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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 <linux/slab.h> |
29 | #include <net/sock.h> |
30 | #include <net/ip.h> |
31 | #include <net/tcp.h> |
32 | #include <net/udp.h> |
33 | #include <net/icmp.h> |
34 | #include <linux/tcp.h> |
35 | #include <linux/udp.h> |
36 | #include <linux/netfilter_ipv4.h> |
37 | #include <net/checksum.h> |
38 | #include <linux/route.h> |
39 | #include <net/route.h> |
40 | #include <net/xfrm.h> |
41 | |
42 | static int ip_forward_finish(struct sk_buff *skb) |
43 | { |
44 | struct ip_options *opt = &(IPCB(skb)->opt); |
45 | |
46 | IP_INC_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_OUTFORWDATAGRAMS); |
47 | IP_ADD_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_OUTOCTETS, skb->len); |
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 (skb_warn_if_lro(skb)) |
62 | goto drop; |
63 | |
64 | if (!xfrm4_policy_check(NULL, XFRM_POLICY_FWD, skb)) |
65 | goto drop; |
66 | |
67 | if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb)) |
68 | return NET_RX_SUCCESS; |
69 | |
70 | if (skb->pkt_type != PACKET_HOST) |
71 | goto drop; |
72 | |
73 | skb_forward_csum(skb); |
74 | |
75 | /* |
76 | * According to the RFC, we must first decrease the TTL field. If |
77 | * that reaches zero, we must reply an ICMP control message telling |
78 | * that the packet's lifetime expired. |
79 | */ |
80 | if (ip_hdr(skb)->ttl <= 1) |
81 | goto too_many_hops; |
82 | |
83 | if (!xfrm4_route_forward(skb)) |
84 | goto drop; |
85 | |
86 | rt = skb_rtable(skb); |
87 | |
88 | if (opt->is_strictroute && rt->rt_uses_gateway) |
89 | goto sr_failed; |
90 | |
91 | if (unlikely(skb->len > dst_mtu(&rt->dst) && !skb_is_gso(skb) && |
92 | (ip_hdr(skb)->frag_off & htons(IP_DF))) && !skb->local_df) { |
93 | IP_INC_STATS(dev_net(rt->dst.dev), IPSTATS_MIB_FRAGFAILS); |
94 | icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED, |
95 | htonl(dst_mtu(&rt->dst))); |
96 | goto drop; |
97 | } |
98 | |
99 | /* We are about to mangle packet. Copy it! */ |
100 | if (skb_cow(skb, LL_RESERVED_SPACE(rt->dst.dev)+rt->dst.header_len)) |
101 | goto drop; |
102 | iph = ip_hdr(skb); |
103 | |
104 | /* Decrease ttl after skb cow done */ |
105 | ip_decrease_ttl(iph); |
106 | |
107 | /* |
108 | * We now generate an ICMP HOST REDIRECT giving the route |
109 | * we calculated. |
110 | */ |
111 | if (rt->rt_flags&RTCF_DOREDIRECT && !opt->srr && !skb_sec_path(skb)) |
112 | ip_rt_send_redirect(skb); |
113 | |
114 | skb->priority = rt_tos2priority(iph->tos); |
115 | |
116 | return NF_HOOK(NFPROTO_IPV4, NF_INET_FORWARD, skb, skb->dev, |
117 | rt->dst.dev, ip_forward_finish); |
118 | |
119 | sr_failed: |
120 | /* |
121 | * Strict routing permits no gatewaying |
122 | */ |
123 | icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0); |
124 | goto drop; |
125 | |
126 | too_many_hops: |
127 | /* Tell the sender its packet died... */ |
128 | IP_INC_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_INHDRERRORS); |
129 | icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0); |
130 | drop: |
131 | kfree_skb(skb); |
132 | return NET_RX_DROP; |
133 | } |
134 |
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