GNU Linux-libre 4.19.211-gnu1
[releases.git] / net / ipv4 / ip_forward.c
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         __IP_INC_STATS(net, IPSTATS_MIB_OUTFORWDATAGRAMS);
70         __IP_ADD_STATS(net, IPSTATS_MIB_OUTOCTETS, skb->len);
71
72         if (unlikely(opt->optlen))
73                 ip_forward_options(skb);
74
75         skb->tstamp = 0;
76         return dst_output(net, sk, skb);
77 }
78
79 int ip_forward(struct sk_buff *skb)
80 {
81         u32 mtu;
82         struct iphdr *iph;      /* Our header */
83         struct rtable *rt;      /* Route we use */
84         struct ip_options *opt  = &(IPCB(skb)->opt);
85         struct net *net;
86
87         /* that should never happen */
88         if (skb->pkt_type != PACKET_HOST)
89                 goto drop;
90
91         if (unlikely(skb->sk))
92                 goto drop;
93
94         if (skb_warn_if_lro(skb))
95                 goto drop;
96
97         if (!xfrm4_policy_check(NULL, XFRM_POLICY_FWD, skb))
98                 goto drop;
99
100         if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb))
101                 return NET_RX_SUCCESS;
102
103         skb_forward_csum(skb);
104         net = dev_net(skb->dev);
105
106         /*
107          *      According to the RFC, we must first decrease the TTL field. If
108          *      that reaches zero, we must reply an ICMP control message telling
109          *      that the packet's lifetime expired.
110          */
111         if (ip_hdr(skb)->ttl <= 1)
112                 goto too_many_hops;
113
114         if (!xfrm4_route_forward(skb))
115                 goto drop;
116
117         rt = skb_rtable(skb);
118
119         if (opt->is_strictroute && rt->rt_uses_gateway)
120                 goto sr_failed;
121
122         IPCB(skb)->flags |= IPSKB_FORWARDED;
123         mtu = ip_dst_mtu_maybe_forward(&rt->dst, true);
124         if (ip_exceeds_mtu(skb, mtu)) {
125                 IP_INC_STATS(net, IPSTATS_MIB_FRAGFAILS);
126                 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED,
127                           htonl(mtu));
128                 goto drop;
129         }
130
131         /* We are about to mangle packet. Copy it! */
132         if (skb_cow(skb, LL_RESERVED_SPACE(rt->dst.dev)+rt->dst.header_len))
133                 goto drop;
134         iph = ip_hdr(skb);
135
136         /* Decrease ttl after skb cow done */
137         ip_decrease_ttl(iph);
138
139         /*
140          *      We now generate an ICMP HOST REDIRECT giving the route
141          *      we calculated.
142          */
143         if (IPCB(skb)->flags & IPSKB_DOREDIRECT && !opt->srr &&
144             !skb_sec_path(skb))
145                 ip_rt_send_redirect(skb);
146
147         if (net->ipv4.sysctl_ip_fwd_update_priority)
148                 skb->priority = rt_tos2priority(iph->tos);
149
150         return NF_HOOK(NFPROTO_IPV4, NF_INET_FORWARD,
151                        net, NULL, skb, skb->dev, rt->dst.dev,
152                        ip_forward_finish);
153
154 sr_failed:
155         /*
156          *      Strict routing permits no gatewaying
157          */
158          icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0);
159          goto drop;
160
161 too_many_hops:
162         /* Tell the sender its packet died... */
163         __IP_INC_STATS(net, IPSTATS_MIB_INHDRERRORS);
164         icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0);
165 drop:
166         kfree_skb(skb);
167         return NET_RX_DROP;
168 }