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