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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
42static 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
48static bool ip_exceeds_mtu(const struct sk_buff *skb, unsigned int mtu)
49{
50 if (skb->len <= mtu)
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
60static int ip_forward_finish(struct sk_buff *skb)
61{
62 struct ip_options *opt = &(IPCB(skb)->opt);
63
64 IP_INC_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_OUTFORWDATAGRAMS);
65 IP_ADD_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_OUTOCTETS, skb->len);
66
67 if (unlikely(opt->optlen))
68 ip_forward_options(skb);
69
70 return dst_output(skb);
71}
72
73int ip_forward(struct sk_buff *skb)
74{
75 u32 mtu;
76 struct iphdr *iph; /* Our header */
77 struct rtable *rt; /* Route we use */
78 struct ip_options *opt = &(IPCB(skb)->opt);
79
80 /* that should never happen */
81 if (skb->pkt_type != PACKET_HOST)
82 goto drop;
83
84 if (skb_warn_if_lro(skb))
85 goto drop;
86
87 if (!xfrm4_policy_check(NULL, XFRM_POLICY_FWD, skb))
88 goto drop;
89
90 if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb))
91 return NET_RX_SUCCESS;
92
93 skb_forward_csum(skb);
94
95 /*
96 * According to the RFC, we must first decrease the TTL field. If
97 * that reaches zero, we must reply an ICMP control message telling
98 * that the packet's lifetime expired.
99 */
100 if (ip_hdr(skb)->ttl <= 1)
101 goto too_many_hops;
102
103 if (!xfrm4_route_forward(skb))
104 goto drop;
105
106 rt = skb_rtable(skb);
107
108 if (opt->is_strictroute && rt->rt_uses_gateway)
109 goto sr_failed;
110
111 IPCB(skb)->flags |= IPSKB_FORWARDED;
112 mtu = ip_dst_mtu_maybe_forward(&rt->dst, true);
113 if (!ip_may_fragment(skb) && ip_exceeds_mtu(skb, mtu)) {
114 IP_INC_STATS(dev_net(rt->dst.dev), IPSTATS_MIB_FRAGFAILS);
115 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED,
116 htonl(mtu));
117 goto drop;
118 }
119
120 /* We are about to mangle packet. Copy it! */
121 if (skb_cow(skb, LL_RESERVED_SPACE(rt->dst.dev)+rt->dst.header_len))
122 goto drop;
123 iph = ip_hdr(skb);
124
125 /* Decrease ttl after skb cow done */
126 ip_decrease_ttl(iph);
127
128 /*
129 * We now generate an ICMP HOST REDIRECT giving the route
130 * we calculated.
131 */
132 if (rt->rt_flags&RTCF_DOREDIRECT && !opt->srr && !skb_sec_path(skb))
133 ip_rt_send_redirect(skb);
134
135 skb->priority = rt_tos2priority(iph->tos);
136
137 return NF_HOOK(NFPROTO_IPV4, NF_INET_FORWARD, skb, skb->dev,
138 rt->dst.dev, ip_forward_finish);
139
140sr_failed:
141 /*
142 * Strict routing permits no gatewaying
143 */
144 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0);
145 goto drop;
146
147too_many_hops:
148 /* Tell the sender its packet died... */
149 IP_INC_STATS_BH(dev_net(skb_dst(skb)->dev), IPSTATS_MIB_INHDRERRORS);
150 icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0);
151drop:
152 kfree_skb(skb);
153 return NET_RX_DROP;
154}
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
43static 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
65static 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 return dst_output(net, sk, skb);
76}
77
78int ip_forward(struct sk_buff *skb)
79{
80 u32 mtu;
81 struct iphdr *iph; /* Our header */
82 struct rtable *rt; /* Route we use */
83 struct ip_options *opt = &(IPCB(skb)->opt);
84 struct net *net;
85
86 /* that should never happen */
87 if (skb->pkt_type != PACKET_HOST)
88 goto drop;
89
90 if (unlikely(skb->sk))
91 goto drop;
92
93 if (skb_warn_if_lro(skb))
94 goto drop;
95
96 if (!xfrm4_policy_check(NULL, XFRM_POLICY_FWD, skb))
97 goto drop;
98
99 if (IPCB(skb)->opt.router_alert && ip_call_ra_chain(skb))
100 return NET_RX_SUCCESS;
101
102 skb_forward_csum(skb);
103 net = dev_net(skb->dev);
104
105 /*
106 * According to the RFC, we must first decrease the TTL field. If
107 * that reaches zero, we must reply an ICMP control message telling
108 * that the packet's lifetime expired.
109 */
110 if (ip_hdr(skb)->ttl <= 1)
111 goto too_many_hops;
112
113 if (!xfrm4_route_forward(skb))
114 goto drop;
115
116 rt = skb_rtable(skb);
117
118 if (opt->is_strictroute && rt->rt_uses_gateway)
119 goto sr_failed;
120
121 IPCB(skb)->flags |= IPSKB_FORWARDED;
122 mtu = ip_dst_mtu_maybe_forward(&rt->dst, true);
123 if (ip_exceeds_mtu(skb, mtu)) {
124 IP_INC_STATS(net, IPSTATS_MIB_FRAGFAILS);
125 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED,
126 htonl(mtu));
127 goto drop;
128 }
129
130 /* We are about to mangle packet. Copy it! */
131 if (skb_cow(skb, LL_RESERVED_SPACE(rt->dst.dev)+rt->dst.header_len))
132 goto drop;
133 iph = ip_hdr(skb);
134
135 /* Decrease ttl after skb cow done */
136 ip_decrease_ttl(iph);
137
138 /*
139 * We now generate an ICMP HOST REDIRECT giving the route
140 * we calculated.
141 */
142 if (IPCB(skb)->flags & IPSKB_DOREDIRECT && !opt->srr &&
143 !skb_sec_path(skb))
144 ip_rt_send_redirect(skb);
145
146 skb->priority = rt_tos2priority(iph->tos);
147
148 return NF_HOOK(NFPROTO_IPV4, NF_INET_FORWARD,
149 net, NULL, skb, skb->dev, rt->dst.dev,
150 ip_forward_finish);
151
152sr_failed:
153 /*
154 * Strict routing permits no gatewaying
155 */
156 icmp_send(skb, ICMP_DEST_UNREACH, ICMP_SR_FAILED, 0);
157 goto drop;
158
159too_many_hops:
160 /* Tell the sender its packet died... */
161 __IP_INC_STATS(net, IPSTATS_MIB_INHDRERRORS);
162 icmp_send(skb, ICMP_TIME_EXCEEDED, ICMP_EXC_TTL, 0);
163drop:
164 kfree_skb(skb);
165 return NET_RX_DROP;
166}