1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * INET An implementation of the TCP/IP protocol suite for the LINUX 4 * operating system. INET is implemented using the BSD Socket 5 * interface as the means of communication with the user level. 6 * 7 * The IP forwarding functionality. 8 * 9 * Authors: see ip.c 10 * 11 * Fixes: 12 * Many : Split from ip.c , see ip_input.c for 13 * history. 14 * Dave Gregorich : NULL ip_rt_put fix for multicast 15 * routing. 16 * Jos Vos : Add call_out_firewall before sending, 17 * use output device for accounting. 18 * Jos Vos : Call forward firewall after routing 19 * (always use output device). 20 * Mike McLagan : Routing by source 21 */ 22 23 #include <linux/types.h> 24 #include <linux/mm.h> 25 #include <linux/skbuff.h> 26 #include <linux/ip.h> 27 #include <linux/icmp.h> 28 #include <linux/netdevice.h> 29 #include <linux/slab.h> 30 #include <net/sock.h> 31 #include <net/ip.h> 32 #include <net/tcp.h> 33 #include <net/udp.h> 34 #include <net/icmp.h> 35 #include <linux/tcp.h> 36 #include <linux/udp.h> 37 #include <linux/netfilter_ipv4.h> 38 #include <net/checksum.h> 39 #include <linux/route.h> 40 #include <net/route.h> 41 #include <net/xfrm.h> 42 43 static bool ip_exceeds_mtu(const struct sk_buff *skb, unsigned int mtu) 44 { 45 if (skb->len <= mtu) 46 return false; 47 48 if (unlikely((ip_hdr(skb)->frag_off & htons(IP_DF)) == 0)) 49 return false; 50 51 /* original fragment exceeds mtu and DF is set */ 52 if (unlikely(IPCB(skb)->frag_max_size > mtu)) 53 return true; 54 55 if (skb->ignore_df) 56 return false; 57 58 if (skb_is_gso(skb) && skb_gso_validate_network_len(skb, mtu)) 59 return false; 60 61 return true; 62 } 63 64 65 static int ip_forward_finish(struct net *net, struct sock *sk, struct sk_buff *skb) 66 { 67 struct ip_options *opt = &(IPCB(skb)->opt); 68 69 #ifdef CONFIG_NET_SWITCHDEV 70 if (skb->offload_l3_fwd_mark) { 71 consume_skb(skb); 72 return 0; 73 } 74 #endif 75 76 if (unlikely(opt->optlen)) 77 ip_forward_options(skb); 78 79 skb_clear_tstamp(skb); 80 return dst_output(net, sk, skb); 81 } 82 83 int ip_forward(struct sk_buff *skb) 84 { 85 u32 mtu; 86 struct iphdr *iph; /* Our header */ 87 struct rtable *rt; /* Route we use */ 88 struct ip_options *opt = &(IPCB(skb)->opt); 89 struct net *net; 90 SKB_DR(reason); 91 92 /* that should never happen */ 93 if (skb->pkt_type != PACKET_HOST) 94 goto drop; 95 96 if (unlikely(skb->sk)) 97 goto drop; 98 99 if (skb_warn_if_lro(skb)) 100 goto drop; 101 102 if (!xfrm4_policy_check(NULL, XFRM_POLICY_FWD, skb)) { 103 SKB_DR_SET(reason, XFRM_POLICY); 104 goto drop; 105 } 106 107 if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb)) 108 return NET_RX_SUCCESS; 109 110 skb_forward_csum(skb); 111 net = dev_net(skb->dev); 112 113 /* 114 * According to the RFC, we must first decrease the TTL field. If 115 * that reaches zero, we must reply an ICMP control message telling 116 * that the packet's lifetime expired. 117 */ 118 if (ip_hdr(skb)->ttl <= 1) 119 goto too_many_hops; 120 121 if (!xfrm4_route_forward(skb)) { 122 SKB_DR_SET(reason, XFRM_POLICY); 123 goto drop; 124 } 125 126 rt = skb_rtable(skb); 127 128 if (opt->is_strictroute && rt->rt_uses_gateway) 129 goto sr_failed; 130 131 __IP_INC_STATS(net, IPSTATS_MIB_OUTFORWDATAGRAMS); 132 133 IPCB(skb)->flags |= IPSKB_FORWARDED; 134 mtu = ip_dst_mtu_maybe_forward(&rt->dst, true); 135 if (ip_exceeds_mtu(skb, mtu)) { 136 IP_INC_STATS(net, IPSTATS_MIB_FRAGFAILS); 137 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED, 138 htonl(mtu)); 139 SKB_DR_SET(reason, PKT_TOO_BIG); 140 goto drop; 141 } 142 143 /* We are about to mangle packet. Copy it! */ 144 if (skb_cow(skb, LL_RESERVED_SPACE(rt->dst.dev)+rt->dst.header_len)) 145 goto drop; 146 iph = ip_hdr(skb); 147 148 /* Decrease ttl after skb cow done */ 149 ip_decrease_ttl(iph); 150 151 /* 152 * We now generate an ICMP HOST REDIRECT giving the route 153 * we calculated. 154 */ 155 if (IPCB(skb)->flags & IPSKB_DOREDIRECT && !opt->srr && 156 !skb_sec_path(skb)) 157 ip_rt_send_redirect(skb); 158 159 if (READ_ONCE(net->ipv4.sysctl_ip_fwd_update_priority)) 160 skb->priority = rt_tos2priority(iph->tos); 161 162 return NF_HOOK(NFPROTO_IPV4, NF_INET_FORWARD, 163 net, NULL, skb, skb->dev, rt->dst.dev, 164 ip_forward_finish); 165 166 sr_failed: 167 /* 168 * Strict routing permits no gatewaying 169 */ 170 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0); 171 goto drop; 172 173 too_many_hops: 174 /* Tell the sender its packet died... */ 175 __IP_INC_STATS(net, IPSTATS_MIB_INHDRERRORS); 176 icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0); 177 SKB_DR_SET(reason, IP_INHDR); 178 drop: 179 kfree_skb_reason(skb, reason); 180 return NET_RX_DROP; 181 } 182