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 IP_ADD_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_OUTOCTETS, skb->len); 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 (skb_warn_if_lro(skb)) 62 goto drop; 63 64 if (!xfrm4_policy_check(NULL, XFRM_POLICY_FWD, skb)) 65 goto drop; 66 67 if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb)) 68 return NET_RX_SUCCESS; 69 70 if (skb->pkt_type != PACKET_HOST) 71 goto drop; 72 73 skb_forward_csum(skb); 74 75 /* 76 * According to the RFC, we must first decrease the TTL field. If 77 * that reaches zero, we must reply an ICMP control message telling 78 * that the packet's lifetime expired. 79 */ 80 if (ip_hdr(skb)->ttl <= 1) 81 goto too_many_hops; 82 83 if (!xfrm4_route_forward(skb)) 84 goto drop; 85 86 rt = skb_rtable(skb); 87 88 if (opt->is_strictroute && opt->nexthop != rt->rt_gateway) 89 goto sr_failed; 90 91 if (unlikely(skb->len > dst_mtu(&rt->dst) && !skb_is_gso(skb) && 92 (ip_hdr(skb)->frag_off & htons(IP_DF))) && !skb->local_df) { 93 IP_INC_STATS(dev_net(rt->dst.dev), IPSTATS_MIB_FRAGFAILS); 94 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED, 95 htonl(dst_mtu(&rt->dst))); 96 goto drop; 97 } 98 99 /* We are about to mangle packet. Copy it! */ 100 if (skb_cow(skb, LL_RESERVED_SPACE(rt->dst.dev)+rt->dst.header_len)) 101 goto drop; 102 iph = ip_hdr(skb); 103 104 /* Decrease ttl after skb cow done */ 105 ip_decrease_ttl(iph); 106 107 /* 108 * We now generate an ICMP HOST REDIRECT giving the route 109 * we calculated. 110 */ 111 if (rt->rt_flags&RTCF_DOREDIRECT && !opt->srr && !skb_sec_path(skb)) 112 ip_rt_send_redirect(skb); 113 114 skb->priority = rt_tos2priority(iph->tos); 115 116 return NF_HOOK(NFPROTO_IPV4, NF_INET_FORWARD, skb, skb->dev, 117 rt->dst.dev, ip_forward_finish); 118 119 sr_failed: 120 /* 121 * Strict routing permits no gatewaying 122 */ 123 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0); 124 goto drop; 125 126 too_many_hops: 127 /* Tell the sender its packet died... */ 128 IP_INC_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_INHDRERRORS); 129 icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0); 130 drop: 131 kfree_skb(skb); 132 return NET_RX_DROP; 133 } 134