netfilter: add struct nf_ct_hook and use it

Move the nf_ct_destroy indirection to the struct nf_ct_hook.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/linux/netfilter.h

@@ -373,13 +373,18 @@ nf_nat_decode_session(struct sk_buff *skb, struct flowi *fl, u_int8_t family)
 
 extern void (*ip_ct_attach)(struct sk_buff *, const struct sk_buff *) __rcu;
 void nf_ct_attach(struct sk_buff *, const struct sk_buff *);
-extern void (*nf_ct_destroy)(struct nf_conntrack *) __rcu;
 #else
 static inline void nf_ct_attach(struct sk_buff *new, struct sk_buff *skb) {}
 #endif
 
 struct nf_conn;
 enum ip_conntrack_info;
+
+struct nf_ct_hook {
+	void (*destroy)(struct nf_conntrack *);
+};
+extern struct nf_ct_hook __rcu *nf_ct_hook;
+
 struct nlattr;
 
 struct nfnl_ct_hook {

net/netfilter/core.c

@@ -563,6 +563,9 @@ EXPORT_SYMBOL(skb_make_writable);
 struct nfnl_ct_hook __rcu *nfnl_ct_hook __read_mostly;
 EXPORT_SYMBOL_GPL(nfnl_ct_hook);
 
+struct nf_ct_hook __rcu *nf_ct_hook __read_mostly;
+EXPORT_SYMBOL_GPL(nf_ct_hook);
+
 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
 /* This does not belong here, but locally generated errors need it if connection
    tracking in use: without this, connection may not be in hash table, and hence
@@ -585,17 +588,14 @@ void nf_ct_attach(struct sk_buff *new, const struct sk_buff *skb)
 }
 EXPORT_SYMBOL(nf_ct_attach);
 
-void (*nf_ct_destroy)(struct nf_conntrack *) __rcu __read_mostly;
-EXPORT_SYMBOL(nf_ct_destroy);
-
 void nf_conntrack_destroy(struct nf_conntrack *nfct)
 {
-	void (*destroy)(struct nf_conntrack *);
+	struct nf_ct_hook *ct_hook;
 
 	rcu_read_lock();
-	destroy = rcu_dereference(nf_ct_destroy);
-	BUG_ON(destroy == NULL);
-	destroy(nfct);
+	ct_hook = rcu_dereference(nf_ct_hook);
+	BUG_ON(ct_hook == NULL);
+	ct_hook->destroy(nfct);
 	rcu_read_unlock();
 }
 EXPORT_SYMBOL(nf_conntrack_destroy);

net/netfilter/nf_conntrack_core.c

@@ -1813,8 +1813,7 @@ void nf_conntrack_cleanup_start(void)
 
 void nf_conntrack_cleanup_end(void)
 {
-	RCU_INIT_POINTER(nf_ct_destroy, NULL);
-
+	RCU_INIT_POINTER(nf_ct_hook, NULL);
 	cancel_delayed_work_sync(&conntrack_gc_work.dwork);
 	nf_ct_free_hashtable(nf_conntrack_hash, nf_conntrack_htable_size);
 
@@ -2131,11 +2130,15 @@ int nf_conntrack_init_start(void)
 	return ret;
 }
 
+static struct nf_ct_hook nf_conntrack_hook = {
+	.destroy	= destroy_conntrack,
+};
+
 void nf_conntrack_init_end(void)
 {
 	/* For use by REJECT target */
 	RCU_INIT_POINTER(ip_ct_attach, nf_conntrack_attach);
-	RCU_INIT_POINTER(nf_ct_destroy, destroy_conntrack);
+	RCU_INIT_POINTER(nf_ct_hook, &nf_conntrack_hook);
 }
 
 /*