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, dir: 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(dev: 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(dst: &rt->dst, forwarding: true); |
135 | if (ip_exceeds_mtu(skb, mtu)) { |
136 | IP_INC_STATS(net, IPSTATS_MIB_FRAGFAILS); |
137 | icmp_send(skb_in: 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(tos: iph->tos); |
161 | |
162 | return NF_HOOK(pf: NFPROTO_IPV4, hook: NF_INET_FORWARD, |
163 | net, NULL, skb, in: skb->dev, out: rt->dst.dev, |
164 | okfn: ip_forward_finish); |
165 | |
166 | sr_failed: |
167 | /* |
168 | * Strict routing permits no gatewaying |
169 | */ |
170 | icmp_send(skb_in: skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, info: 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_in: skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, info: 0); |
177 | SKB_DR_SET(reason, IP_INHDR); |
178 | drop: |
179 | kfree_skb_reason(skb, reason); |
180 | return NET_RX_DROP; |
181 | } |
182 | |