2 * (C) 2007 by Sebastian Claßen <sebastian.classen@freenet.ag>
3 * (C) 2007-2010 by Jan Engelhardt <jengelh@medozas.de>
5 * Extracted from xt_TEE.c
7 * This program is free software; you can redistribute it and/or modify it
8 * under the terms of the GNU General Public License version 2 or later, as
9 * published by the Free Software Foundation.
12 #include <linux/module.h>
13 #include <linux/percpu.h>
14 #include <linux/route.h>
15 #include <linux/skbuff.h>
16 #include <linux/netfilter.h>
17 #include <net/checksum.h>
20 #include <net/route.h>
21 #include <net/netfilter/ipv4/nf_dup_ipv4.h>
22 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
23 #include <net/netfilter/nf_conntrack.h>
26 static bool nf_dup_ipv4_route(struct net *net, struct sk_buff *skb,
27 const struct in_addr *gw, int oif)
29 const struct iphdr *iph = ip_hdr(skb);
33 memset(&fl4, 0, sizeof(fl4));
37 fl4.daddr = gw->s_addr;
38 fl4.flowi4_tos = RT_TOS(iph->tos);
39 fl4.flowi4_scope = RT_SCOPE_UNIVERSE;
40 fl4.flowi4_flags = FLOWI_FLAG_KNOWN_NH;
41 rt = ip_route_output_key(net, &fl4);
46 skb_dst_set(skb, &rt->dst);
47 skb->dev = rt->dst.dev;
48 skb->protocol = htons(ETH_P_IP);
53 void nf_dup_ipv4(struct net *net, struct sk_buff *skb, unsigned int hooknum,
54 const struct in_addr *gw, int oif)
58 if (this_cpu_read(nf_skb_duplicated))
61 * Copy the skb, and route the copy. Will later return %XT_CONTINUE for
62 * the original skb, which should continue on its way as if nothing has
63 * happened. The copy should be independently delivered to the gateway.
65 skb = pskb_copy(skb, GFP_ATOMIC);
69 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
70 /* Avoid counting cloned packets towards the original connection. */
72 nf_ct_set(skb, NULL, IP_CT_UNTRACKED);
75 * If we are in PREROUTING/INPUT, decrease the TTL to mitigate potential
76 * loops between two hosts.
78 * Set %IP_DF so that the original source is notified of a potentially
79 * decreased MTU on the clone route. IPv6 does this too.
81 * IP header checksum will be recalculated at ip_local_out.
84 iph->frag_off |= htons(IP_DF);
85 if (hooknum == NF_INET_PRE_ROUTING ||
86 hooknum == NF_INET_LOCAL_IN)
89 if (nf_dup_ipv4_route(net, skb, gw, oif)) {
90 __this_cpu_write(nf_skb_duplicated, true);
91 ip_local_out(net, skb->sk, skb);
92 __this_cpu_write(nf_skb_duplicated, false);
97 EXPORT_SYMBOL_GPL(nf_dup_ipv4);
99 MODULE_AUTHOR("Sebastian Claßen <sebastian.classen@freenet.ag>");
100 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
101 MODULE_DESCRIPTION("nf_dup_ipv4: Duplicate IPv4 packet");
102 MODULE_LICENSE("GPL");