
2720 static void tcp_rearm_rto(struct sock *sk)
2721 {
2722         struct tcp_sock *tp = tcp_sk(sk);
2723
2724         if (!tp->packets_out) {
2725                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
2726         } else {
2727                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
2728                                           inet_csk(sk)->icsk_rto, TCP_RTO_MAX);
2729         }
2730 }
2731
2732 /* If we get here, the whole TSO packet has not been acked. */
2733 static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
2734 {
2735         struct tcp_sock *tp = tcp_sk(sk);
2736         u32 packets_acked;
2737
2738         BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una));
2739
2740         packets_acked = tcp_skb_pcount(skb);
2741         if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
2742                 return 0;
2743         packets_acked -= tcp_skb_pcount(skb);
2744
2745         if (packets_acked) {
2746                 BUG_ON(tcp_skb_pcount(skb) == 0);
2747                 BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq));
2748         }
2749
2750         return packets_acked;
2751 }
2752
2753 /* Remove acknowledged frames from the retransmission queue. If our packet
2754  * is before the ack sequence we can discard it as it's confirmed to have
2755  * arrived at the other end.
2756  */
2757 static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets)
2758 {
2759         struct tcp_sock *tp = tcp_sk(sk);
2760         const struct inet_connection_sock *icsk = inet_csk(sk);
2761         struct sk_buff *skb;
2762         u32 now = tcp_time_stamp;
2763         int fully_acked = 1;
2764         int flag = 0;
2765         u32 pkts_acked = 0;
2766         u32 reord = tp->packets_out;
2767         s32 seq_rtt = -1;
2768         s32 ca_seq_rtt = -1;
2769         ktime_t last_ackt = net_invalid_timestamp();
2770
2771         while ((skb = tcp_write_queue_head(sk)) && skb != tcp_send_head(sk)) {
2772                 struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
2773                 u32 end_seq;
2774                 u32 acked_pcount;
2775                 u8 sacked = scb->sacked;
2776
2777                 /* Determine how many packets and what bytes were acked, tso and else */
2778                 if (after(scb->end_seq, tp->snd_una)) {
2779                         if (tcp_skb_pcount(skb) == 1 ||
2780                             !after(tp->snd_una, scb->seq))
2781                                 break;
2782
2783                         acked_pcount = tcp_tso_acked(sk, skb);
2784                         if (!acked_pcount)
2785                                 break;
2786
2787                         fully_acked = 0;
2788                         end_seq = tp->snd_una;
2789                 } else {
2790                         acked_pcount = tcp_skb_pcount(skb);
2791                         end_seq = scb->end_seq;
2792                 }
2793
2794                 /* MTU probing checks */
2795                 if (fully_acked && icsk->icsk_mtup.probe_size &&
2796                     !after(tp->mtu_probe.probe_seq_end, scb->end_seq)) {
2797                         tcp_mtup_probe_success(sk, skb);
2798                 }
2799
2800                 if (sacked & TCPCB_RETRANS) {
2801                         if (sacked & TCPCB_SACKED_RETRANS)
2802                                 tp->retrans_out -= acked_pcount;
2803                         flag |= FLAG_RETRANS_DATA_ACKED;
2804                         ca_seq_rtt = -1;
2805                         seq_rtt = -1;
2806                         if ((flag & FLAG_DATA_ACKED) || (acked_pcount > 1))
2807                                 flag |= FLAG_NONHEAD_RETRANS_ACKED;
2808                 } else {
2809                         ca_seq_rtt = now - scb->when;
2810                         last_ackt = skb->tstamp;
2811                         if (seq_rtt < 0) {
2812                                 seq_rtt = ca_seq_rtt;
2813                         }
2814                         if (!(sacked & TCPCB_SACKED_ACKED))
2815                                 reord = min(pkts_acked, reord);
2816                 }
2817
2818                 if (sacked & TCPCB_SACKED_ACKED)
2819                         tp->sacked_out -= acked_pcount;
2820                 if (sacked & TCPCB_LOST)
2821                         tp->lost_out -= acked_pcount;
2822
2823                 if (unlikely(tp->urg_mode && !before(end_seq, tp->snd_up)))
2824                         tp->urg_mode = 0;
2825
2826                 tp->packets_out -= acked_pcount;
2827                 pkts_acked += acked_pcount;
2828
2829                 /* Initial outgoing SYN's get put onto the write_queue
2830                  * just like anything else we transmit.  It is not
2831                  * true data, and if we misinform our callers that
2832                  * this ACK acks real data, we will erroneously exit
2833                  * connection startup slow start one packet too
2834                  * quickly.  This is severely frowned upon behavior.
2835                  */
2836                 if (!(scb->flags & TCPCB_FLAG_SYN)) {
2837                         flag |= FLAG_DATA_ACKED;
2838                 } else {
2839                         flag |= FLAG_SYN_ACKED;
2840                         tp->retrans_stamp = 0;
2841                 }
2842
2843                 if (!fully_acked)
2844                         break;
2845
2846                 tcp_unlink_write_queue(skb, sk);
2847                 sk_wmem_free_skb(sk, skb);
2848                 tcp_clear_all_retrans_hints(tp);
2849         }
2850
2851         if (skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
2852                 flag |= FLAG_SACK_RENEGING;
2853
2854         if (flag & FLAG_ACKED) {
2855                 const struct tcp_congestion_ops *ca_ops
2856                         = inet_csk(sk)->icsk_ca_ops;
2857
2858                 tcp_ack_update_rtt(sk, flag, seq_rtt);
2859                 tcp_rearm_rto(sk);
2860
2861                 if (tcp_is_reno(tp)) {
2862                         tcp_remove_reno_sacks(sk, pkts_acked);
2863                 } else {
2864                         /* Non-retransmitted hole got filled? That's reordering */
2865                         if (reord < prior_fackets)
2866                                 tcp_update_reordering(sk, tp->fackets_out - reord, 0);
2867                 }
2868
2869                 tp->fackets_out -= min(pkts_acked, tp->fackets_out);
2870
2871                 if (ca_ops->pkts_acked) {
2872                         s32 rtt_us = -1;
2873
2874                         /* Is the ACK triggering packet unambiguous? */
2875                         if (!(flag & FLAG_RETRANS_DATA_ACKED)) {
2876                                 /* High resolution needed and available? */
2877                                 if (ca_ops->flags & TCP_CONG_RTT_STAMP &&
2878                                     !ktime_equal(last_ackt,
2879                                                  net_invalid_timestamp()))
2880                                         rtt_us = ktime_us_delta(ktime_get_real(),
2881                                                                 last_ackt);
2882                                 else if (ca_seq_rtt > 0)
2883                                         rtt_us = jiffies_to_usecs(ca_seq_rtt);
2884                         }
2885
2886                         ca_ops->pkts_acked(sk, pkts_acked, rtt_us);
2887                 }
2888         }
2889
2890 #if FASTRETRANS_DEBUG > 0
2891         BUG_TRAP((int)tp->sacked_out >= 0);
2892         BUG_TRAP((int)tp->lost_out >= 0);
2893         BUG_TRAP((int)tp->retrans_out >= 0);
2894         if (!tp->packets_out && tcp_is_sack(tp)) {
2895                 icsk = inet_csk(sk);
2896                 if (tp->lost_out) {
2897                         printk(KERN_DEBUG "Leak l=%u %d\n",
2898                                tp->lost_out, icsk->icsk_ca_state);
2899                         tp->lost_out = 0;
2900                 }
2901                 if (tp->sacked_out) {
2902                         printk(KERN_DEBUG "Leak s=%u %d\n",
2903                                tp->sacked_out, icsk->icsk_ca_state);
2904                         tp->sacked_out = 0;
2905                 }
2906                 if (tp->retrans_out) {
2907                         printk(KERN_DEBUG "Leak r=%u %d\n",
2908                                tp->retrans_out, icsk->icsk_ca_state);
2909                         tp->retrans_out = 0;
2910                 }
2911         }
2912 #endif
2913         return flag;
2914 }
2915
2916 static void tcp_ack_probe(struct sock *sk)
2917 {
2918         const struct tcp_sock *tp = tcp_sk(sk);
2919         struct inet_connection_sock *icsk = inet_csk(sk);
2920
2921         /* Was it a usable window open? */
2922
2923         if (!after(TCP_SKB_CB(tcp_send_head(sk))->end_seq, tcp_wnd_end(tp))) {
2924                 icsk->icsk_backoff = 0;
2925                 inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
2926                 /* Socket must be waked up by subsequent tcp_data_snd_check().
2927                  * This function is not for random using!
2928                  */
2929         } else {
2930                 inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
2931                                           min(icsk->icsk_rto << icsk->icsk_backoff, TCP_RTO_MAX),
2932                                           TCP_RTO_MAX);
2933         }
2934 }
2935
2936 static inline int tcp_ack_is_dubious(const struct sock *sk, const int flag)
2937 {
2938         return (!(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
2939                 inet_csk(sk)->icsk_ca_state != TCP_CA_Open);
2940 }
2941
2942 static inline int tcp_may_raise_cwnd(const struct sock *sk, const int flag)
2943 {
2944         const struct tcp_sock *tp = tcp_sk(sk);
2945         return (!(flag & FLAG_ECE) || tp->snd_cwnd < tp->snd_ssthresh) &&
2946                 !((1 << inet_csk(sk)->icsk_ca_state) & (TCPF_CA_Recovery | TCPF_CA_CWR));
2947 }
2948
2949 /* Check that window update is acceptable.
2950  * The function assumes that snd_una<=ack<=snd_next.
2951  */
2952 static inline int tcp_may_update_window(const struct tcp_sock *tp,
2953                                         const u32 ack, const u32 ack_seq,
2954                                         const u32 nwin)
2955 {
2956         return (after(ack, tp->snd_una) ||
2957                 after(ack_seq, tp->snd_wl1) ||
2958                 (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd));
2959 }
2960
2961 /* Update our send window.
2962  *
2963  * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
2964  * and in FreeBSD. NetBSD's one is even worse.) is wrong.
2965  */
2966 static int tcp_ack_update_window(struct sock *sk, struct sk_buff *skb, u32 ack,
2967                                  u32 ack_seq)
2968 {
2969         struct tcp_sock *tp = tcp_sk(sk);
2970         int flag = 0;
2971         u32 nwin = ntohs(tcp_hdr(skb)->window);
2972
2973         if (likely(!tcp_hdr(skb)->syn))
2974                 nwin <<= tp->rx_opt.snd_wscale;
2975
2976         if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
2977                 flag |= FLAG_WIN_UPDATE;
2978                 tcp_update_wl(tp, ack, ack_seq);
2979
2980                 if (tp->snd_wnd != nwin) {
2981                         tp->snd_wnd = nwin;
2982
2983                         /* Note, it is the only place, where
2984                          * fast path is recovered for sending TCP.
2985                          */
2986                         tp->pred_flags = 0;
2987                         tcp_fast_path_check(sk);
2988
2989                         if (nwin > tp->max_window) {
2990                                 tp->max_window = nwin;
2991                                 tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
2992                         }
2993                 }
2994         }
2995
2996         tp->snd_una = ack;
2997
2998         return flag;
2999 }
3000
3001 /* A very conservative spurious RTO response algorithm: reduce cwnd and
3002  * continue in congestion avoidance.
3003  */
3004 static void tcp_conservative_spur_to_response(struct tcp_sock *tp)
3005 {
3006         tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
3007         tp->snd_cwnd_cnt = 0;
3008         tp->bytes_acked = 0;
3009         TCP_ECN_queue_cwr(tp);
3010         tcp_moderate_cwnd(tp);
3011 }
3012
3013 /* A conservative spurious RTO response algorithm: reduce cwnd using
3014  * rate halving and continue in congestion avoidance.
3015  */
3016 static void tcp_ratehalving_spur_to_response(struct sock *sk)
3017 {
3018         tcp_enter_cwr(sk, 0);
3019 }
3020
3021 static void tcp_undo_spur_to_response(struct sock *sk, int flag)
3022 {
3023         if (flag & FLAG_ECE)
3024                 tcp_ratehalving_spur_to_response(sk);
3025         else
3026                 tcp_undo_cwr(sk, 1);
3027 }
3028
3029 /* F-RTO spurious RTO detection algorithm (RFC4138)
3030  *
3031  * F-RTO affects during two new ACKs following RTO (well, almost, see inline
3032  * comments). State (ACK number) is kept in frto_counter. When ACK advances
3033  * window (but not to or beyond highest sequence sent before RTO):
3034  *   On First ACK,  send two new segments out.
3035  *   On Second ACK, RTO was likely spurious. Do spurious response (response
3036  *                  algorithm is not part of the F-RTO detection algorithm
3037  *                  given in RFC4138 but can be selected separately).
3038  * Otherwise (basically on duplicate ACK), RTO was (likely) caused by a loss
3039  * and TCP falls back to conventional RTO recovery. F-RTO allows overriding
3040  * of Nagle, this is done using frto_counter states 2 and 3, when a new data
3041  * segment of any size sent during F-RTO, state 2 is upgraded to 3.
3042  *
3043  * Rationale: if the RTO was spurious, new ACKs should arrive from the
3044  * original window even after we transmit two new data segments.
3045  *
3046  * SACK version:
3047  *   on first step, wait until first cumulative ACK arrives, then move to
3048  *   the second step. In second step, the next ACK decides.
3049  *
3050  * F-RTO is implemented (mainly) in four functions:
3051  *   - tcp_use_frto() is used to determine if TCP is can use F-RTO
3052  *   - tcp_enter_frto() prepares TCP state on RTO if F-RTO is used, it is
3053  *     called when tcp_use_frto() showed green light
3054  *   - tcp_process_frto() handles incoming ACKs during F-RTO algorithm
3055  *   - tcp_enter_frto_loss() is called if there is not enough evidence
3056  *     to prove that the RTO is indeed spurious. It transfers the control
3057  *     from F-RTO to the conventional RTO recovery
3058  */
3059 static int tcp_process_frto(struct sock *sk, int flag)
3060 {
3061         struct tcp_sock *tp = tcp_sk(sk);
3062
3063         tcp_verify_left_out(tp);
3064
3065         /* Duplicate the behavior from Loss state (fastretrans_alert) */
3066         if (flag & FLAG_DATA_ACKED)
3067                 inet_csk(sk)->icsk_retransmits = 0;
3068
3069         if ((flag & FLAG_NONHEAD_RETRANS_ACKED) ||
3070             ((tp->frto_counter >= 2) && (flag & FLAG_RETRANS_DATA_ACKED)))
3071                 tp->undo_marker = 0;
3072
3073         if (!before(tp->snd_una, tp->frto_highmark)) {
3074                 tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3), flag);
3075                 return 1;
3076         }
3077
3078         if (!IsSackFrto() || tcp_is_reno(tp)) {
3079                 /* RFC4138 shortcoming in step 2; should also have case c):
3080                  * ACK isn't duplicate nor advances window, e.g., opposite dir
3081                  * data, winupdate
3082                  */
3083                 if (!(flag & FLAG_ANY_PROGRESS) && (flag & FLAG_NOT_DUP))
3084                         return 1;
3085
3086                 if (!(flag & FLAG_DATA_ACKED)) {
3087                         tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 0 : 3),
3088                                             flag);
3089                         return 1;
3090                 }
3091         } else {
3092                 if (!(flag & FLAG_DATA_ACKED) && (tp->frto_counter == 1)) {
3093                         /* Prevent sending of new data. */
3094                         tp->snd_cwnd = min(tp->snd_cwnd,
3095                                            tcp_packets_in_flight(tp));
3096                         return 1;
3097                 }
3098
3099                 if ((tp->frto_counter >= 2) &&
3100                     (!(flag & FLAG_FORWARD_PROGRESS) ||
3101                      ((flag & FLAG_DATA_SACKED) &&
3102                       !(flag & FLAG_ONLY_ORIG_SACKED)))) {
3103                         /* RFC4138 shortcoming (see comment above) */
3104                         if (!(flag & FLAG_FORWARD_PROGRESS) &&
3105                             (flag & FLAG_NOT_DUP))
3106                                 return 1;
3107
3108                         tcp_enter_frto_loss(sk, 3, flag);
3109                         return 1;
3110                 }
3111         }
3112
3113         if (tp->frto_counter == 1) {
3114                 /* tcp_may_send_now needs to see updated state */
3115                 tp->snd_cwnd = tcp_packets_in_flight(tp) + 2;
3116                 tp->frto_counter = 2;
3117
3118                 if (!tcp_may_send_now(sk))
3119                         tcp_enter_frto_loss(sk, 2, flag);
3120
3121                 return 1;
3122         } else {
3123                 switch (sysctl_tcp_frto_response) {
3124                 case 2:
3125                         tcp_undo_spur_to_response(sk, flag);
3126                         break;
3127                 case 1:
3128                         tcp_conservative_spur_to_response(tp);
3129                         break;
3130                 default:
3131                         tcp_ratehalving_spur_to_response(sk);
3132                         break;
3133                 }
3134                 tp->frto_counter = 0;
3135                 tp->undo_marker = 0;
3136                 NET_INC_STATS_BH(LINUX_MIB_TCPSPURIOUSRTOS);
3137         }
3138         return 0;
3139 }
3140
3141 /* This routine deals with incoming acks, but not outgoing ones. */
3142 static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
3143 {
3144         struct inet_connection_sock *icsk = inet_csk(sk);
3145         struct tcp_sock *tp = tcp_sk(sk);
3146         u32 prior_snd_una = tp->snd_una;
3147         u32 ack_seq = TCP_SKB_CB(skb)->seq;
3148         u32 ack = TCP_SKB_CB(skb)->ack_seq;
3149         u32 prior_in_flight;
3150         u32 prior_fackets;
3151         int prior_packets;
3152         int frto_cwnd = 0;
3153
3154         /* If the ack is newer than sent or older than previous acks
3155          * then we can probably ignore it.
3156          */
3157         if (after(ack, tp->snd_nxt))
3158                 goto uninteresting_ack;
3159
3160         if (before(ack, prior_snd_una))
3161                 goto old_ack;
3162
3163         if (after(ack, prior_snd_una))
3164                 flag |= FLAG_SND_UNA_ADVANCED;
3165
3166         if (sysctl_tcp_abc) {
3167                 if (icsk->icsk_ca_state < TCP_CA_CWR)
3168                         tp->bytes_acked += ack - prior_snd_una;
3169                 else if (icsk->icsk_ca_state == TCP_CA_Loss)
3170                         /* we assume just one segment left network */
3171                         tp->bytes_acked += min(ack - prior_snd_una,
3172                                                tp->mss_cache);
3173         }
3174
3175         prior_fackets = tp->fackets_out;
3176         prior_in_flight = tcp_packets_in_flight(tp);
3177
3178         if (!(flag & FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
3179                 /* Window is constant, pure forward advance.
3180                  * No more checks are required.
3181                  * Note, we use the fact that SND.UNA>=SND.WL2.
3182                  */
3183                 tcp_update_wl(tp, ack, ack_seq);
3184                 tp->snd_una = ack;
3185                 flag |= FLAG_WIN_UPDATE;
3186
3187                 tcp_ca_event(sk, CA_EVENT_FAST_ACK);
3188
3189                 NET_INC_STATS_BH(LINUX_MIB_TCPHPACKS);
3190         } else {
3191                 if (ack_seq != TCP_SKB_CB(skb)->end_seq)
3192                         flag |= FLAG_DATA;
3193                 else
3194                         NET_INC_STATS_BH(LINUX_MIB_TCPPUREACKS);
3195
3196                 flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
3197
3198                 if (TCP_SKB_CB(skb)->sacked)
3199                         flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una);
3200
3201                 if (TCP_ECN_rcv_ecn_echo(tp, tcp_hdr(skb)))
3202                         flag |= FLAG_ECE;
3203
3204                 tcp_ca_event(sk, CA_EVENT_SLOW_ACK);
3205         }
3206
3207         /* We passed data and got it acked, remove any soft error
3208          * log. Something worked...
3209          */
3210         sk->sk_err_soft = 0;
3211         tp->rcv_tstamp = tcp_time_stamp;
3212         prior_packets = tp->packets_out;
3213         if (!prior_packets)
3214                 goto no_queue;
3215
3216         /* See if we can take anything off of the retransmit queue. */
3217         flag |= tcp_clean_rtx_queue(sk, prior_fackets);
3218
3219         if (tp->frto_counter)
3220                 frto_cwnd = tcp_process_frto(sk, flag);
3221         /* Guarantee sacktag reordering detection against wrap-arounds */
3222         if (before(tp->frto_highmark, tp->snd_una))
3223                 tp->frto_highmark = 0;
3224
3225         if (tcp_ack_is_dubious(sk, flag)) {
3226                 /* Advance CWND, if state allows this. */
3227                 if ((flag & FLAG_DATA_ACKED) && !frto_cwnd &&
3228                     tcp_may_raise_cwnd(sk, flag))
3229                         tcp_cong_avoid(sk, ack, prior_in_flight);
3230                 tcp_fastretrans_alert(sk, prior_packets - tp->packets_out,
3231                                       flag);
3232         } else {
3233                 if ((flag & FLAG_DATA_ACKED) && !frto_cwnd)
3234                         tcp_cong_avoid(sk, ack, prior_in_flight);
3235         }
3236
3237         if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP))
3238                 dst_confirm(sk->sk_dst_cache);
3239
3240         return 1;
3241
3242 no_queue:
3243         icsk->icsk_probes_out = 0;
3244
3245         /* If this ack opens up a zero window, clear backoff.  It was
3246          * being used to time the probes, and is probably far higher than
3247          * it needs to be for normal retransmission.
3248          */
3249         if (tcp_send_head(sk))
3250                 tcp_ack_probe(sk);
3251         return 1;
3252
3253 old_ack:
3254         if (TCP_SKB_CB(skb)->sacked)
3255                 tcp_sacktag_write_queue(sk, skb, prior_snd_una);
3256
3257 uninteresting_ack:
3258         SOCK_DEBUG(sk, "Ack %u out of %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
3259         return 0;
3260 }
3261
3262 /* Look for tcp options. Normally only called on SYN and SYNACK packets.
3263  * But, this can also be called on packets in the established flow when
3264  * the fast version below fails.
3265  */
3266 void tcp_parse_options(struct sk_buff *skb, struct tcp_options_received *opt_rx,
3267                        int estab)
3268 {
3269         unsigned char *ptr;
3270         struct tcphdr *th = tcp_hdr(skb);
3271         int length = (th->doff * 4) - sizeof(struct tcphdr);
3272
3273         ptr = (unsigned char *)(th + 1);
3274         opt_rx->saw_tstamp = 0;
3275
3276         while (length > 0) {
3277                 int opcode = *ptr++;
3278                 int opsize;
3279
3280                 switch (opcode) {
3281                 case TCPOPT_EOL:
3282                         return;
3283                 case TCPOPT_NOP:        /* Ref: RFC 793 section 3.1 */
3284                         length--;
3285                         continue;
3286                 default:
3287                         opsize = *ptr++;
3288                         if (opsize < 2) /* "silly options" */
3289                                 return;
3290                         if (opsize > length)
3291                                 return; /* don't parse partial options */
3292                         switch (opcode) {
3293                         case TCPOPT_MSS:
3294                                 if (opsize == TCPOLEN_MSS && th->syn && !estab) {
3295                                         u16 in_mss = ntohs(get_unaligned((__be16 *)ptr));
3296                                         if (in_mss) {
3297                                                 if (opt_rx->user_mss &&
3298                                                     opt_rx->user_mss < in_mss)
3299                                                         in_mss = opt_rx->user_mss;
3300                                                 opt_rx->mss_clamp = in_mss;
3301                                         }
3302                                 }
3303                                 break;
3304                         case TCPOPT_WINDOW:
3305                                 if (opsize == TCPOLEN_WINDOW && th->syn &&
3306                                     !estab && sysctl_tcp_window_scaling) {
3307                                         __u8 snd_wscale = *(__u8 *)ptr;
3308                                         opt_rx->wscale_ok = 1;
3309                                         if (snd_wscale > 14) {
3310                                                 if (net_ratelimit())
3311                                                         printk(KERN_INFO "tcp_parse_options: Illegal window "
3312                                                                "scaling value %d >14 received.\n",
3313                                                                snd_wscale);
3314                                                 snd_wscale = 14;
3315                                         }
3316                                         opt_rx->snd_wscale = snd_wscale;
3317                                 }
3318                                 break;
3319                         case TCPOPT_TIMESTAMP:
3320                                 if ((opsize == TCPOLEN_TIMESTAMP) &&
3321                                     ((estab && opt_rx->tstamp_ok) ||
3322                                      (!estab && sysctl_tcp_timestamps))) {
3323                                         opt_rx->saw_tstamp = 1;
3324                                         opt_rx->rcv_tsval = ntohl(get_unaligned((__be32 *)ptr));
3325                                         opt_rx->rcv_tsecr = ntohl(get_unaligned((__be32 *)(ptr+4)));
3326                                 }
3327                                 break;
3328                         case TCPOPT_SACK_PERM:
3329                                 if (opsize == TCPOLEN_SACK_PERM && th->syn &&
3330                                     !estab && sysctl_tcp_sack) {
3331                                         opt_rx->sack_ok = 1;
3332                                         tcp_sack_reset(opt_rx);
3333                                 }
3334                                 break;
3335
3336                         case TCPOPT_SACK:
3337                                 if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
3338                                    !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
3339                                    opt_rx->sack_ok) {
3340                                         TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
3341                                 }
3342                                 break;
3343 #ifdef CONFIG_TCP_MD5SIG
3344                         case TCPOPT_MD5SIG:
3345                                 /*
3346                                  * The MD5 Hash has already been
3347                                  * checked (see tcp_v{4,6}_do_rcv()).
3348                                  */
3349                                 break;
3350 #endif
3351                         }
3352
3353                         ptr += opsize-2;
3354                         length -= opsize;
3355                 }
3356         }
3357 }
3358
3359 /* Fast parse options. This hopes to only see timestamps.
3360  * If it is wrong it falls back on tcp_parse_options().
3361  */
3362 static int tcp_fast_parse_options(struct sk_buff *skb, struct tcphdr *th,
3363                                   struct tcp_sock *tp)
3364 {
3365         if (th->doff == sizeof(struct tcphdr) >> 2) {
3366                 tp->rx_opt.saw_tstamp = 0;
3367                 return 0;
3368         } else if (tp->rx_opt.tstamp_ok &&
3369                    th->doff == (sizeof(struct tcphdr)>>2)+(TCPOLEN_TSTAMP_ALIGNED>>2)) {
3370                 __be32 *ptr = (__be32 *)(th + 1);
3371                 if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
3372                                   | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
3373                         tp->rx_opt.saw_tstamp = 1;
3374                         ++ptr;
3375                         tp->rx_opt.rcv_tsval = ntohl(*ptr);
3376                         ++ptr;
3377                         tp->rx_opt.rcv_tsecr = ntohl(*ptr);
3378                         return 1;
3379                 }
3380         }
3381         tcp_parse_options(skb, &tp->rx_opt, 1);
3382         return 1;
3383 }
3384
3385 static inline void tcp_store_ts_recent(struct tcp_sock *tp)
3386 {
3387         tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
3388         tp->rx_opt.ts_recent_stamp = get_seconds();
3389 }
3390
3391 static inline void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
3392 {
3393         if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
3394                 /* PAWS bug workaround wrt. ACK frames, the PAWS discard
3395                  * extra check below makes sure this can only happen
3396                  * for pure ACK frames.  -DaveM
3397                  *
3398                  * Not only, also it occurs for expired timestamps.
3399                  */
3400
3401                 if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) >= 0 ||
3402                    get_seconds() >= tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS)
3403                         tcp_store_ts_recent(tp);
3404         }
3405 }
3406
3407 /* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
3408  *
3409  * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
3410  * it can pass through stack. So, the following predicate verifies that
3411  * this segment is not used for anything but congestion avoidance or
3412  * fast retransmit. Moreover, we even are able to eliminate most of such
3413  * second order effects, if we apply some small "replay" window (~RTO)
3414  * to timestamp space.
3415  *
3416  * All these measures still do not guarantee that we reject wrapped ACKs
3417  * on networks with high bandwidth, when sequence space is recycled fastly,
3418  * but it guarantees that such events will be very rare and do not affect
3419  * connection seriously. This doesn't look nice, but alas, PAWS is really
3420  * buggy extension.
3421  *
3422  * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
3423  * states that events when retransmit arrives after original data are rare.
3424  * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
3425  * the biggest problem on large power networks even with minor reordering.
3426  * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
3427  * up to bandwidth of 18Gigabit/sec. 8) ]
3428  */
3429
3430 static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
3431 {
3432         struct tcp_sock *tp = tcp_sk(sk);
3433         struct tcphdr *th = tcp_hdr(skb);
3434         u32 seq = TCP_SKB_CB(skb)->seq;
3435         u32 ack = TCP_SKB_CB(skb)->ack_seq;
3436
3437         return (/* 1. Pure ACK with correct sequence number. */
3438                 (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
3439
3440                 /* 2. ... and duplicate ACK. */
3441                 ack == tp->snd_una &&
3442
3443                 /* 3. ... and does not update window. */
3444                 !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
3445
3446                 /* 4. ... and sits in replay window. */
3447                 (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
3448 }
3449
3450 static inline int tcp_paws_discard(const struct sock *sk,
3451                                    const struct sk_buff *skb)
3452 {
3453         const struct tcp_sock *tp = tcp_sk(sk);
3454         return ((s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) > TCP_PAWS_WINDOW &&
3455                 get_seconds() < tp->rx_opt.ts_recent_stamp + TCP_PAWS_24DAYS &&
3456                 !tcp_disordered_ack(sk, skb));
3457 }
3458
3459 /* Check segment sequence number for validity.
3460  *
3461  * Segment controls are considered valid, if the segment
3462  * fits to the window after truncation to the window. Acceptability
3463  * of data (and SYN, FIN, of course) is checked separately.
3464  * See tcp_data_queue(), for example.
3465  *
3466  * Also, controls (RST is main one) are accepted using RCV.WUP instead
3467  * of RCV.NXT. Peer still did not advance his SND.UNA when we
3468  * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
3469  * (borrowed from freebsd)
3470  */
3471
3472 static inline int tcp_sequence(struct tcp_sock *tp, u32 seq, u32 end_seq)
3473 {
3474         return  !before(end_seq, tp->rcv_wup) &&
3475                 !after(seq, tp->rcv_nxt + tcp_receive_window(tp));
3476 }
3477
3478 /* When we get a reset we do this. */
3479 static void tcp_reset(struct sock *sk)
3480 {
3481         /* We want the right error as BSD sees it (and indeed as we do). */
3482         switch (sk->sk_state) {
3483         case TCP_SYN_SENT:
3484                 sk->sk_err = ECONNREFUSED;
3485                 break;
3486         case TCP_CLOSE_WAIT:
3487                 sk->sk_err = EPIPE;
3488                 break;
3489         case TCP_CLOSE:
3490                 return;
3491         default:
3492                 sk->sk_err = ECONNRESET;
3493         }
3494
3495         if (!sock_flag(sk, SOCK_DEAD))
3496                 sk->sk_error_report(sk);
3497
3498         tcp_done(sk);
3499 }
3500
3501 /*
3502  *      Process the FIN bit. This now behaves as it is supposed to work
3503  *      and the FIN takes effect when it is validly part of sequence
3504  *      space. Not before when we get holes.
3505  *
3506  *      If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
3507  *      (and thence onto LAST-ACK and finally, CLOSE, we never enter
3508  *      TIME-WAIT)
3509  *
3510  *      If we are in FINWAIT-1, a received FIN indicates simultaneous
3511  *      close and we go into CLOSING (and later onto TIME-WAIT)
3512  *
3513  *      If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
3514  */
3515 static void tcp_fin(struct sk_buff *skb, struct sock *sk, struct tcphdr *th)
3516 {
3517         struct tcp_sock *tp = tcp_sk(sk);
3518
3519         inet_csk_schedule_ack(sk);
3520
3521         sk->sk_shutdown |= RCV_SHUTDOWN;
3522         sock_set_flag(sk, SOCK_DONE);
3523
3524         switch (sk->sk_state) {
3525         case TCP_SYN_RECV:
3526         case TCP_ESTABLISHED:
3527                 /* Move to CLOSE_WAIT */
3528                 tcp_set_state(sk, TCP_CLOSE_WAIT);
3529                 inet_csk(sk)->icsk_ack.pingpong = 1;
3530                 break;
3531
3532         case TCP_CLOSE_WAIT:
3533         case TCP_CLOSING:
3534                 /* Received a retransmission of the FIN, do
3535                  * nothing.
3536                  */
3537                 break;
3538         case TCP_LAST_ACK:
3539                 /* RFC793: Remain in the LAST-ACK state. */
3540                 break;
3541
3542         case TCP_FIN_WAIT1:
3543                 /* This case occurs when a simultaneous close
3544                  * happens, we must ack the received FIN and
3545                  * enter the CLOSING state.
3546                  */
3547                 tcp_send_ack(sk);
3548                 tcp_set_state(sk, TCP_CLOSING);
3549                 break;
3550         case TCP_FIN_WAIT2:
3551                 /* Received a FIN -- send ACK and enter TIME_WAIT. */
3552                 tcp_send_ack(sk);
3553                 tcp_time_wait(sk, TCP_TIME_WAIT, 0);
3554                 break;
3555         default:
3556                 /* Only TCP_LISTEN and TCP_CLOSE are left, in these
3557                  * cases we should never reach this piece of code.
3558                  */
3559                 printk(KERN_ERR "%s: Impossible, sk->sk_state=%d\n",
3560                        __FUNCTION__, sk->sk_state);
3561                 break;
3562         }
3563
3564         /* It _is_ possible, that we have something out-of-order _after_ FIN.
3565          * Probably, we should reset in this case. For now drop them.
3566          */
3567         __skb_queue_purge(&tp->out_of_order_queue);
3568         if (tcp_is_sack(tp))
3569                 tcp_sack_reset(&tp->rx_opt);
3570         sk_mem_reclaim(sk);
3571
3572         if (!sock_flag(sk, SOCK_DEAD)) {
3573                 sk->sk_state_change(sk);
3574
3575                 /* Do not send POLL_HUP for half duplex close. */
3576                 if (sk->sk_shutdown == SHUTDOWN_MASK ||
3577                     sk->sk_state == TCP_CLOSE)
3578                         sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
3579                 else
3580                         sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
3581         }
3582 }
3583
3584 static inline int tcp_sack_extend(struct tcp_sack_block *sp, u32 seq,
3585                                   u32 end_seq)
3586 {
3587         if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
3588                 if (before(seq, sp->start_seq))
3589                         sp->start_seq = seq;
3590                 if (after(end_seq, sp->end_seq))
3591                         sp->end_seq = end_seq;
3592                 return 1;
3593         }
3594         return 0;
3595 }
3596
3597 static void tcp_dsack_set(struct tcp_sock *tp, u32 seq, u32 end_seq)
3598 {
3599         if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
3600                 if (before(seq, tp->rcv_nxt))
3601                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOLDSENT);
3602                 else
3603                         NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFOSENT);
3604
3605                 tp->rx_opt.dsack = 1;
3606                 tp->duplicate_sack[0].start_seq = seq;
3607                 tp->duplicate_sack[0].end_seq = end_seq;
3608                 tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + 1,
3609                                            4 - tp->rx_opt.tstamp_ok);
3610         }
3611 }
3612
3613 static void tcp_dsack_extend(struct tcp_sock *tp, u32 seq, u32 end_seq)
3614 {
3615         if (!tp->rx_opt.dsack)
3616                 tcp_dsack_set(tp, seq, end_seq);
3617         else
3618                 tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
3619 }
3620
3621 static void tcp_send_dupack(struct sock *sk, struct sk_buff *skb)
3622 {
3623         struct tcp_sock *tp = tcp_sk(sk);
3624
3625         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
3626             before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
3627                 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOST);
3628                 tcp_enter_quickack_mode(sk);
3629
3630                 if (tcp_is_sack(tp) && sysctl_tcp_dsack) {
3631                         u32 end_seq = TCP_SKB_CB(skb)->end_seq;
3632
3633                         if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
3634                                 end_seq = tp->rcv_nxt;
3635                         tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, end_seq);
3636                 }
3637         }
3638
3639         tcp_send_ack(sk);
3640 }
3641
3642 /* These routines update the SACK block as out-of-order packets arrive or
3643  * in-order packets close up the sequence space.
3644  */
3645 static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
3646 {
3647         int this_sack;
3648         struct tcp_sack_block *sp = &tp->selective_acks[0];
3649         struct tcp_sack_block *swalk = sp + 1;
3650
3651         /* See if the recent change to the first SACK eats into
3652          * or hits the sequence space of other SACK blocks, if so coalesce.
3653          */
3654         for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) {
3655                 if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
3656                         int i;
3657
3658                         /* Zap SWALK, by moving every further SACK up by one slot.
3659                          * Decrease num_sacks.
3660                          */
3661                         tp->rx_opt.num_sacks--;
3662                         tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks +
3663                                                    tp->rx_opt.dsack,
3664                                                    4 - tp->rx_opt.tstamp_ok);
3665                         for (i = this_sack; i < tp->rx_opt.num_sacks; i++)
3666                                 sp[i] = sp[i + 1];
3667                         continue;
3668                 }
3669                 this_sack++, swalk++;
3670         }
3671 }
3672
3673 static inline void tcp_sack_swap(struct tcp_sack_block *sack1,
3674                                  struct tcp_sack_block *sack2)
3675 {
3676         __u32 tmp;
3677
3678         tmp = sack1->start_seq;
3679         sack1->start_seq = sack2->start_seq;
3680         sack2->start_seq = tmp;
3681
3682         tmp = sack1->end_seq;
3683         sack1->end_seq = sack2->end_seq;
3684         sack2->end_seq = tmp;
3685 }
3686
3687 static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
3688 {
3689         struct tcp_sock *tp = tcp_sk(sk);
3690         struct tcp_sack_block *sp = &tp->selective_acks[0];
3691         int cur_sacks = tp->rx_opt.num_sacks;
3692         int this_sack;
3693
3694         if (!cur_sacks)
3695                 goto new_sack;
3696
3697         for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) {
3698                 if (tcp_sack_extend(sp, seq, end_seq)) {
3699                         /* Rotate this_sack to the first one. */
3700                         for (; this_sack > 0; this_sack--, sp--)
3701                                 tcp_sack_swap(sp, sp - 1);
3702                         if (cur_sacks > 1)
3703                                 tcp_sack_maybe_coalesce(tp);
3704                         return;
3705                 }
3706         }
3707
3708         /* Could not find an adjacent existing SACK, build a new one,
3709          * put it at the front, and shift everyone else down.  We
3710          * always know there is at least one SACK present already here.
3711          *
3712          * If the sack array is full, forget about the last one.
3713          */
3714         if (this_sack >= 4) {
3715                 this_sack--;
3716                 tp->rx_opt.num_sacks--;
3717                 sp--;
3718         }
3719         for (; this_sack > 0; this_sack--, sp--)
3720                 *sp = *(sp - 1);
3721
3722 new_sack:
3723         /* Build the new head SACK, and we're done. */
3724         sp->start_seq = seq;
3725         sp->end_seq = end_seq;
3726         tp->rx_opt.num_sacks++;
3727         tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks + tp->rx_opt.dsack,
3728                                    4 - tp->rx_opt.tstamp_ok);
3729 }
3730
3731 /* RCV.NXT advances, some SACKs should be eaten. */
3732
3733 static void tcp_sack_remove(struct tcp_sock *tp)
3734 {
3735         struct tcp_sack_block *sp = &tp->selective_acks[0];
3736         int num_sacks = tp->rx_opt.num_sacks;
3737         int this_sack;
3738
3739         /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
3740         if (skb_queue_empty(&tp->out_of_order_queue)) {
3741                 tp->rx_opt.num_sacks = 0;
3742                 tp->rx_opt.eff_sacks = tp->rx_opt.dsack;
3743                 return;
3744         }
3745
3746         for (this_sack = 0; this_sack < num_sacks;) {
3747                 /* Check if the start of the sack is covered by RCV.NXT. */
3748                 if (!before(tp->rcv_nxt, sp->start_seq)) {
3749                         int i;
3750
3751                         /* RCV.NXT must cover all the block! */
3752                         BUG_TRAP(!before(tp->rcv_nxt, sp->end_seq));
3753
3754                         /* Zap this SACK, by moving forward any other SACKS. */
3755                         for (i=this_sack+1; i < num_sacks; i++)
3756                                 tp->selective_acks[i-1] = tp->selective_acks[i];
3757                         num_sacks--;
3758                         continue;
3759                 }
3760                 this_sack++;
3761                 sp++;
3762         }
3763         if (num_sacks != tp->rx_opt.num_sacks) {
3764                 tp->rx_opt.num_sacks = num_sacks;
3765                 tp->rx_opt.eff_sacks = min(tp->rx_opt.num_sacks +
3766                                            tp->rx_opt.dsack,
3767                                            4 - tp->rx_opt.tstamp_ok);
3768         }
3769 }
3770
3771 /* This one checks to see if we can put data from the
3772  * out_of_order queue into the receive_queue.
3773  */
3774 static void tcp_ofo_queue(struct sock *sk)
3775 {
3776         struct tcp_sock *tp = tcp_sk(sk);
3777         __u32 dsack_high = tp->rcv_nxt;
3778         struct sk_buff *skb;
3779
3780         while ((skb = skb_peek(&tp->out_of_order_queue)) != NULL) {
3781                 if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
3782                         break;
3783
3784                 if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
3785                         __u32 dsack = dsack_high;
3786                         if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
3787                                 dsack_high = TCP_SKB_CB(skb)->end_seq;
3788                         tcp_dsack_extend(tp, TCP_SKB_CB(skb)->seq, dsack);
3789                 }
3790
3791                 if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
3792                         SOCK_DEBUG(sk, "ofo packet was already received \n");
3793                         __skb_unlink(skb, &tp->out_of_order_queue);
3794                         __kfree_skb(skb);
3795                         continue;
3796                 }
3797                 SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
3798                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
3799                            TCP_SKB_CB(skb)->end_seq);
3800
3801                 __skb_unlink(skb, &tp->out_of_order_queue);
3802                 __skb_queue_tail(&sk->sk_receive_queue, skb);
3803                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
3804                 if (tcp_hdr(skb)->fin)
3805                         tcp_fin(skb, sk, tcp_hdr(skb));
3806         }
3807 }
3808
3809 static int tcp_prune_queue(struct sock *sk);
3810
3811 static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
3812 {
3813         struct tcphdr *th = tcp_hdr(skb);
3814         struct tcp_sock *tp = tcp_sk(sk);
3815         int eaten = -1;
3816
3817         if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq)
3818                 goto drop;
3819
3820         __skb_pull(skb, th->doff * 4);
3821
3822         TCP_ECN_accept_cwr(tp, skb);
3823
3824         if (tp->rx_opt.dsack) {
3825                 tp->rx_opt.dsack = 0;
3826                 tp->rx_opt.eff_sacks = min_t(unsigned int, tp->rx_opt.num_sacks,
3827                                              4 - tp->rx_opt.tstamp_ok);
3828         }
3829
3830         /*  Queue data for delivery to the user.
3831          *  Packets in sequence go to the receive queue.
3832          *  Out of sequence packets to the out_of_order_queue.
3833          */
3834         if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
3835                 if (tcp_receive_window(tp) == 0)
3836                         goto out_of_window;
3837
3838                 /* Ok. In sequence. In window. */
3839                 if (tp->ucopy.task == current &&
3840                     tp->copied_seq == tp->rcv_nxt && tp->ucopy.len &&
3841                     sock_owned_by_user(sk) && !tp->urg_data) {
3842                         int chunk = min_t(unsigned int, skb->len,
3843                                           tp->ucopy.len);
3844
3845                         __set_current_state(TASK_RUNNING);
3846
3847                         local_bh_enable();
3848                         if (!skb_copy_datagram_iovec(skb, 0, tp->ucopy.iov, chunk)) {
3849                                 tp->ucopy.len -= chunk;
3850                                 tp->copied_seq += chunk;
3851                                 eaten = (chunk == skb->len && !th->fin);
3852                                 tcp_rcv_space_adjust(sk);
3853                         }
3854                         local_bh_disable();
3855                 }
3856
3857                 if (eaten <= 0) {
3858 queue_and_out:
3859                         if (eaten < 0 &&
3860                             (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
3861                              !sk_rmem_schedule(sk, skb->truesize))) {
3862                                 if (tcp_prune_queue(sk) < 0 ||
3863                                     !sk_rmem_schedule(sk, skb->truesize))
3864                                         goto drop;
3865                         }
3866                         skb_set_owner_r(skb, sk);
3867                         __skb_queue_tail(&sk->sk_receive_queue, skb);
3868                 }
3869                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
3870                 if (skb->len)
3871                         tcp_event_data_recv(sk, skb);
3872                 if (th->fin)
3873                         tcp_fin(skb, sk, th);
3874
3875                 if (!skb_queue_empty(&tp->out_of_order_queue)) {
3876                         tcp_ofo_queue(sk);
3877
3878                         /* RFC2581. 4.2. SHOULD send immediate ACK, when
3879                          * gap in queue is filled.
3880                          */
3881                         if (skb_queue_empty(&tp->out_of_order_queue))
3882                                 inet_csk(sk)->icsk_ack.pingpong = 0;
3883                 }
3884
3885                 if (tp->rx_opt.num_sacks)
3886                         tcp_sack_remove(tp);
3887
3888                 tcp_fast_path_check(sk);
3889
3890                 if (eaten > 0)
3891                         __kfree_skb(skb);
3892                 else if (!sock_flag(sk, SOCK_DEAD))
3893                         sk->sk_data_ready(sk, 0);
3894                 return;
3895         }
3896
3897         if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
3898                 /* A retransmit, 2nd most common case.  Force an immediate ack. */
3899                 NET_INC_STATS_BH(LINUX_MIB_DELAYEDACKLOST);
3900                 tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
3901
3902 out_of_window:
3903                 tcp_enter_quickack_mode(sk);
3904                 inet_csk_schedule_ack(sk);
3905 drop:
3906                 __kfree_skb(skb);
3907                 return;
3908         }
3909
3910         /* Out of window. F.e. zero window probe. */
3911         if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
3912                 goto out_of_window;
3913
3914         tcp_enter_quickack_mode(sk);
3915
3916         if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
3917                 /* Partial packet, seq < rcv_next < end_seq */
3918                 SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
3919                            tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
3920                            TCP_SKB_CB(skb)->end_seq);
3921
3922                 tcp_dsack_set(tp, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
3923
3924                 /* If window is closed, drop tail of packet. But after
3925                  * remembering D-SACK for its head made in previous line.
3926                  */
3927                 if (!tcp_receive_window(tp))
3928                         goto out_of_window;
3929                 goto queue_and_out;
3930         }
3931
3932         TCP_ECN_check_ce(tp, skb);
3933
3934         if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
3935             !sk_rmem_schedule(sk, skb->truesize)) {
3936                 if (tcp_prune_queue(sk) < 0 ||
3937                     !sk_rmem_schedule(sk, skb->truesize))
3938                         goto drop;
3939         }
3940
3941         /* Disable header prediction. */
3942         tp->pred_flags = 0;
3943         inet_csk_schedule_ack(sk);
3944
3945         SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
3946                    tp->rcv_nxt, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
3947
3948         skb_set_owner_r(skb, sk);
3949
3950         if (!skb_peek(&tp->out_of_order_queue)) {
3951                 /* Initial out of order segment, build 1 SACK. */
3952                 if (tcp_is_sack(tp)) {
3953                         tp->rx_opt.num_sacks = 1;
3954                         tp->rx_opt.dsack     = 0;
3955                         tp->rx_opt.eff_sacks = 1;
3956                         tp->selective_acks[0].start_seq = TCP_SKB_CB(skb)->seq;
3957                         tp->selective_acks[0].end_seq =
3958                                                 TCP_SKB_CB(skb)->end_seq;
3959                 }
3960                 __skb_queue_head(&tp->out_of_order_queue, skb);
3961         } else {
3962                 struct sk_buff *skb1 = tp->out_of_order_queue.prev;
3963                 u32 seq = TCP_SKB_CB(skb)->seq;
3964                 u32 end_seq = TCP_SKB_CB(skb)->end_seq;
3965
3966                 if (seq == TCP_SKB_CB(skb1)->end_seq) {
3967                         __skb_append(skb1, skb, &tp->out_of_order_queue);
3968
3969                         if (!tp->rx_opt.num_sacks ||
3970                             tp->selective_acks[0].end_seq != seq)
3971                                 goto add_sack;
3972
3973                         /* Common case: data arrive in order after hole. */
3974                         tp->selective_acks[0].end_seq = end_seq;
3975                         return;
3976                 }
3977
3978                 /* Find place to insert this segment. */
3979                 do {
3980                         if (!after(TCP_SKB_CB(skb1)->seq, seq))
3981                                 break;
3982                 } while ((skb1 = skb1->prev) !=
3983                          (struct sk_buff *)&tp->out_of_order_queue);
3984
3985                 /* Do skb overlap to previous one? */
3986                 if (skb1 != (struct sk_buff *)&tp->out_of_order_queue &&
3987                     before(seq, TCP_SKB_CB(skb1)->end_seq)) {
3988                         if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
3989                                 /* All the bits are present. Drop. */
3990                                 __kfree_skb(skb);
3991                                 tcp_dsack_set(tp, seq, end_seq);
3992                                 goto add_sack;
3993                         }
3994                         if (after(seq, TCP_SKB_CB(skb1)->seq)) {
3995                                 /* Partial overlap. */
3996                                 tcp_dsack_set(tp, seq,
3997                                               TCP_SKB_CB(skb1)->end_seq);
3998                         } else {
3999                                 skb1 = skb1->prev;
4000                         }
4001                 }
4002                 __skb_insert(skb, skb1, skb1->next, &tp->out_of_order_queue);
4003
4004                 /* And clean segments covered by new one as whole. */
4005                 while ((skb1 = skb->next) !=
4006                        (struct sk_buff *)&tp->out_of_order_queue &&
4007                        after(end_seq, TCP_SKB_CB(skb1)->seq)) {
4008                         if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
4009                                 tcp_dsack_extend(tp, TCP_SKB_CB(skb1)->seq,
4010                                                  end_seq);
4011                                 break;
4012                         }
4013                         __skb_unlink(skb1, &tp->out_of_order_queue);
4014                         tcp_dsack_extend(tp, TCP_SKB_CB(skb1)->seq,
4015                                          TCP_SKB_CB(skb1)->end_seq);
4016                         __kfree_skb(skb1);
4017                 }
4018
4019 add_sack:
4020                 if (tcp_is_sack(tp))
4021                         tcp_sack_new_ofo_skb(sk, seq, end_seq);
4022         }
4023 }
4024
4025 /* Collapse contiguous sequence of skbs head..tail with
4026  * sequence numbers start..end.
4027  * Segments with FIN/SYN are not collapsed (only because this
4028  * simplifies code)
4029  */
4030 static void
4031 tcp_collapse(struct sock *sk, struct sk_buff_head *list,
4032              struct sk_buff *head, struct sk_buff *tail,
4033              u32 start, u32 end)
4034 {
4035         struct sk_buff *skb;
4036
4037         /* First, check that queue is collapsible and find
4038          * the point where collapsing can be useful. */
4039         for (skb = head; skb != tail;) {
4040                 /* No new bits? It is possible on ofo queue. */
4041                 if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4042                         struct sk_buff *next = skb->next;
4043                         __skb_unlink(skb, list);
4044                         __kfree_skb(skb);
4045                         NET_INC_STATS_BH(LINUX_MIB_TCPRCVCOLLAPSED);
4046                         skb = next;
4047                         continue;
4048                 }
4049
4050                 /* The first skb to collapse is:
4051                  * - not SYN/FIN and
4052                  * - bloated or contains data before "start" or
4053                  *   overlaps to the next one.
4054                  */
4055                 if (!tcp_hdr(skb)->syn && !tcp_hdr(skb)->fin &&
4056                     (tcp_win_from_space(skb->truesize) > skb->len ||
4057                      before(TCP_SKB_CB(skb)->seq, start) ||
4058                      (skb->next != tail &&
4059                       TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb->next)->seq)))
4060                         break;
4061
4062                 /* Decided to skip this, advance start seq. */
4063                 start = TCP_SKB_CB(skb)->end_seq;
4064                 skb = skb->next;
4065         }
4066         if (skb == tail || tcp_hdr(skb)->syn || tcp_hdr(skb)->fin)
4067                 return;
4068
4069         while (before(start, end)) {
4070                 struct sk_buff *nskb;
4071                 unsigned int header = skb_headroom(skb);
4072                 int copy = SKB_MAX_ORDER(header, 0);
4073
4074                 /* Too big header? This can happen with IPv6. */
4075                 if (copy < 0)
4076                         return;
4077                 if (end - start < copy)
4078                         copy = end - start;
4079                 nskb = alloc_skb(copy + header, GFP_ATOMIC);
4080                 if (!nskb)
4081                         return;
4082
4083                 skb_set_mac_header(nskb, skb_mac_header(skb) - skb->head);
4084                 skb_set_network_header(nskb, (skb_network_header(skb) -
4085                                               skb->head));
4086                 skb_set_transport_header(nskb, (skb_transport_header(skb) -
4087                                                 skb->head));
4088                 skb_reserve(nskb, header);
4089                 memcpy(nskb->head, skb->head, header);
4090                 memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
4091                 TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
4092                 __skb_insert(nskb, skb->prev, skb, list);
4093                 skb_set_owner_r(nskb, sk);
4094
4095                 /* Copy data, releasing collapsed skbs. */
4096                 while (copy > 0) {
4097                         int offset = start - TCP_SKB_CB(skb)->seq;
4098                         int size = TCP_SKB_CB(skb)->end_seq - start;
4099
4100                         BUG_ON(offset < 0);
4101                         if (size > 0) {
4102                                 size = min(copy, size);
4103                                 if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
4104                                         BUG();
4105                                 TCP_SKB_CB(nskb)->end_seq += size;
4106                                 copy -= size;
4107                                 start += size;
4108                         }
4109                         if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
4110                                 struct sk_buff *next = skb->next;
4111                                 __skb_unlink(skb, list);
4112                                 __kfree_skb(skb);
4113                                 NET_INC_STATS_BH(LINUX_MIB_TCPRCVCOLLAPSED);
4114                                 skb = next;
4115                                 if (skb == tail ||
4116                                     tcp_hdr(skb)->syn ||
4117                                     tcp_hdr(skb)->fin)
4118                                         return;
4119                         }
4120                 }
4121         }
4122 }
4123
4124 /* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
4125  * and tcp_collapse() them until all the queue is collapsed.
4126  */
4127 static void tcp_collapse_ofo_queue(struct sock *sk)
4128 {
4129         struct tcp_sock *tp = tcp_sk(sk);
4130         struct sk_buff *skb = skb_peek(&tp->out_of_order_queue);
4131         struct sk_buff *head;
4132         u32 start, end;
4133
4134         if (skb == NULL)
4135                 return;
4136
4137         start = TCP_SKB_CB(skb)->seq;
4138         end = TCP_SKB_CB(skb)->end_seq;
4139         head = skb;
4140
4141         for (;;) {
4142                 skb = skb->next;
4143
4144                 /* Segment is terminated when we see gap or when
4145                  * we are at the end of all the queue. */
4146                 if (skb == (struct sk_buff *)&tp->out_of_order_queue ||
4147                     after(TCP_SKB_CB(skb)->seq, end) ||
4148                     before(TCP_SKB_CB(skb)->end_seq, start)) {
4149                         tcp_collapse(sk, &tp->out_of_order_queue,
4150                                      head, skb, start, end);
4151                         head = skb;
4152                         if (skb == (struct sk_buff *)&tp->out_of_order_queue)
4153                                 break;
4154                         /* Start new segment */
4155                         start = TCP_SKB_CB(skb)->seq;
4156                         end = TCP_SKB_CB(skb)->end_seq;
4157                 } else {
4158                         if (before(TCP_SKB_CB(skb)->seq, start))
4159                                 start = TCP_SKB_CB(skb)->seq;
4160                         if (after(TCP_SKB_CB(skb)->end_seq, end))
4161                                 end = TCP_SKB_CB(skb)->end_seq;
4162                 }
4163         }
4164 }
4165
4166 /* Reduce allocated memory if we can, trying to get
4167  * the socket within its memory limits again.
4168  *
4169  * Return less than zero if we should start dropping frames
4170  * until the socket owning process reads some of the data
4171  * to stabilize the situation.
4172  */
4173 static int tcp_prune_queue(struct sock *sk)
4174 {
4175         struct tcp_sock *tp = tcp_sk(sk);
4176
4177         SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq);
4178
4179         NET_INC_STATS_BH(LINUX_MIB_PRUNECALLED);
4180
4181         if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
4182                 tcp_clamp_window(sk);
4183         else if (tcp_memory_pressure)
4184                 tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
4185
4186         tcp_collapse_ofo_queue(sk);
4187         tcp_collapse(sk, &sk->sk_receive_queue,
4188                      sk->sk_receive_queue.next,
4189                      (struct sk_buff *)&sk->sk_receive_queue,
4190                      tp->copied_seq, tp->rcv_nxt);
4191         sk_mem_reclaim(sk);
4192
4193         if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4194                 return 0;
4195
4196         /* Collapsing did not help, destructive actions follow.
4197          * This must not ever occur. */
4198
4199         /* First, purge the out_of_order queue. */
4200         if (!skb_queue_empty(&tp->out_of_order_queue)) {
4201                 NET_INC_STATS_BH(LINUX_MIB_OFOPRUNED);
4202                 __skb_queue_purge(&tp->out_of_order_queue);
4203
4204                 /* Reset SACK state.  A conforming SACK implementation will
4205                  * do the same at a timeout based retransmit.  When a connection
4206                  * is in a sad state like this, we care only about integrity
4207                  * of the connection not performance.
4208                  */
4209                 if (tcp_is_sack(tp))
4210                         tcp_sack_reset(&tp->rx_opt);
4211                 sk_mem_reclaim(sk);
4212         }
4213
4214         if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
4215                 return 0;
4216
4217         /* If we are really being abused, tell the caller to silently
4218          * drop receive data on the floor.  It will get retransmitted
4219          * and hopefully then we'll have sufficient space.
4220          */
4221         NET_INC_STATS_BH(LINUX_MIB_RCVPRUNED);
4222
4223         /* Massive buffer overcommit. */
4224         tp->pred_flags = 0;
4225         return -1;
4226 }
4227
4228 /* RFC2861, slow part. Adjust cwnd, after it was not full during one rto.
4229  * As additional protections, we do not touch cwnd in retransmission phases,
4230  * and if application hit its sndbuf limit recently.
4231  */
4232 void tcp_cwnd_application_limited(struct sock *sk)
4233 {
4234         struct tcp_sock *tp = tcp_sk(sk);
4235
4236         if (inet_csk(sk)->icsk_ca_state == TCP_CA_Open &&
4237             sk->sk_socket && !test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
4238                 /* Limited by application or receiver window. */
4239                 u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
4240                 u32 win_used = max(tp->snd_cwnd_used, init_win);
4241                 if (win_used < tp->snd_cwnd) {
4242                         tp->snd_ssthresh = tcp_current_ssthresh(sk);
4243                         tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
4244                 }
4245                 tp->snd_cwnd_used = 0;
4246         }
4247         tp->snd_cwnd_stamp = tcp_time_stamp;
4248 }
4249
4250 static int tcp_should_expand_sndbuf(struct sock *sk)
4251 {
4252         struct tcp_sock *tp = tcp_sk(sk);
4253
4254         /* If the user specified a specific send buffer setting, do
4255          * not modify it.
4256          */
4257         if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
4258                 return 0;
4259
4260         /* If we are under global TCP memory pressure, do not expand.  */
4261         if (tcp_memory_pressure)
4262                 return 0;
4263
4264         /* If we are under soft global TCP memory pressure, do not expand.  */
4265         if (atomic_read(&tcp_memory_allocated) >= sysctl_tcp_mem[0])
4266                 return 0;
4267
4268         /* If we filled the congestion window, do not expand.  */
4269         if (tp->packets_out >= tp->snd_cwnd)
4270                 return 0;
4271
4272         return 1;
4273 }
4274
4275 /* When incoming ACK allowed to free some skb from write_queue,
4276  * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
4277  * on the exit from tcp input handler.
4278  *
4279  * PROBLEM: sndbuf expansion does not work well with largesend.
4280  */
4281 static void tcp_new_space(struct sock *sk)
4282 {
4283         struct tcp_sock *tp = tcp_sk(sk);
4284
4285         if (tcp_should_expand_sndbuf(sk)) {
4286                 int sndmem = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
4287                         MAX_TCP_HEADER + 16 + sizeof(struct sk_buff),
4288                     demanded = max_t(unsigned int, tp->snd_cwnd,
4289                                      tp->reordering + 1);
4290                 sndmem *= 2 * demanded;
4291                 if (sndmem > sk->sk_sndbuf)
4292                         sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
4293                 tp->snd_cwnd_stamp = tcp_time_stamp;
4294         }
4295
4296         sk->sk_write_space(sk);
4297 }
4298
4299 static void tcp_check_space(struct sock *sk)
4300 {
4301         if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
4302                 sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
4303                 if (sk->sk_socket &&
4304                     test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
4305                         tcp_new_space(sk);
4306         }
4307 }
4308
4309 static inline void tcp_data_snd_check(struct sock *sk)
4310 {
4311         tcp_push_pending_frames(sk);
4312         tcp_check_space(sk);
4313 }
4314
4315 /*
4316  * Check if sending an ack is needed.
4317  */
4318 static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
4319 {
4320         struct tcp_sock *tp = tcp_sk(sk);
4321
4322             /* More than one full frame received... */
4323         if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss
4324              /* ... and right edge of window advances far enough.
4325               * (tcp_recvmsg() will send ACK otherwise). Or...
4326               */
4327              && __tcp_select_window(sk) >= tp->rcv_wnd) ||
4328             /* We ACK each frame or... */
4329             tcp_in_quickack_mode(sk) ||
4330             /* We have out of order data. */
4331             (ofo_possible && skb_peek(&tp->out_of_order_queue))) {
4332                 /* Then ack it now */
4333                 tcp_send_ack(sk);
4334         } else {
4335                 /* Else, send delayed ack. */
4336                 tcp_send_delayed_ack(sk);
4337         }
4338 }
4339
4340 static inline void tcp_ack_snd_check(struct sock *sk)
4341 {
4342         if (!inet_csk_ack_scheduled(sk)) {
4343                 /* We sent a data segment already. */
4344                 return;
4345         }
4346         __tcp_ack_snd_check(sk, 1);
4347 }
4348
4349 /*
4350  *      This routine is only called when we have urgent data
4351  *      signaled. Its the 'slow' part of tcp_urg. It could be
4352  *      moved inline now as tcp_urg is only called from one
4353  *      place. We handle URGent data wrong. We have to - as
4354  *      BSD still doesn't use the correction from RFC961.
4355  *      For 1003.1g we should support a new option TCP_STDURG to permit
4356  *      either form (or just set the sysctl tcp_stdurg).
4357  */
4358
4359 static void tcp_check_urg(struct sock *sk, struct tcphdr *th)
4360 {
4361         struct tcp_sock *tp = tcp_sk(sk);
4362         u32 ptr = ntohs(th->urg_ptr);
4363
4364         if (ptr && !sysctl_tcp_stdurg)
4365                 ptr--;
4366         ptr += ntohl(th->seq);
4367
4368         /* Ignore urgent data that we've already seen and read. */
4369         if (after(tp->copied_seq, ptr))
4370                 return;
4371
4372         /* Do not replay urg ptr.
4373          *
4374          * NOTE: interesting situation not covered by specs.
4375          * Misbehaving sender may send urg ptr, pointing to segment,
4376          * which we already have in ofo queue. We are not able to fetch
4377          * such data and will stay in TCP_URG_NOTYET until will be eaten
4378          * by recvmsg(). Seems, we are not obliged to handle such wicked
4379          * situations. But it is worth to think about possibility of some
4380          * DoSes using some hypothetical application level deadlock.
4381          */
4382         if (before(ptr, tp->rcv_nxt))
4383                 return;
4384
4385         /* Do we already have a newer (or duplicate) urgent pointer? */
4386         if (tp->urg_data && !after(ptr, tp->urg_seq))
4387                 return;
4388
4389         /* Tell the world about our new urgent pointer. */
4390         sk_send_sigurg(sk);
4391
4392         /* We may be adding urgent data when the last byte read was
4393          * urgent. To do this requires some care. We cannot just ignore
4394          * tp->copied_seq since we would read the last urgent byte again
4395          * as data, nor can we alter copied_seq until this data arrives
4396          * or we break the semantics of SIOCATMARK (and thus sockatmark())
4397          *
4398          * NOTE. Double Dutch. Rendering to plain English: author of comment
4399          * above did something sort of  send("A", MSG_OOB); send("B", MSG_OOB);
4400          * and expect that both A and B disappear from stream. This is _wrong_.
4401          * Though this happens in BSD with high probability, this is occasional.
4402          * Any application relying on this is buggy. Note also, that fix "works"
4403          * only in this artificial test. Insert some normal data between A and B and we will
4404          * decline of BSD again. Verdict: it is better to remove to trap
4405          * buggy users.
4406          */
4407         if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
4408             !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) {
4409                 struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
4410                 tp->copied_seq++;
4411                 if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
4412                         __skb_unlink(skb, &sk->sk_receive_queue);
4413                         __kfree_skb(skb);
4414                 }
4415         }
4416
4417         tp->urg_data = TCP_URG_NOTYET;
4418         tp->urg_seq = ptr;
4419
4420         /* Disable header prediction. */
4421         tp->pred_flags = 0;
4422 }
4423
4424 /* This is the 'fast' part of urgent handling. */
4425 static void tcp_urg(struct sock *sk, struct sk_buff *skb, struct tcphdr *th)
4426 {
4427         struct tcp_sock *tp = tcp_sk(sk);
4428
4429         /* Check if we get a new urgent pointer - normally not. */
4430         if (th->urg)
4431                 tcp_check_urg(sk, th);
4432
4433         /* Do we wait for any urgent data? - normally not... */
4434         if (tp->urg_data == TCP_URG_NOTYET) {
4435                 u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
4436                           th->syn;
4437
4438                 /* Is the urgent pointer pointing into this packet? */
4439                 if (ptr < skb->len) {
4440                         u8 tmp;
4441                         if (skb_copy_bits(skb, ptr, &tmp, 1))
4442                                 BUG();
4443                         tp->urg_data = TCP_URG_VALID | tmp;
4444                         if (!sock_flag(sk, SOCK_DEAD))
4445                                 sk->sk_data_ready(sk, 0);
4446                 }
4447         }
4448 }
4449
4450 static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
4451 {
4452         struct tcp_sock *tp = tcp_sk(sk);
4453         int chunk = skb->len - hlen;
4454         int err;
4455
4456         local_bh_enable();
4457         if (skb_csum_unnecessary(skb))
4458                 err = skb_copy_datagram_iovec(skb, hlen, tp->ucopy.iov, chunk);
4459         else
4460                 err = skb_copy_and_csum_datagram_iovec(skb, hlen,
4461                                                        tp->ucopy.iov);
4462
4463         if (!err) {
4464                 tp->ucopy.len -= chunk;
4465                 tp->copied_seq += chunk;
4466                 tcp_rcv_space_adjust(sk);
4467         }
4468
4469         local_bh_disable();
4470         return err;
4471 }
4472
4473 static __sum16 __tcp_checksum_complete_user(struct sock *sk,
4474                                             struct sk_buff *skb)
4475 {
4476         __sum16 result;
4477
4478         if (sock_owned_by_user(sk)) {
4479                 local_bh_enable();
4480                 result = __tcp_checksum_complete(skb);
4481                 local_bh_disable();
4482         } else {
4483                 result = __tcp_checksum_complete(skb);
4484         }
4485         return result;
4486 }
4487
4488 static inline int tcp_checksum_complete_user(struct sock *sk,
4489                                              struct sk_buff *skb)
4490 {
4491         return !skb_csum_unnecessary(skb) &&
4492                __tcp_checksum_complete_user(sk, skb);
4493 }
4494
4495 #ifdef CONFIG_NET_DMA
4496 static int tcp_dma_try_early_copy(struct sock *sk, struct sk_buff *skb,
4497                                   int hlen)
4498 {
4499         struct tcp_sock *tp = tcp_sk(sk);
4500         int chunk = skb->len - hlen;
4501         int dma_cookie;
4502         int copied_early = 0;
4503
4504         if (tp->ucopy.wakeup)
4505                 return 0;
4506
4507         if (!tp->ucopy.dma_chan && tp->ucopy.pinned_list)
4508                 tp->ucopy.dma_chan = get_softnet_dma();
4509
4510         if (tp->ucopy.dma_chan && skb_csum_unnecessary(skb)) {
4511
4512                 dma_cookie = dma_skb_copy_datagram_iovec(tp->ucopy.dma_chan,
4513                                                          skb, hlen,
4514                                                          tp->ucopy.iov, chunk,
4515                                                          tp->ucopy.pinned_list);
4516
4517                 if (dma_cookie < 0)
4518                         goto out;
4519
4520                 tp->ucopy.dma_cookie = dma_cookie;
4521                 copied_early = 1;
4522
4523                 tp->ucopy.len -= chunk;
4524                 tp->copied_seq += chunk;
4525                 tcp_rcv_space_adjust(sk);
4526
4527                 if ((tp->ucopy.len == 0) ||
4528                     (tcp_flag_word(tcp_hdr(skb)) & TCP_FLAG_PSH) ||
4529                     (atomic_read(&sk->sk_rmem_alloc) > (sk->sk_rcvbuf >> 1))) {
4530                         tp->ucopy.wakeup = 1;
4531                         sk->sk_data_ready(sk, 0);
4532                 }
4533         } else if (chunk > 0) {
4534                 tp->ucopy.wakeup = 1;
4535                 sk->sk_data_ready(sk, 0);
4536         }
4537 out:
4538         return copied_early;
4539 }
4540 #endif /* CONFIG_NET_DMA */
4541
4542 /*
4543  *      TCP receive function for the ESTABLISHED state.
4544  *
4545  *      It is split into a fast path and a slow path. The fast path is
4546  *      disabled when:
4547  *      - A zero window was announced from us - zero window probing
4548  *        is only handled properly in the slow path.
4549  *      - Out of order segments arrived.
4550  *      - Urgent data is expected.
4551  *      - There is no buffer space left
4552  *      - Unexpected TCP flags/window values/header lengths are received
4553  *        (detected by checking the TCP header against pred_flags)
4554  *      - Data is sent in both directions. Fast path only supports pure senders
4555  *        or pure receivers (this means either the sequence number or the ack
4556  *        value must stay constant)
4557  *      - Unexpected TCP option.
4558  *
4559  *      When these conditions are not satisfied it drops into a standard
4560  *      receive procedure patterned after RFC793 to handle all cases.
4561  *      The first three cases are guaranteed by proper pred_flags setting,
4562  *      the rest is checked inline. Fast processing is turned on in
4563  *      tcp_data_queue when everything is OK.
4564  */
4565 int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
4566                         struct tcphdr *th, unsigned len)
4567 {
4568         struct tcp_sock *tp = tcp_sk(sk);
4569
4570         /*
4571          *      Header prediction.
4572          *      The code loosely follows the one in the famous
4573          *      "30 instruction TCP receive" Van Jacobson mail.
4574          *
4575          *      Van's trick is to deposit buffers into socket queue
4576          *      on a device interrupt, to call tcp_recv function
4577          *      on the receive process context and checksum and copy
4578          *      the buffer to user space. smart...
4579          *
4580          *      Our current scheme is not silly either but we take the
4581          *      extra cost of the net_bh soft interrupt processing...
4582          *      We do checksum and copy also but from device to kernel.
4583          */
4584
4585         tp->rx_opt.saw_tstamp = 0;
4586
4587         /*      pred_flags is 0xS?10 << 16 + snd_wnd
4588          *      if header_prediction is to be made
4589          *      'S' will always be tp->tcp_header_len >> 2
4590          *      '?' will be 0 for the fast path, otherwise pred_flags is 0 to
4591          *  turn it off (when there are holes in the receive
4592          *       space for instance)
4593          *      PSH flag is ignored.
4594          */
4595
4596         if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
4597             TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
4598                 int tcp_header_len = tp->tcp_header_len;
4599
4600                 /* Timestamp header prediction: tcp_header_len
4601                  * is automatically equal to th->doff*4 due to pred_flags
4602                  * match.
4603                  */
4604
4605                 /* Check timestamp */
4606                 if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
4607                         __be32 *ptr = (__be32 *)(th + 1);
4608
4609                         /* No? Slow path! */
4610                         if (*ptr != htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
4611                                           | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP))
4612                                 goto slow_path;
4613
4614                         tp->rx_opt.saw_tstamp = 1;
4615                         ++ptr;
4616                         tp->rx_opt.rcv_tsval = ntohl(*ptr);
4617                         ++ptr;
4618                         tp->rx_opt.rcv_tsecr = ntohl(*ptr);
4619
4620                         /* If PAWS failed, check it more carefully in slow path */
4621                         if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
4622                                 goto slow_path;
4623
4624                         /* DO NOT update ts_recent here, if checksum fails
4625                          * and timestamp was corrupted part, it will result
4626                          * in a hung connection since we will drop all
4627                          * future packets due to the PAWS test.
4628                          */
4629                 }
4630
4631                 if (len <= tcp_header_len) {
4632                         /* Bulk data transfer: sender */
4633                         if (len == tcp_header_len) {
4634                                 /* Predicted packet is in window by definition.
4635                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
4636                                  * Hence, check seq<=rcv_wup reduces to:
4637                                  */
4638                                 if (tcp_header_len ==
4639                                     (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
4640                                     tp->rcv_nxt == tp->rcv_wup)
4641                                         tcp_store_ts_recent(tp);
4642
4643                                 /* We know that such packets are checksummed
4644                                  * on entry.
4645                                  */
4646                                 tcp_ack(sk, skb, 0);
4647                                 __kfree_skb(skb);
4648                                 tcp_data_snd_check(sk);
4649                                 return 0;
4650                         } else { /* Header too small */
4651                                 TCP_INC_STATS_BH(TCP_MIB_INERRS);
4652                                 goto discard;
4653                         }
4654                 } else {
4655                         int eaten = 0;
4656                         int copied_early = 0;
4657
4658                         if (tp->copied_seq == tp->rcv_nxt &&
4659                             len - tcp_header_len <= tp->ucopy.len) {
4660 #ifdef CONFIG_NET_DMA
4661                                 if (tcp_dma_try_early_copy(sk, skb, tcp_header_len)) {
4662                                         copied_early = 1;
4663                                         eaten = 1;
4664                                 }
4665 #endif
4666                                 if (tp->ucopy.task == current &&
4667                                     sock_owned_by_user(sk) && !copied_early) {
4668                                         __set_current_state(TASK_RUNNING);
4669
4670                                         if (!tcp_copy_to_iovec(sk, skb, tcp_header_len))
4671                                                 eaten = 1;
4672                                 }
4673                                 if (eaten) {
4674                                         /* Predicted packet is in window by definition.
4675                                          * seq == rcv_nxt and rcv_wup <= rcv_nxt.
4676                                          * Hence, check seq<=rcv_wup reduces to:
4677                                          */
4678                                         if (tcp_header_len ==
4679                                             (sizeof(struct tcphdr) +
4680                                              TCPOLEN_TSTAMP_ALIGNED) &&
4681                                             tp->rcv_nxt == tp->rcv_wup)
4682                                                 tcp_store_ts_recent(tp);
4683
4684                                         tcp_rcv_rtt_measure_ts(sk, skb);
4685
4686                                         __skb_pull(skb, tcp_header_len);
4687                                         tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
4688                                         NET_INC_STATS_BH(LINUX_MIB_TCPHPHITSTOUSER);
4689                                 }
4690                                 if (copied_early)
4691                                         tcp_cleanup_rbuf(sk, skb->len);
4692                         }
4693                         if (!eaten) {
4694                                 if (tcp_checksum_complete_user(sk, skb))
4695                                         goto csum_error;
4696
4697                                 /* Predicted packet is in window by definition.
4698                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
4699                                  * Hence, check seq<=rcv_wup reduces to:
4700                                  */
4701                                 if (tcp_header_len ==
4702                                     (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
4703                                     tp->rcv_nxt == tp->rcv_wup)
4704                                         tcp_store_ts_recent(tp);
4705
4706                                 tcp_rcv_rtt_measure_ts(sk, skb);
4707
4708                                 if ((int)skb->truesize > sk->sk_forward_alloc)
4709                                         goto step5;
4710
4711                                 NET_INC_STATS_BH(LINUX_MIB_TCPHPHITS);
4712
4713                                 /* Bulk data transfer: receiver */
4714                                 __skb_pull(skb, tcp_header_len);
4715                                 __skb_queue_tail(&sk->sk_receive_queue, skb);
4716                                 skb_set_owner_r(skb, sk);
4717                                 tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
4718                         }
4719
4720                         tcp_event_data_recv(sk, skb);
4721
4722                         if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
4723                                 /* Well, only one small jumplet in fast path... */
4724                                 tcp_ack(sk, skb, FLAG_DATA);
4725                                 tcp_data_snd_check(sk);
4726                                 if (!inet_csk_ack_scheduled(sk))
4727                                         goto no_ack;
4728                         }
4729
4730                         __tcp_ack_snd_check(sk, 0);
4731 no_ack:
4732 #ifdef CONFIG_NET_DMA
4733                         if (copied_early)
4734                                 __skb_queue_tail(&sk->sk_async_wait_queue, skb);
4735                         else
4736 #endif
4737                         if (eaten)
4738                                 __kfree_skb(skb);
4739                         else
4740                                 sk->sk_data_ready(sk, 0);
4741                         return 0;
4742                 }
4743         }
4744
4745 slow_path:
4746         if (len < (th->doff << 2) || tcp_checksum_complete_user(sk, skb))
4747                 goto csum_error;
4748
4749         /*
4750          * RFC1323: H1. Apply PAWS check first.
4751          */
4752         if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
4753             tcp_paws_discard(sk, skb)) {
4754                 if (!th->rst) {
4755                         NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED);
4756                         tcp_send_dupack(sk, skb);
4757                         goto discard;
4758                 }
4759                 /* Resets are accepted even if PAWS failed.
4760
4761                    ts_recent update must be made after we are sure
4762                    that the packet is in window.
4763                  */
4764         }
4765
4766         /*
4767          *      Standard slow path.
4768          */
4769
4770         if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
4771                 /* RFC793, page 37: "In all states except SYN-SENT, all reset
4772                  * (RST) segments are validated by checking their SEQ-fields."
4773                  * And page 69: "If an incoming segment is not acceptable,
4774                  * an acknowledgment should be sent in reply (unless the RST bit
4775                  * is set, if so drop the segment and return)".
4776                  */
4777                 if (!th->rst)
4778                         tcp_send_dupack(sk, skb);
4779                 goto discard;
4780         }
4781
4782         if (th->rst) {
4783                 tcp_reset(sk);
4784                 goto discard;
4785         }
4786
4787         tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
4788
4789         if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
4790                 TCP_INC_STATS_BH(TCP_MIB_INERRS);
4791                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONSYN);
4792                 tcp_reset(sk);
4793                 return 1;
4794         }
4795
4796 step5:
4797         if (th->ack)
4798                 tcp_ack(sk, skb, FLAG_SLOWPATH);
4799
4800         tcp_rcv_rtt_measure_ts(sk, skb);
4801
4802         /* Process urgent data. */
4803         tcp_urg(sk, skb, th);
4804
4805         /* step 7: process the segment text */
4806         tcp_data_queue(sk, skb);
4807
4808         tcp_data_snd_check(sk);
4809         tcp_ack_snd_check(sk);
4810         return 0;
4811
4812 csum_error:
4813         TCP_INC_STATS_BH(TCP_MIB_INERRS);
4814
4815 discard:
4816         __kfree_skb(skb);
4817         return 0;
4818 }
4819
4820 static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
4821                                          struct tcphdr *th, unsigned len)
4822 {
4823         struct tcp_sock *tp = tcp_sk(sk);
4824         struct inet_connection_sock *icsk = inet_csk(sk);
4825         int saved_clamp = tp->rx_opt.mss_clamp;
4826
4827         tcp_parse_options(skb, &tp->rx_opt, 0);
4828
4829         if (th->ack) {
4830                 /* rfc793:
4831                  * "If the state is SYN-SENT then
4832                  *    first check the ACK bit
4833                  *      If the ACK bit is set
4834                  *        If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
4835                  *        a reset (unless the RST bit is set, if so drop
4836                  *        the segment and return)"
4837                  *
4838                  *  We do not send data with SYN, so that RFC-correct
4839                  *  test reduces to:
4840                  */
4841                 if (TCP_SKB_CB(skb)->ack_seq != tp->snd_nxt)
4842                         goto reset_and_undo;
4843
4844                 if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
4845                     !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
4846                              tcp_time_stamp)) {
4847                         NET_INC_STATS_BH(LINUX_MIB_PAWSACTIVEREJECTED);
4848                         goto reset_and_undo;
4849                 }
4850
4851                 /* Now ACK is acceptable.
4852                  *
4853                  * "If the RST bit is set
4854                  *    If the ACK was acceptable then signal the user "error:
4855                  *    connection reset", drop the segment, enter CLOSED state,
4856                  *    delete TCB, and return."
4857                  */
4858
4859                 if (th->rst) {
4860                         tcp_reset(sk);
4861                         goto discard;
4862                 }
4863
4864                 /* rfc793:
4865                  *   "fifth, if neither of the SYN or RST bits is set then
4866                  *    drop the segment and return."
4867                  *
4868                  *    See note below!
4869                  *                                        --ANK(990513)
4870                  */
4871                 if (!th->syn)
4872                         goto discard_and_undo;
4873
4874                 /* rfc793:
4875                  *   "If the SYN bit is on ...
4876                  *    are acceptable then ...
4877                  *    (our SYN has been ACKed), change the connection
4878                  *    state to ESTABLISHED..."
4879                  */
4880
4881                 TCP_ECN_rcv_synack(tp, th);
4882
4883                 tp->snd_wl1 = TCP_SKB_CB(skb)->seq;
4884                 tcp_ack(sk, skb, FLAG_SLOWPATH);
4885
4886                 /* Ok.. it's good. Set up sequence numbers and
4887                  * move to established.
4888                  */
4889                 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
4890                 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
4891
4892                 /* RFC1323: The window in SYN & SYN/ACK segments is
4893                  * never scaled.
4894                  */
4895                 tp->snd_wnd = ntohs(th->window);
4896                 tcp_init_wl(tp, TCP_SKB_CB(skb)->ack_seq, TCP_SKB_CB(skb)->seq);
4897
4898                 if (!tp->rx_opt.wscale_ok) {
4899                         tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
4900                         tp->window_clamp = min(tp->window_clamp, 65535U);
4901                 }
4902
4903                 if (tp->rx_opt.saw_tstamp) {
4904                         tp->rx_opt.tstamp_ok       = 1;
4905                         tp->tcp_header_len =
4906                                 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
4907                         tp->advmss          -= TCPOLEN_TSTAMP_ALIGNED;
4908                         tcp_store_ts_recent(tp);
4909                 } else {
4910                         tp->tcp_header_len = sizeof(struct tcphdr);
4911                 }
4912
4913                 if (tcp_is_sack(tp) && sysctl_tcp_fack)
4914                         tcp_enable_fack(tp);
4915
4916                 tcp_mtup_init(sk);
4917                 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
4918                 tcp_initialize_rcv_mss(sk);
4919
4920                 /* Remember, tcp_poll() does not lock socket!
4921                  * Change state from SYN-SENT only after copied_seq
4922                  * is initialized. */
4923                 tp->copied_seq = tp->rcv_nxt;
4924                 smp_mb();
4925                 tcp_set_state(sk, TCP_ESTABLISHED);
4926
4927                 security_inet_conn_established(sk, skb);
4928
4929                 /* Make sure socket is routed, for correct metrics.  */
4930                 icsk->icsk_af_ops->rebuild_header(sk);
4931
4932                 tcp_init_metrics(sk);
4933
4934                 tcp_init_congestion_control(sk);
4935
4936                 /* Prevent spurious tcp_cwnd_restart() on first data
4937                  * packet.
4938                  */
4939                 tp->lsndtime = tcp_time_stamp;
4940
4941                 tcp_init_buffer_space(sk);
4942
4943                 if (sock_flag(sk, SOCK_KEEPOPEN))
4944                         inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
4945
4946                 if (!tp->rx_opt.snd_wscale)
4947                         __tcp_fast_path_on(tp, tp->snd_wnd);
4948                 else
4949                         tp->pred_flags = 0;
4950
4951                 if (!sock_flag(sk, SOCK_DEAD)) {
4952                         sk->sk_state_change(sk);
4953                         sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
4954                 }
4955
4956                 if (sk->sk_write_pending ||
4957                     icsk->icsk_accept_queue.rskq_defer_accept ||
4958                     icsk->icsk_ack.pingpong) {
4959                         /* Save one ACK. Data will be ready after
4960                          * several ticks, if write_pending is set.
4961                          *
4962                          * It may be deleted, but with this feature tcpdumps
4963                          * look so _wonderfully_ clever, that I was not able
4964                          * to stand against the temptation 8)     --ANK
4965                          */
4966                         inet_csk_schedule_ack(sk);
4967                         icsk->icsk_ack.lrcvtime = tcp_time_stamp;
4968                         icsk->icsk_ack.ato       = TCP_ATO_MIN;
4969                         tcp_incr_quickack(sk);
4970                         tcp_enter_quickack_mode(sk);
4971                         inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
4972                                                   TCP_DELACK_MAX, TCP_RTO_MAX);
4973
4974 discard:
4975                         __kfree_skb(skb);
4976                         return 0;
4977                 } else {
4978                         tcp_send_ack(sk);
4979                 }
4980                 return -1;
4981         }
4982
4983         /* No ACK in the segment */
4984
4985         if (th->rst) {
4986                 /* rfc793:
4987                  * "If the RST bit is set
4988                  *
4989                  *      Otherwise (no ACK) drop the segment and return."
4990                  */
4991
4992                 goto discard_and_undo;
4993         }
4994
4995         /* PAWS check. */
4996         if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp &&
4997             tcp_paws_check(&tp->rx_opt, 0))
4998                 goto discard_and_undo;
4999
5000         if (th->syn) {
5001                 /* We see SYN without ACK. It is attempt of
5002                  * simultaneous connect with crossed SYNs.
5003                  * Particularly, it can be connect to self.
5004                  */
5005                 tcp_set_state(sk, TCP_SYN_RECV);
5006
5007                 if (tp->rx_opt.saw_tstamp) {
5008                         tp->rx_opt.tstamp_ok = 1;
5009                         tcp_store_ts_recent(tp);
5010                         tp->tcp_header_len =
5011                                 sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
5012                 } else {
5013                         tp->tcp_header_len = sizeof(struct tcphdr);
5014                 }
5015
5016                 tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
5017                 tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
5018
5019                 /* RFC1323: The window in SYN & SYN/ACK segments is
5020                  * never scaled.
5021                  */
5022                 tp->snd_wnd    = ntohs(th->window);
5023                 tp->snd_wl1    = TCP_SKB_CB(skb)->seq;
5024                 tp->max_window = tp->snd_wnd;
5025
5026                 TCP_ECN_rcv_syn(tp, th);
5027
5028                 tcp_mtup_init(sk);
5029                 tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
5030                 tcp_initialize_rcv_mss(sk);
5031
5032                 tcp_send_synack(sk);
5033 #if 0
5034                 /* Note, we could accept data and URG from this segment.
5035                  * There are no obstacles to make this.
5036                  *
5037                  * However, if we ignore data in ACKless segments sometimes,
5038                  * we have no reasons to accept it sometimes.
5039                  * Also, seems the code doing it in step6 of tcp_rcv_state_process
5040                  * is not flawless. So, discard packet for sanity.
5041                  * Uncomment this return to process the data.
5042                  */
5043                 return -1;
5044 #else
5045                 goto discard;
5046 #endif
5047         }
5048         /* "fifth, if neither of the SYN or RST bits is set then
5049          * drop the segment and return."
5050          */
5051
5052 discard_and_undo:
5053         tcp_clear_options(&tp->rx_opt);
5054         tp->rx_opt.mss_clamp = saved_clamp;
5055         goto discard;
5056
5057 reset_and_undo:
5058         tcp_clear_options(&tp->rx_opt);
5059         tp->rx_opt.mss_clamp = saved_clamp;
5060         return 1;
5061 }
5062
5063 /*
5064  *      This function implements the receiving procedure of RFC 793 for
5065  *      all states except ESTABLISHED and TIME_WAIT.
5066  *      It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
5067  *      address independent.
5068  */
5069
5070 int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
5071                           struct tcphdr *th, unsigned len)
5072 {
5073         struct tcp_sock *tp = tcp_sk(sk);
5074         struct inet_connection_sock *icsk = inet_csk(sk);
5075         int queued = 0;
5076
5077         tp->rx_opt.saw_tstamp = 0;
5078
5079         switch (sk->sk_state) {
5080         case TCP_CLOSE:
5081                 goto discard;
5082
5083         case TCP_LISTEN:
5084                 if (th->ack)
5085                         return 1;
5086
5087                 if (th->rst)
5088                         goto discard;
5089
5090                 if (th->syn) {
5091                         if (icsk->icsk_af_ops->conn_request(sk, skb) < 0)
5092                                 return 1;
5093
5094                         /* Now we have several options: In theory there is
5095                          * nothing else in the frame. KA9Q has an option to
5096                          * send data with the syn, BSD accepts data with the
5097                          * syn up to the [to be] advertised window and
5098                          * Solaris 2.1 gives you a protocol error. For now
5099                          * we just ignore it, that fits the spec precisely
5100                          * and avoids incompatibilities. It would be nice in
5101                          * future to drop through and process the data.
5102                          *
5103                          * Now that TTCP is starting to be used we ought to
5104                          * queue this data.
5105                          * But, this leaves one open to an easy denial of
5106                          * service attack, and SYN cookies can't defend
5107                          * against this problem. So, we drop the data
5108                          * in the interest of security over speed unless
5109                          * it's still in use.
5110                          */
5111                         kfree_skb(skb);
5112                         return 0;
5113                 }
5114                 goto discard;
5115
5116         case TCP_SYN_SENT:
5117                 queued = tcp_rcv_synsent_state_process(sk, skb, th, len);
5118                 if (queued >= 0)
5119                         return queued;
5120
5121                 /* Do step6 onward by hand. */
5122                 tcp_urg(sk, skb, th);
5123                 __kfree_skb(skb);
5124                 tcp_data_snd_check(sk);
5125                 return 0;
5126         }
5127
5128         if (tcp_fast_parse_options(skb, th, tp) && tp->rx_opt.saw_tstamp &&
5129             tcp_paws_discard(sk, skb)) {
5130                 if (!th->rst) {
5131                         NET_INC_STATS_BH(LINUX_MIB_PAWSESTABREJECTED);
5132                         tcp_send_dupack(sk, skb);
5133                         goto discard;
5134                 }
5135                 /* Reset is accepted even if it did not pass PAWS. */
5136         }
5137
5138         /* step 1: check sequence number */
5139         if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
5140                 if (!th->rst)
5141                         tcp_send_dupack(sk, skb);
5142                 goto discard;
5143         }
5144
5145         /* step 2: check RST bit */
5146         if (th->rst) {
5147                 tcp_reset(sk);
5148                 goto discard;
5149         }
5150
5151         tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
5152
5153         /* step 3: check security and precedence [ignored] */
5154
5155         /*      step 4:
5156          *
5157          *      Check for a SYN in window.
5158          */
5159         if (th->syn && !before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
5160                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONSYN);
5161                 tcp_reset(sk);
5162                 return 1;
5163         }
5164
5165         /* step 5: check the ACK field */
5166         if (th->ack) {
5167                 int acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH);
5168
5169                 switch (sk->sk_state) {
5170                 case TCP_SYN_RECV:
5171                         if (acceptable) {
5172                                 tp->copied_seq = tp->rcv_nxt;
5173                                 smp_mb();
5174                                 tcp_set_state(sk, TCP_ESTABLISHED);
5175                                 sk->sk_state_change(sk);
5176
5177                                 /* Note, that this wakeup is only for marginal
5178                                  * crossed SYN case. Passively open sockets
5179                                  * are not waked up, because sk->sk_sleep ==
5180                                  * NULL and sk->sk_socket == NULL.
5181                                  */
5182                                 if (sk->sk_socket)
5183                                         sk_wake_async(sk,
5184                                                       SOCK_WAKE_IO, POLL_OUT);
5185
5186                                 tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
5187                                 tp->snd_wnd = ntohs(th->window) <<
5188                                               tp->rx_opt.snd_wscale;
5189                                 tcp_init_wl(tp, TCP_SKB_CB(skb)->ack_seq,
5190                                             TCP_SKB_CB(skb)->seq);
5191
5192                                 /* tcp_ack considers this ACK as duplicate
5193                                  * and does not calculate rtt.
5194                                  * Fix it at least with timestamps.
5195                                  */
5196                                 if (tp->rx_opt.saw_tstamp &&
5197                                     tp->rx_opt.rcv_tsecr && !tp->srtt)
5198                                         tcp_ack_saw_tstamp(sk, 0);
5199
5200                                 if (tp->rx_opt.tstamp_ok)
5201                                         tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
5202
5203                                 /* Make sure socket is routed, for
5204                                  * correct metrics.
5205                                  */
5206                                 icsk->icsk_af_ops->rebuild_header(sk);
5207
5208                                 tcp_init_metrics(sk);
5209
5210                                 tcp_init_congestion_control(sk);
5211
5212                                 /* Prevent spurious tcp_cwnd_restart() on
5213                                  * first data packet.
5214                                  */
5215                                 tp->lsndtime = tcp_time_stamp;
5216
5217                                 tcp_mtup_init(sk);
5218                                 tcp_initialize_rcv_mss(sk);
5219                                 tcp_init_buffer_space(sk);
5220                                 tcp_fast_path_on(tp);
5221                         } else {
5222                                 return 1;
5223                         }
5224                         break;
5225
5226                 case TCP_FIN_WAIT1:
5227                         if (tp->snd_una == tp->write_seq) {
5228                                 tcp_set_state(sk, TCP_FIN_WAIT2);
5229                                 sk->sk_shutdown |= SEND_SHUTDOWN;
5230                                 dst_confirm(sk->sk_dst_cache);
5231
5232                                 if (!sock_flag(sk, SOCK_DEAD))
5233                                         /* Wake up lingering close() */
5234                                         sk->sk_state_change(sk);
5235                                 else {
5236                                         int tmo;
5237
5238                                         if (tp->linger2 < 0 ||
5239                                             (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
5240                                              after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt))) {
5241                                                 tcp_done(sk);
5242                                                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONDATA);
5243                                                 return 1;
5244                                         }
5245
5246                                         tmo = tcp_fin_time(sk);
5247                                         if (tmo > TCP_TIMEWAIT_LEN) {
5248                                                 inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
5249                                         } else if (th->fin || sock_owned_by_user(sk)) {
5250                                                 /* Bad case. We could lose such FIN otherwise.
5251                                                  * It is not a big problem, but it looks confusing
5252                                                  * and not so rare event. We still can lose it now,
5253                                                  * if it spins in bh_lock_sock(), but it is really
5254                                                  * marginal case.
5255                                                  */
5256                                                 inet_csk_reset_keepalive_timer(sk, tmo);
5257                                         } else {
5258                                                 tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
5259                                                 goto discard;
5260                                         }
5261                                 }
5262                         }
5263                         break;
5264
5265                 case TCP_CLOSING:
5266                         if (tp->snd_una == tp->write_seq) {
5267                                 tcp_time_wait(sk, TCP_TIME_WAIT, 0);
5268                                 goto discard;
5269                         }
5270                         break;
5271
5272                 case TCP_LAST_ACK:
5273                         if (tp->snd_una == tp->write_seq) {
5274                                 tcp_update_metrics(sk);
5275                                 tcp_done(sk);
5276                                 goto discard;
5277                         }
5278                         break;
5279                 }
5280         } else
5281                 goto discard;
5282
5283         /* step 6: check the URG bit */
5284         tcp_urg(sk, skb, th);
5285
5286         /* step 7: process the segment text */
5287         switch (sk->sk_state) {
5288         case TCP_CLOSE_WAIT:
5289         case TCP_CLOSING:
5290         case TCP_LAST_ACK:
5291                 if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
5292                         break;
5293         case TCP_FIN_WAIT1:
5294         case TCP_FIN_WAIT2:
5295                 /* RFC 793 says to queue data in these states,
5296                  * RFC 1122 says we MUST send a reset.
5297                  * BSD 4.4 also does reset.
5298                  */
5299                 if (sk->sk_shutdown & RCV_SHUTDOWN) {
5300                         if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
5301                             after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
5302                                 NET_INC_STATS_BH(LINUX_MIB_TCPABORTONDATA);
5303                                 tcp_reset(sk);
5304                                 return 1;
5305                         }
5306                 }
5307                 /* Fall through */
5308         case TCP_ESTABLISHED:
5309                 tcp_data_queue(sk, skb);
5310                 queued = 1;
5311                 break;
5312         }
5313
5314         /* tcp_data could move socket to TIME-WAIT */
5315         if (sk->sk_state != TCP_CLOSE) {
5316                 tcp_data_snd_check(sk);
5317                 tcp_ack_snd_check(sk);
5318         }
5319
5320         if (!queued) {
5321 discard:
5322                 __kfree_skb(skb);
5323         }
5324         return 0;
5325 }
5326
5327 EXPORT_SYMBOL(sysctl_tcp_ecn);
5328 EXPORT_SYMBOL(sysctl_tcp_reordering);
5329 EXPORT_SYMBOL(tcp_parse_options);
5330 EXPORT_SYMBOL(tcp_rcv_established);
5331 EXPORT_SYMBOL(tcp_rcv_state_process);
5332 EXPORT_SYMBOL(tcp_initialize_rcv_mss);