net/netfilter/xt_TPROXY.c - linux - Git at Google

 /*
  * Transparent proxy support for Linux/iptables
  *
  * Copyright (c) 2006-2010 BalaBit IT Ltd.
  * Author: Balazs Scheidler, Krisztian Kovacs
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as
  * published by the Free Software Foundation.
  *
  */
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 #include <linux/module.h>
 #include <linux/skbuff.h>
 #include <linux/ip.h>
 #include <net/checksum.h>
 #include <net/udp.h>
 #include <net/inet_sock.h>
 #include <linux/inetdevice.h>
 #include <linux/netfilter/x_tables.h>
 #include <linux/netfilter_ipv4/ip_tables.h>

 #include <net/netfilter/ipv4/nf_defrag_ipv4.h>

 #if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
 #define XT_TPROXY_HAVE_IPV6 1
 #include <net/if_inet6.h>
 #include <net/addrconf.h>
 #include <linux/netfilter_ipv6/ip6_tables.h>
 #include <net/netfilter/ipv6/nf_defrag_ipv6.h>
 #endif

 #include <net/netfilter/nf_tproxy_core.h>
 #include <linux/netfilter/xt_TPROXY.h>

 static bool tproxy_sk_is_transparent(struct sock *sk)
 {
 	if (sk->sk_state != TCP_TIME_WAIT) {
 		if (inet_sk(sk)->transparent)
 			return true;
 		sock_put(sk);
 	} else {
 		if (inet_twsk(sk)->tw_transparent)
 			return true;
 		inet_twsk_put(inet_twsk(sk));
 	}
 	return false;
 }

 static inline __be32
 tproxy_laddr4(struct sk_buff *skb, __be32 user_laddr, __be32 daddr)
 {
 	struct in_device *indev;
 	__be32 laddr;

 	if (user_laddr)
 		return user_laddr;

 	laddr = 0;
 	rcu_read_lock();
 	indev = __in_dev_get_rcu(skb->dev);
 	for_primary_ifa(indev) {
 		laddr = ifa->ifa_local;
 		break;
 	} endfor_ifa(indev);
 	rcu_read_unlock();

 	return laddr ? laddr : daddr;
 }

 /**
  * tproxy_handle_time_wait4() - handle IPv4 TCP TIME_WAIT reopen redirections
  * @skb:	The skb being processed.
  * @laddr:	IPv4 address to redirect to or zero.
  * @lport:	TCP port to redirect to or zero.
  * @sk:		The TIME_WAIT TCP socket found by the lookup.
  *
  * We have to handle SYN packets arriving to TIME_WAIT sockets
  * differently: instead of reopening the connection we should rather
  * redirect the new connection to the proxy if there's a listener
  * socket present.
  *
  * tproxy_handle_time_wait4() consumes the socket reference passed in.
  *
  * Returns the listener socket if there's one, the TIME_WAIT socket if
  * no such listener is found, or NULL if the TCP header is incomplete.
  */
 static struct sock *
 tproxy_handle_time_wait4(struct sk_buff *skb, __be32 laddr, __be16 lport,
 			struct sock *sk)
 {
 	const struct iphdr *iph = ip_hdr(skb);
 	struct tcphdr _hdr, *hp;

 	hp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_hdr), &_hdr);
 	if (hp == NULL) {
 		inet_twsk_put(inet_twsk(sk));
 		return NULL;
 	}

 	if (hp->syn && !hp->rst && !hp->ack && !hp->fin) {
 		/* SYN to a TIME_WAIT socket, we'd rather redirect it
 		 * to a listener socket if there's one */
 		struct sock *sk2;

 		sk2 = nf_tproxy_get_sock_v4(dev_net(skb->dev), iph->protocol,
 					    iph->saddr, laddr ? laddr : iph->daddr,
 					    hp->source, lport ? lport : hp->dest,
 					    skb->dev, NFT_LOOKUP_LISTENER);
 		if (sk2) {
 			inet_twsk_deschedule(inet_twsk(sk), &tcp_death_row);
 			inet_twsk_put(inet_twsk(sk));
 			sk = sk2;
 		}
 	}

 	return sk;
 }

 static unsigned int
 tproxy_tg4(struct sk_buff *skb, __be32 laddr, __be16 lport,
 	   u_int32_t mark_mask, u_int32_t mark_value)
 {
 	const struct iphdr *iph = ip_hdr(skb);
 	struct udphdr _hdr, *hp;
 	struct sock *sk;

 	hp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_hdr), &_hdr);
 	if (hp == NULL)
 		return NF_DROP;

 	/* check if there's an ongoing connection on the packet
 	 * addresses, this happens if the redirect already happened
 	 * and the current packet belongs to an already established
 	 * connection */
 	sk = nf_tproxy_get_sock_v4(dev_net(skb->dev), iph->protocol,
 				   iph->saddr, iph->daddr,
 				   hp->source, hp->dest,
 				   skb->dev, NFT_LOOKUP_ESTABLISHED);

 	laddr = tproxy_laddr4(skb, laddr, iph->daddr);
 	if (!lport)
 		lport = hp->dest;

 	/* UDP has no TCP_TIME_WAIT state, so we never enter here */
 	if (sk && sk->sk_state == TCP_TIME_WAIT)
 		/* reopening a TIME_WAIT connection needs special handling */
 		sk = tproxy_handle_time_wait4(skb, laddr, lport, sk);
 	else if (!sk)
 		/* no, there's no established connection, check if
 		 * there's a listener on the redirected addr/port */
 		sk = nf_tproxy_get_sock_v4(dev_net(skb->dev), iph->protocol,
 					   iph->saddr, laddr,
 					   hp->source, lport,
 					   skb->dev, NFT_LOOKUP_LISTENER);

 	/* NOTE: assign_sock consumes our sk reference */
 	if (sk && tproxy_sk_is_transparent(sk)) {
 		/* This should be in a separate target, but we don't do multiple
 		   targets on the same rule yet */
 		skb->mark = (skb->mark & ~mark_mask) ^ mark_value;

 		pr_debug("redirecting: proto %hhu %pI4:%hu -> %pI4:%hu, mark: %x\n",
 			 iph->protocol, &iph->daddr, ntohs(hp->dest),
 			 &laddr, ntohs(lport), skb->mark);

 		nf_tproxy_assign_sock(skb, sk);
 		return NF_ACCEPT;
 	}

 	pr_debug("no socket, dropping: proto %hhu %pI4:%hu -> %pI4:%hu, mark: %x\n",
 		 iph->protocol, &iph->saddr, ntohs(hp->source),
 		 &iph->daddr, ntohs(hp->dest), skb->mark);
 	return NF_DROP;
 }

 static unsigned int
 tproxy_tg4_v0(struct sk_buff *skb, const struct xt_action_param *par)
 {
 	const struct xt_tproxy_target_info *tgi = par->targinfo;

 	return tproxy_tg4(skb, tgi->laddr, tgi->lport, tgi->mark_mask, tgi->mark_value);
 }

 static unsigned int
 tproxy_tg4_v1(struct sk_buff *skb, const struct xt_action_param *par)
 {
 	const struct xt_tproxy_target_info_v1 *tgi = par->targinfo;

 	return tproxy_tg4(skb, tgi->laddr.ip, tgi->lport, tgi->mark_mask, tgi->mark_value);
 }

 #ifdef XT_TPROXY_HAVE_IPV6

 static inline const struct in6_addr *
 tproxy_laddr6(struct sk_buff *skb, const struct in6_addr *user_laddr,
 	      const struct in6_addr *daddr)
 {
 	struct inet6_dev *indev;
 	struct inet6_ifaddr *ifa;
 	struct in6_addr *laddr;

 	if (!ipv6_addr_any(user_laddr))
 		return user_laddr;
 	laddr = NULL;

 	rcu_read_lock();
 	indev = __in6_dev_get(skb->dev);
 	if (indev)
 		list_for_each_entry(ifa, &indev->addr_list, if_list) {
 			if (ifa->flags & (IFA_F_TENTATIVE | IFA_F_DEPRECATED))
 				continue;

 			laddr = &ifa->addr;
 			break;
 		}
 	rcu_read_unlock();

 	return laddr ? laddr : daddr;
 }

 /**
  * tproxy_handle_time_wait6() - handle IPv6 TCP TIME_WAIT reopen redirections
  * @skb:	The skb being processed.
  * @tproto:	Transport protocol.
  * @thoff:	Transport protocol header offset.
  * @par:	Iptables target parameters.
  * @sk:		The TIME_WAIT TCP socket found by the lookup.
  *
  * We have to handle SYN packets arriving to TIME_WAIT sockets
  * differently: instead of reopening the connection we should rather
  * redirect the new connection to the proxy if there's a listener
  * socket present.
  *
  * tproxy_handle_time_wait6() consumes the socket reference passed in.
  *
  * Returns the listener socket if there's one, the TIME_WAIT socket if
  * no such listener is found, or NULL if the TCP header is incomplete.
  */
 static struct sock *
 tproxy_handle_time_wait6(struct sk_buff *skb, int tproto, int thoff,
 			 const struct xt_action_param *par,
 			 struct sock *sk)
 {
 	const struct ipv6hdr *iph = ipv6_hdr(skb);
 	struct tcphdr _hdr, *hp;
 	const struct xt_tproxy_target_info_v1 *tgi = par->targinfo;

 	hp = skb_header_pointer(skb, thoff, sizeof(_hdr), &_hdr);
 	if (hp == NULL) {
 		inet_twsk_put(inet_twsk(sk));
 		return NULL;
 	}

 	if (hp->syn && !hp->rst && !hp->ack && !hp->fin) {
 		/* SYN to a TIME_WAIT socket, we'd rather redirect it
 		 * to a listener socket if there's one */
 		struct sock *sk2;

 		sk2 = nf_tproxy_get_sock_v6(dev_net(skb->dev), tproto,
 					    &iph->saddr,
 					    tproxy_laddr6(skb, &tgi->laddr.in6, &iph->daddr),
 					    hp->source,
 					    tgi->lport ? tgi->lport : hp->dest,
 					    skb->dev, NFT_LOOKUP_LISTENER);
 		if (sk2) {
 			inet_twsk_deschedule(inet_twsk(sk), &tcp_death_row);
 			inet_twsk_put(inet_twsk(sk));
 			sk = sk2;
 		}
 	}

 	return sk;
 }

 static unsigned int
 tproxy_tg6_v1(struct sk_buff *skb, const struct xt_action_param *par)
 {
 	const struct ipv6hdr *iph = ipv6_hdr(skb);
 	const struct xt_tproxy_target_info_v1 *tgi = par->targinfo;
 	struct udphdr _hdr, *hp;
 	struct sock *sk;
 	const struct in6_addr *laddr;
 	__be16 lport;
 	int thoff = 0;
 	int tproto;

 	tproto = ipv6_find_hdr(skb, &thoff, -1, NULL, NULL);
 	if (tproto < 0) {
 		pr_debug("unable to find transport header in IPv6 packet, dropping\n");
 		return NF_DROP;
 	}

 	hp = skb_header_pointer(skb, thoff, sizeof(_hdr), &_hdr);
 	if (hp == NULL) {
 		pr_debug("unable to grab transport header contents in IPv6 packet, dropping\n");
 		return NF_DROP;
 	}

 	/* check if there's an ongoing connection on the packet
 	 * addresses, this happens if the redirect already happened
 	 * and the current packet belongs to an already established
 	 * connection */
 	sk = nf_tproxy_get_sock_v6(dev_net(skb->dev), tproto,
 				   &iph->saddr, &iph->daddr,
 				   hp->source, hp->dest,
 				   par->in, NFT_LOOKUP_ESTABLISHED);

 	laddr = tproxy_laddr6(skb, &tgi->laddr.in6, &iph->daddr);
 	lport = tgi->lport ? tgi->lport : hp->dest;

 	/* UDP has no TCP_TIME_WAIT state, so we never enter here */
 	if (sk && sk->sk_state == TCP_TIME_WAIT)
 		/* reopening a TIME_WAIT connection needs special handling */
 		sk = tproxy_handle_time_wait6(skb, tproto, thoff, par, sk);
 	else if (!sk)
 		/* no there's no established connection, check if
 		 * there's a listener on the redirected addr/port */
 		sk = nf_tproxy_get_sock_v6(dev_net(skb->dev), tproto,
 					   &iph->saddr, laddr,
 					   hp->source, lport,
 					   par->in, NFT_LOOKUP_LISTENER);

 	/* NOTE: assign_sock consumes our sk reference */
 	if (sk && tproxy_sk_is_transparent(sk)) {
 		/* This should be in a separate target, but we don't do multiple
 		   targets on the same rule yet */
 		skb->mark = (skb->mark & ~tgi->mark_mask) ^ tgi->mark_value;

 		pr_debug("redirecting: proto %hhu %pI6:%hu -> %pI6:%hu, mark: %x\n",
 			 tproto, &iph->saddr, ntohs(hp->source),
 			 laddr, ntohs(lport), skb->mark);

 		nf_tproxy_assign_sock(skb, sk);
 		return NF_ACCEPT;
 	}

 	pr_debug("no socket, dropping: proto %hhu %pI6:%hu -> %pI6:%hu, mark: %x\n",
 		 tproto, &iph->saddr, ntohs(hp->source),
 		 &iph->daddr, ntohs(hp->dest), skb->mark);

 	return NF_DROP;
 }

 static int tproxy_tg6_check(const struct xt_tgchk_param *par)
 {
 	const struct ip6t_ip6 *i = par->entryinfo;

 	if ((i->proto == IPPROTO_TCP || i->proto == IPPROTO_UDP)
 	    && !(i->flags & IP6T_INV_PROTO))
 		return 0;

 	pr_info("Can be used only in combination with "
 		"either -p tcp or -p udp\n");
 	return -EINVAL;
 }
 #endif

 static int tproxy_tg4_check(const struct xt_tgchk_param *par)
 {
 	const struct ipt_ip *i = par->entryinfo;

 	if ((i->proto == IPPROTO_TCP || i->proto == IPPROTO_UDP)
 	    && !(i->invflags & IPT_INV_PROTO))
 		return 0;

 	pr_info("Can be used only in combination with "
 		"either -p tcp or -p udp\n");
 	return -EINVAL;
 }

 static struct xt_target tproxy_tg_reg[] __read_mostly = {
 	{
 		.name		= "TPROXY",
 		.family		= NFPROTO_IPV4,
 		.table		= "mangle",
 		.target		= tproxy_tg4_v0,
 		.revision	= 0,
 		.targetsize	= sizeof(struct xt_tproxy_target_info),
 		.checkentry	= tproxy_tg4_check,
 		.hooks		= 1 << NF_INET_PRE_ROUTING,
 		.me		= THIS_MODULE,
 	},
 	{
 		.name		= "TPROXY",
 		.family		= NFPROTO_IPV4,
 		.table		= "mangle",
 		.target		= tproxy_tg4_v1,
 		.revision	= 1,
 		.targetsize	= sizeof(struct xt_tproxy_target_info_v1),
 		.checkentry	= tproxy_tg4_check,
 		.hooks		= 1 << NF_INET_PRE_ROUTING,
 		.me		= THIS_MODULE,
 	},
 #ifdef XT_TPROXY_HAVE_IPV6
 	{
 		.name		= "TPROXY",
 		.family		= NFPROTO_IPV6,
 		.table		= "mangle",
 		.target		= tproxy_tg6_v1,
 		.revision	= 1,
 		.targetsize	= sizeof(struct xt_tproxy_target_info_v1),
 		.checkentry	= tproxy_tg6_check,
 		.hooks		= 1 << NF_INET_PRE_ROUTING,
 		.me		= THIS_MODULE,
 	},
 #endif

 };

 static int __init tproxy_tg_init(void)
 {
 	nf_defrag_ipv4_enable();
 #ifdef XT_TPROXY_HAVE_IPV6
 	nf_defrag_ipv6_enable();
 #endif

 	return xt_register_targets(tproxy_tg_reg, ARRAY_SIZE(tproxy_tg_reg));
 }

 static void __exit tproxy_tg_exit(void)
 {
 	xt_unregister_targets(tproxy_tg_reg, ARRAY_SIZE(tproxy_tg_reg));
 }

 module_init(tproxy_tg_init);
 module_exit(tproxy_tg_exit);
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Balazs Scheidler, Krisztian Kovacs");
 MODULE_DESCRIPTION("Netfilter transparent proxy (TPROXY) target module.");
 MODULE_ALIAS("ipt_TPROXY");
 MODULE_ALIAS("ip6t_TPROXY");
	/*
	* Transparent proxy support for Linux/iptables
	*
	* Copyright (c) 2006-2010 BalaBit IT Ltd.
	* Author: Balazs Scheidler, Krisztian Kovacs
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License version 2 as
	* published by the Free Software Foundation.
	*
	*/
	#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
	#include <linux/module.h>
	#include <linux/skbuff.h>
	#include <linux/ip.h>
	#include <net/checksum.h>
	#include <net/udp.h>
	#include <net/inet_sock.h>
	#include <linux/inetdevice.h>
	#include <linux/netfilter/x_tables.h>
	#include <linux/netfilter_ipv4/ip_tables.h>

	#include <net/netfilter/ipv4/nf_defrag_ipv4.h>

	#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
	#define XT_TPROXY_HAVE_IPV6 1
	#include <net/if_inet6.h>
	#include <net/addrconf.h>
	#include <linux/netfilter_ipv6/ip6_tables.h>
	#include <net/netfilter/ipv6/nf_defrag_ipv6.h>
	#endif

	#include <net/netfilter/nf_tproxy_core.h>
	#include <linux/netfilter/xt_TPROXY.h>

	static bool tproxy_sk_is_transparent(struct sock *sk)
	{
	if (sk->sk_state != TCP_TIME_WAIT) {
	if (inet_sk(sk)->transparent)
	return true;
	sock_put(sk);
	} else {
	if (inet_twsk(sk)->tw_transparent)
	return true;
	inet_twsk_put(inet_twsk(sk));
	}
	return false;
	}

	static inline __be32
	tproxy_laddr4(struct sk_buff *skb, __be32 user_laddr, __be32 daddr)
	{
	struct in_device *indev;
	__be32 laddr;

	if (user_laddr)
	return user_laddr;

	laddr = 0;
	rcu_read_lock();
	indev = __in_dev_get_rcu(skb->dev);
	for_primary_ifa(indev) {
	laddr = ifa->ifa_local;
	break;
	} endfor_ifa(indev);
	rcu_read_unlock();

	return laddr ? laddr : daddr;
	}

	/**
	* tproxy_handle_time_wait4() - handle IPv4 TCP TIME_WAIT reopen redirections
	* @skb: The skb being processed.
	* @laddr: IPv4 address to redirect to or zero.
	* @lport: TCP port to redirect to or zero.
	* @sk: The TIME_WAIT TCP socket found by the lookup.
	*
	* We have to handle SYN packets arriving to TIME_WAIT sockets
	* differently: instead of reopening the connection we should rather
	* redirect the new connection to the proxy if there's a listener
	* socket present.
	*
	* tproxy_handle_time_wait4() consumes the socket reference passed in.
	*
	* Returns the listener socket if there's one, the TIME_WAIT socket if
	* no such listener is found, or NULL if the TCP header is incomplete.
	*/
	static struct sock *
	tproxy_handle_time_wait4(struct sk_buff *skb, __be32 laddr, __be16 lport,
	struct sock *sk)
	{
	const struct iphdr *iph = ip_hdr(skb);
	struct tcphdr _hdr, *hp;

	hp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_hdr), &_hdr);
	if (hp == NULL) {
	inet_twsk_put(inet_twsk(sk));
	return NULL;
	}

	if (hp->syn && !hp->rst && !hp->ack && !hp->fin) {
	/* SYN to a TIME_WAIT socket, we'd rather redirect it
	* to a listener socket if there's one */
	struct sock *sk2;

	sk2 = nf_tproxy_get_sock_v4(dev_net(skb->dev), iph->protocol,
	iph->saddr, laddr ? laddr : iph->daddr,
	hp->source, lport ? lport : hp->dest,
	skb->dev, NFT_LOOKUP_LISTENER);
	if (sk2) {
	inet_twsk_deschedule(inet_twsk(sk), &tcp_death_row);
	inet_twsk_put(inet_twsk(sk));
	sk = sk2;
	}
	}

	return sk;
	}

	static unsigned int
	tproxy_tg4(struct sk_buff *skb, __be32 laddr, __be16 lport,
	u_int32_t mark_mask, u_int32_t mark_value)
	{
	const struct iphdr *iph = ip_hdr(skb);
	struct udphdr _hdr, *hp;
	struct sock *sk;

	hp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(_hdr), &_hdr);
	if (hp == NULL)
	return NF_DROP;

	/* check if there's an ongoing connection on the packet
	* addresses, this happens if the redirect already happened
	* and the current packet belongs to an already established
	* connection */
	sk = nf_tproxy_get_sock_v4(dev_net(skb->dev), iph->protocol,
	iph->saddr, iph->daddr,
	hp->source, hp->dest,
	skb->dev, NFT_LOOKUP_ESTABLISHED);

	laddr = tproxy_laddr4(skb, laddr, iph->daddr);
	if (!lport)
	lport = hp->dest;

	/* UDP has no TCP_TIME_WAIT state, so we never enter here */
	if (sk && sk->sk_state == TCP_TIME_WAIT)
	/* reopening a TIME_WAIT connection needs special handling */
	sk = tproxy_handle_time_wait4(skb, laddr, lport, sk);
	else if (!sk)
	/* no, there's no established connection, check if
	* there's a listener on the redirected addr/port */
	sk = nf_tproxy_get_sock_v4(dev_net(skb->dev), iph->protocol,
	iph->saddr, laddr,
	hp->source, lport,
	skb->dev, NFT_LOOKUP_LISTENER);

	/* NOTE: assign_sock consumes our sk reference */
	if (sk && tproxy_sk_is_transparent(sk)) {
	/* This should be in a separate target, but we don't do multiple
	targets on the same rule yet */
	skb->mark = (skb->mark & ~mark_mask) ^ mark_value;

	pr_debug("redirecting: proto %hhu %pI4:%hu -> %pI4:%hu, mark: %x\n",
	iph->protocol, &iph->daddr, ntohs(hp->dest),
	&laddr, ntohs(lport), skb->mark);

	nf_tproxy_assign_sock(skb, sk);
	return NF_ACCEPT;
	}

	pr_debug("no socket, dropping: proto %hhu %pI4:%hu -> %pI4:%hu, mark: %x\n",
	iph->protocol, &iph->saddr, ntohs(hp->source),
	&iph->daddr, ntohs(hp->dest), skb->mark);
	return NF_DROP;
	}

	static unsigned int
	tproxy_tg4_v0(struct sk_buff skb, const struct xt_action_param par)
	{
	const struct xt_tproxy_target_info *tgi = par->targinfo;

	return tproxy_tg4(skb, tgi->laddr, tgi->lport, tgi->mark_mask, tgi->mark_value);
	}

	static unsigned int
	tproxy_tg4_v1(struct sk_buff skb, const struct xt_action_param par)
	{
	const struct xt_tproxy_target_info_v1 *tgi = par->targinfo;

	return tproxy_tg4(skb, tgi->laddr.ip, tgi->lport, tgi->mark_mask, tgi->mark_value);
	}

	#ifdef XT_TPROXY_HAVE_IPV6

	static inline const struct in6_addr *
	tproxy_laddr6(struct sk_buff skb, const struct in6_addr user_laddr,
	const struct in6_addr *daddr)
	{
	struct inet6_dev *indev;
	struct inet6_ifaddr *ifa;
	struct in6_addr *laddr;

	if (!ipv6_addr_any(user_laddr))
	return user_laddr;
	laddr = NULL;

	rcu_read_lock();
	indev = __in6_dev_get(skb->dev);
	if (indev)
	list_for_each_entry(ifa, &indev->addr_list, if_list) {
	if (ifa->flags & (IFA_F_TENTATIVE \| IFA_F_DEPRECATED))
	continue;

	laddr = &ifa->addr;
	break;
	}
	rcu_read_unlock();

	return laddr ? laddr : daddr;
	}

	/**
	* tproxy_handle_time_wait6() - handle IPv6 TCP TIME_WAIT reopen redirections
	* @skb: The skb being processed.
	* @tproto: Transport protocol.
	* @thoff: Transport protocol header offset.
	* @par: Iptables target parameters.
	* @sk: The TIME_WAIT TCP socket found by the lookup.
	*
	* We have to handle SYN packets arriving to TIME_WAIT sockets
	* differently: instead of reopening the connection we should rather
	* redirect the new connection to the proxy if there's a listener
	* socket present.
	*
	* tproxy_handle_time_wait6() consumes the socket reference passed in.
	*
	* Returns the listener socket if there's one, the TIME_WAIT socket if
	* no such listener is found, or NULL if the TCP header is incomplete.
	*/
	static struct sock *
	tproxy_handle_time_wait6(struct sk_buff *skb, int tproto, int thoff,
	const struct xt_action_param *par,
	struct sock *sk)
	{
	const struct ipv6hdr *iph = ipv6_hdr(skb);
	struct tcphdr _hdr, *hp;
	const struct xt_tproxy_target_info_v1 *tgi = par->targinfo;

	hp = skb_header_pointer(skb, thoff, sizeof(_hdr), &_hdr);
	if (hp == NULL) {
	inet_twsk_put(inet_twsk(sk));
	return NULL;
	}

	if (hp->syn && !hp->rst && !hp->ack && !hp->fin) {
	/* SYN to a TIME_WAIT socket, we'd rather redirect it
	* to a listener socket if there's one */
	struct sock *sk2;

	sk2 = nf_tproxy_get_sock_v6(dev_net(skb->dev), tproto,
	&iph->saddr,
	tproxy_laddr6(skb, &tgi->laddr.in6, &iph->daddr),
	hp->source,
	tgi->lport ? tgi->lport : hp->dest,
	skb->dev, NFT_LOOKUP_LISTENER);
	if (sk2) {
	inet_twsk_deschedule(inet_twsk(sk), &tcp_death_row);
	inet_twsk_put(inet_twsk(sk));
	sk = sk2;
	}
	}

	return sk;
	}

	static unsigned int
	tproxy_tg6_v1(struct sk_buff skb, const struct xt_action_param par)
	{
	const struct ipv6hdr *iph = ipv6_hdr(skb);
	const struct xt_tproxy_target_info_v1 *tgi = par->targinfo;
	struct udphdr _hdr, *hp;
	struct sock *sk;
	const struct in6_addr *laddr;
	__be16 lport;
	int thoff = 0;
	int tproto;

	tproto = ipv6_find_hdr(skb, &thoff, -1, NULL, NULL);
	if (tproto < 0) {
	pr_debug("unable to find transport header in IPv6 packet, dropping\n");
	return NF_DROP;
	}

	hp = skb_header_pointer(skb, thoff, sizeof(_hdr), &_hdr);
	if (hp == NULL) {
	pr_debug("unable to grab transport header contents in IPv6 packet, dropping\n");
	return NF_DROP;
	}

	/* check if there's an ongoing connection on the packet
	* addresses, this happens if the redirect already happened
	* and the current packet belongs to an already established
	* connection */
	sk = nf_tproxy_get_sock_v6(dev_net(skb->dev), tproto,
	&iph->saddr, &iph->daddr,
	hp->source, hp->dest,
	par->in, NFT_LOOKUP_ESTABLISHED);

	laddr = tproxy_laddr6(skb, &tgi->laddr.in6, &iph->daddr);
	lport = tgi->lport ? tgi->lport : hp->dest;

	/* UDP has no TCP_TIME_WAIT state, so we never enter here */
	if (sk && sk->sk_state == TCP_TIME_WAIT)
	/* reopening a TIME_WAIT connection needs special handling */
	sk = tproxy_handle_time_wait6(skb, tproto, thoff, par, sk);
	else if (!sk)
	/* no there's no established connection, check if
	* there's a listener on the redirected addr/port */
	sk = nf_tproxy_get_sock_v6(dev_net(skb->dev), tproto,
	&iph->saddr, laddr,
	hp->source, lport,
	par->in, NFT_LOOKUP_LISTENER);

	/* NOTE: assign_sock consumes our sk reference */
	if (sk && tproxy_sk_is_transparent(sk)) {
	/* This should be in a separate target, but we don't do multiple
	targets on the same rule yet */
	skb->mark = (skb->mark & ~tgi->mark_mask) ^ tgi->mark_value;

	pr_debug("redirecting: proto %hhu %pI6:%hu -> %pI6:%hu, mark: %x\n",
	tproto, &iph->saddr, ntohs(hp->source),
	laddr, ntohs(lport), skb->mark);

	nf_tproxy_assign_sock(skb, sk);
	return NF_ACCEPT;
	}

	pr_debug("no socket, dropping: proto %hhu %pI6:%hu -> %pI6:%hu, mark: %x\n",
	tproto, &iph->saddr, ntohs(hp->source),
	&iph->daddr, ntohs(hp->dest), skb->mark);

	return NF_DROP;
	}

	static int tproxy_tg6_check(const struct xt_tgchk_param *par)
	{
	const struct ip6t_ip6 *i = par->entryinfo;

	if ((i->proto == IPPROTO_TCP \|\| i->proto == IPPROTO_UDP)
	&& !(i->flags & IP6T_INV_PROTO))
	return 0;

	pr_info("Can be used only in combination with "
	"either -p tcp or -p udp\n");
	return -EINVAL;
	}
	#endif

	static int tproxy_tg4_check(const struct xt_tgchk_param *par)
	{
	const struct ipt_ip *i = par->entryinfo;

	if ((i->proto == IPPROTO_TCP \|\| i->proto == IPPROTO_UDP)
	&& !(i->invflags & IPT_INV_PROTO))
	return 0;

	pr_info("Can be used only in combination with "
	"either -p tcp or -p udp\n");
	return -EINVAL;
	}

	static struct xt_target tproxy_tg_reg[] __read_mostly = {
	{
	.name = "TPROXY",
	.family = NFPROTO_IPV4,
	.table = "mangle",
	.target = tproxy_tg4_v0,
	.revision = 0,
	.targetsize = sizeof(struct xt_tproxy_target_info),
	.checkentry = tproxy_tg4_check,
	.hooks = 1 << NF_INET_PRE_ROUTING,
	.me = THIS_MODULE,
	},
	{
	.name = "TPROXY",
	.family = NFPROTO_IPV4,
	.table = "mangle",
	.target = tproxy_tg4_v1,
	.revision = 1,
	.targetsize = sizeof(struct xt_tproxy_target_info_v1),
	.checkentry = tproxy_tg4_check,
	.hooks = 1 << NF_INET_PRE_ROUTING,
	.me = THIS_MODULE,
	},
	#ifdef XT_TPROXY_HAVE_IPV6
	{
	.name = "TPROXY",
	.family = NFPROTO_IPV6,
	.table = "mangle",
	.target = tproxy_tg6_v1,
	.revision = 1,
	.targetsize = sizeof(struct xt_tproxy_target_info_v1),
	.checkentry = tproxy_tg6_check,
	.hooks = 1 << NF_INET_PRE_ROUTING,
	.me = THIS_MODULE,
	},
	#endif

	};

	static int __init tproxy_tg_init(void)
	{
	nf_defrag_ipv4_enable();
	#ifdef XT_TPROXY_HAVE_IPV6
	nf_defrag_ipv6_enable();
	#endif

	return xt_register_targets(tproxy_tg_reg, ARRAY_SIZE(tproxy_tg_reg));
	}

	static void __exit tproxy_tg_exit(void)
	{
	xt_unregister_targets(tproxy_tg_reg, ARRAY_SIZE(tproxy_tg_reg));
	}

	module_init(tproxy_tg_init);
	module_exit(tproxy_tg_exit);
	MODULE_LICENSE("GPL");
	MODULE_AUTHOR("Balazs Scheidler, Krisztian Kovacs");
	MODULE_DESCRIPTION("Netfilter transparent proxy (TPROXY) target module.");
	MODULE_ALIAS("ipt_TPROXY");
	MODULE_ALIAS("ip6t_TPROXY");