netfilter: ctnetlink: fix double helper assignation for NAT'ed conntracks

If we create a conntrack that has NAT handlings and a helper, the helper
is assigned twice. This happens because nf_nat_setup_info() - via
nf_conntrack_alter_reply() - sets the helper before ctnetlink, which
indeed does not check if the conntrack already has a helper as it thinks that
it is a brand new conntrack.

The fix moves the helper assignation before the set of the status flags.
This avoids a bogus assertion in __nf_ct_ext_add (if netfilter assertions are
enabled) which checks that the conntrack must not be confirmed.

This problem was introduced in 2.6.23 with the netfilter extension
infrastructure.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Patrick McHardy <kaber@trash.net>

net/netfilter/nf_conntrack_netlink.c

@@ -1136,16 +1136,33 @@ ctnetlink_create_conntrack(struct nlattr *cda[],
 	ct->timeout.expires = jiffies + ct->timeout.expires * HZ;
 	ct->status |= IPS_CONFIRMED;
 
+	rcu_read_lock();
+	helper = __nf_ct_helper_find(rtuple);
+	if (helper) {
+		help = nf_ct_helper_ext_add(ct, GFP_KERNEL);
+		if (help == NULL) {
+			rcu_read_unlock();
+			err = -ENOMEM;
+			goto err;
+		}
+		/* not in hash table yet so not strictly necessary */
+		rcu_assign_pointer(help->helper, helper);
+	}
+
 	if (cda[CTA_STATUS]) {
 		err = ctnetlink_change_status(ct, cda);
-		if (err < 0)
+		if (err < 0) {
+			rcu_read_unlock();
 			goto err;
+		}
 	}
 
 	if (cda[CTA_PROTOINFO]) {
 		err = ctnetlink_change_protoinfo(ct, cda);
-		if (err < 0)
+		if (err < 0) {
+			rcu_read_unlock();
 			goto err;
+		}
 	}
 
 	nf_ct_acct_ext_add(ct, GFP_KERNEL);
@@ -1155,19 +1172,6 @@ ctnetlink_create_conntrack(struct nlattr *cda[],
 		ct->mark = ntohl(nla_get_be32(cda[CTA_MARK]));
 #endif
 
-	rcu_read_lock();
-	helper = __nf_ct_helper_find(rtuple);
-	if (helper) {
-		help = nf_ct_helper_ext_add(ct, GFP_KERNEL);
-		if (help == NULL) {
-			rcu_read_unlock();
-			err = -ENOMEM;
-			goto err;
-		}
-		/* not in hash table yet so not strictly necessary */
-		rcu_assign_pointer(help->helper, helper);
-	}
-
 	/* setup master conntrack: this is a confirmed expectation */
 	if (master_ct) {
 		__set_bit(IPS_EXPECTED_BIT, &ct->status);