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/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
ip_forward_finish(struct sk_buff * skb)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
ip_forward(struct sk_buff * skb)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 skb->ip_summed = CHECKSUM_NONE;
88
89 /*
90 * According to the RFC, we must first decrease the TTL field. If
91 * that reaches zero, we must reply an ICMP control message telling
92 * that the packet's lifetime expired.
93 */
94
95 iph = skb->nh.iph;
96 rt = (struct rtable*)skb->dst;
97
98 if (iph->ttl <= 1)
99 goto too_many_hops;
100
101 if (opt->is_strictroute && rt->rt_dst != rt->rt_gateway)
102 goto sr_failed;
103
104 /*
105 * Having picked a route we can now send the frame out
106 * after asking the firewall permission to do so.
107 */
108
109 skb->priority = rt_tos2priority(iph->tos);
110 dev2 = rt->u.dst.dev;
111 mtu = rt->u.dst.pmtu;
112
113 /*
114 * We now generate an ICMP HOST REDIRECT giving the route
115 * we calculated.
116 */
117 if (rt->rt_flags&RTCF_DOREDIRECT && !opt->srr)
118 ip_rt_send_redirect(skb);
119
120 /* We are about to mangle packet. Copy it! */
121 if (skb_cow(skb, dev2->hard_header_len))
122 goto drop;
123 iph = skb->nh.iph;
124
125 /* Decrease ttl after skb cow done */
126 ip_decrease_ttl(iph);
127
128 /*
129 * We now may allocate a new buffer, and copy the datagram into it.
130 * If the indicated interface is up and running, kick it.
131 */
132
133 if (skb->len > mtu && (ntohs(iph->frag_off) & IP_DF))
134 goto frag_needed;
135
136 #ifdef CONFIG_IP_ROUTE_NAT
137 if (rt->rt_flags & RTCF_NAT) {
138 if (ip_do_nat(skb)) {
139 kfree_skb(skb);
140 return NET_RX_BAD;
141 }
142 }
143 #endif
144
145 return NF_HOOK(PF_INET, NF_IP_FORWARD, skb, skb->dev, dev2,
146 ip_forward_finish);
147
148 frag_needed:
149 IP_INC_STATS_BH(IpFragFails);
150 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED, htonl(mtu));
151 goto drop;
152
153 sr_failed:
154 /*
155 * Strict routing permits no gatewaying
156 */
157 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0);
158 goto drop;
159
160 too_many_hops:
161 /* Tell the sender its packet died... */
162 icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0);
163 drop:
164 kfree_skb(skb);
165 return NET_RX_DROP;
166 }
167