[NETFILTER]: nf_nat: don't add NAT extension for confirmed conntracks

Adding extensions to confirmed conntracks is not allowed to avoid races
on reallocation. Don't setup NAT for confirmed conntracks in case NAT
module is loaded late.

The has one side-effect, the connections existing before the NAT module
was loaded won't enter the bysource hash. The only case where this actually
makes a difference is in case of SNAT to a multirange where the IP before
NAT is also part of the range. Since old connections don't enter the
bysource hash the first new connection from the IP will have a new address
selected. This shouldn't matter at all.
Signed-off-by: Patrick McHardy <kaber@trash.net>

include/net/netfilter/nf_nat_rule.h

@@ -14,7 +14,4 @@ extern int nf_nat_rule_find(struct sk_buff *skb,
 
 extern unsigned int
 alloc_null_binding(struct nf_conn *ct, unsigned int hooknum);
-
-extern unsigned int
-alloc_null_binding_confirmed(struct nf_conn *ct, unsigned int hooknum);
 #endif /* _NF_NAT_RULE_H */

net/ipv4/netfilter/nf_nat_rule.c

@@ -188,25 +188,6 @@ alloc_null_binding(struct nf_conn *ct, unsigned int hooknum)
 	return nf_nat_setup_info(ct, &range, HOOK2MANIP(hooknum));
 }
 
-unsigned int
-alloc_null_binding_confirmed(struct nf_conn *ct, unsigned int hooknum)
-{
-	__be32 ip
-		= (HOOK2MANIP(hooknum) == IP_NAT_MANIP_SRC
-		   ? ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u3.ip
-		   : ct->tuplehash[IP_CT_DIR_REPLY].tuple.src.u3.ip);
-	__be16 all
-		= (HOOK2MANIP(hooknum) == IP_NAT_MANIP_SRC
-		   ? ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u.all
-		   : ct->tuplehash[IP_CT_DIR_REPLY].tuple.src.u.all);
-	struct nf_nat_range range
-		= { IP_NAT_RANGE_MAP_IPS, ip, ip, { all }, { all } };
-
-	pr_debug("Allocating NULL binding for confirmed %p (%u.%u.%u.%u)\n",
-		 ct, NIPQUAD(ip));
-	return nf_nat_setup_info(ct, &range, HOOK2MANIP(hooknum));
-}
-
 int nf_nat_rule_find(struct sk_buff *skb,
 		     unsigned int hooknum,
 		     const struct net_device *in,

net/ipv4/netfilter/nf_nat_standalone.c

@@ -102,6 +102,9 @@ nf_nat_fn(unsigned int hooknum,
 
 	nat = nfct_nat(ct);
 	if (!nat) {
+		/* NAT module was loaded late. */
+		if (nf_ct_is_confirmed(ct))
+			return NF_ACCEPT;
 		nat = nf_ct_ext_add(ct, NF_CT_EXT_NAT, GFP_ATOMIC);
 		if (nat == NULL) {
 			pr_debug("failed to add NAT extension\n");
@@ -127,10 +130,7 @@ nf_nat_fn(unsigned int hooknum,
 		if (!nf_nat_initialized(ct, maniptype)) {
 			unsigned int ret;
 
-			if (unlikely(nf_ct_is_confirmed(ct)))
-				/* NAT module was loaded late */
-				ret = alloc_null_binding_confirmed(ct, hooknum);
-			else if (hooknum == NF_INET_LOCAL_IN)
+			if (hooknum == NF_INET_LOCAL_IN)
 				/* LOCAL_IN hook doesn't have a chain!  */
 				ret = alloc_null_binding(ct, hooknum);
 			else