[TCP]: tcp_simple_retransmit can cause S+L
[linux-2.6] / net / ipv4 / ip_forward.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 forwarding functionality.
7  *
8  * Version:     $Id: ip_forward.c,v 1.48 2000/12/13 18:31:48 davem Exp $
9  *
10  * Authors:     see ip.c
11  *
12  * Fixes:
13  *              Many            :       Split from ip.c , see ip_input.c for
14  *                                      history.
15  *              Dave Gregorich  :       NULL ip_rt_put fix for multicast
16  *                                      routing.
17  *              Jos Vos         :       Add call_out_firewall before sending,
18  *                                      use output device for accounting.
19  *              Jos Vos         :       Call forward firewall after routing
20  *                                      (always use output device).
21  *              Mike McLagan    :       Routing by source
22  */
23
24 #include <linux/types.h>
25 #include <linux/mm.h>
26 #include <linux/skbuff.h>
27 #include <linux/ip.h>
28 #include <linux/icmp.h>
29 #include <linux/netdevice.h>
30 #include <net/sock.h>
31 #include <net/ip.h>
32 #include <net/tcp.h>
33 #include <net/udp.h>
34 #include <net/icmp.h>
35 #include <linux/tcp.h>
36 #include <linux/udp.h>
37 #include <linux/netfilter_ipv4.h>
38 #include <net/checksum.h>
39 #include <linux/route.h>
40 #include <net/route.h>
41 #include <net/xfrm.h>
42
43 static int ip_forward_finish(struct sk_buff *skb)
44 {
45         struct ip_options * opt = &(IPCB(skb)->opt);
46
47         IP_INC_STATS_BH(IPSTATS_MIB_OUTFORWDATAGRAMS);
48
49         if (unlikely(opt->optlen))
50                 ip_forward_options(skb);
51
52         return dst_output(skb);
53 }
54
55 int ip_forward(struct sk_buff *skb)
56 {
57         struct iphdr *iph;      /* Our header */
58         struct rtable *rt;      /* Route we use */
59         struct ip_options * opt = &(IPCB(skb)->opt);
60
61         if (!xfrm4_policy_check(NULL, XFRM_POLICY_FWD, skb))
62                 goto drop;
63
64         if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb))
65                 return NET_RX_SUCCESS;
66
67         if (skb->pkt_type != PACKET_HOST)
68                 goto drop;
69
70         skb_forward_csum(skb);
71
72         /*
73          *      According to the RFC, we must first decrease the TTL field. If
74          *      that reaches zero, we must reply an ICMP control message telling
75          *      that the packet's lifetime expired.
76          */
77         if (ip_hdr(skb)->ttl <= 1)
78                 goto too_many_hops;
79
80         if (!xfrm4_route_forward(skb))
81                 goto drop;
82
83         rt = (struct rtable*)skb->dst;
84
85         if (opt->is_strictroute && rt->rt_dst != rt->rt_gateway)
86                 goto sr_failed;
87
88         if (unlikely(skb->len > dst_mtu(&rt->u.dst) && !skb_is_gso(skb) &&
89                      (ip_hdr(skb)->frag_off & htons(IP_DF))) && !skb->local_df) {
90                 IP_INC_STATS(IPSTATS_MIB_FRAGFAILS);
91                 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED,
92                           htonl(dst_mtu(&rt->u.dst)));
93                 goto drop;
94         }
95
96         /* We are about to mangle packet. Copy it! */
97         if (skb_cow(skb, LL_RESERVED_SPACE(rt->u.dst.dev)+rt->u.dst.header_len))
98                 goto drop;
99         iph = ip_hdr(skb);
100
101         /* Decrease ttl after skb cow done */
102         ip_decrease_ttl(iph);
103
104         /*
105          *      We now generate an ICMP HOST REDIRECT giving the route
106          *      we calculated.
107          */
108         if (rt->rt_flags&RTCF_DOREDIRECT && !opt->srr && !skb->sp)
109                 ip_rt_send_redirect(skb);
110
111         skb->priority = rt_tos2priority(iph->tos);
112
113         return NF_HOOK(PF_INET, NF_INET_FORWARD, skb, skb->dev, rt->u.dst.dev,
114                        ip_forward_finish);
115
116 sr_failed:
117         /*
118          *      Strict routing permits no gatewaying
119          */
120          icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0);
121          goto drop;
122
123 too_many_hops:
124         /* Tell the sender its packet died... */
125         IP_INC_STATS_BH(IPSTATS_MIB_INHDRERRORS);
126         icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0);
127 drop:
128         kfree_skb(skb);
129         return NET_RX_DROP;
130 }