[NETFILTER]: Add NAT support for nf_conntrack

Add NAT support for nf_conntrack. Joint work of Jozsef Kadlecsik,
Yasuyuki Kozakai, Martin Josefsson and myself.

Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 647 insertions, 0 deletions

diff --git a/net/ipv4/netfilter/nf_nat_core.c b/net/ipv4/netfilter/nf_nat_core.c
new file mode 100644
index 000000000000..86a92272b053
--- /dev/null
+++ b/net/ipv4/netfilter/nf_nat_core.c
@@ -0,0 +1,647 @@
+/* NAT for netfilter; shared with compatibility layer. */
+
+/* (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/module.h>
+#include <linux/types.h>
+#include <linux/timer.h>
+#include <linux/skbuff.h>
+#include <linux/vmalloc.h>
+#include <net/checksum.h>
+#include <net/icmp.h>
+#include <net/ip.h>
+#include <net/tcp.h>  /* For tcp_prot in getorigdst */
+#include <linux/icmp.h>
+#include <linux/udp.h>
+#include <linux/jhash.h>
+
+#include <linux/netfilter_ipv4.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_protocol.h>
+#include <net/netfilter/nf_nat_core.h>
+#include <net/netfilter/nf_nat_helper.h>
+#include <net/netfilter/nf_conntrack_helper.h>
+#include <net/netfilter/nf_conntrack_l3proto.h>
+#include <net/netfilter/nf_conntrack_l4proto.h>
+
+#if 0
+#define DEBUGP printk
+#else
+#define DEBUGP(format, args...)
+#endif
+
+static DEFINE_RWLOCK(nf_nat_lock);
+
+static struct nf_conntrack_l3proto *l3proto = NULL;
+
+/* Calculated at init based on memory size */
+static unsigned int nf_nat_htable_size;
+
+static struct list_head *bysource;
+
+#define MAX_IP_NAT_PROTO 256
+static struct nf_nat_protocol *nf_nat_protos[MAX_IP_NAT_PROTO];
+
+static inline struct nf_nat_protocol *
+__nf_nat_proto_find(u_int8_t protonum)
+{
+	return nf_nat_protos[protonum];
+}
+
+struct nf_nat_protocol *
+nf_nat_proto_find_get(u_int8_t protonum)
+{
+	struct nf_nat_protocol *p;
+
+	/* we need to disable preemption to make sure 'p' doesn't get
+	 * removed until we've grabbed the reference */
+	preempt_disable();
+	p = __nf_nat_proto_find(protonum);
+	if (!try_module_get(p->me))
+		p = &nf_nat_unknown_protocol;
+	preempt_enable();
+
+	return p;
+}
+EXPORT_SYMBOL_GPL(nf_nat_proto_find_get);
+
+void
+nf_nat_proto_put(struct nf_nat_protocol *p)
+{
+	module_put(p->me);
+}
+EXPORT_SYMBOL_GPL(nf_nat_proto_put);
+
+/* We keep an extra hash for each conntrack, for fast searching. */
+static inline unsigned int
+hash_by_src(const struct nf_conntrack_tuple *tuple)
+{
+	/* Original src, to ensure we map it consistently if poss. */
+	return jhash_3words((__force u32)tuple->src.u3.ip, tuple->src.u.all,
+			    tuple->dst.protonum, 0) % nf_nat_htable_size;
+}
+
+/* Noone using conntrack by the time this called. */
+static void nf_nat_cleanup_conntrack(struct nf_conn *conn)
+{
+	struct nf_conn_nat *nat;
+	if (!(conn->status & IPS_NAT_DONE_MASK))
+		return;
+
+	nat = nfct_nat(conn);
+	write_lock_bh(&nf_nat_lock);
+	list_del(&nat->info.bysource);
+	write_unlock_bh(&nf_nat_lock);
+}
+
+/* Is this tuple already taken? (not by us) */
+int
+nf_nat_used_tuple(const struct nf_conntrack_tuple *tuple,
+		  const struct nf_conn *ignored_conntrack)
+{
+	/* Conntrack tracking doesn't keep track of outgoing tuples; only
+	   incoming ones.  NAT means they don't have a fixed mapping,
+	   so we invert the tuple and look for the incoming reply.
+
+	   We could keep a separate hash if this proves too slow. */
+	struct nf_conntrack_tuple reply;
+
+	nf_ct_invert_tuplepr(&reply, tuple);
+	return nf_conntrack_tuple_taken(&reply, ignored_conntrack);
+}
+EXPORT_SYMBOL(nf_nat_used_tuple);
+
+/* If we source map this tuple so reply looks like reply_tuple, will
+ * that meet the constraints of range. */
+static int
+in_range(const struct nf_conntrack_tuple *tuple,
+	 const struct nf_nat_range *range)
+{
+	struct nf_nat_protocol *proto;
+
+	proto = __nf_nat_proto_find(tuple->dst.protonum);
+	/* If we are supposed to map IPs, then we must be in the
+	   range specified, otherwise let this drag us onto a new src IP. */
+	if (range->flags & IP_NAT_RANGE_MAP_IPS) {
+		if (ntohl(tuple->src.u3.ip) < ntohl(range->min_ip) ||
+		    ntohl(tuple->src.u3.ip) > ntohl(range->max_ip))
+			return 0;
+	}
+
+	if (!(range->flags & IP_NAT_RANGE_PROTO_SPECIFIED) ||
+	    proto->in_range(tuple, IP_NAT_MANIP_SRC,
+			    &range->min, &range->max))
+		return 1;
+
+	return 0;
+}
+
+static inline int
+same_src(const struct nf_conn *ct,
+	 const struct nf_conntrack_tuple *tuple)
+{
+	const struct nf_conntrack_tuple *t;
+
+	t = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
+	return (t->dst.protonum == tuple->dst.protonum &&
+		t->src.u3.ip == tuple->src.u3.ip &&
+		t->src.u.all == tuple->src.u.all);
+}
+
+/* Only called for SRC manip */
+static int
+find_appropriate_src(const struct nf_conntrack_tuple *tuple,
+		     struct nf_conntrack_tuple *result,
+		     const struct nf_nat_range *range)
+{
+	unsigned int h = hash_by_src(tuple);
+	struct nf_conn_nat *nat;
+	struct nf_conn *ct;
+
+	read_lock_bh(&nf_nat_lock);
+	list_for_each_entry(nat, &bysource[h], info.bysource) {
+		ct = (struct nf_conn *)((char *)nat - offsetof(struct nf_conn, data));
+		if (same_src(ct, tuple)) {
+			/* Copy source part from reply tuple. */
+			nf_ct_invert_tuplepr(result,
+				       &ct->tuplehash[IP_CT_DIR_REPLY].tuple);
+			result->dst = tuple->dst;
+
+			if (in_range(result, range)) {
+				read_unlock_bh(&nf_nat_lock);
+				return 1;
+			}
+		}
+	}
+	read_unlock_bh(&nf_nat_lock);
+	return 0;
+}
+
+/* For [FUTURE] fragmentation handling, we want the least-used
+   src-ip/dst-ip/proto triple.  Fairness doesn't come into it.  Thus
+   if the range specifies 1.2.3.4 ports 10000-10005 and 1.2.3.5 ports
+   1-65535, we don't do pro-rata allocation based on ports; we choose
+   the ip with the lowest src-ip/dst-ip/proto usage.
+*/
+static void
+find_best_ips_proto(struct nf_conntrack_tuple *tuple,
+		    const struct nf_nat_range *range,
+		    const struct nf_conn *ct,
+		    enum nf_nat_manip_type maniptype)
+{
+	__be32 *var_ipp;
+	/* Host order */
+	u_int32_t minip, maxip, j;
+
+	/* No IP mapping?  Do nothing. */
+	if (!(range->flags & IP_NAT_RANGE_MAP_IPS))
+		return;
+
+	if (maniptype == IP_NAT_MANIP_SRC)
+		var_ipp = &tuple->src.u3.ip;
+	else
+		var_ipp = &tuple->dst.u3.ip;
+
+	/* Fast path: only one choice. */
+	if (range->min_ip == range->max_ip) {
+		*var_ipp = range->min_ip;
+		return;
+	}
+
+	/* Hashing source and destination IPs gives a fairly even
+	 * spread in practice (if there are a small number of IPs
+	 * involved, there usually aren't that many connections
+	 * anyway).  The consistency means that servers see the same
+	 * client coming from the same IP (some Internet Banking sites
+	 * like this), even across reboots. */
+	minip = ntohl(range->min_ip);
+	maxip = ntohl(range->max_ip);
+	j = jhash_2words((__force u32)tuple->src.u3.ip,
+			 (__force u32)tuple->dst.u3.ip, 0);
+	*var_ipp = htonl(minip + j % (maxip - minip + 1));
+}
+
+/* Manipulate the tuple into the range given.  For NF_IP_POST_ROUTING,
+ * we change the source to map into the range.  For NF_IP_PRE_ROUTING
+ * and NF_IP_LOCAL_OUT, we change the destination to map into the
+ * range.  It might not be possible to get a unique tuple, but we try.
+ * At worst (or if we race), we will end up with a final duplicate in
+ * __ip_conntrack_confirm and drop the packet. */
+static void
+get_unique_tuple(struct nf_conntrack_tuple *tuple,
+		 const struct nf_conntrack_tuple *orig_tuple,
+		 const struct nf_nat_range *range,
+		 struct nf_conn *ct,
+		 enum nf_nat_manip_type maniptype)
+{
+	struct nf_nat_protocol *proto;
+
+	/* 1) If this srcip/proto/src-proto-part is currently mapped,
+	   and that same mapping gives a unique tuple within the given
+	   range, use that.
+
+	   This is only required for source (ie. NAT/masq) mappings.
+	   So far, we don't do local source mappings, so multiple
+	   manips not an issue.  */
+	if (maniptype == IP_NAT_MANIP_SRC) {
+		if (find_appropriate_src(orig_tuple, tuple, range)) {
+			DEBUGP("get_unique_tuple: Found current src map\n");
+			if (!nf_nat_used_tuple(tuple, ct))
+				return;
+		}
+	}
+
+	/* 2) Select the least-used IP/proto combination in the given
+	   range. */
+	*tuple = *orig_tuple;
+	find_best_ips_proto(tuple, range, ct, maniptype);
+
+	/* 3) The per-protocol part of the manip is made to map into
+	   the range to make a unique tuple. */
+
+	proto = nf_nat_proto_find_get(orig_tuple->dst.protonum);
+
+	/* Only bother mapping if it's not already in range and unique */
+	if ((!(range->flags & IP_NAT_RANGE_PROTO_SPECIFIED) ||
+	     proto->in_range(tuple, maniptype, &range->min, &range->max)) &&
+	    !nf_nat_used_tuple(tuple, ct)) {
+		nf_nat_proto_put(proto);
+		return;
+	}
+
+	/* Last change: get protocol to try to obtain unique tuple. */
+	proto->unique_tuple(tuple, range, maniptype, ct);
+
+	nf_nat_proto_put(proto);
+}
+
+unsigned int
+nf_nat_setup_info(struct nf_conn *ct,
+		  const struct nf_nat_range *range,
+		  unsigned int hooknum)
+{
+	struct nf_conntrack_tuple curr_tuple, new_tuple;
+	struct nf_conn_nat *nat = nfct_nat(ct);
+	struct nf_nat_info *info = &nat->info;
+	int have_to_hash = !(ct->status & IPS_NAT_DONE_MASK);
+	enum nf_nat_manip_type maniptype = HOOK2MANIP(hooknum);
+
+	NF_CT_ASSERT(hooknum == NF_IP_PRE_ROUTING ||
+		     hooknum == NF_IP_POST_ROUTING ||
+		     hooknum == NF_IP_LOCAL_IN ||
+		     hooknum == NF_IP_LOCAL_OUT);
+	BUG_ON(nf_nat_initialized(ct, maniptype));
+
+	/* What we've got will look like inverse of reply. Normally
+	   this is what is in the conntrack, except for prior
+	   manipulations (future optimization: if num_manips == 0,
+	   orig_tp =
+	   conntrack->tuplehash[IP_CT_DIR_ORIGINAL].tuple) */
+	nf_ct_invert_tuplepr(&curr_tuple,
+			     &ct->tuplehash[IP_CT_DIR_REPLY].tuple);
+
+	get_unique_tuple(&new_tuple, &curr_tuple, range, ct, maniptype);
+
+	if (!nf_ct_tuple_equal(&new_tuple, &curr_tuple)) {
+		struct nf_conntrack_tuple reply;
+
+		/* Alter conntrack table so will recognize replies. */
+		nf_ct_invert_tuplepr(&reply, &new_tuple);
+		nf_conntrack_alter_reply(ct, &reply);
+
+		/* Non-atomic: we own this at the moment. */
+		if (maniptype == IP_NAT_MANIP_SRC)
+			ct->status |= IPS_SRC_NAT;
+		else
+			ct->status |= IPS_DST_NAT;
+	}
+
+	/* Place in source hash if this is the first time. */
+	if (have_to_hash) {
+		unsigned int srchash;
+
+		srchash = hash_by_src(&ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple);
+		write_lock_bh(&nf_nat_lock);
+		list_add(&info->bysource, &bysource[srchash]);
+		write_unlock_bh(&nf_nat_lock);
+	}
+
+	/* It's done. */
+	if (maniptype == IP_NAT_MANIP_DST)
+		set_bit(IPS_DST_NAT_DONE_BIT, &ct->status);
+	else
+		set_bit(IPS_SRC_NAT_DONE_BIT, &ct->status);
+
+	return NF_ACCEPT;
+}
+EXPORT_SYMBOL(nf_nat_setup_info);
+
+/* Returns true if succeeded. */
+static int
+manip_pkt(u_int16_t proto,
+	  struct sk_buff **pskb,
+	  unsigned int iphdroff,
+	  const struct nf_conntrack_tuple *target,
+	  enum nf_nat_manip_type maniptype)
+{
+	struct iphdr *iph;
+	struct nf_nat_protocol *p;
+
+	if (!skb_make_writable(pskb, iphdroff + sizeof(*iph)))
+		return 0;
+
+	iph = (void *)(*pskb)->data + iphdroff;
+
+	/* Manipulate protcol part. */
+	p = nf_nat_proto_find_get(proto);
+	if (!p->manip_pkt(pskb, iphdroff, target, maniptype)) {
+		nf_nat_proto_put(p);
+		return 0;
+	}
+	nf_nat_proto_put(p);
+
+	iph = (void *)(*pskb)->data + iphdroff;
+
+	if (maniptype == IP_NAT_MANIP_SRC) {
+		nf_csum_replace4(&iph->check, iph->saddr, target->src.u3.ip);
+		iph->saddr = target->src.u3.ip;
+	} else {
+		nf_csum_replace4(&iph->check, iph->daddr, target->dst.u3.ip);
+		iph->daddr = target->dst.u3.ip;
+	}
+	return 1;
+}
+
+/* Do packet manipulations according to nf_nat_setup_info. */
+unsigned int nf_nat_packet(struct nf_conn *ct,
+			   enum ip_conntrack_info ctinfo,
+			   unsigned int hooknum,
+			   struct sk_buff **pskb)
+{
+	enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
+	unsigned long statusbit;
+	enum nf_nat_manip_type mtype = HOOK2MANIP(hooknum);
+
+	if (mtype == IP_NAT_MANIP_SRC)
+		statusbit = IPS_SRC_NAT;
+	else
+		statusbit = IPS_DST_NAT;
+
+	/* Invert if this is reply dir. */
+	if (dir == IP_CT_DIR_REPLY)
+		statusbit ^= IPS_NAT_MASK;
+
+	/* Non-atomic: these bits don't change. */
+	if (ct->status & statusbit) {
+		struct nf_conntrack_tuple target;
+
+		/* We are aiming to look like inverse of other direction. */
+		nf_ct_invert_tuplepr(&target, &ct->tuplehash[!dir].tuple);
+
+		if (!manip_pkt(target.dst.protonum, pskb, 0, &target, mtype))
+			return NF_DROP;
+	}
+	return NF_ACCEPT;
+}
+EXPORT_SYMBOL_GPL(nf_nat_packet);
+
+/* Dir is direction ICMP is coming from (opposite to packet it contains) */
+int nf_nat_icmp_reply_translation(struct nf_conn *ct,
+				  enum ip_conntrack_info ctinfo,
+				  unsigned int hooknum,
+				  struct sk_buff **pskb)
+{
+	struct {
+		struct icmphdr icmp;
+		struct iphdr ip;
+	} *inside;
+	struct nf_conntrack_tuple inner, target;
+	int hdrlen = (*pskb)->nh.iph->ihl * 4;
+	enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
+	unsigned long statusbit;
+	enum nf_nat_manip_type manip = HOOK2MANIP(hooknum);
+
+	if (!skb_make_writable(pskb, hdrlen + sizeof(*inside)))
+		return 0;
+
+	inside = (void *)(*pskb)->data + (*pskb)->nh.iph->ihl*4;
+
+	/* We're actually going to mangle it beyond trivial checksum
+	   adjustment, so make sure the current checksum is correct. */
+	if (nf_ip_checksum(*pskb, hooknum, hdrlen, 0))
+		return 0;
+
+	/* Must be RELATED */
+	NF_CT_ASSERT((*pskb)->nfctinfo == IP_CT_RELATED ||
+		     (*pskb)->nfctinfo == IP_CT_RELATED+IP_CT_IS_REPLY);
+
+	/* Redirects on non-null nats must be dropped, else they'll
+           start talking to each other without our translation, and be
+           confused... --RR */
+	if (inside->icmp.type == ICMP_REDIRECT) {
+		/* If NAT isn't finished, assume it and drop. */
+		if ((ct->status & IPS_NAT_DONE_MASK) != IPS_NAT_DONE_MASK)
+			return 0;
+
+		if (ct->status & IPS_NAT_MASK)
+			return 0;
+	}
+
+	DEBUGP("icmp_reply_translation: translating error %p manp %u dir %s\n",
+	       *pskb, manip, dir == IP_CT_DIR_ORIGINAL ? "ORIG" : "REPLY");
+
+	if (!nf_ct_get_tuple(*pskb,
+			     (*pskb)->nh.iph->ihl*4 + sizeof(struct icmphdr),
+			     (*pskb)->nh.iph->ihl*4 +
+	                     sizeof(struct icmphdr) + inside->ip.ihl*4,
+	                     (u_int16_t)AF_INET,
+	                     inside->ip.protocol,
+	                     &inner,
+	                     l3proto,
+			     __nf_ct_l4proto_find((u_int16_t)PF_INET,
+			     			  inside->ip.protocol)))
+		return 0;
+
+	/* Change inner back to look like incoming packet.  We do the
+	   opposite manip on this hook to normal, because it might not
+	   pass all hooks (locally-generated ICMP).  Consider incoming
+	   packet: PREROUTING (DST manip), routing produces ICMP, goes
+	   through POSTROUTING (which must correct the DST manip). */
+	if (!manip_pkt(inside->ip.protocol, pskb,
+		       (*pskb)->nh.iph->ihl*4 + sizeof(inside->icmp),
+		       &ct->tuplehash[!dir].tuple,
+		       !manip))
+		return 0;
+
+	if ((*pskb)->ip_summed != CHECKSUM_PARTIAL) {
+		/* Reloading "inside" here since manip_pkt inner. */
+		inside = (void *)(*pskb)->data + (*pskb)->nh.iph->ihl*4;
+		inside->icmp.checksum = 0;
+		inside->icmp.checksum =
+			csum_fold(skb_checksum(*pskb, hdrlen,
+					       (*pskb)->len - hdrlen, 0));
+	}
+
+	/* Change outer to look the reply to an incoming packet
+	 * (proto 0 means don't invert per-proto part). */
+	if (manip == IP_NAT_MANIP_SRC)
+		statusbit = IPS_SRC_NAT;
+	else
+		statusbit = IPS_DST_NAT;
+
+	/* Invert if this is reply dir. */
+	if (dir == IP_CT_DIR_REPLY)
+		statusbit ^= IPS_NAT_MASK;
+
+	if (ct->status & statusbit) {
+		nf_ct_invert_tuplepr(&target, &ct->tuplehash[!dir].tuple);
+		if (!manip_pkt(0, pskb, 0, &target, manip))
+			return 0;
+	}
+
+	return 1;
+}
+EXPORT_SYMBOL_GPL(nf_nat_icmp_reply_translation);
+
+/* Protocol registration. */
+int nf_nat_protocol_register(struct nf_nat_protocol *proto)
+{
+	int ret = 0;
+
+	write_lock_bh(&nf_nat_lock);
+	if (nf_nat_protos[proto->protonum] != &nf_nat_unknown_protocol) {
+		ret = -EBUSY;
+		goto out;
+	}
+	nf_nat_protos[proto->protonum] = proto;
+ out:
+	write_unlock_bh(&nf_nat_lock);
+	return ret;
+}
+EXPORT_SYMBOL(nf_nat_protocol_register);
+
+/* Noone stores the protocol anywhere; simply delete it. */
+void nf_nat_protocol_unregister(struct nf_nat_protocol *proto)
+{
+	write_lock_bh(&nf_nat_lock);
+	nf_nat_protos[proto->protonum] = &nf_nat_unknown_protocol;
+	write_unlock_bh(&nf_nat_lock);
+
+	/* Someone could be still looking at the proto in a bh. */
+	synchronize_net();
+}
+EXPORT_SYMBOL(nf_nat_protocol_unregister);
+
+#if defined(CONFIG_IP_NF_CONNTRACK_NETLINK) || \
+    defined(CONFIG_IP_NF_CONNTRACK_NETLINK_MODULE)
+int
+nf_nat_port_range_to_nfattr(struct sk_buff *skb,
+			    const struct nf_nat_range *range)
+{
+	NFA_PUT(skb, CTA_PROTONAT_PORT_MIN, sizeof(__be16),
+		&range->min.tcp.port);
+	NFA_PUT(skb, CTA_PROTONAT_PORT_MAX, sizeof(__be16),
+		&range->max.tcp.port);
+
+	return 0;
+
+nfattr_failure:
+	return -1;
+}
+EXPORT_SYMBOL_GPL(nf_nat_port_nfattr_to_range);
+
+int
+nf_nat_port_nfattr_to_range(struct nfattr *tb[], struct nf_nat_range *range)
+{
+	int ret = 0;
+
+	/* we have to return whether we actually parsed something or not */
+
+	if (tb[CTA_PROTONAT_PORT_MIN-1]) {
+		ret = 1;
+		range->min.tcp.port =
+			*(__be16 *)NFA_DATA(tb[CTA_PROTONAT_PORT_MIN-1]);
+	}
+
+	if (!tb[CTA_PROTONAT_PORT_MAX-1]) {
+		if (ret)
+			range->max.tcp.port = range->min.tcp.port;
+	} else {
+		ret = 1;
+		range->max.tcp.port =
+			*(__be16 *)NFA_DATA(tb[CTA_PROTONAT_PORT_MAX-1]);
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(nf_nat_port_range_to_nfattr);
+#endif
+
+static int __init nf_nat_init(void)
+{
+	size_t i;
+
+	/* Leave them the same for the moment. */
+	nf_nat_htable_size = nf_conntrack_htable_size;
+
+	/* One vmalloc for both hash tables */
+	bysource = vmalloc(sizeof(struct list_head) * nf_nat_htable_size);
+	if (!bysource)
+		return -ENOMEM;
+
+	/* Sew in builtin protocols. */
+	write_lock_bh(&nf_nat_lock);
+	for (i = 0; i < MAX_IP_NAT_PROTO; i++)
+		nf_nat_protos[i] = &nf_nat_unknown_protocol;
+	nf_nat_protos[IPPROTO_TCP] = &nf_nat_protocol_tcp;
+	nf_nat_protos[IPPROTO_UDP] = &nf_nat_protocol_udp;
+	nf_nat_protos[IPPROTO_ICMP] = &nf_nat_protocol_icmp;
+	write_unlock_bh(&nf_nat_lock);
+
+	for (i = 0; i < nf_nat_htable_size; i++) {
+		INIT_LIST_HEAD(&bysource[i]);
+	}
+
+	/* FIXME: Man, this is a hack.  <SIGH> */
+	NF_CT_ASSERT(nf_conntrack_destroyed == NULL);
+	nf_conntrack_destroyed = &nf_nat_cleanup_conntrack;
+
+	/* Initialize fake conntrack so that NAT will skip it */
+	nf_conntrack_untracked.status |= IPS_NAT_DONE_MASK;
+
+	l3proto = nf_ct_l3proto_find_get((u_int16_t)AF_INET);
+	return 0;
+}
+
+/* Clear NAT section of all conntracks, in case we're loaded again. */
+static int clean_nat(struct nf_conn *i, void *data)
+{
+	struct nf_conn_nat *nat = nfct_nat(i);
+
+	if (!nat)
+		return 0;
+	memset(nat, 0, sizeof(nat));
+	i->status &= ~(IPS_NAT_MASK | IPS_NAT_DONE_MASK | IPS_SEQ_ADJUST);
+	return 0;
+}
+
+static void __exit nf_nat_cleanup(void)
+{
+	nf_ct_iterate_cleanup(&clean_nat, NULL);
+	nf_conntrack_destroyed = NULL;
+	vfree(bysource);
+	nf_ct_l3proto_put(l3proto);
+}
+
+MODULE_LICENSE("GPL");
+
+module_init(nf_nat_init);
+module_exit(nf_nat_cleanup);