l2tp: remove useless duplicate session detection in l2tp_netlink

commit af87ae465abdc070de0dc35d6c6a9e7a8cd82987 upstream.

There's no point in checking for duplicate sessions at the beginning of
l2tp_nl_cmd_session_create(); the ->session_create() callbacks already
return -EEXIST when the session already exists.

Furthermore, even if l2tp_session_find() returns NULL, a new session
might be created right after the test. So relying on ->session_create()
to avoid duplicate session is the only sane behaviour.

Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Giuliano Procida <gprocida@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/net/l2tp/l2tp_netlink.c b/net/l2tp/l2tp_netlink.c
index d6fccfdc..36651b6 100644
--- a/net/l2tp/l2tp_netlink.c
+++ b/net/l2tp/l2tp_netlink.c
@@ -513,11 +513,6 @@
 		goto out;
 	session_id = nla_get_u32(info->attrs[L2TP_ATTR_SESSION_ID]);
-	session = l2tp_session_find(net, tunnel, session_id);
-	if (session) {
-		ret = -EEXIST;
-		goto out;
-	}
 	if (!info->attrs[L2TP_ATTR_PEER_SESSION_ID]) {
 		ret = -EINVAL;