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b2441318 | 1 | // SPDX-License-Identifier: GPL-2.0 |
1da177e4 LT |
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. | |
e905a9ed | 8 | * |
1da177e4 LT |
9 | * Authors: see ip.c |
10 | * | |
11 | * Fixes: | |
e905a9ed | 12 | * Many : Split from ip.c , see ip_input.c for |
1da177e4 | 13 | * history. |
e905a9ed | 14 | * Dave Gregorich : NULL ip_rt_put fix for multicast |
1da177e4 LT |
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 | ||
1da177e4 LT |
23 | #include <linux/types.h> |
24 | #include <linux/mm.h> | |
1da177e4 LT |
25 | #include <linux/skbuff.h> |
26 | #include <linux/ip.h> | |
27 | #include <linux/icmp.h> | |
28 | #include <linux/netdevice.h> | |
5a0e3ad6 | 29 | #include <linux/slab.h> |
1da177e4 LT |
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 | ||
fe6cc55f FW |
43 | static bool ip_exceeds_mtu(const struct sk_buff *skb, unsigned int mtu) |
44 | { | |
ca6c5d4a | 45 | if (skb->len <= mtu) |
fe6cc55f FW |
46 | return false; |
47 | ||
cf826244 FW |
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 | ||
779b7931 | 58 | if (skb_is_gso(skb) && skb_gso_validate_network_len(skb, mtu)) |
fe6cc55f FW |
59 | return false; |
60 | ||
61 | return true; | |
62 | } | |
63 | ||
fe6cc55f | 64 | |
0c4b51f0 | 65 | static int ip_forward_finish(struct net *net, struct sock *sk, struct sk_buff *skb) |
1da177e4 | 66 | { |
5e73ea1a | 67 | struct ip_options *opt = &(IPCB(skb)->opt); |
1da177e4 | 68 | |
b45386ef | 69 | __IP_INC_STATS(net, IPSTATS_MIB_OUTFORWDATAGRAMS); |
98f61995 | 70 | __IP_ADD_STATS(net, IPSTATS_MIB_OUTOCTETS, skb->len); |
1da177e4 | 71 | |
f839a6c9 IS |
72 | #ifdef CONFIG_NET_SWITCHDEV |
73 | if (skb->offload_l3_fwd_mark) { | |
74 | consume_skb(skb); | |
75 | return 0; | |
76 | } | |
77 | #endif | |
78 | ||
1da177e4 LT |
79 | if (unlikely(opt->optlen)) |
80 | ip_forward_options(skb); | |
81 | ||
8203e2d8 | 82 | skb->tstamp = 0; |
13206b6b | 83 | return dst_output(net, sk, skb); |
1da177e4 LT |
84 | } |
85 | ||
86 | int ip_forward(struct sk_buff *skb) | |
87 | { | |
f87c10a8 | 88 | u32 mtu; |
1da177e4 LT |
89 | struct iphdr *iph; /* Our header */ |
90 | struct rtable *rt; /* Route we use */ | |
5e73ea1a | 91 | struct ip_options *opt = &(IPCB(skb)->opt); |
fcad0ac2 | 92 | struct net *net; |
1da177e4 | 93 | |
d4f2fa6a DK |
94 | /* that should never happen */ |
95 | if (skb->pkt_type != PACKET_HOST) | |
96 | goto drop; | |
97 | ||
2ab95749 SP |
98 | if (unlikely(skb->sk)) |
99 | goto drop; | |
100 | ||
4497b076 BH |
101 | if (skb_warn_if_lro(skb)) |
102 | goto drop; | |
103 | ||
1da177e4 LT |
104 | if (!xfrm4_policy_check(NULL, XFRM_POLICY_FWD, skb)) |
105 | goto drop; | |
106 | ||
107 | if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb)) | |
108 | return NET_RX_SUCCESS; | |
109 | ||
35fc92a9 | 110 | skb_forward_csum(skb); |
fcad0ac2 | 111 | net = dev_net(skb->dev); |
e905a9ed | 112 | |
1da177e4 LT |
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 | */ | |
eddc9ec5 | 118 | if (ip_hdr(skb)->ttl <= 1) |
e905a9ed | 119 | goto too_many_hops; |
1da177e4 LT |
120 | |
121 | if (!xfrm4_route_forward(skb)) | |
122 | goto drop; | |
123 | ||
511c3f92 | 124 | rt = skb_rtable(skb); |
1da177e4 | 125 | |
77d5bc7e | 126 | if (opt->is_strictroute && rt->rt_uses_gateway) |
1da177e4 LT |
127 | goto sr_failed; |
128 | ||
9ee6c5dc | 129 | IPCB(skb)->flags |= IPSKB_FORWARDED; |
f87c10a8 | 130 | mtu = ip_dst_mtu_maybe_forward(&rt->dst, true); |
cf826244 | 131 | if (ip_exceeds_mtu(skb, mtu)) { |
fcad0ac2 | 132 | IP_INC_STATS(net, IPSTATS_MIB_FRAGFAILS); |
9af3912e | 133 | icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED, |
f87c10a8 | 134 | htonl(mtu)); |
9af3912e JH |
135 | goto drop; |
136 | } | |
137 | ||
1da177e4 | 138 | /* We are about to mangle packet. Copy it! */ |
d8d1f30b | 139 | if (skb_cow(skb, LL_RESERVED_SPACE(rt->dst.dev)+rt->dst.header_len)) |
1da177e4 | 140 | goto drop; |
eddc9ec5 | 141 | iph = ip_hdr(skb); |
1da177e4 LT |
142 | |
143 | /* Decrease ttl after skb cow done */ | |
144 | ip_decrease_ttl(iph); | |
145 | ||
146 | /* | |
147 | * We now generate an ICMP HOST REDIRECT giving the route | |
148 | * we calculated. | |
149 | */ | |
df4d9254 HFS |
150 | if (IPCB(skb)->flags & IPSKB_DOREDIRECT && !opt->srr && |
151 | !skb_sec_path(skb)) | |
1da177e4 LT |
152 | ip_rt_send_redirect(skb); |
153 | ||
432e05d3 PM |
154 | if (net->ipv4.sysctl_ip_fwd_update_priority) |
155 | skb->priority = rt_tos2priority(iph->tos); | |
1da177e4 | 156 | |
29a26a56 EB |
157 | return NF_HOOK(NFPROTO_IPV4, NF_INET_FORWARD, |
158 | net, NULL, skb, skb->dev, rt->dst.dev, | |
159 | ip_forward_finish); | |
1da177e4 LT |
160 | |
161 | sr_failed: | |
e905a9ed | 162 | /* |
1da177e4 LT |
163 | * Strict routing permits no gatewaying |
164 | */ | |
e905a9ed YH |
165 | icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0); |
166 | goto drop; | |
1da177e4 LT |
167 | |
168 | too_many_hops: | |
e905a9ed | 169 | /* Tell the sender its packet died... */ |
b45386ef | 170 | __IP_INC_STATS(net, IPSTATS_MIB_INHDRERRORS); |
e905a9ed | 171 | icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0); |
1da177e4 LT |
172 | drop: |
173 | kfree_skb(skb); | |
174 | return NET_RX_DROP; | |
175 | } |