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 * Authors: see ip.c 9 * 10 * Fixes: 11 * Many : Split from ip.c , see ip_input.c for 12 * history. 13 * Dave Gregorich : NULL ip_rt_put fix for multicast 14 * routing. 15 * Jos Vos : Add call_out_firewall before sending, 16 * use output device for accounting. 17 * Jos Vos : Call forward firewall after routing 18 * (always use output device). 19 * Mike McLagan : Routing by source 20 */ 21 22 #include <linux/types.h> 23 #include <linux/mm.h> 24 #include <linux/skbuff.h> 25 #include <linux/ip.h> 26 #include <linux/icmp.h> 27 #include <linux/netdevice.h> 28 #include <net/sock.h> 29 #include <net/ip.h> 30 #include <net/tcp.h> 31 #include <net/udp.h> 32 #include <net/icmp.h> 33 #include <linux/tcp.h> 34 #include <linux/udp.h> 35 #include <linux/netfilter_ipv4.h> 36 #include <net/checksum.h> 37 #include <linux/route.h> 38 #include <net/route.h> 39 #include <net/xfrm.h> 40 41 static int ip_forward_finish(struct sk_buff *skb) 42 { 43 struct ip_options * opt = &(IPCB(skb)->opt); 44 45 IP_INC_STATS_BH(dev_net(skb->dst->dev), IPSTATS_MIB_OUTFORWDATAGRAMS); 46 47 if (unlikely(opt->optlen)) 48 ip_forward_options(skb); 49 50 return dst_output(skb); 51 } 52 53 int ip_forward(struct sk_buff *skb) 54 { 55 struct iphdr *iph; /* Our header */ 56 struct rtable *rt; /* Route we use */ 57 struct ip_options * opt = &(IPCB(skb)->opt); 58 59 if (skb_warn_if_lro(skb)) 60 goto drop; 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_forward_csum(skb); 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 (ip_hdr(skb)->ttl <= 1) 79 goto too_many_hops; 80 81 if (!xfrm4_route_forward(skb)) 82 goto drop; 83 84 rt = skb->rtable; 85 86 if (opt->is_strictroute && rt->rt_dst != rt->rt_gateway) 87 goto sr_failed; 88 89 if (unlikely(skb->len > dst_mtu(&rt->u.dst) && !skb_is_gso(skb) && 90 (ip_hdr(skb)->frag_off & htons(IP_DF))) && !skb->local_df) { 91 IP_INC_STATS(dev_net(rt->u.dst.dev), IPSTATS_MIB_FRAGFAILS); 92 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED, 93 htonl(dst_mtu(&rt->u.dst))); 94 goto drop; 95 } 96 97 /* We are about to mangle packet. Copy it! */ 98 if (skb_cow(skb, LL_RESERVED_SPACE(rt->u.dst.dev)+rt->u.dst.header_len)) 99 goto drop; 100 iph = ip_hdr(skb); 101 102 /* Decrease ttl after skb cow done */ 103 ip_decrease_ttl(iph); 104 105 /* 106 * We now generate an ICMP HOST REDIRECT giving the route 107 * we calculated. 108 */ 109 if (rt->rt_flags&RTCF_DOREDIRECT && !opt->srr && !skb->sp) 110 ip_rt_send_redirect(skb); 111 112 skb->priority = rt_tos2priority(iph->tos); 113 114 return NF_HOOK(PF_INET, NF_INET_FORWARD, skb, skb->dev, rt->u.dst.dev, 115 ip_forward_finish); 116 117 sr_failed: 118 /* 119 * Strict routing permits no gatewaying 120 */ 121 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0); 122 goto drop; 123 124 too_many_hops: 125 /* Tell the sender its packet died... */ 126 IP_INC_STATS_BH(dev_net(skb->dst->dev), IPSTATS_MIB_INHDRERRORS); 127 icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0); 128 drop: 129 kfree_skb(skb); 130 return NET_RX_DROP; 131 } 132