1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * (C) 2007 by Sebastian Claßen <sebastian.classen@freenet.ag>
4 * (C) 2007-2010 by Jan Engelhardt <jengelh@medozas.de>
5 *
6 * Extracted from xt_TEE.c
7 */
8#include <linux/ip.h>
9#include <linux/module.h>
10#include <linux/percpu.h>
11#include <linux/route.h>
12#include <linux/skbuff.h>
13#include <linux/netfilter.h>
14#include <net/checksum.h>
15#include <net/icmp.h>
16#include <net/ip.h>
17#include <net/route.h>
18#include <net/netfilter/ipv4/nf_dup_ipv4.h>
19#if IS_ENABLED(CONFIG_NF_CONNTRACK)
20#include <net/netfilter/nf_conntrack.h>
21#endif
22
23static bool nf_dup_ipv4_route(struct net *net, struct sk_buff *skb,
24 const struct in_addr *gw, int oif)
25{
26 const struct iphdr *iph = ip_hdr(skb);
27 struct rtable *rt;
28 struct flowi4 fl4;
29
30 memset(&fl4, 0, sizeof(fl4));
31 if (oif != -1)
32 fl4.flowi4_oif = oif;
33
34 fl4.daddr = gw->s_addr;
35 fl4.flowi4_tos = RT_TOS(iph->tos);
36 fl4.flowi4_scope = RT_SCOPE_UNIVERSE;
37 fl4.flowi4_flags = FLOWI_FLAG_KNOWN_NH;
38 rt = ip_route_output_key(net, flp: &fl4);
39 if (IS_ERR(ptr: rt))
40 return false;
41
42 skb_dst_drop(skb);
43 skb_dst_set(skb, dst: &rt->dst);
44 skb->dev = rt->dst.dev;
45 skb->protocol = htons(ETH_P_IP);
46
47 return true;
48}
49
50void nf_dup_ipv4(struct net *net, struct sk_buff *skb, unsigned int hooknum,
51 const struct in_addr *gw, int oif)
52{
53 struct iphdr *iph;
54
55 if (this_cpu_read(nf_skb_duplicated))
56 return;
57 /*
58 * Copy the skb, and route the copy. Will later return %XT_CONTINUE for
59 * the original skb, which should continue on its way as if nothing has
60 * happened. The copy should be independently delivered to the gateway.
61 */
62 skb = pskb_copy(skb, GFP_ATOMIC);
63 if (skb == NULL)
64 return;
65
66#if IS_ENABLED(CONFIG_NF_CONNTRACK)
67 /* Avoid counting cloned packets towards the original connection. */
68 nf_reset_ct(skb);
69 nf_ct_set(skb, NULL, info: IP_CT_UNTRACKED);
70#endif
71 /*
72 * If we are in PREROUTING/INPUT, decrease the TTL to mitigate potential
73 * loops between two hosts.
74 *
75 * Set %IP_DF so that the original source is notified of a potentially
76 * decreased MTU on the clone route. IPv6 does this too.
77 *
78 * IP header checksum will be recalculated at ip_local_out.
79 */
80 iph = ip_hdr(skb);
81 iph->frag_off |= htons(IP_DF);
82 if (hooknum == NF_INET_PRE_ROUTING ||
83 hooknum == NF_INET_LOCAL_IN)
84 --iph->ttl;
85
86 if (nf_dup_ipv4_route(net, skb, gw, oif)) {
87 __this_cpu_write(nf_skb_duplicated, true);
88 ip_local_out(net, sk: skb->sk, skb);
89 __this_cpu_write(nf_skb_duplicated, false);
90 } else {
91 kfree_skb(skb);
92 }
93}
94EXPORT_SYMBOL_GPL(nf_dup_ipv4);
95
96MODULE_AUTHOR("Sebastian Claßen <sebastian.classen@freenet.ag>");
97MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
98MODULE_DESCRIPTION("nf_dup_ipv4: Duplicate IPv4 packet");
99MODULE_LICENSE("GPL");
100

source code of linux/net/ipv4/netfilter/nf_dup_ipv4.c