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 bool ip_may_fragment(const struct sk_buff *skb) 43 { 44 return unlikely((ip_hdr(skb)->frag_off & htons(IP_DF)) == 0) || 45 skb->ignore_df; 46 } 47 48 static bool ip_exceeds_mtu(const struct sk_buff *skb, unsigned int mtu) 49 { 50 if (skb->len <= mtu) 51 return false; 52 53 if (skb_is_gso(skb) && skb_gso_network_seglen(skb) <= mtu) 54 return false; 55 56 return true; 57 } 58 59 60 static int ip_forward_finish(struct sock *sk, struct sk_buff *skb) 61 { 62 struct ip_options *opt = &(IPCB(skb)->opt); 63 64 IP_INC_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_OUTFORWDATAGRAMS); 65 IP_ADD_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_OUTOCTETS, skb->len); 66 67 if (unlikely(opt->optlen)) 68 ip_forward_options(skb); 69 70 skb_sender_cpu_clear(skb); 71 return dst_output_sk(sk, skb); 72 } 73 74 int ip_forward(struct sk_buff *skb) 75 { 76 u32 mtu; 77 struct iphdr *iph; /* Our header */ 78 struct rtable *rt; /* Route we use */ 79 struct ip_options *opt = &(IPCB(skb)->opt); 80 81 /* that should never happen */ 82 if (skb->pkt_type != PACKET_HOST) 83 goto drop; 84 85 if (unlikely(skb->sk)) 86 goto drop; 87 88 if (skb_warn_if_lro(skb)) 89 goto drop; 90 91 if (!xfrm4_policy_check(NULL, XFRM_POLICY_FWD, skb)) 92 goto drop; 93 94 if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb)) 95 return NET_RX_SUCCESS; 96 97 skb_forward_csum(skb); 98 99 /* 100 * According to the RFC, we must first decrease the TTL field. If 101 * that reaches zero, we must reply an ICMP control message telling 102 * that the packet's lifetime expired. 103 */ 104 if (ip_hdr(skb)->ttl <= 1) 105 goto too_many_hops; 106 107 if (!xfrm4_route_forward(skb)) 108 goto drop; 109 110 rt = skb_rtable(skb); 111 112 if (opt->is_strictroute && rt->rt_uses_gateway) 113 goto sr_failed; 114 115 IPCB(skb)->flags |= IPSKB_FORWARDED; 116 mtu = ip_dst_mtu_maybe_forward(&rt->dst, true); 117 if (!ip_may_fragment(skb) && ip_exceeds_mtu(skb, mtu)) { 118 IP_INC_STATS(dev_net(rt->dst.dev), IPSTATS_MIB_FRAGFAILS); 119 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED, 120 htonl(mtu)); 121 goto drop; 122 } 123 124 /* We are about to mangle packet. Copy it! */ 125 if (skb_cow(skb, LL_RESERVED_SPACE(rt->dst.dev)+rt->dst.header_len)) 126 goto drop; 127 iph = ip_hdr(skb); 128 129 /* Decrease ttl after skb cow done */ 130 ip_decrease_ttl(iph); 131 132 /* 133 * We now generate an ICMP HOST REDIRECT giving the route 134 * we calculated. 135 */ 136 if (IPCB(skb)->flags & IPSKB_DOREDIRECT && !opt->srr && 137 !skb_sec_path(skb)) 138 ip_rt_send_redirect(skb); 139 140 skb->priority = rt_tos2priority(iph->tos); 141 142 return NF_HOOK(NFPROTO_IPV4, NF_INET_FORWARD, NULL, skb, 143 skb->dev, rt->dst.dev, ip_forward_finish); 144 145 sr_failed: 146 /* 147 * Strict routing permits no gatewaying 148 */ 149 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0); 150 goto drop; 151 152 too_many_hops: 153 /* Tell the sender its packet died... */ 154 IP_INC_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_INHDRERRORS); 155 icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0); 156 drop: 157 kfree_skb(skb); 158 return NET_RX_DROP; 159 } 160