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 1.47 2000/10/24 22:54:26 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/config.h>
25 #include <linux/types.h>
26 #include <linux/mm.h>
27 #include <linux/sched.h>
28 #include <linux/skbuff.h>
29 #include <linux/ip.h>
30 #include <linux/icmp.h>
31 #include <linux/netdevice.h>
32 #include <net/sock.h>
33 #include <net/ip.h>
34 #include <net/tcp.h>
35 #include <net/udp.h>
36 #include <net/icmp.h>
37 #include <linux/tcp.h>
38 #include <linux/udp.h>
39 #include <linux/netfilter_ipv4.h>
40 #include <net/checksum.h>
41 #include <linux/route.h>
42 #include <net/route.h>
43
44 static inline int ip_forward_finish(struct sk_buff *skb)
45 {
46 struct ip_options * opt = &(IPCB(skb)->opt);
47
48 IP_INC_STATS_BH(IpForwDatagrams);
49
50 if (opt->optlen == 0) {
51 #ifdef CONFIG_NET_FASTROUTE
52 struct rtable *rt = (struct rtable*)skb->dst;
53
54 if (rt->rt_flags&RTCF_FAST && !netdev_fastroute_obstacles) {
55 struct dst_entry *old_dst;
56 unsigned h = ((*(u8*)&rt->key.dst)^(*(u8*)&rt->key.src))&NETDEV_FASTROUTE_HMASK;
57
58 write_lock_irq(&skb->dev->fastpath_lock);
59 old_dst = skb->dev->fastpath[h];
60 skb->dev->fastpath[h] = dst_clone(&rt->u.dst);
61 write_unlock_irq(&skb->dev->fastpath_lock);
62
63 dst_release(old_dst);
64 }
65 #endif
66 return (ip_send(skb));
67 }
68
69 ip_forward_options(skb);
70 return (ip_send(skb));
71 }
72
73 int ip_forward(struct sk_buff *skb)
74 {
75 struct net_device *dev2; /* Output device */
76 struct iphdr *iph; /* Our header */
77 struct rtable *rt; /* Route we use */
78 struct ip_options * opt = &(IPCB(skb)->opt);
79 unsigned short mtu;
80
81 if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb))
82 return NET_RX_SUCCESS;
83
84 if (skb->pkt_type != PACKET_HOST)
85 goto drop;
86
87 /*
88 * According to the RFC, we must first decrease the TTL field. If
89 * that reaches zero, we must reply an ICMP control message telling
90 * that the packet's lifetime expired.
91 */
92
93 iph = skb->nh.iph;
94 rt = (struct rtable*)skb->dst;
95
96 if (iph->ttl <= 1)
97 goto too_many_hops;
98
99 if (opt->is_strictroute && rt->rt_dst != rt->rt_gateway)
100 goto sr_failed;
101
102 /*
103 * Having picked a route we can now send the frame out
104 * after asking the firewall permission to do so.
105 */
106
107 skb->priority = rt_tos2priority(iph->tos);
108 dev2 = rt->u.dst.dev;
109 mtu = rt->u.dst.pmtu;
110
111 /*
112 * We now generate an ICMP HOST REDIRECT giving the route
113 * we calculated.
114 */
115 if (rt->rt_flags&RTCF_DOREDIRECT && !opt->srr)
116 ip_rt_send_redirect(skb);
117
118 /* We are about to mangle packet. Copy it! */
119 if ((skb = skb_cow(skb, dev2->hard_header_len)) == NULL)
120 return NET_RX_DROP;
121 iph = skb->nh.iph;
122 opt = &(IPCB(skb)->opt);
123
124 /* Decrease ttl after skb cow done */
125 ip_decrease_ttl(iph);
126
127 /*
128 * We now may allocate a new buffer, and copy the datagram into it.
129 * If the indicated interface is up and running, kick it.
130 */
131
132 if (skb->len > mtu && (ntohs(iph->frag_off) & IP_DF))
133 goto frag_needed;
134
135 #ifdef CONFIG_IP_ROUTE_NAT
136 if (rt->rt_flags & RTCF_NAT) {
137 if (ip_do_nat(skb)) {
138 kfree_skb(skb);
139 return NET_RX_BAD;
140 }
141 }
142 #endif
143
144 return NF_HOOK(PF_INET, NF_IP_FORWARD, skb, skb->dev, dev2,
145 ip_forward_finish);
146
147 frag_needed:
148 IP_INC_STATS_BH(IpFragFails);
149 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED, htonl(mtu));
150 goto drop;
151
152 sr_failed:
153 /*
154 * Strict routing permits no gatewaying
155 */
156 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0);
157 goto drop;
158
159 too_many_hops:
160 /* Tell the sender its packet died... */
161 icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0);
162 drop:
163 kfree_skb(skb);
164 return NET_RX_DROP;
165 }
166
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