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 #include <net/xfrm.h> 44 45 static inline int ip_forward_finish(struct sk_buff *skb) 46 { 47 struct ip_options * opt = &(IPCB(skb)->opt); 48 49 IP_INC_STATS_BH(IPSTATS_MIB_OUTFORWDATAGRAMS); 50 51 if (unlikely(opt->optlen)) 52 ip_forward_options(skb); 53 54 return dst_output(skb); 55 } 56 57 int ip_forward(struct sk_buff *skb) 58 { 59 struct iphdr *iph; /* Our header */ 60 struct rtable *rt; /* Route we use */ 61 struct ip_options * opt = &(IPCB(skb)->opt); 62 63 if (!xfrm4_policy_check(NULL, XFRM_POLICY_FWD, skb)) 64 goto drop; 65 66 if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb)) 67 return NET_RX_SUCCESS; 68 69 if (skb->pkt_type != PACKET_HOST) 70 goto drop; 71 72 skb->ip_summed = CHECKSUM_NONE; 73 74 /* 75 * According to the RFC, we must first decrease the TTL field. If 76 * that reaches zero, we must reply an ICMP control message telling 77 * that the packet's lifetime expired. 78 */ 79 80 iph = skb->nh.iph; 81 82 if (iph->ttl <= 1) 83 goto too_many_hops; 84 85 if (!xfrm4_route_forward(skb)) 86 goto drop; 87 88 iph = skb->nh.iph; 89 rt = (struct rtable*)skb->dst; 90 91 if (opt->is_strictroute && rt->rt_dst != rt->rt_gateway) 92 goto sr_failed; 93 94 /* We are about to mangle packet. Copy it! */ 95 if (skb_cow(skb, LL_RESERVED_SPACE(rt->u.dst.dev)+rt->u.dst.header_len)) 96 goto drop; 97 iph = skb->nh.iph; 98 99 /* Decrease ttl after skb cow done */ 100 ip_decrease_ttl(iph); 101 102 /* 103 * We now generate an ICMP HOST REDIRECT giving the route 104 * we calculated. 105 */ 106 if (rt->rt_flags&RTCF_DOREDIRECT && !opt->srr) 107 ip_rt_send_redirect(skb); 108 109 skb->priority = rt_tos2priority(iph->tos); 110 111 return NF_HOOK(PF_INET, NF_IP_FORWARD, skb, skb->dev, rt->u.dst.dev, 112 ip_forward_finish); 113 114 sr_failed: 115 /* 116 * Strict routing permits no gatewaying 117 */ 118 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0); 119 goto drop; 120 121 too_many_hops: 122 /* Tell the sender its packet died... */ 123 icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0); 124 drop: 125 kfree_skb(skb); 126 return NET_RX_DROP; 127 } 128