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 1.1.1.1 2007/08/03 18:53:51 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
43static inline 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
55int 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) &&
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)
109		ip_rt_send_redirect(skb);
110
111	skb->priority = rt_tos2priority(iph->tos);
112
113	return NF_HOOK(PF_INET, NF_IP_FORWARD, skb, skb->dev, rt->u.dst.dev,
114		       ip_forward_finish);
115
116sr_failed:
117	/*
118	 *	Strict routing permits no gatewaying
119	 */
120	 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0);
121	 goto drop;
122
123too_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);
127drop:
128	kfree_skb(skb);
129	return NET_RX_DROP;
130}
131