netfilter: conntrack: handle ->destroy hook via nat_ops instead

The nat module already exposes a few functions to the conntrack core.
Move the nat extension destroy hook to it.

After this, no conntrack extension needs a destroy hook.
'struct nf_ct_ext_type' and the register/unregister api can be removed
in a followup patch.

Signed-off-by: Florian Westphal <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

include/linux/netfilter.h

···
 	unsigned int (*manip_pkt)(struct sk_buff *skb, struct nf_conn *ct,
 				  enum nf_nat_manip_type mtype,
 				  enum ip_conntrack_dir dir);
+	void (*remove_nat_bysrc)(struct nf_conn *ct);
 };
 
 extern const struct nf_nat_hook __rcu *nf_nat_hook;

include/net/netfilter/nf_conntrack_extend.h

···
 void *nf_ct_ext_add(struct nf_conn *ct, enum nf_ct_ext_id id, gfp_t gfp);
 
 struct nf_ct_ext_type {
-	/* Destroys relationships (can be NULL). */
-	void (*destroy)(struct nf_conn *ct);
-
 	enum nf_ct_ext_id id;
 };
 

net/netfilter/nf_conntrack_core.c

···
 
 void nf_ct_tmpl_free(struct nf_conn *tmpl)
 {
-	nf_ct_ext_destroy(tmpl);
+	kfree(tmpl->ext);
 
 	if (ARCH_KMALLOC_MINALIGN <= NFCT_INFOMASK)
 		kfree((char *)tmpl - tmpl->proto.tmpl_padto);
···
 	 */
 	WARN_ON(refcount_read(&ct->ct_general.use) != 0);
 
-	nf_ct_ext_destroy(ct);
+	if (ct->status & IPS_SRC_NAT_DONE) {
+		const struct nf_nat_hook *nat_hook;
+
+		rcu_read_lock();
+		nat_hook = rcu_dereference(nf_nat_hook);
+		if (nat_hook)
+			nat_hook->remove_nat_bysrc(ct);
+		rcu_read_unlock();
+	}
+
+	kfree(ct->ext);
 	kmem_cache_free(nf_conntrack_cachep, ct);
 	cnet = nf_ct_pernet(net);
 

net/netfilter/nf_conntrack_extend.c

···
 	;
 }
 
-void nf_ct_ext_destroy(struct nf_conn *ct)
-{
-	unsigned int i;
-	struct nf_ct_ext_type *t;
-
-	for (i = 0; i < NF_CT_EXT_NUM; i++) {
-		rcu_read_lock();
-		t = rcu_dereference(nf_ct_ext_types[i]);
-
-		/* Here the nf_ct_ext_type might have been unregisterd.
-		 * I.e., it has responsible to cleanup private
-		 * area in all conntracks when it is unregisterd.
-		 */
-		if (t && t->destroy)
-			t->destroy(ct);
-		rcu_read_unlock();
-	}
-
-	kfree(ct->ext);
-}
-
 void *nf_ct_ext_add(struct nf_conn *ct, enum nf_ct_ext_id id, gfp_t gfp)
 {
 	unsigned int newlen, newoff, oldlen, alloc;

net/netfilter/nf_nat_core.c

···
 	return i->status & IPS_NAT_MASK ? 1 : 0;
 }
 
-static void __nf_nat_cleanup_conntrack(struct nf_conn *ct)
+static void nf_nat_cleanup_conntrack(struct nf_conn *ct)
 {
 	unsigned int h;
 
···
 	 * will delete entry from already-freed table.
 	 */
 	if (test_and_clear_bit(IPS_SRC_NAT_DONE_BIT, &ct->status))
-		__nf_nat_cleanup_conntrack(ct);
+		nf_nat_cleanup_conntrack(ct);
 
 	/* don't delete conntrack.  Although that would make things a lot
 	 * simpler, we'd end up flushing all conntracks on nat rmmod.
···
 	return 0;
 }
 
-/* No one using conntrack by the time this called. */
-static void nf_nat_cleanup_conntrack(struct nf_conn *ct)
-{
-	if (ct->status & IPS_SRC_NAT_DONE)
-		__nf_nat_cleanup_conntrack(ct);
-}
-
 static struct nf_ct_ext_type nat_extend __read_mostly = {
-	.destroy	= nf_nat_cleanup_conntrack,
 	.id		= NF_CT_EXT_NAT,
 };
 
···
 	.decode_session		= __nf_nat_decode_session,
 #endif
 	.manip_pkt		= nf_nat_manip_pkt,
+	.remove_nat_bysrc	= nf_nat_cleanup_conntrack,
 };
 
 static int __init nf_nat_init(void)