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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 | * Authors: see ip.c | |
9 | * | |
10 | * Fixes: | |
11 | * Many : Split from ip.c , see ip_input.c for | |
12 | * history. | |
13 | * Dave Gregorich : NULL ip_rt_put fix for multicast | |
14 | * routing. | |
15 | * Jos Vos : Add call_out_firewall before sending, | |
16 | * use output device for accounting. | |
17 | * Jos Vos : Call forward firewall after routing | |
18 | * (always use output device). | |
19 | * Mike McLagan : Routing by source | |
20 | */ | |
21 | ||
22 | #include <linux/types.h> | |
23 | #include <linux/mm.h> | |
24 | #include <linux/skbuff.h> | |
25 | #include <linux/ip.h> | |
26 | #include <linux/icmp.h> | |
27 | #include <linux/netdevice.h> | |
28 | #include <net/sock.h> | |
29 | #include <net/ip.h> | |
30 | #include <net/tcp.h> | |
31 | #include <net/udp.h> | |
32 | #include <net/icmp.h> | |
33 | #include <linux/tcp.h> | |
34 | #include <linux/udp.h> | |
35 | #include <linux/netfilter_ipv4.h> | |
36 | #include <net/checksum.h> | |
37 | #include <linux/route.h> | |
38 | #include <net/route.h> | |
39 | #include <net/xfrm.h> | |
40 | ||
41 | static int ip_forward_finish(struct sk_buff *skb) | |
42 | { | |
43 | struct ip_options * opt = &(IPCB(skb)->opt); | |
44 | ||
45 | IP_INC_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_OUTFORWDATAGRAMS); | |
46 | ||
47 | if (unlikely(opt->optlen)) | |
48 | ip_forward_options(skb); | |
49 | ||
50 | return dst_output(skb); | |
51 | } | |
52 | ||
53 | int ip_forward(struct sk_buff *skb) | |
54 | { | |
55 | struct iphdr *iph; /* Our header */ | |
56 | struct rtable *rt; /* Route we use */ | |
57 | struct ip_options * opt = &(IPCB(skb)->opt); | |
58 | ||
59 | if (skb_warn_if_lro(skb)) | |
60 | goto drop; | |
61 | ||
62 | if (!xfrm4_policy_check(NULL, XFRM_POLICY_FWD, skb)) | |
63 | goto drop; | |
64 | ||
65 | if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb)) | |
66 | return NET_RX_SUCCESS; | |
67 | ||
68 | if (skb->pkt_type != PACKET_HOST) | |
69 | goto drop; | |
70 | ||
71 | skb_forward_csum(skb); | |
72 | ||
73 | /* | |
74 | * According to the RFC, we must first decrease the TTL field. If | |
75 | * that reaches zero, we must reply an ICMP control message telling | |
76 | * that the packet's lifetime expired. | |
77 | */ | |
78 | if (ip_hdr(skb)->ttl <= 1) | |
79 | goto too_many_hops; | |
80 | ||
81 | if (!xfrm4_route_forward(skb)) | |
82 | goto drop; | |
83 | ||
84 | rt = skb_rtable(skb); | |
85 | ||
86 | if (opt->is_strictroute && rt->rt_dst != rt->rt_gateway) | |
87 | goto sr_failed; | |
88 | ||
89 | if (unlikely(skb->len > dst_mtu(&rt->u.dst) && !skb_is_gso(skb) && | |
90 | (ip_hdr(skb)->frag_off & htons(IP_DF))) && !skb->local_df) { | |
91 | IP_INC_STATS(dev_net(rt->u.dst.dev), IPSTATS_MIB_FRAGFAILS); | |
92 | icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED, | |
93 | htonl(dst_mtu(&rt->u.dst))); | |
94 | goto drop; | |
95 | } | |
96 | ||
97 | /* We are about to mangle packet. Copy it! */ | |
98 | if (skb_cow(skb, LL_RESERVED_SPACE(rt->u.dst.dev)+rt->u.dst.header_len)) | |
99 | goto drop; | |
100 | iph = ip_hdr(skb); | |
101 | ||
102 | /* Decrease ttl after skb cow done */ | |
103 | ip_decrease_ttl(iph); | |
104 | ||
105 | /* | |
106 | * We now generate an ICMP HOST REDIRECT giving the route | |
107 | * we calculated. | |
108 | */ | |
109 | if (rt->rt_flags&RTCF_DOREDIRECT && !opt->srr && !skb_sec_path(skb)) | |
110 | ip_rt_send_redirect(skb); | |
111 | ||
112 | skb->priority = rt_tos2priority(iph->tos); | |
113 | ||
114 | return NF_HOOK(NFPROTO_IPV4, NF_INET_FORWARD, skb, skb->dev, | |
115 | rt->u.dst.dev, ip_forward_finish); | |
116 | ||
117 | sr_failed: | |
118 | /* | |
119 | * Strict routing permits no gatewaying | |
120 | */ | |
121 | icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0); | |
122 | goto drop; | |
123 | ||
124 | too_many_hops: | |
125 | /* Tell the sender its packet died... */ | |
126 | IP_INC_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_INHDRERRORS); | |
127 | icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0); | |
128 | drop: | |
129 | kfree_skb(skb); | |
130 | return NET_RX_DROP; | |
131 | } |