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 <linux/slab.h> 29 #include <net/sock.h> 30 #include <net/ip.h> 31 #include <net/tcp.h> 32 #include <net/udp.h> 33 #include <net/icmp.h> 34 #include <linux/tcp.h> 35 #include <linux/udp.h> 36 #include <linux/netfilter_ipv4.h> 37 #include <net/checksum.h> 38 #include <linux/route.h> 39 #include <net/route.h> 40 #include <net/xfrm.h> 41 42 static int ip_forward_finish(struct sk_buff *skb) 43 { 44 struct ip_options * opt = &(IPCB(skb)->opt); 45 46 IP_INC_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_OUTFORWDATAGRAMS); 47 48 if (unlikely(opt->optlen)) 49 ip_forward_options(skb); 50 51 return dst_output(skb); 52 } 53 54 int ip_forward(struct sk_buff *skb) 55 { 56 struct iphdr *iph; /* Our header */ 57 struct rtable *rt; /* Route we use */ 58 struct ip_options * opt = &(IPCB(skb)->opt); 59 60 if (skb_warn_if_lro(skb)) 61 goto drop; 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_forward_csum(skb); 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 if (ip_hdr(skb)->ttl <= 1) 80 goto too_many_hops; 81 82 if (!xfrm4_route_forward(skb)) 83 goto drop; 84 85 rt = skb_rtable(skb); 86 87 if (opt->is_strictroute && rt->rt_dst != rt->rt_gateway) 88 goto sr_failed; 89 90 if (unlikely(skb->len > dst_mtu(&rt->u.dst) && !skb_is_gso(skb) && 91 (ip_hdr(skb)->frag_off & htons(IP_DF))) && !skb->local_df) { 92 IP_INC_STATS(dev_net(rt->u.dst.dev), IPSTATS_MIB_FRAGFAILS); 93 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED, 94 htonl(dst_mtu(&rt->u.dst))); 95 goto drop; 96 } 97 98 /* We are about to mangle packet. Copy it! */ 99 if (skb_cow(skb, LL_RESERVED_SPACE(rt->u.dst.dev)+rt->u.dst.header_len)) 100 goto drop; 101 iph = ip_hdr(skb); 102 103 /* Decrease ttl after skb cow done */ 104 ip_decrease_ttl(iph); 105 106 /* 107 * We now generate an ICMP HOST REDIRECT giving the route 108 * we calculated. 109 */ 110 if (rt->rt_flags&RTCF_DOREDIRECT && !opt->srr && !skb_sec_path(skb)) 111 ip_rt_send_redirect(skb); 112 113 skb->priority = rt_tos2priority(iph->tos); 114 115 return NF_HOOK(NFPROTO_IPV4, NF_INET_FORWARD, skb, skb->dev, 116 rt->u.dst.dev, ip_forward_finish); 117 118 sr_failed: 119 /* 120 * Strict routing permits no gatewaying 121 */ 122 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0); 123 goto drop; 124 125 too_many_hops: 126 /* Tell the sender its packet died... */ 127 IP_INC_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_INHDRERRORS); 128 icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0); 129 drop: 130 kfree_skb(skb); 131 return NET_RX_DROP; 132 } 133