git.oblomov.eu Git - linux-2.6/blob - net/ipv4/ip_fragment.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  *              The IP fragmentation functionality.
   7  *
   8  * Version:     $Id: ip_fragment.c,v 1.59 2002/01/12 07:54:56 davem Exp $
   9  *
  10  * Authors:     Fred N. van Kempen <waltje@uWalt.NL.Mugnet.ORG>
  11  *              Alan Cox <Alan.Cox@linux.org>
  12  *
  13  * Fixes:
  14  *              Alan Cox        :       Split from ip.c , see ip_input.c for history.
  15  *              David S. Miller :       Begin massive cleanup...
  16  *              Andi Kleen      :       Add sysctls.
  17  *              xxxx            :       Overlapfrag bug.
  18  *              Ultima          :       ip_expire() kernel panic.
  19  *              Bill Hawes      :       Frag accounting and evictor fixes.
  20  *              John McDonald   :       0 length frag bug.
  21  *              Alexey Kuznetsov:       SMP races, threading, cleanup.
  22  *              Patrick McHardy :       LRU queue of frag heads for evictor.
  23  */
  24
  25 #include <linux/config.h>
  26 #include <linux/module.h>
  27 #include <linux/types.h>
  28 #include <linux/mm.h>
  29 #include <linux/jiffies.h>
  30 #include <linux/skbuff.h>
  31 #include <linux/list.h>
  32 #include <linux/ip.h>
  33 #include <linux/icmp.h>
  34 #include <linux/netdevice.h>
  35 #include <linux/jhash.h>
  36 #include <linux/random.h>
  37 #include <net/sock.h>
  38 #include <net/ip.h>
  39 #include <net/icmp.h>
  40 #include <net/checksum.h>
  41 #include <linux/tcp.h>
  42 #include <linux/udp.h>
  43 #include <linux/inet.h>
  44 #include <linux/netfilter_ipv4.h>
  45
  46 /* NOTE. Logic of IP defragmentation is parallel to corresponding IPv6
  47  * code now. If you change something here, _PLEASE_ update ipv6/reassembly.c
  48  * as well. Or notify me, at least. --ANK
  49  */
  50
  51 /* Fragment cache limits. We will commit 256K at one time. Should we
  52  * cross that limit we will prune down to 192K. This should cope with
  53  * even the most extreme cases without allowing an attacker to measurably
  54  * harm machine performance.
  55  */
  56 int sysctl_ipfrag_high_thresh = 256*1024;
  57 int sysctl_ipfrag_low_thresh = 192*1024;
  58
  59 /* Important NOTE! Fragment queue must be destroyed before MSL expires.
  60  * RFC791 is wrong proposing to prolongate timer each fragment arrival by TTL.
  61  */
  62 int sysctl_ipfrag_time = IP_FRAG_TIME;
  63
  64 struct ipfrag_skb_cb
  65 {
  66         struct inet_skb_parm    h;
  67         int                     offset;
  68 };
  69
  70 #define FRAG_CB(skb)    ((struct ipfrag_skb_cb*)((skb)->cb))
  71
  72 /* Describe an entry in the "incomplete datagrams" queue. */
  73 struct ipq {
  74         struct ipq      *next;          /* linked list pointers                 */
  75         struct list_head lru_list;      /* lru list member                      */
  76         u32             user;
  77         u32             saddr;
  78         u32             daddr;
  79         u16             id;
  80         u8              protocol;
  81         u8              last_in;
  82 #define COMPLETE                4
  83 #define FIRST_IN                2
  84 #define LAST_IN                 1
  85
  86         struct sk_buff  *fragments;     /* linked list of received fragments    */
  87         int             len;            /* total length of original datagram    */
  88         int             meat;
  89         spinlock_t      lock;
  90         atomic_t        refcnt;
  91         struct timer_list timer;        /* when will this queue expire?         */
  92         struct ipq      **pprev;
  93         int             iif;
  94         struct timeval  stamp;
  95 };
  96
  97 /* Hash table. */
  98
  99 #define IPQ_HASHSZ      64
 100
 101 /* Per-bucket lock is easy to add now. */
 102 static struct ipq *ipq_hash[IPQ_HASHSZ];
 103 static DEFINE_RWLOCK(ipfrag_lock);
 104 static u32 ipfrag_hash_rnd;
 105 static LIST_HEAD(ipq_lru_list);
 106 int ip_frag_nqueues = 0;
 107
 108 static __inline__ void __ipq_unlink(struct ipq *qp)
 109 {
 110         if(qp->next)
 111                 qp->next->pprev = qp->pprev;
 112         *qp->pprev = qp->next;
 113         list_del(&qp->lru_list);
 114         ip_frag_nqueues--;
 115 }
 116
 117 static __inline__ void ipq_unlink(struct ipq *ipq)
 118 {
 119         write_lock(&ipfrag_lock);
 120         __ipq_unlink(ipq);
 121         write_unlock(&ipfrag_lock);
 122 }
 123
 124 static unsigned int ipqhashfn(u16 id, u32 saddr, u32 daddr, u8 prot)
 125 {
 126         return jhash_3words((u32)id << 16 | prot, saddr, daddr,
 127                             ipfrag_hash_rnd) & (IPQ_HASHSZ - 1);
 128 }
 129
 130 static struct timer_list ipfrag_secret_timer;
 131 int sysctl_ipfrag_secret_interval = 10 * 60 * HZ;
 132
 133 static void ipfrag_secret_rebuild(unsigned long dummy)
 134 {
 135         unsigned long now = jiffies;
 136         int i;
 137
 138         write_lock(&ipfrag_lock);
 139         get_random_bytes(&ipfrag_hash_rnd, sizeof(u32));
 140         for (i = 0; i < IPQ_HASHSZ; i++) {
 141                 struct ipq *q;
 142
 143                 q = ipq_hash[i];
 144                 while (q) {
 145                         struct ipq *next = q->next;
 146                         unsigned int hval = ipqhashfn(q->id, q->saddr,
 147                                                       q->daddr, q->protocol);
 148
 149                         if (hval != i) {
 150                                 /* Unlink. */
 151                                 if (q->next)
 152                                         q->next->pprev = q->pprev;
 153                                 *q->pprev = q->next;
 154
 155                                 /* Relink to new hash chain. */
 156                                 if ((q->next = ipq_hash[hval]) != NULL)
 157                                         q->next->pprev = &q->next;
 158                                 ipq_hash[hval] = q;
 159                                 q->pprev = &ipq_hash[hval];
 160                         }
 161
 162                         q = next;
 163                 }
 164         }
 165         write_unlock(&ipfrag_lock);
 166
 167         mod_timer(&ipfrag_secret_timer, now + sysctl_ipfrag_secret_interval);
 168 }
 169
 170 atomic_t ip_frag_mem = ATOMIC_INIT(0);  /* Memory used for fragments */
 171
 172 /* Memory Tracking Functions. */
 173 static __inline__ void frag_kfree_skb(struct sk_buff *skb, int *work)
 174 {
 175         if (work)
 176                 *work -= skb->truesize;
 177         atomic_sub(skb->truesize, &ip_frag_mem);
 178         kfree_skb(skb);
 179 }
 180
 181 static __inline__ void frag_free_queue(struct ipq *qp, int *work)
 182 {
 183         if (work)
 184                 *work -= sizeof(struct ipq);
 185         atomic_sub(sizeof(struct ipq), &ip_frag_mem);
 186         kfree(qp);
 187 }
 188
 189 static __inline__ struct ipq *frag_alloc_queue(void)
 190 {
 191         struct ipq *qp = kmalloc(sizeof(struct ipq), GFP_ATOMIC);
 192
 193         if(!qp)
 194                 return NULL;
 195         atomic_add(sizeof(struct ipq), &ip_frag_mem);
 196         return qp;
 197 }
 198
 199
 200 /* Destruction primitives. */
 201
 202 /* Complete destruction of ipq. */
 203 static void ip_frag_destroy(struct ipq *qp, int *work)
 204 {
 205         struct sk_buff *fp;
 206
 207         BUG_TRAP(qp->last_in&COMPLETE);
 208         BUG_TRAP(del_timer(&qp->timer) == 0);
 209
 210         /* Release all fragment data. */
 211         fp = qp->fragments;
 212         while (fp) {
 213                 struct sk_buff *xp = fp->next;
 214
 215                 frag_kfree_skb(fp, work);
 216                 fp = xp;
 217         }
 218
 219         /* Finally, release the queue descriptor itself. */
 220         frag_free_queue(qp, work);
 221 }
 222
 223 static __inline__ void ipq_put(struct ipq *ipq, int *work)
 224 {
 225         if (atomic_dec_and_test(&ipq->refcnt))
 226                 ip_frag_destroy(ipq, work);
 227 }
 228
 229 /* Kill ipq entry. It is not destroyed immediately,
 230  * because caller (and someone more) holds reference count.
 231  */
 232 static void ipq_kill(struct ipq *ipq)
 233 {
 234         if (del_timer(&ipq->timer))
 235                 atomic_dec(&ipq->refcnt);
 236
 237         if (!(ipq->last_in & COMPLETE)) {
 238                 ipq_unlink(ipq);
 239                 atomic_dec(&ipq->refcnt);
 240                 ipq->last_in |= COMPLETE;
 241         }
 242 }
 243
 244 /* Memory limiting on fragments.  Evictor trashes the oldest
 245  * fragment queue until we are back under the threshold.
 246  */
 247 static void ip_evictor(void)
 248 {
 249         struct ipq *qp;
 250         struct list_head *tmp;
 251         int work;
 252
 253         work = atomic_read(&ip_frag_mem) - sysctl_ipfrag_low_thresh;
 254         if (work <= 0)
 255                 return;
 256
 257         while (work > 0) {
 258                 read_lock(&ipfrag_lock);
 259                 if (list_empty(&ipq_lru_list)) {
 260                         read_unlock(&ipfrag_lock);
 261                         return;
 262                 }
 263                 tmp = ipq_lru_list.next;
 264                 qp = list_entry(tmp, struct ipq, lru_list);
 265                 atomic_inc(&qp->refcnt);
 266                 read_unlock(&ipfrag_lock);
 267
 268                 spin_lock(&qp->lock);
 269                 if (!(qp->last_in&COMPLETE))
 270                         ipq_kill(qp);
 271                 spin_unlock(&qp->lock);
 272
 273                 ipq_put(qp, &work);
 274                 IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
 275         }
 276 }
 277
 278 /*
 279  * Oops, a fragment queue timed out.  Kill it and send an ICMP reply.
 280  */
 281 static void ip_expire(unsigned long arg)
 282 {
 283         struct ipq *qp = (struct ipq *) arg;
 284
 285         spin_lock(&qp->lock);
 286
 287         if (qp->last_in & COMPLETE)
 288                 goto out;
 289
 290         ipq_kill(qp);
 291
 292         IP_INC_STATS_BH(IPSTATS_MIB_REASMTIMEOUT);
 293         IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
 294
 295         if ((qp->last_in&FIRST_IN) && qp->fragments != NULL) {
 296                 struct sk_buff *head = qp->fragments;
 297                 /* Send an ICMP "Fragment Reassembly Timeout" message. */
 298                 if ((head->dev = dev_get_by_index(qp->iif)) != NULL) {
 299                         icmp_send(head, ICMP_TIME_EXCEEDED, ICMP_EXC_FRAGTIME, 0);
 300                         dev_put(head->dev);
 301                 }
 302         }
 303 out:
 304         spin_unlock(&qp->lock);
 305         ipq_put(qp, NULL);
 306 }
 307
 308 /* Creation primitives. */
 309
 310 static struct ipq *ip_frag_intern(unsigned int hash, struct ipq *qp_in)
 311 {
 312         struct ipq *qp;
 313
 314         write_lock(&ipfrag_lock);
 315 #ifdef CONFIG_SMP
 316         /* With SMP race we have to recheck hash table, because
 317          * such entry could be created on other cpu, while we
 318          * promoted read lock to write lock.
 319          */
 320         for(qp = ipq_hash[hash]; qp; qp = qp->next) {
 321                 if(qp->id == qp_in->id          &&
 322                    qp->saddr == qp_in->saddr    &&
 323                    qp->daddr == qp_in->daddr    &&
 324                    qp->protocol == qp_in->protocol &&
 325                    qp->user == qp_in->user) {
 326                         atomic_inc(&qp->refcnt);
 327                         write_unlock(&ipfrag_lock);
 328                         qp_in->last_in |= COMPLETE;
 329                         ipq_put(qp_in, NULL);
 330                         return qp;
 331                 }
 332         }
 333 #endif
 334         qp = qp_in;
 335
 336         if (!mod_timer(&qp->timer, jiffies + sysctl_ipfrag_time))
 337                 atomic_inc(&qp->refcnt);
 338
 339         atomic_inc(&qp->refcnt);
 340         if((qp->next = ipq_hash[hash]) != NULL)
 341                 qp->next->pprev = &qp->next;
 342         ipq_hash[hash] = qp;
 343         qp->pprev = &ipq_hash[hash];
 344         INIT_LIST_HEAD(&qp->lru_list);
 345         list_add_tail(&qp->lru_list, &ipq_lru_list);
 346         ip_frag_nqueues++;
 347         write_unlock(&ipfrag_lock);
 348         return qp;
 349 }
 350
 351 /* Add an entry to the 'ipq' queue for a newly received IP datagram. */
 352 static struct ipq *ip_frag_create(unsigned hash, struct iphdr *iph, u32 user)
 353 {
 354         struct ipq *qp;
 355
 356         if ((qp = frag_alloc_queue()) == NULL)
 357                 goto out_nomem;
 358
 359         qp->protocol = iph->protocol;
 360         qp->last_in = 0;
 361         qp->id = iph->id;
 362         qp->saddr = iph->saddr;
 363         qp->daddr = iph->daddr;
 364         qp->user = user;
 365         qp->len = 0;
 366         qp->meat = 0;
 367         qp->fragments = NULL;
 368         qp->iif = 0;
 369
 370         /* Initialize a timer for this entry. */
 371         init_timer(&qp->timer);
 372         qp->timer.data = (unsigned long) qp;    /* pointer to queue     */
 373         qp->timer.function = ip_expire;         /* expire function      */
 374         spin_lock_init(&qp->lock);
 375         atomic_set(&qp->refcnt, 1);
 376
 377         return ip_frag_intern(hash, qp);
 378
 379 out_nomem:
 380         LIMIT_NETDEBUG(printk(KERN_ERR "ip_frag_create: no memory left !\n"));
 381         return NULL;
 382 }
 383
 384 /* Find the correct entry in the "incomplete datagrams" queue for
 385  * this IP datagram, and create new one, if nothing is found.
 386  */
 387 static inline struct ipq *ip_find(struct iphdr *iph, u32 user)
 388 {
 389         __u16 id = iph->id;
 390         __u32 saddr = iph->saddr;
 391         __u32 daddr = iph->daddr;
 392         __u8 protocol = iph->protocol;
 393         unsigned int hash = ipqhashfn(id, saddr, daddr, protocol);
 394         struct ipq *qp;
 395
 396         read_lock(&ipfrag_lock);
 397         for(qp = ipq_hash[hash]; qp; qp = qp->next) {
 398                 if(qp->id == id         &&
 399                    qp->saddr == saddr   &&
 400                    qp->daddr == daddr   &&
 401                    qp->protocol == protocol &&
 402                    qp->user == user) {
 403                         atomic_inc(&qp->refcnt);
 404                         read_unlock(&ipfrag_lock);
 405                         return qp;
 406                 }
 407         }
 408         read_unlock(&ipfrag_lock);
 409
 410         return ip_frag_create(hash, iph, user);
 411 }
 412
 413 /* Add new segment to existing queue. */
 414 static void ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
 415 {
 416         struct sk_buff *prev, *next;
 417         int flags, offset;
 418         int ihl, end;
 419
 420         if (qp->last_in & COMPLETE)
 421                 goto err;
 422
 423         offset = ntohs(skb->nh.iph->frag_off);
 424         flags = offset & ~IP_OFFSET;
 425         offset &= IP_OFFSET;
 426         offset <<= 3;           /* offset is in 8-byte chunks */
 427         ihl = skb->nh.iph->ihl * 4;
 428
 429         /* Determine the position of this fragment. */
 430         end = offset + skb->len - ihl;
 431
 432         /* Is this the final fragment? */
 433         if ((flags & IP_MF) == 0) {
 434                 /* If we already have some bits beyond end
 435                  * or have different end, the segment is corrrupted.
 436                  */
 437                 if (end < qp->len ||
 438                     ((qp->last_in & LAST_IN) && end != qp->len))
 439                         goto err;
 440                 qp->last_in |= LAST_IN;
 441                 qp->len = end;
 442         } else {
 443                 if (end&7) {
 444                         end &= ~7;
 445                         if (skb->ip_summed != CHECKSUM_UNNECESSARY)
 446                                 skb->ip_summed = CHECKSUM_NONE;
 447                 }
 448                 if (end > qp->len) {
 449                         /* Some bits beyond end -> corruption. */
 450                         if (qp->last_in & LAST_IN)
 451                                 goto err;
 452                         qp->len = end;
 453                 }
 454         }
 455         if (end == offset)
 456                 goto err;
 457
 458         if (pskb_pull(skb, ihl) == NULL)
 459                 goto err;
 460         if (pskb_trim(skb, end-offset))
 461                 goto err;
 462
 463         /* Find out which fragments are in front and at the back of us
 464          * in the chain of fragments so far.  We must know where to put
 465          * this fragment, right?
 466          */
 467         prev = NULL;
 468         for(next = qp->fragments; next != NULL; next = next->next) {
 469                 if (FRAG_CB(next)->offset >= offset)
 470                         break;  /* bingo! */
 471                 prev = next;
 472         }
 473
 474         /* We found where to put this one.  Check for overlap with
 475          * preceding fragment, and, if needed, align things so that
 476          * any overlaps are eliminated.
 477          */
 478         if (prev) {
 479                 int i = (FRAG_CB(prev)->offset + prev->len) - offset;
 480
 481                 if (i > 0) {
 482                         offset += i;
 483                         if (end <= offset)
 484                                 goto err;
 485                         if (!pskb_pull(skb, i))
 486                                 goto err;
 487                         if (skb->ip_summed != CHECKSUM_UNNECESSARY)
 488                                 skb->ip_summed = CHECKSUM_NONE;
 489                 }
 490         }
 491
 492         while (next && FRAG_CB(next)->offset < end) {
 493                 int i = end - FRAG_CB(next)->offset; /* overlap is 'i' bytes */
 494
 495                 if (i < next->len) {
 496                         /* Eat head of the next overlapped fragment
 497                          * and leave the loop. The next ones cannot overlap.
 498                          */
 499                         if (!pskb_pull(next, i))
 500                                 goto err;
 501                         FRAG_CB(next)->offset += i;
 502                         qp->meat -= i;
 503                         if (next->ip_summed != CHECKSUM_UNNECESSARY)
 504                                 next->ip_summed = CHECKSUM_NONE;
 505                         break;
 506                 } else {
 507                         struct sk_buff *free_it = next;
 508
 509                         /* Old fragmnet is completely overridden with
 510                          * new one drop it.
 511                          */
 512                         next = next->next;
 513
 514                         if (prev)
 515                                 prev->next = next;
 516                         else
 517                                 qp->fragments = next;
 518
 519                         qp->meat -= free_it->len;
 520                         frag_kfree_skb(free_it, NULL);
 521                 }
 522         }
 523
 524         FRAG_CB(skb)->offset = offset;
 525
 526         /* Insert this fragment in the chain of fragments. */
 527         skb->next = next;
 528         if (prev)
 529                 prev->next = skb;
 530         else
 531                 qp->fragments = skb;
 532
 533         if (skb->dev)
 534                 qp->iif = skb->dev->ifindex;
 535         skb->dev = NULL;
 536         qp->stamp = skb->stamp;
 537         qp->meat += skb->len;
 538         atomic_add(skb->truesize, &ip_frag_mem);
 539         if (offset == 0)
 540                 qp->last_in |= FIRST_IN;
 541
 542         write_lock(&ipfrag_lock);
 543         list_move_tail(&qp->lru_list, &ipq_lru_list);
 544         write_unlock(&ipfrag_lock);
 545
 546         return;
 547
 548 err:
 549         kfree_skb(skb);
 550 }
 551
 552
 553 /* Build a new IP datagram from all its fragments. */
 554
 555 static struct sk_buff *ip_frag_reasm(struct ipq *qp, struct net_device *dev)
 556 {
 557         struct iphdr *iph;
 558         struct sk_buff *fp, *head = qp->fragments;
 559         int len;
 560         int ihlen;
 561
 562         ipq_kill(qp);
 563
 564         BUG_TRAP(head != NULL);
 565         BUG_TRAP(FRAG_CB(head)->offset == 0);
 566
 567         /* Allocate a new buffer for the datagram. */
 568         ihlen = head->nh.iph->ihl*4;
 569         len = ihlen + qp->len;
 570
 571         if(len > 65535)
 572                 goto out_oversize;
 573
 574         /* Head of list must not be cloned. */
 575         if (skb_cloned(head) && pskb_expand_head(head, 0, 0, GFP_ATOMIC))
 576                 goto out_nomem;
 577
 578         /* If the first fragment is fragmented itself, we split
 579          * it to two chunks: the first with data and paged part
 580          * and the second, holding only fragments. */
 581         if (skb_shinfo(head)->frag_list) {
 582                 struct sk_buff *clone;
 583                 int i, plen = 0;
 584
 585                 if ((clone = alloc_skb(0, GFP_ATOMIC)) == NULL)
 586                         goto out_nomem;
 587                 clone->next = head->next;
 588                 head->next = clone;
 589                 skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list;
 590                 skb_shinfo(head)->frag_list = NULL;
 591                 for (i=0; i<skb_shinfo(head)->nr_frags; i++)
 592                         plen += skb_shinfo(head)->frags[i].size;
 593                 clone->len = clone->data_len = head->data_len - plen;
 594                 head->data_len -= clone->len;
 595                 head->len -= clone->len;
 596                 clone->csum = 0;
 597                 clone->ip_summed = head->ip_summed;
 598                 atomic_add(clone->truesize, &ip_frag_mem);
 599         }
 600
 601         skb_shinfo(head)->frag_list = head->next;
 602         skb_push(head, head->data - head->nh.raw);
 603         atomic_sub(head->truesize, &ip_frag_mem);
 604
 605         for (fp=head->next; fp; fp = fp->next) {
 606                 head->data_len += fp->len;
 607                 head->len += fp->len;
 608                 if (head->ip_summed != fp->ip_summed)
 609                         head->ip_summed = CHECKSUM_NONE;
 610                 else if (head->ip_summed == CHECKSUM_HW)
 611                         head->csum = csum_add(head->csum, fp->csum);
 612                 head->truesize += fp->truesize;
 613                 atomic_sub(fp->truesize, &ip_frag_mem);
 614         }
 615
 616         head->next = NULL;
 617         head->dev = dev;
 618         head->stamp = qp->stamp;
 619
 620         iph = head->nh.iph;
 621         iph->frag_off = 0;
 622         iph->tot_len = htons(len);
 623         IP_INC_STATS_BH(IPSTATS_MIB_REASMOKS);
 624         qp->fragments = NULL;
 625         return head;
 626
 627 out_nomem:
 628         LIMIT_NETDEBUG(printk(KERN_ERR "IP: queue_glue: no memory for gluing "
 629                               "queue %p\n", qp));
 630         goto out_fail;
 631 out_oversize:
 632         if (net_ratelimit())
 633                 printk(KERN_INFO
 634                         "Oversized IP packet from %d.%d.%d.%d.\n",
 635                         NIPQUAD(qp->saddr));
 636 out_fail:
 637         IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
 638         return NULL;
 639 }
 640
 641 /* Process an incoming IP datagram fragment. */
 642 struct sk_buff *ip_defrag(struct sk_buff *skb, u32 user)
 643 {
 644         struct iphdr *iph = skb->nh.iph;
 645         struct ipq *qp;
 646         struct net_device *dev;
 647
 648         IP_INC_STATS_BH(IPSTATS_MIB_REASMREQDS);
 649
 650         /* Start by cleaning up the memory. */
 651         if (atomic_read(&ip_frag_mem) > sysctl_ipfrag_high_thresh)
 652                 ip_evictor();
 653
 654         dev = skb->dev;
 655
 656         /* Lookup (or create) queue header */
 657         if ((qp = ip_find(iph, user)) != NULL) {
 658                 struct sk_buff *ret = NULL;
 659
 660                 spin_lock(&qp->lock);
 661
 662                 ip_frag_queue(qp, skb);
 663
 664                 if (qp->last_in == (FIRST_IN|LAST_IN) &&
 665                     qp->meat == qp->len)
 666                         ret = ip_frag_reasm(qp, dev);
 667
 668                 spin_unlock(&qp->lock);
 669                 ipq_put(qp, NULL);
 670                 return ret;
 671         }
 672
 673         IP_INC_STATS_BH(IPSTATS_MIB_REASMFAILS);
 674         kfree_skb(skb);
 675         return NULL;
 676 }
 677
 678 void ipfrag_init(void)
 679 {
 680         ipfrag_hash_rnd = (u32) ((num_physpages ^ (num_physpages>>7)) ^
 681                                  (jiffies ^ (jiffies >> 6)));
 682
 683         init_timer(&ipfrag_secret_timer);
 684         ipfrag_secret_timer.function = ipfrag_secret_rebuild;
 685         ipfrag_secret_timer.expires = jiffies + sysctl_ipfrag_secret_interval;
 686         add_timer(&ipfrag_secret_timer);
 687 }
 688
 689 EXPORT_SYMBOL(ip_defrag);