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Commit bbde9fc1 authored by Pablo Neira Ayuso's avatar Pablo Neira Ayuso
Browse files

netfilter: factor out packet duplication for IPv4/IPv6 



Extracted from the xtables TEE target. This creates two new modules for IPv4
and IPv6 that are shared between the TEE target and the new nf_tables dup
expressions.

Signed-off-by: default avatarPablo Neira Ayuso <pablo@netfilter.org>
parent 24b7811f

include/net/netfilter/ipv4/nf_dup_ipv4.h

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+7 −0
Original line number Diff line number Diff line 
#ifndef _NF_DUP_IPV4_H_

#define _NF_DUP_IPV4_H_



void nf_dup_ipv4(struct sk_buff *skb, unsigned int hooknum,

		 const struct in_addr *gw, int oif);



#endif /* _NF_DUP_IPV4_H_ */

include/net/netfilter/ipv6/nf_dup_ipv6.h

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+7 −0
Original line number Diff line number Diff line 
#ifndef _NF_DUP_IPV6_H_

#define _NF_DUP_IPV6_H_



void nf_dup_ipv6(struct sk_buff *skb, unsigned int hooknum,

		 const struct in6_addr *gw, int oif);



#endif /* _NF_DUP_IPV6_H_ */

net/ipv4/netfilter/Kconfig

+6 −0
Original line number Diff line number Diff line
@@ -67,6 +67,12 @@ config NF_TABLES_ARP 


endif # NF_TABLES



config NF_DUP_IPV4

	tristate "Netfilter IPv4 packet duplication to alternate destination"

	help

	  This option enables the nf_dup_ipv4 core, which duplicates an IPv4

	  packet to be rerouted to another destination.



config NF_LOG_ARP

	tristate "ARP packet logging"

	default m if NETFILTER_ADVANCED=n

net/ipv4/netfilter/Makefile

+2 −0
Original line number Diff line number Diff line
@@ -70,3 +70,5 @@ obj-$(CONFIG_IP_NF_ARP_MANGLE) += arpt_mangle.o 


# just filtering instance of ARP tables for now

obj-$(CONFIG_IP_NF_ARPFILTER) += arptable_filter.o



obj-$(CONFIG_NF_DUP_IPV4) += nf_dup_ipv4.o

net/ipv4/netfilter/nf_dup_ipv4.c

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+120 −0
Original line number Diff line number Diff line 
/*

 * (C) 2007 by Sebastian Claßen <sebastian.classen@freenet.ag>

 * (C) 2007-2010 by Jan Engelhardt <jengelh@medozas.de>

 *

 * Extracted from xt_TEE.c

 *

 * This program is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 or later, as

 * published by the Free Software Foundation.

 */

#include <linux/ip.h>

#include <linux/module.h>

#include <linux/percpu.h>

#include <linux/route.h>

#include <linux/skbuff.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>

#if IS_ENABLED(CONFIG_NF_CONNTRACK)

#include <net/netfilter/nf_conntrack.h>

#endif



static struct net *pick_net(struct sk_buff *skb)

{

#ifdef CONFIG_NET_NS

	const struct dst_entry *dst;



	if (skb->dev != NULL)

		return dev_net(skb->dev);

	dst = skb_dst(skb);

	if (dst != NULL && dst->dev != NULL)

		return dev_net(dst->dev);

#endif

	return &init_net;

}



static bool nf_dup_ipv4_route(struct sk_buff *skb, const struct in_addr *gw,

			      int oif)

{

	const struct iphdr *iph = ip_hdr(skb);

	struct net *net = pick_net(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_drop(skb);

	skb_dst_set(skb, &rt->dst);

	skb->dev      = rt->dst.dev;

	skb->protocol = htons(ETH_P_IP);



	return true;

}



void nf_dup_ipv4(struct sk_buff *skb, unsigned int hooknum,

		 const struct in_addr *gw, int oif)

{

	struct iphdr *iph;



	if (__this_cpu_read(nf_skb_duplicated))

		return;

	/*

	 * 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)

		return;



#if IS_ENABLED(CONFIG_NF_CONNTRACK)

	/* Avoid counting cloned packets towards the original connection. */

	nf_conntrack_put(skb->nfct);

	skb->nfct     = &nf_ct_untracked_get()->ct_general;

	skb->nfctinfo = IP_CT_NEW;

	nf_conntrack_get(skb->nfct);

#endif

	/*

	 * If we are in PREROUTING/INPUT, the checksum must be recalculated

	 * since the length could have changed as a result of defragmentation.

	 *

	 * We also 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.

	 */

	iph = ip_hdr(skb);

	iph->frag_off |= htons(IP_DF);

	if (hooknum == NF_INET_PRE_ROUTING ||

	    hooknum == NF_INET_LOCAL_IN)

		--iph->ttl;

	ip_send_check(iph);



	if (nf_dup_ipv4_route(skb, gw, oif)) {

		__this_cpu_write(nf_skb_duplicated, true);

		ip_local_out(skb);

		__this_cpu_write(nf_skb_duplicated, false);

	} else {

		kfree_skb(skb);

	}

}

EXPORT_SYMBOL_GPL(nf_dup_ipv4);



MODULE_AUTHOR("Sebastian Claßen <sebastian.classen@freenet.ag>");

MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");

MODULE_DESCRIPTION("nf_dup_ipv4: Duplicate IPv4 packet");

MODULE_LICENSE("GPL");