xref: /linux-2.4.37.9/net/ipv4/netfilter/ip_conntrack_core.c

/* Connection state tracking for netfilter.  This is separated from,
   but required by, the NAT layer; it can also be used by an iptables
   extension. */

/* (c) 1999 Paul `Rusty' Russell.  Licenced under the GNU General
 * Public Licence.
 *
 * 23 Apr 2001: Harald Welte <laforge@gnumonks.org>
 * 	- new API and handling of conntrack/nat helpers
 * 	- now capable of multiple expectations for one master
 * 16 Jul 2002: Harald Welte <laforge@gnumonks.org>
 * 	- add usage/reference counts to ip_conntrack_expect
 *	- export ip_conntrack[_expect]_{find_get,put} functions
 * */

#include <linux/version.h>
#include <linux/config.h>
#include <linux/types.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 <linux/vmalloc.h>
#include <linux/brlock.h>
#include <net/checksum.h>
#include <linux/stddef.h>
#include <linux/sysctl.h>
#include <linux/slab.h>
#include <linux/random.h>
#include <linux/jhash.h>
/* For ERR_PTR().  Yeah, I know... --RR */
#include <linux/fs.h>

/* This rwlock protects the main hash table, protocol/helper/expected
   registrations, conntrack timers*/
#define ASSERT_READ_LOCK(x) MUST_BE_READ_LOCKED(&ip_conntrack_lock)
#define ASSERT_WRITE_LOCK(x) MUST_BE_WRITE_LOCKED(&ip_conntrack_lock)

#include <linux/netfilter_ipv4/ip_conntrack.h>
#include <linux/netfilter_ipv4/ip_conntrack_protocol.h>
#include <linux/netfilter_ipv4/ip_conntrack_helper.h>
#include <linux/netfilter_ipv4/ip_conntrack_core.h>
#include <linux/netfilter_ipv4/listhelp.h>

#define IP_CONNTRACK_VERSION	"2.1"

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

DECLARE_RWLOCK(ip_conntrack_lock);
DECLARE_RWLOCK(ip_conntrack_expect_tuple_lock);

void (*ip_conntrack_destroyed)(struct ip_conntrack *conntrack) = NULL;
LIST_HEAD(ip_conntrack_expect_list);
LIST_HEAD(protocol_list);
static LIST_HEAD(helpers);
unsigned int ip_conntrack_htable_size = 0;
int ip_conntrack_max = 0;
static atomic_t ip_conntrack_count = ATOMIC_INIT(0);
struct list_head *ip_conntrack_hash;
static kmem_cache_t *ip_conntrack_cachep;
static LIST_HEAD(unconfirmed);

extern struct ip_conntrack_protocol ip_conntrack_generic_protocol;

static inline int proto_cmpfn(const struct ip_conntrack_protocol *curr,
			      u_int8_t protocol)
{
	return protocol == curr->proto;
}

struct ip_conntrack_protocol *__ip_ct_find_proto(u_int8_t protocol)
{
	struct ip_conntrack_protocol *p;

	MUST_BE_READ_LOCKED(&ip_conntrack_lock);
	p = LIST_FIND(&protocol_list, proto_cmpfn,
		      struct ip_conntrack_protocol *, protocol);
	if (!p)
		p = &ip_conntrack_generic_protocol;

	return p;
}

struct ip_conntrack_protocol *ip_ct_find_proto(u_int8_t protocol)
{
	struct ip_conntrack_protocol *p;

	READ_LOCK(&ip_conntrack_lock);
	p = __ip_ct_find_proto(protocol);
	READ_UNLOCK(&ip_conntrack_lock);
	return p;
}

inline void
ip_conntrack_put(struct ip_conntrack *ct)
{
	IP_NF_ASSERT(ct);
	IP_NF_ASSERT(ct->infos[0].master);
	/* nf_conntrack_put wants to go via an info struct, so feed it
           one at random. */
	nf_conntrack_put(&ct->infos[0]);
}

static int ip_conntrack_hash_rnd_initted;
static unsigned int ip_conntrack_hash_rnd;

static u_int32_t
hash_conntrack(const struct ip_conntrack_tuple *tuple)
{
#if 0
	dump_tuple(tuple);
#endif
	return (jhash_3words(tuple->src.ip,
	                     (tuple->dst.ip ^ tuple->dst.protonum),
	                     (tuple->src.u.all | (tuple->dst.u.all << 16)),
	                     ip_conntrack_hash_rnd) % ip_conntrack_htable_size);
}

inline int
ip_ct_get_tuple(const struct iphdr *iph, size_t len,
                struct ip_conntrack_tuple *tuple,
                struct ip_conntrack_protocol *protocol)
{
	int ret;

	/* Never happen */
	if (iph->frag_off & htons(IP_OFFSET)) {
		printk("ip_conntrack_core: Frag of proto %u.\n",
		       iph->protocol);
		return 0;
	}
	/* Guarantee 8 protocol bytes: if more wanted, use len param */
	else if (iph->ihl * 4 + 8 > len)
		return 0;

	tuple->src.ip = iph->saddr;
	tuple->dst.ip = iph->daddr;
	tuple->dst.protonum = iph->protocol;

	ret = protocol->pkt_to_tuple((u_int32_t *)iph + iph->ihl,
				     len - 4*iph->ihl,
				     tuple);
	return ret;
}

static int
invert_tuple(struct ip_conntrack_tuple *inverse,
	     const struct ip_conntrack_tuple *orig,
	     const struct ip_conntrack_protocol *protocol)
{
	inverse->src.ip = orig->dst.ip;
	inverse->dst.ip = orig->src.ip;
	inverse->dst.protonum = orig->dst.protonum;

	return protocol->invert_tuple(inverse, orig);
}


/* ip_conntrack_expect helper functions */

/* Compare tuple parts depending on mask. */
static inline int expect_cmp(const struct ip_conntrack_expect *i,
			     const struct ip_conntrack_tuple *tuple)
{
	MUST_BE_READ_LOCKED(&ip_conntrack_expect_tuple_lock);
	return ip_ct_tuple_mask_cmp(tuple, &i->tuple, &i->mask);
}

static void
destroy_expect(struct ip_conntrack_expect *exp)
{
	DEBUGP("destroy_expect(%p) use=%d\n", exp, atomic_read(&exp->use));
	IP_NF_ASSERT(atomic_read(&exp->use) == 0);
	IP_NF_ASSERT(!timer_pending(&exp->timeout));

	kfree(exp);
}

inline void ip_conntrack_expect_put(struct ip_conntrack_expect *exp)
{
	IP_NF_ASSERT(exp);

	if (atomic_dec_and_test(&exp->use)) {
		/* usage count dropped to zero */
		destroy_expect(exp);
	}
}

static inline struct ip_conntrack_expect *
__ip_ct_expect_find(const struct ip_conntrack_tuple *tuple)
{
	MUST_BE_READ_LOCKED(&ip_conntrack_lock);
	MUST_BE_READ_LOCKED(&ip_conntrack_expect_tuple_lock);
	return LIST_FIND(&ip_conntrack_expect_list, expect_cmp,
			 struct ip_conntrack_expect *, tuple);
}

/* Find a expectation corresponding to a tuple. */
struct ip_conntrack_expect *
ip_conntrack_expect_find_get(const struct ip_conntrack_tuple *tuple)
{
	struct ip_conntrack_expect *exp;

	READ_LOCK(&ip_conntrack_lock);
	READ_LOCK(&ip_conntrack_expect_tuple_lock);
	exp = __ip_ct_expect_find(tuple);
	if (exp)
		atomic_inc(&exp->use);
	READ_UNLOCK(&ip_conntrack_expect_tuple_lock);
	READ_UNLOCK(&ip_conntrack_lock);

	return exp;
}

/* remove one specific expectation from all lists and drop refcount,
 * does _NOT_ delete the timer. */
static void __unexpect_related(struct ip_conntrack_expect *expect)
{
	DEBUGP("unexpect_related(%p)\n", expect);
	MUST_BE_WRITE_LOCKED(&ip_conntrack_lock);

	/* we're not allowed to unexpect a confirmed expectation! */
	IP_NF_ASSERT(!expect->sibling);

	/* delete from global and local lists */
	list_del(&expect->list);
	list_del(&expect->expected_list);

	/* decrement expect-count of master conntrack */
	if (expect->expectant)
		expect->expectant->expecting--;

	ip_conntrack_expect_put(expect);
}

/* remove one specific expecatation from all lists, drop refcount
 * and expire timer.
 * This function can _NOT_ be called for confirmed expects! */
static void unexpect_related(struct ip_conntrack_expect *expect)
{
	IP_NF_ASSERT(expect->expectant);
	IP_NF_ASSERT(expect->expectant->helper);
	/* if we are supposed to have a timer, but we can't delete
	 * it: race condition.  __unexpect_related will
	 * be calledd by timeout function */
	if (expect->expectant->helper->timeout
	    && !del_timer(&expect->timeout))
		return;

	__unexpect_related(expect);
}

/* delete all unconfirmed expectations for this conntrack */
static void remove_expectations(struct ip_conntrack *ct, int drop_refcount)
{
	struct list_head *exp_entry, *next;
	struct ip_conntrack_expect *exp;

	DEBUGP("remove_expectations(%p)\n", ct);

	list_for_each_safe(exp_entry, next, &ct->sibling_list) {
		exp = list_entry(exp_entry, struct ip_conntrack_expect,
				 expected_list);

		/* we skip established expectations, as we want to delete
		 * the un-established ones only */
		if (exp->sibling) {
			DEBUGP("remove_expectations: skipping established %p of %p\n", exp->sibling, ct);
			if (drop_refcount) {
				/* Indicate that this expectations parent is dead */
				ip_conntrack_put(exp->expectant);
				exp->expectant = NULL;
			}
			continue;
		}

		IP_NF_ASSERT(list_inlist(&ip_conntrack_expect_list, exp));
		IP_NF_ASSERT(exp->expectant == ct);

		/* delete expectation from global and private lists */
		unexpect_related(exp);
	}
}

static void
clean_from_lists(struct ip_conntrack *ct)
{
	unsigned int ho, hr;

	DEBUGP("clean_from_lists(%p)\n", ct);
	MUST_BE_WRITE_LOCKED(&ip_conntrack_lock);

	ho = hash_conntrack(&ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple);
	hr = hash_conntrack(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
	LIST_DELETE(&ip_conntrack_hash[ho], &ct->tuplehash[IP_CT_DIR_ORIGINAL]);
	LIST_DELETE(&ip_conntrack_hash[hr], &ct->tuplehash[IP_CT_DIR_REPLY]);

	/* Destroy all un-established, pending expectations */
	remove_expectations(ct, 1);
}

static void
destroy_conntrack(struct nf_conntrack *nfct)
{
	struct ip_conntrack *ct = (struct ip_conntrack *)nfct, *master = NULL;
	struct ip_conntrack_protocol *proto;

	DEBUGP("destroy_conntrack(%p)\n", ct);
	IP_NF_ASSERT(atomic_read(&nfct->use) == 0);
	IP_NF_ASSERT(!timer_pending(&ct->timeout));

	/* To make sure we don't get any weird locking issues here:
	 * destroy_conntrack() MUST NOT be called with a write lock
	 * to ip_conntrack_lock!!! -HW */
	proto = ip_ct_find_proto(ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.protonum);
	if (proto && proto->destroy)
		proto->destroy(ct);

	if (ip_conntrack_destroyed)
		ip_conntrack_destroyed(ct);

	WRITE_LOCK(&ip_conntrack_lock);
	/* Make sure don't leave any orphaned expectations lying around */
	if (ct->expecting)
		remove_expectations(ct, 1);

	/* We overload first tuple to link into unconfirmed list. */
	if (!is_confirmed(ct)) {
		BUG_ON(list_empty(&ct->tuplehash[IP_CT_DIR_ORIGINAL].list));
		list_del(&ct->tuplehash[IP_CT_DIR_ORIGINAL].list);
	}

	/* Delete our master expectation */
	if (ct->master) {
		if (ct->master->expectant) {
			/* can't call __unexpect_related here,
			 * since it would screw up expect_list */
			list_del(&ct->master->expected_list);
			master = ct->master->expectant;
		}
		kfree(ct->master);
	}
	WRITE_UNLOCK(&ip_conntrack_lock);

	if (master)
		ip_conntrack_put(master);

	DEBUGP("destroy_conntrack: returning ct=%p to slab\n", ct);
	kmem_cache_free(ip_conntrack_cachep, ct);
	atomic_dec(&ip_conntrack_count);
}

static void death_by_timeout(unsigned long ul_conntrack)
{
	struct ip_conntrack *ct = (void *)ul_conntrack;

	WRITE_LOCK(&ip_conntrack_lock);
	clean_from_lists(ct);
	WRITE_UNLOCK(&ip_conntrack_lock);
	ip_conntrack_put(ct);
}

static inline int
conntrack_tuple_cmp(const struct ip_conntrack_tuple_hash *i,
		    const struct ip_conntrack_tuple *tuple,
		    const struct ip_conntrack *ignored_conntrack)
{
	MUST_BE_READ_LOCKED(&ip_conntrack_lock);
	return i->ctrack != ignored_conntrack
		&& ip_ct_tuple_equal(tuple, &i->tuple);
}

static struct ip_conntrack_tuple_hash *
__ip_conntrack_find(const struct ip_conntrack_tuple *tuple,
		    const struct ip_conntrack *ignored_conntrack)
{
	struct ip_conntrack_tuple_hash *h;
	unsigned int hash = hash_conntrack(tuple);

	MUST_BE_READ_LOCKED(&ip_conntrack_lock);
	h = LIST_FIND(&ip_conntrack_hash[hash],
		      conntrack_tuple_cmp,
		      struct ip_conntrack_tuple_hash *,
		      tuple, ignored_conntrack);
	return h;
}

/* Find a connection corresponding to a tuple. */
struct ip_conntrack_tuple_hash *
ip_conntrack_find_get(const struct ip_conntrack_tuple *tuple,
		      const struct ip_conntrack *ignored_conntrack)
{
	struct ip_conntrack_tuple_hash *h;

	READ_LOCK(&ip_conntrack_lock);
	h = __ip_conntrack_find(tuple, ignored_conntrack);
	if (h)
		atomic_inc(&h->ctrack->ct_general.use);
	READ_UNLOCK(&ip_conntrack_lock);

	return h;
}

static inline struct ip_conntrack *
__ip_conntrack_get(struct nf_ct_info *nfct, enum ip_conntrack_info *ctinfo)
{
	struct ip_conntrack *ct
		= (struct ip_conntrack *)nfct->master;

	/* ctinfo is the index of the nfct inside the conntrack */
	*ctinfo = nfct - ct->infos;
	IP_NF_ASSERT(*ctinfo >= 0 && *ctinfo < IP_CT_NUMBER);
	return ct;
}

/* Return conntrack and conntrack_info given skb->nfct->master */
struct ip_conntrack *
ip_conntrack_get(struct sk_buff *skb, enum ip_conntrack_info *ctinfo)
{
	if (skb->nfct)
		return __ip_conntrack_get(skb->nfct, ctinfo);
	return NULL;
}

/* Confirm a connection given skb->nfct; places it in hash table */
int
__ip_conntrack_confirm(struct nf_ct_info *nfct)
{
	unsigned int hash, repl_hash;
	struct ip_conntrack *ct;
	enum ip_conntrack_info ctinfo;

	ct = __ip_conntrack_get(nfct, &ctinfo);

	/* ipt_REJECT uses ip_conntrack_attach to attach related
	   ICMP/TCP RST packets in other direction.  Actual packet
	   which created connection will be IP_CT_NEW or for an
	   expected connection, IP_CT_RELATED. */
	if (CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL)
		return NF_ACCEPT;

	hash = hash_conntrack(&ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple);
	repl_hash = hash_conntrack(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);

	/* We're not in hash table, and we refuse to set up related
	   connections for unconfirmed conns.  But packet copies and
	   REJECT will give spurious warnings here. */
	/* IP_NF_ASSERT(atomic_read(&ct->ct_general.use) == 1); */

	/* No external references means noone else could have
           confirmed us. */
	IP_NF_ASSERT(!is_confirmed(ct));
	DEBUGP("Confirming conntrack %p\n", ct);

	WRITE_LOCK(&ip_conntrack_lock);
	/* See if there's one in the list already, including reverse:
           NAT could have grabbed it without realizing, since we're
           not in the hash.  If there is, we lost race. */
	if (!LIST_FIND(&ip_conntrack_hash[hash],
		       conntrack_tuple_cmp,
		       struct ip_conntrack_tuple_hash *,
		       &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple, NULL)
	    && !LIST_FIND(&ip_conntrack_hash[repl_hash],
			  conntrack_tuple_cmp,
			  struct ip_conntrack_tuple_hash *,
			  &ct->tuplehash[IP_CT_DIR_REPLY].tuple, NULL)) {
		/* Remove from unconfirmed list */
		list_del(&ct->tuplehash[IP_CT_DIR_ORIGINAL].list);

		list_prepend(&ip_conntrack_hash[hash],
			     &ct->tuplehash[IP_CT_DIR_ORIGINAL]);
		list_prepend(&ip_conntrack_hash[repl_hash],
			     &ct->tuplehash[IP_CT_DIR_REPLY]);
		/* Timer relative to confirmation time, not original
		   setting time, otherwise we'd get timer wrap in
		   weird delay cases. */
		ct->timeout.expires += jiffies;
		add_timer(&ct->timeout);
		atomic_inc(&ct->ct_general.use);
		set_bit(IPS_CONFIRMED_BIT, &ct->status);
		WRITE_UNLOCK(&ip_conntrack_lock);
		return NF_ACCEPT;
	}

	WRITE_UNLOCK(&ip_conntrack_lock);
	return NF_DROP;
}

/* Returns true if a connection correspondings to the tuple (required
   for NAT). */
int
ip_conntrack_tuple_taken(const struct ip_conntrack_tuple *tuple,
			 const struct ip_conntrack *ignored_conntrack)
{
	struct ip_conntrack_tuple_hash *h;

	READ_LOCK(&ip_conntrack_lock);
	h = __ip_conntrack_find(tuple, ignored_conntrack);
	READ_UNLOCK(&ip_conntrack_lock);

	return h != NULL;
}

/* Returns conntrack if it dealt with ICMP, and filled in skb fields */
struct ip_conntrack *
icmp_error_track(struct sk_buff *skb,
		 enum ip_conntrack_info *ctinfo,
		 unsigned int hooknum)
{
	const struct iphdr *iph = skb->nh.iph;
	struct icmphdr *hdr;
	struct ip_conntrack_tuple innertuple, origtuple;
	struct iphdr *inner;
	size_t datalen;
	struct ip_conntrack_protocol *innerproto;
	struct ip_conntrack_tuple_hash *h;

	IP_NF_ASSERT(iph->protocol == IPPROTO_ICMP);
	IP_NF_ASSERT(skb->nfct == NULL);

	hdr = (struct icmphdr *)((u_int32_t *)iph + iph->ihl);
	inner = (struct iphdr *)(hdr + 1);
	datalen = skb->len - iph->ihl*4 - sizeof(*hdr);

	if (skb->len < iph->ihl * 4 + sizeof(*hdr) + sizeof(*iph)) {
		DEBUGP("icmp_error_track: too short\n");
		return NULL;
	}

	if (hdr->type != ICMP_DEST_UNREACH
	    && hdr->type != ICMP_SOURCE_QUENCH
	    && hdr->type != ICMP_TIME_EXCEEDED
	    && hdr->type != ICMP_PARAMETERPROB
	    && hdr->type != ICMP_REDIRECT)
		return NULL;

	/* Ignore ICMP's containing fragments (shouldn't happen) */
	if (inner->frag_off & htons(IP_OFFSET)) {
		DEBUGP("icmp_error_track: fragment of proto %u\n",
		       inner->protocol);
		return NULL;
	}

	/* Ignore it if the checksum's bogus. */
	if (ip_compute_csum((unsigned char *)hdr, sizeof(*hdr) + datalen)) {
		DEBUGP("icmp_error_track: bad csum\n");
		return NULL;
	}

	innerproto = ip_ct_find_proto(inner->protocol);
	/* Are they talking about one of our connections? */
	if (inner->ihl * 4 + 8 > datalen
	    || !ip_ct_get_tuple(inner, datalen, &origtuple, innerproto)) {
		DEBUGP("icmp_error: ! get_tuple p=%u (%u*4+%u dlen=%u)\n",
		       inner->protocol, inner->ihl, 8,
		       datalen);
		return NULL;
	}

	/* Ordinarily, we'd expect the inverted tupleproto, but it's
	   been preserved inside the ICMP. */
	if (!invert_tuple(&innertuple, &origtuple, innerproto)) {
		DEBUGP("icmp_error_track: Can't invert tuple\n");
		return NULL;
	}

	*ctinfo = IP_CT_RELATED;

	h = ip_conntrack_find_get(&innertuple, NULL);
	if (!h) {
		/* Locally generated ICMPs will match inverted if they
		   haven't been SNAT'ed yet */
		/* FIXME: NAT code has to handle half-done double NAT --RR */
		if (hooknum == NF_IP_LOCAL_OUT)
			h = ip_conntrack_find_get(&origtuple, NULL);

		if (!h) {
			DEBUGP("icmp_error_track: no match\n");
			return NULL;
		}
		/* Reverse direction from that found */
		if (DIRECTION(h) != IP_CT_DIR_REPLY)
			*ctinfo += IP_CT_IS_REPLY;
	} else {
		if (DIRECTION(h) == IP_CT_DIR_REPLY)
			*ctinfo += IP_CT_IS_REPLY;
	}

	/* Update skb to refer to this connection */
	skb->nfct = &h->ctrack->infos[*ctinfo];
	return h->ctrack;
}

/* There's a small race here where we may free a just-assured
   connection.  Too bad: we're in trouble anyway. */
static inline int unreplied(const struct ip_conntrack_tuple_hash *i)
{
	return !(test_bit(IPS_ASSURED_BIT, &i->ctrack->status));
}

static int early_drop(struct list_head *chain)
{
	/* Traverse backwards: gives us oldest, which is roughly LRU */
	struct ip_conntrack_tuple_hash *h;
	int dropped = 0;

	READ_LOCK(&ip_conntrack_lock);
	h = LIST_FIND_B(chain, unreplied, struct ip_conntrack_tuple_hash *);
	if (h)
		atomic_inc(&h->ctrack->ct_general.use);
	READ_UNLOCK(&ip_conntrack_lock);

	if (!h)
		return dropped;

	if (del_timer(&h->ctrack->timeout)) {
		death_by_timeout((unsigned long)h->ctrack);
		dropped = 1;
	}
	ip_conntrack_put(h->ctrack);
	return dropped;
}

static inline int helper_cmp(const struct ip_conntrack_helper *i,
			     const struct ip_conntrack_tuple *rtuple)
{
	return ip_ct_tuple_mask_cmp(rtuple, &i->tuple, &i->mask);
}

struct ip_conntrack_helper *ip_ct_find_helper(const struct ip_conntrack_tuple *tuple)
{
	return LIST_FIND(&helpers, helper_cmp,
			 struct ip_conntrack_helper *,
			 tuple);
}

/* Allocate a new conntrack: we return -ENOMEM if classification
   failed due to stress.  Otherwise it really is unclassifiable. */
static struct ip_conntrack_tuple_hash *
init_conntrack(const struct ip_conntrack_tuple *tuple,
	       struct ip_conntrack_protocol *protocol,
	       struct sk_buff *skb)
{
	struct ip_conntrack *conntrack;
	struct ip_conntrack_tuple repl_tuple;
	size_t hash;
	struct ip_conntrack_expect *expected;
	int i;
	static unsigned int drop_next = 0;

	if (!ip_conntrack_hash_rnd_initted) {
		get_random_bytes(&ip_conntrack_hash_rnd, 4);
		ip_conntrack_hash_rnd_initted = 1;
	}

	hash = hash_conntrack(tuple);

	if (ip_conntrack_max &&
	    atomic_read(&ip_conntrack_count) >= ip_conntrack_max) {
		/* Try dropping from random chain, or else from the
                   chain about to put into (in case they're trying to
                   bomb one hash chain). */
		unsigned int next = (drop_next++)%ip_conntrack_htable_size;

		if (!early_drop(&ip_conntrack_hash[next])
		    && !early_drop(&ip_conntrack_hash[hash])) {
			if (net_ratelimit())
				printk(KERN_WARNING
				       "ip_conntrack: table full, dropping"
				       " packet.\n");
			return ERR_PTR(-ENOMEM);
		}
	}

	if (!invert_tuple(&repl_tuple, tuple, protocol)) {
		DEBUGP("Can't invert tuple.\n");
		return NULL;
	}

	conntrack = kmem_cache_alloc(ip_conntrack_cachep, GFP_ATOMIC);
	if (!conntrack) {
		DEBUGP("Can't allocate conntrack.\n");
		return ERR_PTR(-ENOMEM);
	}

	memset(conntrack, 0, sizeof(*conntrack));
	atomic_set(&conntrack->ct_general.use, 1);
	conntrack->ct_general.destroy = destroy_conntrack;
	conntrack->tuplehash[IP_CT_DIR_ORIGINAL].tuple = *tuple;
	conntrack->tuplehash[IP_CT_DIR_ORIGINAL].ctrack = conntrack;
	conntrack->tuplehash[IP_CT_DIR_REPLY].tuple = repl_tuple;
	conntrack->tuplehash[IP_CT_DIR_REPLY].ctrack = conntrack;
	for (i=0; i < IP_CT_NUMBER; i++)
		conntrack->infos[i].master = &conntrack->ct_general;

	if (!protocol->new(conntrack, skb->nh.iph, skb->len)) {
		kmem_cache_free(ip_conntrack_cachep, conntrack);
		return NULL;
	}
	/* Don't set timer yet: wait for confirmation */
	init_timer(&conntrack->timeout);
	conntrack->timeout.data = (unsigned long)conntrack;
	conntrack->timeout.function = death_by_timeout;

	INIT_LIST_HEAD(&conntrack->sibling_list);

	WRITE_LOCK(&ip_conntrack_lock);
	/* Need finding and deleting of expected ONLY if we win race */
	READ_LOCK(&ip_conntrack_expect_tuple_lock);
	expected = LIST_FIND(&ip_conntrack_expect_list, expect_cmp,
			     struct ip_conntrack_expect *, tuple);
	READ_UNLOCK(&ip_conntrack_expect_tuple_lock);

	/* If master is not in hash table yet (ie. packet hasn't left
	   this machine yet), how can other end know about expected?
	   Hence these are not the droids you are looking for (if
	   master ct never got confirmed, we'd hold a reference to it
	   and weird things would happen to future packets). */
	if (expected && !is_confirmed(expected->expectant))
		expected = NULL;

	/* Look up the conntrack helper for master connections only */
	if (!expected)
		conntrack->helper = ip_ct_find_helper(&repl_tuple);

	/* If the expectation is dying, then this is a looser. */
	if (expected
	    && expected->expectant->helper->timeout
	    && ! del_timer(&expected->timeout))
		expected = NULL;

	if (expected) {
		DEBUGP("conntrack: expectation arrives ct=%p exp=%p\n",
			conntrack, expected);
		/* Welcome, Mr. Bond.  We've been expecting you... */
		__set_bit(IPS_EXPECTED_BIT, &conntrack->status);
		conntrack->master = expected;
		expected->sibling = conntrack;
		LIST_DELETE(&ip_conntrack_expect_list, expected);
		expected->expectant->expecting--;
		nf_conntrack_get(&master_ct(conntrack)->infos[0]);
	}
	/* Overload tuple linked list to put us in unconfirmed list. */
	list_add(&conntrack->tuplehash[IP_CT_DIR_ORIGINAL].list,
	         &unconfirmed);

	atomic_inc(&ip_conntrack_count);
	WRITE_UNLOCK(&ip_conntrack_lock);

	if (expected && expected->expectfn)
		expected->expectfn(conntrack);
	return &conntrack->tuplehash[IP_CT_DIR_ORIGINAL];
}

/* On success, returns conntrack ptr, sets skb->nfct and ctinfo */
static inline struct ip_conntrack *
resolve_normal_ct(struct sk_buff *skb,
		  struct ip_conntrack_protocol *proto,
		  int *set_reply,
		  unsigned int hooknum,
		  enum ip_conntrack_info *ctinfo)
{
	struct ip_conntrack_tuple tuple;
	struct ip_conntrack_tuple_hash *h;

	IP_NF_ASSERT((skb->nh.iph->frag_off & htons(IP_OFFSET)) == 0);

	if (!ip_ct_get_tuple(skb->nh.iph, skb->len, &tuple, proto))
		return NULL;

	/* look for tuple match */
	h = ip_conntrack_find_get(&tuple, NULL);
	if (!h) {
		h = init_conntrack(&tuple, proto, skb);
		if (!h)
			return NULL;
		if (IS_ERR(h))
			return (void *)h;
	}

	/* It exists; we have (non-exclusive) reference. */
	if (DIRECTION(h) == IP_CT_DIR_REPLY) {
		*ctinfo = IP_CT_ESTABLISHED + IP_CT_IS_REPLY;
		/* Please set reply bit if this packet OK */
		*set_reply = 1;
	} else {
		/* Once we've had two way comms, always ESTABLISHED. */
		if (test_bit(IPS_SEEN_REPLY_BIT, &h->ctrack->status)) {
			DEBUGP("ip_conntrack_in: normal packet for %p\n",
			       h->ctrack);
		        *ctinfo = IP_CT_ESTABLISHED;
		} else if (test_bit(IPS_EXPECTED_BIT, &h->ctrack->status)) {
			DEBUGP("ip_conntrack_in: related packet for %p\n",
			       h->ctrack);
			*ctinfo = IP_CT_RELATED;
		} else {
			DEBUGP("ip_conntrack_in: new packet for %p\n",
			       h->ctrack);
			*ctinfo = IP_CT_NEW;
		}
		*set_reply = 0;
	}
	skb->nfct = &h->ctrack->infos[*ctinfo];
	return h->ctrack;
}

/* Netfilter hook itself. */
unsigned int ip_conntrack_in(unsigned int hooknum,
			     struct sk_buff **pskb,
			     const struct net_device *in,
			     const struct net_device *out,
			     int (*okfn)(struct sk_buff *))
{
	struct ip_conntrack *ct;
	enum ip_conntrack_info ctinfo;
	struct ip_conntrack_protocol *proto;
	int set_reply;
	int ret;

	/* FIXME: Do this right please. --RR */
	(*pskb)->nfcache |= NFC_UNKNOWN;

/* Doesn't cover locally-generated broadcast, so not worth it. */
#if 0
	/* Ignore broadcast: no `connection'. */
	if ((*pskb)->pkt_type == PACKET_BROADCAST) {
		printk("Broadcast packet!\n");
		return NF_ACCEPT;
	} else if (((*pskb)->nh.iph->daddr & htonl(0x000000FF))
		   == htonl(0x000000FF)) {
		printk("Should bcast: %u.%u.%u.%u->%u.%u.%u.%u (sk=%p, ptype=%u)\n",
		       NIPQUAD((*pskb)->nh.iph->saddr),
		       NIPQUAD((*pskb)->nh.iph->daddr),
		       (*pskb)->sk, (*pskb)->pkt_type);
	}
#endif

	/* Previously seen (loopback)?  Ignore.  Do this before
           fragment check. */
	if ((*pskb)->nfct)
		return NF_ACCEPT;

	/* Gather fragments. */
	if ((*pskb)->nh.iph->frag_off & htons(IP_MF|IP_OFFSET)) {
		*pskb = ip_ct_gather_frags(*pskb,
		                           hooknum == NF_IP_PRE_ROUTING ?
		                           IP_DEFRAG_CONNTRACK_IN :
		                           IP_DEFRAG_CONNTRACK_OUT);
		if (!*pskb)
			return NF_STOLEN;
	}

	proto = ip_ct_find_proto((*pskb)->nh.iph->protocol);

	/* It may be an icmp error... */
	if ((*pskb)->nh.iph->protocol == IPPROTO_ICMP
	    && icmp_error_track(*pskb, &ctinfo, hooknum))
		return NF_ACCEPT;

	if (!(ct = resolve_normal_ct(*pskb, proto,&set_reply,hooknum,&ctinfo)))
		/* Not valid part of a connection */
		return NF_ACCEPT;

	if (IS_ERR(ct))
		/* Too stressed to deal. */
		return NF_DROP;

	IP_NF_ASSERT((*pskb)->nfct);

	ret = proto->packet(ct, (*pskb)->nh.iph, (*pskb)->len, ctinfo);
	if (ret == -1) {
		/* Invalid */
		nf_conntrack_put((*pskb)->nfct);
		(*pskb)->nfct = NULL;
		return NF_ACCEPT;
	}

	if (ret != NF_DROP && ct->helper) {
		ret = ct->helper->help((*pskb)->nh.iph, (*pskb)->len,
				       ct, ctinfo);
		if (ret == -1) {
			/* Invalid */
			nf_conntrack_put((*pskb)->nfct);
			(*pskb)->nfct = NULL;
			return NF_ACCEPT;
		}
	}
	if (set_reply)
		set_bit(IPS_SEEN_REPLY_BIT, &ct->status);

	return ret;
}

int invert_tuplepr(struct ip_conntrack_tuple *inverse,
		   const struct ip_conntrack_tuple *orig)
{
	return invert_tuple(inverse, orig, ip_ct_find_proto(orig->dst.protonum));
}

static inline int resent_expect(const struct ip_conntrack_expect *i,
			        const struct ip_conntrack_tuple *tuple,
			        const struct ip_conntrack_tuple *mask)
{
	DEBUGP("resent_expect\n");
	DEBUGP("   tuple:   "); DUMP_TUPLE(&i->tuple);
	DEBUGP("ct_tuple:   "); DUMP_TUPLE(&i->ct_tuple);
	DEBUGP("test tuple: "); DUMP_TUPLE(tuple);
	return (((i->ct_tuple.dst.protonum == 0 && ip_ct_tuple_equal(&i->tuple, tuple))
	         || (i->ct_tuple.dst.protonum && ip_ct_tuple_equal(&i->ct_tuple, tuple)))
		&& ip_ct_tuple_equal(&i->mask, mask));
}

/* Would two expected things clash? */
static inline int expect_clash(const struct ip_conntrack_expect *i,
			       const struct ip_conntrack_tuple *tuple,
			       const struct ip_conntrack_tuple *mask)
{
	/* Part covered by intersection of masks must be unequal,
           otherwise they clash */
	struct ip_conntrack_tuple intersect_mask
		= { { i->mask.src.ip & mask->src.ip,
		      { i->mask.src.u.all & mask->src.u.all } },
		    { i->mask.dst.ip & mask->dst.ip,
		      { i->mask.dst.u.all & mask->dst.u.all },
		      i->mask.dst.protonum & mask->dst.protonum } };

	return ip_ct_tuple_mask_cmp(&i->tuple, tuple, &intersect_mask);
}

inline void ip_conntrack_unexpect_related(struct ip_conntrack_expect *expect)
{
	WRITE_LOCK(&ip_conntrack_lock);
	unexpect_related(expect);
	WRITE_UNLOCK(&ip_conntrack_lock);
}

static void expectation_timed_out(unsigned long ul_expect)
{
	struct ip_conntrack_expect *expect = (void *) ul_expect;

	DEBUGP("expectation %p timed out\n", expect);
	WRITE_LOCK(&ip_conntrack_lock);
	__unexpect_related(expect);
	WRITE_UNLOCK(&ip_conntrack_lock);
}

/* Add a related connection. */
int ip_conntrack_expect_related(struct ip_conntrack *related_to,
				struct ip_conntrack_expect *expect)
{
	struct ip_conntrack_expect *old, *new;
	int ret = 0;

	WRITE_LOCK(&ip_conntrack_lock);
	/* Because of the write lock, no reader can walk the lists,
	 * so there is no need to use the tuple lock too */

	DEBUGP("ip_conntrack_expect_related %p\n", related_to);
	DEBUGP("tuple: "); DUMP_TUPLE(&expect->tuple);
	DEBUGP("mask:  "); DUMP_TUPLE(&expect->mask);

	old = LIST_FIND(&ip_conntrack_expect_list, resent_expect,
		        struct ip_conntrack_expect *, &expect->tuple,
			&expect->mask);
	if (old) {
		/* Helper private data may contain offsets but no pointers
		   pointing into the payload - otherwise we should have to copy
		   the data filled out by the helper over the old one */
		DEBUGP("expect_related: resent packet\n");
		if (old->expectant == related_to &&
		    related_to->helper->timeout) {
			if (!del_timer(&old->timeout)) {
				/* expectation is dying. Fall through */
				old = NULL;
			} else {
				old->timeout.expires = jiffies +
					related_to->helper->timeout * HZ;
				add_timer(&old->timeout);
			}
		}

		if (old) {
			WRITE_UNLOCK(&ip_conntrack_lock);
			return -EEXIST;
		}
	} else if (related_to->helper->max_expected &&
		   related_to->expecting >= related_to->helper->max_expected) {
		/* old == NULL */
		if (!(related_to->helper->flags &
		      IP_CT_HELPER_F_REUSE_EXPECT)) {
			WRITE_UNLOCK(&ip_conntrack_lock);
 		    	if (net_ratelimit())
 			    	printk(KERN_WARNING
				       "ip_conntrack: max number of expected "
				       "connections %i of %s reached for "
				       "%u.%u.%u.%u->%u.%u.%u.%u\n",
				       related_to->helper->max_expected,
				       related_to->helper->name,
 		    	       	       NIPQUAD(related_to->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.ip),
 		    	       	       NIPQUAD(related_to->tuplehash[IP_CT_DIR_ORIGINAL].tuple.dst.ip));
			return -EPERM;
		}
		DEBUGP("ip_conntrack: max number of expected "
		       "connections %i of %s reached for "
		       "%u.%u.%u.%u->%u.%u.%u.%u, reusing\n",
 		       related_to->helper->max_expected,
		       related_to->helper->name,
		       NIPQUAD(related_to->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.ip),
		       NIPQUAD(related_to->tuplehash[IP_CT_DIR_ORIGINAL].tuple.dst.ip));

		/* choose the the oldest expectation to evict */
		list_for_each_entry(old, &related_to->sibling_list,
		                                      expected_list)
			if (old->sibling == NULL)
				break;

		/* We cannot fail since related_to->expecting is the number
		 * of unconfirmed expectations */
		IP_NF_ASSERT(old && old->sibling == NULL);

		/* newnat14 does not reuse the real allocated memory
		 * structures but rather unexpects the old and
		 * allocates a new.  unexpect_related will decrement
		 * related_to->expecting.
		 */
		unexpect_related(old);
		ret = -EPERM;
	} else if (LIST_FIND(&ip_conntrack_expect_list, expect_clash,
			     struct ip_conntrack_expect *, &expect->tuple,
			     &expect->mask)) {
		WRITE_UNLOCK(&ip_conntrack_lock);
		DEBUGP("expect_related: busy!\n");
		return -EBUSY;
	}

	new = (struct ip_conntrack_expect *)
	      kmalloc(sizeof(struct ip_conntrack_expect), GFP_ATOMIC);
	if (!new) {
		WRITE_UNLOCK(&ip_conntrack_lock);
		DEBUGP("expect_relaed: OOM allocating expect\n");
		return -ENOMEM;
	}

	DEBUGP("new expectation %p of conntrack %p\n", new, related_to);
	memcpy(new, expect, sizeof(*expect));
	new->expectant = related_to;
	new->sibling = NULL;
	atomic_set(&new->use, 1);

	/* add to expected list for this connection */
	list_add_tail(&new->expected_list, &related_to->sibling_list);
	/* add to global list of expectations */
	list_prepend(&ip_conntrack_expect_list, &new->list);
	/* add and start timer if required */
	if (related_to->helper->timeout) {
		init_timer(&new->timeout);
		new->timeout.data = (unsigned long)new;
		new->timeout.function = expectation_timed_out;
		new->timeout.expires = jiffies +
					related_to->helper->timeout * HZ;
		add_timer(&new->timeout);
	}
	related_to->expecting++;

	WRITE_UNLOCK(&ip_conntrack_lock);

	return ret;
}

/* Change tuple in an existing expectation */
int ip_conntrack_change_expect(struct ip_conntrack_expect *expect,
			       struct ip_conntrack_tuple *newtuple)
{
	int ret;

	MUST_BE_READ_LOCKED(&ip_conntrack_lock);
	WRITE_LOCK(&ip_conntrack_expect_tuple_lock);

	DEBUGP("change_expect:\n");
	DEBUGP("exp tuple: "); DUMP_TUPLE(&expect->tuple);
	DEBUGP("exp mask:  "); DUMP_TUPLE(&expect->mask);
	DEBUGP("newtuple:  "); DUMP_TUPLE(newtuple);
	if (expect->ct_tuple.dst.protonum == 0) {
		/* Never seen before */
		DEBUGP("change expect: never seen before\n");
		if (!ip_ct_tuple_equal(&expect->tuple, newtuple)
		    && LIST_FIND(&ip_conntrack_expect_list, expect_clash,
			         struct ip_conntrack_expect *, newtuple, &expect->mask)) {
			/* Force NAT to find an unused tuple */
			ret = -1;
		} else {
			memcpy(&expect->ct_tuple, &expect->tuple, sizeof(expect->tuple));
			memcpy(&expect->tuple, newtuple, sizeof(expect->tuple));
			ret = 0;
		}
	} else {
		/* Resent packet */
		DEBUGP("change expect: resent packet\n");
		if (ip_ct_tuple_equal(&expect->tuple, newtuple)) {
			ret = 0;
		} else {
			/* Force NAT to choose again the same port */
			ret = -1;
		}
	}
	WRITE_UNLOCK(&ip_conntrack_expect_tuple_lock);

	return ret;
}

/* Alter reply tuple (maybe alter helper).  If it's already taken,
   return 0 and don't do alteration. */
int ip_conntrack_alter_reply(struct ip_conntrack *conntrack,
			     const struct ip_conntrack_tuple *newreply)
{
	WRITE_LOCK(&ip_conntrack_lock);
	if (__ip_conntrack_find(newreply, conntrack)) {
		WRITE_UNLOCK(&ip_conntrack_lock);
		return 0;
	}
	/* Should be unconfirmed, so not in hash table yet */
	IP_NF_ASSERT(!is_confirmed(conntrack));

	DEBUGP("Altering reply tuple of %p to ", conntrack);
	DUMP_TUPLE(newreply);

	conntrack->tuplehash[IP_CT_DIR_REPLY].tuple = *newreply;
	if (!conntrack->master && list_empty(&conntrack->sibling_list))
		conntrack->helper = ip_ct_find_helper(newreply);
	WRITE_UNLOCK(&ip_conntrack_lock);

	return 1;
}

int ip_conntrack_helper_register(struct ip_conntrack_helper *me)
{
	MOD_INC_USE_COUNT;

	WRITE_LOCK(&ip_conntrack_lock);
	list_prepend(&helpers, me);
	WRITE_UNLOCK(&ip_conntrack_lock);

	return 0;
}

static inline int unhelp(struct ip_conntrack_tuple_hash *i,
			 const struct ip_conntrack_helper *me)
{
	if (i->ctrack->helper == me) {
		/* Get rid of any expected. */
		remove_expectations(i->ctrack, 0);
		/* And *then* set helper to NULL */
		i->ctrack->helper = NULL;
	}
	return 0;
}

void ip_conntrack_helper_unregister(struct ip_conntrack_helper *me)
{
	unsigned int i;

	/* Need write lock here, to delete helper. */
	WRITE_LOCK(&ip_conntrack_lock);
	LIST_DELETE(&helpers, me);

	/* Get rid of expecteds, set helpers to NULL. */
	LIST_FIND_W(&unconfirmed, unhelp, struct ip_conntrack_tuple_hash*, me);
	for (i = 0; i < ip_conntrack_htable_size; i++)
		LIST_FIND_W(&ip_conntrack_hash[i], unhelp,
			    struct ip_conntrack_tuple_hash *, me);
	WRITE_UNLOCK(&ip_conntrack_lock);

	/* Someone could be still looking at the helper in a bh. */
	br_write_lock_bh(BR_NETPROTO_LOCK);
	br_write_unlock_bh(BR_NETPROTO_LOCK);

	MOD_DEC_USE_COUNT;
}

/* Refresh conntrack for this many jiffies. */
void ip_ct_refresh(struct ip_conntrack *ct, unsigned long extra_jiffies)
{
	IP_NF_ASSERT(ct->timeout.data == (unsigned long)ct);

	WRITE_LOCK(&ip_conntrack_lock);
	/* If not in hash table, timer will not be active yet */
	if (!is_confirmed(ct))
		ct->timeout.expires = extra_jiffies;
	else {
		/* Need del_timer for race avoidance (may already be dying). */
		if (del_timer(&ct->timeout)) {
			ct->timeout.expires = jiffies + extra_jiffies;
			add_timer(&ct->timeout);
		}
	}
	WRITE_UNLOCK(&ip_conntrack_lock);
}

/* Returns new sk_buff, or NULL */
struct sk_buff *
ip_ct_gather_frags(struct sk_buff *skb, u_int32_t user)
{
	struct sock *sk = skb->sk;
#ifdef CONFIG_NETFILTER_DEBUG
	unsigned int olddebug = skb->nf_debug;
#endif

	if (sk) {
		sock_hold(sk);
		skb_orphan(skb);
	}

	local_bh_disable();
	skb = ip_defrag(skb, user);
	local_bh_enable();

	if (!skb) {
		if (sk) sock_put(sk);
		return skb;
	} else if (skb_is_nonlinear(skb) && skb_linearize(skb, GFP_ATOMIC) != 0) {
		kfree_skb(skb);
		if (sk) sock_put(sk);
		return NULL;
	}

	if (sk) {
		skb_set_owner_w(skb, sk);
		sock_put(sk);
	}

	ip_send_check(skb->nh.iph);
	skb->nfcache |= NFC_ALTERED;
#ifdef CONFIG_NETFILTER_DEBUG
	/* Packet path as if nothing had happened. */
	skb->nf_debug = olddebug;
#endif
	return skb;
}

/* Used by ipt_REJECT. */
static void ip_conntrack_attach(struct sk_buff *nskb, struct nf_ct_info *nfct)
{
	struct ip_conntrack *ct;
	enum ip_conntrack_info ctinfo;

	ct = __ip_conntrack_get(nfct, &ctinfo);

	/* This ICMP is in reverse direction to the packet which
           caused it */
	if (CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL)
		ctinfo = IP_CT_RELATED + IP_CT_IS_REPLY;
	else
		ctinfo = IP_CT_RELATED;

	/* Attach new skbuff, and increment count */
	nskb->nfct = &ct->infos[ctinfo];
	atomic_inc(&ct->ct_general.use);
}

static inline int
do_iter(const struct ip_conntrack_tuple_hash *i,
        int (*iter)(struct ip_conntrack *i, void *data),
	void *data)
{
	return iter(i->ctrack, data);
}

/* Bring out ya dead! */
static struct ip_conntrack_tuple_hash *
get_next_corpse(int (*iter)(struct ip_conntrack *i, void *data),
		void *data, unsigned int *bucket)
{
	struct ip_conntrack_tuple_hash *h = NULL;

	WRITE_LOCK(&ip_conntrack_lock);
	for (; *bucket < ip_conntrack_htable_size; (*bucket)++) {
		h = LIST_FIND_W(&ip_conntrack_hash[*bucket], do_iter,
		                struct ip_conntrack_tuple_hash *, iter, data);
		if (h)
			break;
	}
	if (!h)
		h = LIST_FIND_W(&unconfirmed, do_iter,
		                struct ip_conntrack_tuple_hash *, iter, data);
	if (h)
		atomic_inc(&h->ctrack->ct_general.use);
	WRITE_UNLOCK(&ip_conntrack_lock);

	return h;
}

void
ip_ct_iterate_cleanup(int (*iter)(struct ip_conntrack *i, void *), void *data)
{
	struct ip_conntrack_tuple_hash *h;
	unsigned int bucket = 0;

	while ((h = get_next_corpse(iter, data, &bucket)) != NULL) {
		/* Time to push up daises... */
		if (del_timer(&h->ctrack->timeout))
			death_by_timeout((unsigned long)h->ctrack);
		/* ... else the timer will get him soon. */

		ip_conntrack_put(h->ctrack);
	}
}

/* Fast function for those who don't want to parse /proc (and I don't
   blame them). */
/* Reversing the socket's dst/src point of view gives us the reply
   mapping. */
static int
getorigdst(struct sock *sk, int optval, void *user, int *len)
{
	struct ip_conntrack_tuple_hash *h;
	struct ip_conntrack_tuple tuple;

	IP_CT_TUPLE_U_BLANK(&tuple);
	tuple.src.ip = sk->rcv_saddr;
	tuple.src.u.tcp.port = sk->sport;
	tuple.dst.ip = sk->daddr;
	tuple.dst.u.tcp.port = sk->dport;
	tuple.dst.protonum = IPPROTO_TCP;

	/* We only do TCP at the moment: is there a better way? */
	if (strcmp(sk->prot->name, "TCP") != 0) {
		DEBUGP("SO_ORIGINAL_DST: Not a TCP socket\n");
		return -ENOPROTOOPT;
	}

	if ((unsigned int) *len < sizeof(struct sockaddr_in)) {
		DEBUGP("SO_ORIGINAL_DST: len %u not %u\n",
		       *len, sizeof(struct sockaddr_in));
		return -EINVAL;
	}

	h = ip_conntrack_find_get(&tuple, NULL);
	if (h) {
		struct sockaddr_in sin;

		sin.sin_family = AF_INET;
		sin.sin_port = h->ctrack->tuplehash[IP_CT_DIR_ORIGINAL]
			.tuple.dst.u.tcp.port;
		sin.sin_addr.s_addr = h->ctrack->tuplehash[IP_CT_DIR_ORIGINAL]
			.tuple.dst.ip;
		memset(sin.sin_zero, 0, sizeof(sin.sin_zero));

		DEBUGP("SO_ORIGINAL_DST: %u.%u.%u.%u %u\n",
		       NIPQUAD(sin.sin_addr.s_addr), ntohs(sin.sin_port));
		ip_conntrack_put(h->ctrack);
		if (copy_to_user(user, &sin, sizeof(sin)) != 0)
			return -EFAULT;
		else
			return 0;
	}
	DEBUGP("SO_ORIGINAL_DST: Can't find %u.%u.%u.%u/%u-%u.%u.%u.%u/%u.\n",
	       NIPQUAD(tuple.src.ip), ntohs(tuple.src.u.tcp.port),
	       NIPQUAD(tuple.dst.ip), ntohs(tuple.dst.u.tcp.port));
	return -ENOENT;
}

static struct nf_sockopt_ops so_getorigdst
= { { NULL, NULL }, PF_INET,
    0, 0, NULL, /* Setsockopts */
    SO_ORIGINAL_DST, SO_ORIGINAL_DST+1, &getorigdst,
    0, NULL };

static int kill_all(struct ip_conntrack *i, void *data)
{
	return 1;
}

/* Mishearing the voices in his head, our hero wonders how he's
   supposed to kill the mall. */
void ip_conntrack_cleanup(void)
{
	ip_ct_attach = NULL;
	/* This makes sure all current packets have passed through
           netfilter framework.  Roll on, two-stage module
           delete... */
	br_write_lock_bh(BR_NETPROTO_LOCK);
	br_write_unlock_bh(BR_NETPROTO_LOCK);

 i_see_dead_people:
	ip_ct_iterate_cleanup(kill_all, NULL);
	if (atomic_read(&ip_conntrack_count) != 0) {
		schedule();
		goto i_see_dead_people;
	}

	kmem_cache_destroy(ip_conntrack_cachep);
	vfree(ip_conntrack_hash);
	nf_unregister_sockopt(&so_getorigdst);
}

static int hashsize = 0;
MODULE_PARM(hashsize, "i");

int __init ip_conntrack_init(void)
{
	unsigned int i;
	int ret;

	/* Idea from tcp.c: use 1/16384 of memory.  On i386: 32MB
	 * machine has 256 buckets.  >= 1GB machines have 8192 buckets. */
 	if (hashsize) {
 		ip_conntrack_htable_size = hashsize;
 	} else {
		ip_conntrack_htable_size
			= (((num_physpages << PAGE_SHIFT) / 16384)
			   / sizeof(struct list_head));
		if (num_physpages > (1024 * 1024 * 1024 / PAGE_SIZE))
			ip_conntrack_htable_size = 8192;
		if (ip_conntrack_htable_size < 16)
			ip_conntrack_htable_size = 16;
	}
	ip_conntrack_max = 8 * ip_conntrack_htable_size;

	printk("ip_conntrack version %s (%u buckets, %d max)"
	       " - %Zd bytes per conntrack\n", IP_CONNTRACK_VERSION,
	       ip_conntrack_htable_size, ip_conntrack_max,
	       sizeof(struct ip_conntrack));

	ret = nf_register_sockopt(&so_getorigdst);
	if (ret != 0) {
		printk(KERN_ERR "Unable to register netfilter socket option\n");
		return ret;
	}

	ip_conntrack_hash = vmalloc(sizeof(struct list_head)
				    * ip_conntrack_htable_size);
	if (!ip_conntrack_hash) {
		printk(KERN_ERR "Unable to create ip_conntrack_hash\n");
		goto err_unreg_sockopt;
	}

	ip_conntrack_cachep = kmem_cache_create("ip_conntrack",
	                                        sizeof(struct ip_conntrack), 0,
	                                        SLAB_HWCACHE_ALIGN, NULL, NULL);
	if (!ip_conntrack_cachep) {
		printk(KERN_ERR "Unable to create ip_conntrack slab cache\n");
		goto err_free_hash;
	}
	/* Don't NEED lock here, but good form anyway. */
	WRITE_LOCK(&ip_conntrack_lock);
	/* Sew in builtin protocols. */
	list_append(&protocol_list, &ip_conntrack_protocol_tcp);
	list_append(&protocol_list, &ip_conntrack_protocol_udp);
	list_append(&protocol_list, &ip_conntrack_protocol_icmp);
	WRITE_UNLOCK(&ip_conntrack_lock);

	for (i = 0; i < ip_conntrack_htable_size; i++)
		INIT_LIST_HEAD(&ip_conntrack_hash[i]);

	/* For use by ipt_REJECT */
	ip_ct_attach = ip_conntrack_attach;
	return ret;

err_free_hash:
	vfree(ip_conntrack_hash);
err_unreg_sockopt:
	nf_unregister_sockopt(&so_getorigdst);

	return -ENOMEM;
}