Revert "netfilter: conntrack: fix race in __nf_conntrack_confirm against get_next_corpse"

This reverts commit 88fd8709 which was
commit 5195c14c upstream, which was
reverted in commit 43612d7c.
Reported-by: Pablo Neira Ayuso <pablo@netfilter.org>
Cc: Daniel Borkmann <dborkman@redhat.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

net/netfilter/nf_conntrack_core.c

@@ -611,16 +611,12 @@ __nf_conntrack_confirm(struct sk_buff *skb)
 	 */
 	NF_CT_ASSERT(!nf_ct_is_confirmed(ct));
 	pr_debug("Confirming conntrack %p\n", ct);
-
-	/* We have to check the DYING flag after unlink to prevent
-	 * a race against nf_ct_get_next_corpse() possibly called from
-	 * user context, else we insert an already 'dead' hash, blocking
-	 * further use of that particular connection -JM.
-	 */
-	nf_ct_del_from_dying_or_unconfirmed_list(ct);
+	/* We have to check the DYING flag inside the lock to prevent
+	   a race against nf_ct_get_next_corpse() possibly called from
+	   user context, else we insert an already 'dead' hash, blocking
+	   further use of that particular connection -JM */
 
 	if (unlikely(nf_ct_is_dying(ct))) {
-		nf_ct_add_to_dying_list(ct);
 		nf_conntrack_double_unlock(hash, reply_hash);
 		local_bh_enable();
 		return NF_ACCEPT;
@@ -640,6 +636,8 @@ __nf_conntrack_confirm(struct sk_buff *skb)
 		    zone == nf_ct_zone(nf_ct_tuplehash_to_ctrack(h)))
 			goto out;
 
+	nf_ct_del_from_dying_or_unconfirmed_list(ct);
+
 	/* Timer relative to confirmation time, not original
 	   setting time, otherwise we'd get timer wrap in
 	   weird delay cases. */