blob: 6cc5743c553a02fd82ee97fab94f36019b6a1f7c [file] [log] [blame]
// SPDX-License-Identifier: GPL-2.0-or-later
* (C) 2007 by Sebastian Claßen <>
* (C) 2007-2010 by Jan Engelhardt <>
* Extracted from xt_TEE.c
#include <linux/ip.h>
#include <linux/module.h>
#include <linux/percpu.h>
#include <linux/route.h>
#include <linux/skbuff.h>
#include <linux/netfilter.h>
#include <net/checksum.h>
#include <net/icmp.h>
#include <net/ip.h>
#include <net/route.h>
#include <net/netfilter/ipv4/nf_dup_ipv4.h>
#include <net/netfilter/nf_conntrack.h>
static bool nf_dup_ipv4_route(struct net *net, struct sk_buff *skb,
const struct in_addr *gw, int oif)
const struct iphdr *iph = ip_hdr(skb);
struct rtable *rt;
struct flowi4 fl4;
memset(&fl4, 0, sizeof(fl4));
if (oif != -1)
fl4.flowi4_oif = oif;
fl4.daddr = gw->s_addr;
fl4.flowi4_tos = RT_TOS(iph->tos);
fl4.flowi4_scope = RT_SCOPE_UNIVERSE;
fl4.flowi4_flags = FLOWI_FLAG_KNOWN_NH;
rt = ip_route_output_key(net, &fl4);
if (IS_ERR(rt))
return false;
skb_dst_set(skb, &rt->dst);
skb->dev = rt->;
skb->protocol = htons(ETH_P_IP);
return true;
void nf_dup_ipv4(struct net *net, struct sk_buff *skb, unsigned int hooknum,
const struct in_addr *gw, int oif)
struct iphdr *iph;
if (this_cpu_read(nf_skb_duplicated))
* Copy the skb, and route the copy. Will later return %XT_CONTINUE for
* the original skb, which should continue on its way as if nothing has
* happened. The copy should be independently delivered to the gateway.
skb = pskb_copy(skb, GFP_ATOMIC);
if (skb == NULL)
/* Avoid counting cloned packets towards the original connection. */
nf_ct_set(skb, NULL, IP_CT_UNTRACKED);
* If we are in PREROUTING/INPUT, decrease the TTL to mitigate potential
* loops between two hosts.
* Set %IP_DF so that the original source is notified of a potentially
* decreased MTU on the clone route. IPv6 does this too.
* IP header checksum will be recalculated at ip_local_out.
iph = ip_hdr(skb);
iph->frag_off |= htons(IP_DF);
if (hooknum == NF_INET_PRE_ROUTING ||
hooknum == NF_INET_LOCAL_IN)
if (nf_dup_ipv4_route(net, skb, gw, oif)) {
__this_cpu_write(nf_skb_duplicated, true);
ip_local_out(net, skb->sk, skb);
__this_cpu_write(nf_skb_duplicated, false);
} else {
MODULE_AUTHOR("Sebastian Claßen <>");
MODULE_AUTHOR("Jan Engelhardt <>");
MODULE_DESCRIPTION("nf_dup_ipv4: Duplicate IPv4 packet");