[NETFILTER]: nf_nat: properly use RCU for ip_nat_decode_session

We need to use rcu_assign_pointer/rcu_dereference to avoid races.
Also remove an obsolete CONFIG_IP_NAT_NEEDED ifdef.
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netfilter.h

@@ -256,11 +256,16 @@ extern void (*ip_nat_decode_session)(struct sk_buff *, struct flowi *);
 static inline void
 nf_nat_decode_session(struct sk_buff *skb, struct flowi *fl, int family)
 {
-#if defined(CONFIG_IP_NF_NAT_NEEDED) || defined(CONFIG_NF_NAT_NEEDED)
+#ifdef CONFIG_NF_NAT_NEEDED
 	void (*decodefn)(struct sk_buff *, struct flowi *);
 
-	if (family == AF_INET && (decodefn = ip_nat_decode_session) != NULL)
+	if (family == AF_INET) {
+		rcu_read_lock();
+		decodefn = rcu_dereference(ip_nat_decode_session);
+		if (decodefn)
 			decodefn(skb, fl);
+		rcu_read_unlock();
+	}
 #endif
 }
 

net/ipv4/netfilter/nf_nat_standalone.c

@@ -332,7 +332,7 @@ static int __init nf_nat_standalone_init(void)
 
 #ifdef CONFIG_XFRM
 	BUG_ON(ip_nat_decode_session != NULL);
-	ip_nat_decode_session = nat_decode_session;
+	rcu_assign_pointer(ip_nat_decode_session, nat_decode_session);
 #endif
 	ret = nf_nat_rule_init();
 	if (ret < 0) {
@@ -350,7 +350,7 @@ static int __init nf_nat_standalone_init(void)
 	nf_nat_rule_cleanup();
  cleanup_decode_session:
 #ifdef CONFIG_XFRM
-	ip_nat_decode_session = NULL;
+	rcu_assign_pointer(ip_nat_decode_session, NULL);
 	synchronize_net();
 #endif
 	return ret;
@@ -361,7 +361,7 @@ static void __exit nf_nat_standalone_fini(void)
 	nf_unregister_hooks(nf_nat_ops, ARRAY_SIZE(nf_nat_ops));
 	nf_nat_rule_cleanup();
 #ifdef CONFIG_XFRM
-	ip_nat_decode_session = NULL;
+	rcu_assign_pointer(ip_nat_decode_session, NULL);
 	synchronize_net();
 #endif
 	/* Conntrack caches are unregistered in nf_conntrack_cleanup */