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->local_df; 46 } 47 48 static bool ip_exceeds_mtu(const struct sk_buff *skb, unsigned int mtu) 49 { 50 if (skb->len <= mtu || skb->local_df) 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 static bool ip_gso_exceeds_dst_mtu(const struct sk_buff *skb) 60 { 61 unsigned int mtu; 62 63 if (skb->local_df || !skb_is_gso(skb)) 64 return false; 65 66 mtu = ip_dst_mtu_maybe_forward(skb_dst(skb), true); 67 68 /* if seglen > mtu, do software segmentation for IP fragmentation on 69 * output. DF bit cannot be set since ip_forward would have sent 70 * icmp error. 71 */ 72 return skb_gso_network_seglen(skb) > mtu; 73 } 74 75 /* called if GSO skb needs to be fragmented on forward */ 76 static int ip_forward_finish_gso(struct sk_buff *skb) 77 { 78 struct dst_entry *dst = skb_dst(skb); 79 netdev_features_t features; 80 struct sk_buff *segs; 81 int ret = 0; 82 83 features = netif_skb_dev_features(skb, dst->dev); 84 segs = skb_gso_segment(skb, features & ~NETIF_F_GSO_MASK); 85 if (IS_ERR(segs)) { 86 kfree_skb(skb); 87 return -ENOMEM; 88 } 89 90 consume_skb(skb); 91 92 do { 93 struct sk_buff *nskb = segs->next; 94 int err; 95 96 segs->next = NULL; 97 err = dst_output(segs); 98 99 if (err && ret == 0) 100 ret = err; 101 segs = nskb; 102 } while (segs); 103 104 return ret; 105 } 106 107 static int ip_forward_finish(struct sk_buff *skb) 108 { 109 struct ip_options *opt = &(IPCB(skb)->opt); 110 111 IP_INC_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_OUTFORWDATAGRAMS); 112 IP_ADD_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_OUTOCTETS, skb->len); 113 114 if (unlikely(opt->optlen)) 115 ip_forward_options(skb); 116 117 if (ip_gso_exceeds_dst_mtu(skb)) 118 return ip_forward_finish_gso(skb); 119 120 return dst_output(skb); 121 } 122 123 int ip_forward(struct sk_buff *skb) 124 { 125 u32 mtu; 126 struct iphdr *iph; /* Our header */ 127 struct rtable *rt; /* Route we use */ 128 struct ip_options *opt = &(IPCB(skb)->opt); 129 130 if (skb_warn_if_lro(skb)) 131 goto drop; 132 133 if (!xfrm4_policy_check(NULL, XFRM_POLICY_FWD, skb)) 134 goto drop; 135 136 if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb)) 137 return NET_RX_SUCCESS; 138 139 if (skb->pkt_type != PACKET_HOST) 140 goto drop; 141 142 skb_forward_csum(skb); 143 144 /* 145 * According to the RFC, we must first decrease the TTL field. If 146 * that reaches zero, we must reply an ICMP control message telling 147 * that the packet's lifetime expired. 148 */ 149 if (ip_hdr(skb)->ttl <= 1) 150 goto too_many_hops; 151 152 if (!xfrm4_route_forward(skb)) 153 goto drop; 154 155 rt = skb_rtable(skb); 156 157 if (opt->is_strictroute && rt->rt_uses_gateway) 158 goto sr_failed; 159 160 IPCB(skb)->flags |= IPSKB_FORWARDED; 161 mtu = ip_dst_mtu_maybe_forward(&rt->dst, true); 162 if (!ip_may_fragment(skb) && ip_exceeds_mtu(skb, mtu)) { 163 IP_INC_STATS(dev_net(rt->dst.dev), IPSTATS_MIB_FRAGFAILS); 164 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED, 165 htonl(mtu)); 166 goto drop; 167 } 168 169 /* We are about to mangle packet. Copy it! */ 170 if (skb_cow(skb, LL_RESERVED_SPACE(rt->dst.dev)+rt->dst.header_len)) 171 goto drop; 172 iph = ip_hdr(skb); 173 174 /* Decrease ttl after skb cow done */ 175 ip_decrease_ttl(iph); 176 177 /* 178 * We now generate an ICMP HOST REDIRECT giving the route 179 * we calculated. 180 */ 181 if (rt->rt_flags&RTCF_DOREDIRECT && !opt->srr && !skb_sec_path(skb)) 182 ip_rt_send_redirect(skb); 183 184 skb->priority = rt_tos2priority(iph->tos); 185 186 return NF_HOOK(NFPROTO_IPV4, NF_INET_FORWARD, skb, skb->dev, 187 rt->dst.dev, ip_forward_finish); 188 189 sr_failed: 190 /* 191 * Strict routing permits no gatewaying 192 */ 193 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0); 194 goto drop; 195 196 too_many_hops: 197 /* Tell the sender its packet died... */ 198 IP_INC_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_INHDRERRORS); 199 icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0); 200 drop: 201 kfree_skb(skb); 202 return NET_RX_DROP; 203 } 204