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/types.h> 25 #include <linux/mm.h> 26 #include <linux/sched.h> 27 #include <linux/skbuff.h> 28 #include <linux/ip.h> 29 #include <linux/icmp.h> 30 #include <linux/netdevice.h> 31 #include <net/sock.h> 32 #include <net/ip.h> 33 #include <net/tcp.h> 34 #include <net/udp.h> 35 #include <net/icmp.h> 36 #include <linux/tcp.h> 37 #include <linux/udp.h> 38 #include <linux/netfilter_ipv4.h> 39 #include <net/checksum.h> 40 #include <linux/route.h> 41 #include <net/route.h> 42 #include <net/xfrm.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(IPSTATS_MIB_OUTFORWDATAGRAMS); 49 50 if (unlikely(opt->optlen)) 51 ip_forward_options(skb); 52 53 return dst_output(skb); 54 } 55 56 int ip_forward(struct sk_buff *skb) 57 { 58 struct iphdr *iph; /* Our header */ 59 struct rtable *rt; /* Route we use */ 60 struct ip_options * opt = &(IPCB(skb)->opt); 61 62 if (!xfrm4_policy_check(NULL, XFRM_POLICY_FWD, skb)) 63 goto drop; 64 65 if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb)) 66 return NET_RX_SUCCESS; 67 68 if (skb->pkt_type != PACKET_HOST) 69 goto drop; 70 71 skb->ip_summed = CHECKSUM_NONE; 72 73 /* 74 * According to the RFC, we must first decrease the TTL field. If 75 * that reaches zero, we must reply an ICMP control message telling 76 * that the packet's lifetime expired. 77 */ 78 if (skb->nh.iph->ttl <= 1) 79 goto too_many_hops; 80 81 if (!xfrm4_route_forward(skb)) 82 goto drop; 83 84 rt = (struct rtable*)skb->dst; 85 86 if (opt->is_strictroute && rt->rt_dst != rt->rt_gateway) 87 goto sr_failed; 88 89 /* We are about to mangle packet. Copy it! */ 90 if (skb_cow(skb, LL_RESERVED_SPACE(rt->u.dst.dev)+rt->u.dst.header_len)) 91 goto drop; 92 iph = skb->nh.iph; 93 94 /* Decrease ttl after skb cow done */ 95 ip_decrease_ttl(iph); 96 97 /* 98 * We now generate an ICMP HOST REDIRECT giving the route 99 * we calculated. 100 */ 101 if (rt->rt_flags&RTCF_DOREDIRECT && !opt->srr) 102 ip_rt_send_redirect(skb); 103 104 skb->priority = rt_tos2priority(iph->tos); 105 106 return NF_HOOK(PF_INET, NF_IP_FORWARD, skb, skb->dev, rt->u.dst.dev, 107 ip_forward_finish); 108 109 sr_failed: 110 /* 111 * Strict routing permits no gatewaying 112 */ 113 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0); 114 goto drop; 115 116 too_many_hops: 117 /* Tell the sender its packet died... */ 118 IP_INC_STATS_BH(IPSTATS_MIB_INHDRERRORS); 119 icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0); 120 drop: 121 kfree_skb(skb); 122 return NET_RX_DROP; 123 } 124