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