net/ipv4/netfilter/nf_nat_standalone.c - linux/kernel/git/gregkh/char-misc - Git at Google

 /* (C) 1999-2001 Paul `Rusty' Russell
  * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
  *
  * 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.
  */
 #include <linux/types.h>
 #include <linux/icmp.h>
 #include <linux/ip.h>
 #include <linux/netfilter.h>
 #include <linux/netfilter_ipv4.h>
 #include <linux/module.h>
 #include <linux/skbuff.h>
 #include <linux/proc_fs.h>
 #include <net/ip.h>
 #include <net/checksum.h>
 #include <linux/spinlock.h>

 #include <net/netfilter/nf_conntrack.h>
 #include <net/netfilter/nf_conntrack_core.h>
 #include <net/netfilter/nf_nat.h>
 #include <net/netfilter/nf_nat_rule.h>
 #include <net/netfilter/nf_nat_protocol.h>
 #include <net/netfilter/nf_nat_core.h>
 #include <net/netfilter/nf_nat_helper.h>
 #include <linux/netfilter_ipv4/ip_tables.h>

 #if 0
 #define DEBUGP printk
 #else
 #define DEBUGP(format, args...)
 #endif

 #define HOOKNAME(hooknum) ((hooknum) == NF_IP_POST_ROUTING ? "POST_ROUTING"  \
 			   : ((hooknum) == NF_IP_PRE_ROUTING ? "PRE_ROUTING" \
 			      : ((hooknum) == NF_IP_LOCAL_OUT ? "LOCAL_OUT"  \
 			         : ((hooknum) == NF_IP_LOCAL_IN ? "LOCAL_IN"  \
 				    : "*ERROR*")))

 #ifdef CONFIG_XFRM
 static void nat_decode_session(struct sk_buff *skb, struct flowi *fl)
 {
 	struct nf_conn *ct;
 	struct nf_conntrack_tuple *t;
 	enum ip_conntrack_info ctinfo;
 	enum ip_conntrack_dir dir;
 	unsigned long statusbit;

 	ct = nf_ct_get(skb, &ctinfo);
 	if (ct == NULL)
 		return;
 	dir = CTINFO2DIR(ctinfo);
 	t = &ct->tuplehash[dir].tuple;

 	if (dir == IP_CT_DIR_ORIGINAL)
 		statusbit = IPS_DST_NAT;
 	else
 		statusbit = IPS_SRC_NAT;

 	if (ct->status & statusbit) {
 		fl->fl4_dst = t->dst.u3.ip;
 		if (t->dst.protonum == IPPROTO_TCP ||
 		    t->dst.protonum == IPPROTO_UDP)
 			fl->fl_ip_dport = t->dst.u.tcp.port;
 	}

 	statusbit ^= IPS_NAT_MASK;

 	if (ct->status & statusbit) {
 		fl->fl4_src = t->src.u3.ip;
 		if (t->dst.protonum == IPPROTO_TCP ||
 		    t->dst.protonum == IPPROTO_UDP)
 			fl->fl_ip_sport = t->src.u.tcp.port;
 	}
 }
 #endif

 static unsigned int
 nf_nat_fn(unsigned int hooknum,
 	  struct sk_buff **pskb,
 	  const struct net_device *in,
 	  const struct net_device *out,
 	  int (*okfn)(struct sk_buff *))
 {
 	struct nf_conn *ct;
 	enum ip_conntrack_info ctinfo;
 	struct nf_conn_nat *nat;
 	struct nf_nat_info *info;
 	/* maniptype == SRC for postrouting. */
 	enum nf_nat_manip_type maniptype = HOOK2MANIP(hooknum);

 	/* We never see fragments: conntrack defrags on pre-routing
 	   and local-out, and nf_nat_out protects post-routing. */
 	NF_CT_ASSERT(!((*pskb)->nh.iph->frag_off
 		       & htons(IP_MF|IP_OFFSET)));

 	ct = nf_ct_get(*pskb, &ctinfo);
 	/* Can't track?  It's not due to stress, or conntrack would
 	   have dropped it.  Hence it's the user's responsibilty to
 	   packet filter it out, or implement conntrack/NAT for that
 	   protocol. 8) --RR */
 	if (!ct) {
 		/* Exception: ICMP redirect to new connection (not in
                    hash table yet).  We must not let this through, in
                    case we're doing NAT to the same network. */
 		if ((*pskb)->nh.iph->protocol == IPPROTO_ICMP) {
 			struct icmphdr _hdr, *hp;

 			hp = skb_header_pointer(*pskb,
 						(*pskb)->nh.iph->ihl*4,
 						sizeof(_hdr), &_hdr);
 			if (hp != NULL &&
 			    hp->type == ICMP_REDIRECT)
 				return NF_DROP;
 		}
 		return NF_ACCEPT;
 	}

 	/* Don't try to NAT if this packet is not conntracked */
 	if (ct == &nf_conntrack_untracked)
 		return NF_ACCEPT;

 	nat = nfct_nat(ct);
 	if (!nat)
 		return NF_DROP;

 	switch (ctinfo) {
 	case IP_CT_RELATED:
 	case IP_CT_RELATED+IP_CT_IS_REPLY:
 		if ((*pskb)->nh.iph->protocol == IPPROTO_ICMP) {
 			if (!nf_nat_icmp_reply_translation(ct, ctinfo,
 							   hooknum, pskb))
 				return NF_DROP;
 			else
 				return NF_ACCEPT;
 		}
 		/* Fall thru... (Only ICMPs can be IP_CT_IS_REPLY) */
 	case IP_CT_NEW:
 		info = &nat->info;

 		/* Seen it before?  This can happen for loopback, retrans,
 		   or local packets.. */
 		if (!nf_nat_initialized(ct, maniptype)) {
 			unsigned int ret;

 			if (unlikely(nf_ct_is_confirmed(ct)))
 				/* NAT module was loaded late */
 				ret = alloc_null_binding_confirmed(ct, info,
 				                                   hooknum);
 			else if (hooknum == NF_IP_LOCAL_IN)
 				/* LOCAL_IN hook doesn't have a chain!  */
 				ret = alloc_null_binding(ct, info, hooknum);
 			else
 				ret = nf_nat_rule_find(pskb, hooknum, in, out,
 						       ct, info);

 			if (ret != NF_ACCEPT) {
 				return ret;
 			}
 		} else
 			DEBUGP("Already setup manip %s for ct %p\n",
 			       maniptype == IP_NAT_MANIP_SRC ? "SRC" : "DST",
 			       ct);
 		break;

 	default:
 		/* ESTABLISHED */
 		NF_CT_ASSERT(ctinfo == IP_CT_ESTABLISHED ||
 			     ctinfo == (IP_CT_ESTABLISHED+IP_CT_IS_REPLY));
 		info = &nat->info;
 	}

 	NF_CT_ASSERT(info);
 	return nf_nat_packet(ct, ctinfo, hooknum, pskb);
 }

 static unsigned int
 nf_nat_in(unsigned int hooknum,
           struct sk_buff **pskb,
           const struct net_device *in,
           const struct net_device *out,
           int (*okfn)(struct sk_buff *))
 {
 	unsigned int ret;
 	__be32 daddr = (*pskb)->nh.iph->daddr;

 	ret = nf_nat_fn(hooknum, pskb, in, out, okfn);
 	if (ret != NF_DROP && ret != NF_STOLEN &&
 	    daddr != (*pskb)->nh.iph->daddr) {
 		dst_release((*pskb)->dst);
 		(*pskb)->dst = NULL;
 	}
 	return ret;
 }

 static unsigned int
 nf_nat_out(unsigned int hooknum,
 	   struct sk_buff **pskb,
 	   const struct net_device *in,
 	   const struct net_device *out,
 	   int (*okfn)(struct sk_buff *))
 {
 #ifdef CONFIG_XFRM
 	struct nf_conn *ct;
 	enum ip_conntrack_info ctinfo;
 #endif
 	unsigned int ret;

 	/* root is playing with raw sockets. */
 	if ((*pskb)->len < sizeof(struct iphdr) ||
 	    (*pskb)->nh.iph->ihl * 4 < sizeof(struct iphdr))
 		return NF_ACCEPT;

 	ret = nf_nat_fn(hooknum, pskb, in, out, okfn);
 #ifdef CONFIG_XFRM
 	if (ret != NF_DROP && ret != NF_STOLEN &&
 	    (ct = nf_ct_get(*pskb, &ctinfo)) != NULL) {
 		enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);

 		if (ct->tuplehash[dir].tuple.src.u3.ip !=
 		    ct->tuplehash[!dir].tuple.dst.u3.ip
 		    || ct->tuplehash[dir].tuple.src.u.all !=
 		       ct->tuplehash[!dir].tuple.dst.u.all
 		    )
 			return ip_xfrm_me_harder(pskb) == 0 ? ret : NF_DROP;
 	}
 #endif
 	return ret;
 }

 static unsigned int
 nf_nat_local_fn(unsigned int hooknum,
 		struct sk_buff **pskb,
 		const struct net_device *in,
 		const struct net_device *out,
 		int (*okfn)(struct sk_buff *))
 {
 	struct nf_conn *ct;
 	enum ip_conntrack_info ctinfo;
 	unsigned int ret;

 	/* root is playing with raw sockets. */
 	if ((*pskb)->len < sizeof(struct iphdr) ||
 	    (*pskb)->nh.iph->ihl * 4 < sizeof(struct iphdr))
 		return NF_ACCEPT;

 	ret = nf_nat_fn(hooknum, pskb, in, out, okfn);
 	if (ret != NF_DROP && ret != NF_STOLEN &&
 	    (ct = nf_ct_get(*pskb, &ctinfo)) != NULL) {
 		enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);

 		if (ct->tuplehash[dir].tuple.dst.u3.ip !=
 		    ct->tuplehash[!dir].tuple.src.u3.ip
 #ifdef CONFIG_XFRM
 		    || ct->tuplehash[dir].tuple.dst.u.all !=
 		       ct->tuplehash[!dir].tuple.src.u.all
 #endif
 		    )
 			if (ip_route_me_harder(pskb, RTN_UNSPEC))
 				ret = NF_DROP;
 	}
 	return ret;
 }

 static unsigned int
 nf_nat_adjust(unsigned int hooknum,
 	      struct sk_buff **pskb,
 	      const struct net_device *in,
 	      const struct net_device *out,
 	      int (*okfn)(struct sk_buff *))
 {
 	struct nf_conn *ct;
 	enum ip_conntrack_info ctinfo;

 	ct = nf_ct_get(*pskb, &ctinfo);
 	if (ct && test_bit(IPS_SEQ_ADJUST_BIT, &ct->status)) {
 	        DEBUGP("nf_nat_standalone: adjusting sequence number\n");
 	        if (!nf_nat_seq_adjust(pskb, ct, ctinfo))
 	                return NF_DROP;
 	}
 	return NF_ACCEPT;
 }

 /* We must be after connection tracking and before packet filtering. */

 static struct nf_hook_ops nf_nat_ops[] = {
 	/* Before packet filtering, change destination */
 	{
 		.hook		= nf_nat_in,
 		.owner		= THIS_MODULE,
 		.pf		= PF_INET,
 		.hooknum	= NF_IP_PRE_ROUTING,
 		.priority	= NF_IP_PRI_NAT_DST,
 	},
 	/* After packet filtering, change source */
 	{
 		.hook		= nf_nat_out,
 		.owner		= THIS_MODULE,
 		.pf		= PF_INET,
 		.hooknum	= NF_IP_POST_ROUTING,
 		.priority	= NF_IP_PRI_NAT_SRC,
 	},
 	/* After conntrack, adjust sequence number */
 	{
 		.hook		= nf_nat_adjust,
 		.owner		= THIS_MODULE,
 		.pf		= PF_INET,
 		.hooknum	= NF_IP_POST_ROUTING,
 		.priority	= NF_IP_PRI_NAT_SEQ_ADJUST,
 	},
 	/* Before packet filtering, change destination */
 	{
 		.hook		= nf_nat_local_fn,
 		.owner		= THIS_MODULE,
 		.pf		= PF_INET,
 		.hooknum	= NF_IP_LOCAL_OUT,
 		.priority	= NF_IP_PRI_NAT_DST,
 	},
 	/* After packet filtering, change source */
 	{
 		.hook		= nf_nat_fn,
 		.owner		= THIS_MODULE,
 		.pf		= PF_INET,
 		.hooknum	= NF_IP_LOCAL_IN,
 		.priority	= NF_IP_PRI_NAT_SRC,
 	},
 	/* After conntrack, adjust sequence number */
 	{
 		.hook		= nf_nat_adjust,
 		.owner		= THIS_MODULE,
 		.pf		= PF_INET,
 		.hooknum	= NF_IP_LOCAL_IN,
 		.priority	= NF_IP_PRI_NAT_SEQ_ADJUST,
 	},
 };

 static int __init nf_nat_standalone_init(void)
 {
 	int size, ret = 0;

 	need_conntrack();

 	size = ALIGN(sizeof(struct nf_conn), __alignof__(struct nf_conn_nat)) +
 	       sizeof(struct nf_conn_nat);
 	ret = nf_conntrack_register_cache(NF_CT_F_NAT, "nf_nat:base", size);
 	if (ret < 0) {
 		printk(KERN_ERR "nf_nat_init: Unable to create slab cache\n");
 		return ret;
 	}

 	size = ALIGN(size, __alignof__(struct nf_conn_help)) +
 	       sizeof(struct nf_conn_help);
 	ret = nf_conntrack_register_cache(NF_CT_F_NAT|NF_CT_F_HELP,
 					  "nf_nat:help", size);
 	if (ret < 0) {
 		printk(KERN_ERR "nf_nat_init: Unable to create slab cache\n");
 		goto cleanup_register_cache;
 	}
 #ifdef CONFIG_XFRM
 	BUG_ON(ip_nat_decode_session != NULL);
 	ip_nat_decode_session = nat_decode_session;
 #endif
 	ret = nf_nat_rule_init();
 	if (ret < 0) {
 		printk("nf_nat_init: can't setup rules.\n");
 		goto cleanup_decode_session;
 	}
 	ret = nf_register_hooks(nf_nat_ops, ARRAY_SIZE(nf_nat_ops));
 	if (ret < 0) {
 		printk("nf_nat_init: can't register hooks.\n");
 		goto cleanup_rule_init;
 	}
 	nf_nat_module_is_loaded = 1;
 	return ret;

  cleanup_rule_init:
 	nf_nat_rule_cleanup();
  cleanup_decode_session:
 #ifdef CONFIG_XFRM
 	ip_nat_decode_session = NULL;
 	synchronize_net();
 #endif
 	nf_conntrack_unregister_cache(NF_CT_F_NAT|NF_CT_F_HELP);
  cleanup_register_cache:
 	nf_conntrack_unregister_cache(NF_CT_F_NAT);
 	return ret;
 }

 static void __exit nf_nat_standalone_fini(void)
 {
 	nf_unregister_hooks(nf_nat_ops, ARRAY_SIZE(nf_nat_ops));
 	nf_nat_rule_cleanup();
 	nf_nat_module_is_loaded = 0;
 #ifdef CONFIG_XFRM
 	ip_nat_decode_session = NULL;
 	synchronize_net();
 #endif
 	/* Conntrack caches are unregistered in nf_conntrack_cleanup */
 }

 module_init(nf_nat_standalone_init);
 module_exit(nf_nat_standalone_fini);

 MODULE_LICENSE("GPL");
 MODULE_ALIAS("ip_nat");
	/* (C) 1999-2001 Paul `Rusty' Russell
	* (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
	*
	* 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.
	*/
	#include <linux/types.h>
	#include <linux/icmp.h>
	#include <linux/ip.h>
	#include <linux/netfilter.h>
	#include <linux/netfilter_ipv4.h>
	#include <linux/module.h>
	#include <linux/skbuff.h>
	#include <linux/proc_fs.h>
	#include <net/ip.h>
	#include <net/checksum.h>
	#include <linux/spinlock.h>

	#include <net/netfilter/nf_conntrack.h>
	#include <net/netfilter/nf_conntrack_core.h>
	#include <net/netfilter/nf_nat.h>
	#include <net/netfilter/nf_nat_rule.h>
	#include <net/netfilter/nf_nat_protocol.h>
	#include <net/netfilter/nf_nat_core.h>
	#include <net/netfilter/nf_nat_helper.h>
	#include <linux/netfilter_ipv4/ip_tables.h>

	#if 0
	#define DEBUGP printk
	#else
	#define DEBUGP(format, args...)
	#endif

	#define HOOKNAME(hooknum) ((hooknum) == NF_IP_POST_ROUTING ? "POST_ROUTING" \
	: ((hooknum) == NF_IP_PRE_ROUTING ? "PRE_ROUTING" \
	: ((hooknum) == NF_IP_LOCAL_OUT ? "LOCAL_OUT" \
	: ((hooknum) == NF_IP_LOCAL_IN ? "LOCAL_IN" \
	: "ERROR")))

	#ifdef CONFIG_XFRM
	static void nat_decode_session(struct sk_buff skb, struct flowi fl)
	{
	struct nf_conn *ct;
	struct nf_conntrack_tuple *t;
	enum ip_conntrack_info ctinfo;
	enum ip_conntrack_dir dir;
	unsigned long statusbit;

	ct = nf_ct_get(skb, &ctinfo);
	if (ct == NULL)
	return;
	dir = CTINFO2DIR(ctinfo);
	t = &ct->tuplehash[dir].tuple;

	if (dir == IP_CT_DIR_ORIGINAL)
	statusbit = IPS_DST_NAT;
	else
	statusbit = IPS_SRC_NAT;

	if (ct->status & statusbit) {
	fl->fl4_dst = t->dst.u3.ip;
	if (t->dst.protonum == IPPROTO_TCP \|\|
	t->dst.protonum == IPPROTO_UDP)
	fl->fl_ip_dport = t->dst.u.tcp.port;
	}

	statusbit ^= IPS_NAT_MASK;

	if (ct->status & statusbit) {
	fl->fl4_src = t->src.u3.ip;
	if (t->dst.protonum == IPPROTO_TCP \|\|
	t->dst.protonum == IPPROTO_UDP)
	fl->fl_ip_sport = t->src.u.tcp.port;
	}
	}
	#endif

	static unsigned int
	nf_nat_fn(unsigned int hooknum,
	struct sk_buff **pskb,
	const struct net_device *in,
	const struct net_device *out,
	int (okfn)(struct sk_buff ))
	{
	struct nf_conn *ct;
	enum ip_conntrack_info ctinfo;
	struct nf_conn_nat *nat;
	struct nf_nat_info *info;
	/* maniptype == SRC for postrouting. */
	enum nf_nat_manip_type maniptype = HOOK2MANIP(hooknum);

	/* We never see fragments: conntrack defrags on pre-routing
	and local-out, and nf_nat_out protects post-routing. */
	NF_CT_ASSERT(!((*pskb)->nh.iph->frag_off
	& htons(IP_MF\|IP_OFFSET)));

	ct = nf_ct_get(*pskb, &ctinfo);
	/* Can't track? It's not due to stress, or conntrack would
	have dropped it. Hence it's the user's responsibilty to
	packet filter it out, or implement conntrack/NAT for that
	protocol. 8) --RR */
	if (!ct) {
	/* Exception: ICMP redirect to new connection (not in
	hash table yet). We must not let this through, in
	case we're doing NAT to the same network. */
	if ((*pskb)->nh.iph->protocol == IPPROTO_ICMP) {
	struct icmphdr _hdr, *hp;

	hp = skb_header_pointer(*pskb,
	(pskb)->nh.iph->ihl4,
	sizeof(_hdr), &_hdr);
	if (hp != NULL &&
	hp->type == ICMP_REDIRECT)
	return NF_DROP;
	}
	return NF_ACCEPT;
	}

	/* Don't try to NAT if this packet is not conntracked */
	if (ct == &nf_conntrack_untracked)
	return NF_ACCEPT;

	nat = nfct_nat(ct);
	if (!nat)
	return NF_DROP;

	switch (ctinfo) {
	case IP_CT_RELATED:
	case IP_CT_RELATED+IP_CT_IS_REPLY:
	if ((*pskb)->nh.iph->protocol == IPPROTO_ICMP) {
	if (!nf_nat_icmp_reply_translation(ct, ctinfo,
	hooknum, pskb))
	return NF_DROP;
	else
	return NF_ACCEPT;
	}
	/* Fall thru... (Only ICMPs can be IP_CT_IS_REPLY) */
	case IP_CT_NEW:
	info = &nat->info;

	/* Seen it before? This can happen for loopback, retrans,
	or local packets.. */
	if (!nf_nat_initialized(ct, maniptype)) {
	unsigned int ret;

	if (unlikely(nf_ct_is_confirmed(ct)))
	/* NAT module was loaded late */
	ret = alloc_null_binding_confirmed(ct, info,
	hooknum);
	else if (hooknum == NF_IP_LOCAL_IN)
	/* LOCAL_IN hook doesn't have a chain! */
	ret = alloc_null_binding(ct, info, hooknum);
	else
	ret = nf_nat_rule_find(pskb, hooknum, in, out,
	ct, info);

	if (ret != NF_ACCEPT) {
	return ret;
	}
	} else
	DEBUGP("Already setup manip %s for ct %p\n",
	maniptype == IP_NAT_MANIP_SRC ? "SRC" : "DST",
	ct);
	break;

	default:
	/* ESTABLISHED */
	NF_CT_ASSERT(ctinfo == IP_CT_ESTABLISHED \|\|
	ctinfo == (IP_CT_ESTABLISHED+IP_CT_IS_REPLY));
	info = &nat->info;
	}

	NF_CT_ASSERT(info);
	return nf_nat_packet(ct, ctinfo, hooknum, pskb);
	}

	static unsigned int
	nf_nat_in(unsigned int hooknum,
	struct sk_buff **pskb,
	const struct net_device *in,
	const struct net_device *out,
	int (okfn)(struct sk_buff ))
	{
	unsigned int ret;
	__be32 daddr = (*pskb)->nh.iph->daddr;

	ret = nf_nat_fn(hooknum, pskb, in, out, okfn);
	if (ret != NF_DROP && ret != NF_STOLEN &&
	daddr != (*pskb)->nh.iph->daddr) {
	dst_release((*pskb)->dst);
	(*pskb)->dst = NULL;
	}
	return ret;
	}

	static unsigned int
	nf_nat_out(unsigned int hooknum,
	struct sk_buff **pskb,
	const struct net_device *in,
	const struct net_device *out,
	int (okfn)(struct sk_buff ))
	{
	#ifdef CONFIG_XFRM
	struct nf_conn *ct;
	enum ip_conntrack_info ctinfo;
	#endif
	unsigned int ret;

	/* root is playing with raw sockets. */
	if ((*pskb)->len < sizeof(struct iphdr) \|\|
	(pskb)->nh.iph->ihl 4 < sizeof(struct iphdr))
	return NF_ACCEPT;

	ret = nf_nat_fn(hooknum, pskb, in, out, okfn);
	#ifdef CONFIG_XFRM
	if (ret != NF_DROP && ret != NF_STOLEN &&
	(ct = nf_ct_get(*pskb, &ctinfo)) != NULL) {
	enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);

	if (ct->tuplehash[dir].tuple.src.u3.ip !=
	ct->tuplehash[!dir].tuple.dst.u3.ip
	\|\| ct->tuplehash[dir].tuple.src.u.all !=
	ct->tuplehash[!dir].tuple.dst.u.all
	)
	return ip_xfrm_me_harder(pskb) == 0 ? ret : NF_DROP;
	}
	#endif
	return ret;
	}

	static unsigned int
	nf_nat_local_fn(unsigned int hooknum,
	struct sk_buff **pskb,
	const struct net_device *in,
	const struct net_device *out,
	int (okfn)(struct sk_buff ))
	{
	struct nf_conn *ct;
	enum ip_conntrack_info ctinfo;
	unsigned int ret;

	/* root is playing with raw sockets. */
	if ((*pskb)->len < sizeof(struct iphdr) \|\|
	(pskb)->nh.iph->ihl 4 < sizeof(struct iphdr))
	return NF_ACCEPT;

	ret = nf_nat_fn(hooknum, pskb, in, out, okfn);
	if (ret != NF_DROP && ret != NF_STOLEN &&
	(ct = nf_ct_get(*pskb, &ctinfo)) != NULL) {
	enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);

	if (ct->tuplehash[dir].tuple.dst.u3.ip !=
	ct->tuplehash[!dir].tuple.src.u3.ip
	#ifdef CONFIG_XFRM
	\|\| ct->tuplehash[dir].tuple.dst.u.all !=
	ct->tuplehash[!dir].tuple.src.u.all
	#endif
	)
	if (ip_route_me_harder(pskb, RTN_UNSPEC))
	ret = NF_DROP;
	}
	return ret;
	}

	static unsigned int
	nf_nat_adjust(unsigned int hooknum,
	struct sk_buff **pskb,
	const struct net_device *in,
	const struct net_device *out,
	int (okfn)(struct sk_buff ))
	{
	struct nf_conn *ct;
	enum ip_conntrack_info ctinfo;

	ct = nf_ct_get(*pskb, &ctinfo);
	if (ct && test_bit(IPS_SEQ_ADJUST_BIT, &ct->status)) {
	DEBUGP("nf_nat_standalone: adjusting sequence number\n");
	if (!nf_nat_seq_adjust(pskb, ct, ctinfo))
	return NF_DROP;
	}
	return NF_ACCEPT;
	}

	/* We must be after connection tracking and before packet filtering. */

	static struct nf_hook_ops nf_nat_ops[] = {
	/* Before packet filtering, change destination */
	{
	.hook = nf_nat_in,
	.owner = THIS_MODULE,
	.pf = PF_INET,
	.hooknum = NF_IP_PRE_ROUTING,
	.priority = NF_IP_PRI_NAT_DST,
	},
	/* After packet filtering, change source */
	{
	.hook = nf_nat_out,
	.owner = THIS_MODULE,
	.pf = PF_INET,
	.hooknum = NF_IP_POST_ROUTING,
	.priority = NF_IP_PRI_NAT_SRC,
	},
	/* After conntrack, adjust sequence number */
	{
	.hook = nf_nat_adjust,
	.owner = THIS_MODULE,
	.pf = PF_INET,
	.hooknum = NF_IP_POST_ROUTING,
	.priority = NF_IP_PRI_NAT_SEQ_ADJUST,
	},
	/* Before packet filtering, change destination */
	{
	.hook = nf_nat_local_fn,
	.owner = THIS_MODULE,
	.pf = PF_INET,
	.hooknum = NF_IP_LOCAL_OUT,
	.priority = NF_IP_PRI_NAT_DST,
	},
	/* After packet filtering, change source */
	{
	.hook = nf_nat_fn,
	.owner = THIS_MODULE,
	.pf = PF_INET,
	.hooknum = NF_IP_LOCAL_IN,
	.priority = NF_IP_PRI_NAT_SRC,
	},
	/* After conntrack, adjust sequence number */
	{
	.hook = nf_nat_adjust,
	.owner = THIS_MODULE,
	.pf = PF_INET,
	.hooknum = NF_IP_LOCAL_IN,
	.priority = NF_IP_PRI_NAT_SEQ_ADJUST,
	},
	};

	static int __init nf_nat_standalone_init(void)
	{
	int size, ret = 0;

	need_conntrack();

	size = ALIGN(sizeof(struct nf_conn), __alignof__(struct nf_conn_nat)) +
	sizeof(struct nf_conn_nat);
	ret = nf_conntrack_register_cache(NF_CT_F_NAT, "nf_nat:base", size);
	if (ret < 0) {
	printk(KERN_ERR "nf_nat_init: Unable to create slab cache\n");
	return ret;
	}

	size = ALIGN(size, __alignof__(struct nf_conn_help)) +
	sizeof(struct nf_conn_help);
	ret = nf_conntrack_register_cache(NF_CT_F_NAT\|NF_CT_F_HELP,
	"nf_nat:help", size);
	if (ret < 0) {
	printk(KERN_ERR "nf_nat_init: Unable to create slab cache\n");
	goto cleanup_register_cache;
	}
	#ifdef CONFIG_XFRM
	BUG_ON(ip_nat_decode_session != NULL);
	ip_nat_decode_session = nat_decode_session;
	#endif
	ret = nf_nat_rule_init();
	if (ret < 0) {
	printk("nf_nat_init: can't setup rules.\n");
	goto cleanup_decode_session;
	}
	ret = nf_register_hooks(nf_nat_ops, ARRAY_SIZE(nf_nat_ops));
	if (ret < 0) {
	printk("nf_nat_init: can't register hooks.\n");
	goto cleanup_rule_init;
	}
	nf_nat_module_is_loaded = 1;
	return ret;

	cleanup_rule_init:
	nf_nat_rule_cleanup();
	cleanup_decode_session:
	#ifdef CONFIG_XFRM
	ip_nat_decode_session = NULL;
	synchronize_net();
	#endif
	nf_conntrack_unregister_cache(NF_CT_F_NAT\|NF_CT_F_HELP);
	cleanup_register_cache:
	nf_conntrack_unregister_cache(NF_CT_F_NAT);
	return ret;
	}

	static void __exit nf_nat_standalone_fini(void)
	{
	nf_unregister_hooks(nf_nat_ops, ARRAY_SIZE(nf_nat_ops));
	nf_nat_rule_cleanup();
	nf_nat_module_is_loaded = 0;
	#ifdef CONFIG_XFRM
	ip_nat_decode_session = NULL;
	synchronize_net();
	#endif
	/* Conntrack caches are unregistered in nf_conntrack_cleanup */
	}

	module_init(nf_nat_standalone_init);
	module_exit(nf_nat_standalone_fini);

	MODULE_LICENSE("GPL");
	MODULE_ALIAS("ip_nat");