[PATCH 3.16 155/294] l2tp: initialise session's refcount before making it reachable

[Ben Hutchings]

3.16.50-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Guillaume Nault <g.nault@xxxxxxxxxxxx>

commit 9ee369a405c57613d7c83a3967780c3e30c52ecc upstream.

Sessions must be fully initialised before calling
l2tp_session_add_to_tunnel(). Otherwise, there's a short time frame
where partially initialised sessions can be accessed by external users.

Fixes: dbdbc73b4478 ("l2tp: fix duplicate session creation")
Signed-off-by: Guillaume Nault <g.nault@xxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
[bwh: Backported to 3.16: keep using l2tp_session_inc_refcount()]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 net/l2tp/l2tp_core.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -1929,6 +1929,8 @@ struct l2tp_session *l2tp_session_create
 
 		l2tp_session_set_header_len(session, tunnel->version);
 
+		l2tp_session_inc_refcount(session);
+
 		err = l2tp_session_add_to_tunnel(tunnel, session);
 		if (err) {
 			kfree(session);
@@ -1936,10 +1938,6 @@ struct l2tp_session *l2tp_session_create
 			return ERR_PTR(err);
 		}
 
-		/* Bump the reference count. The session context is deleted
-		 * only when this drops to zero.
-		 */
-		l2tp_session_inc_refcount(session);
 		l2tp_tunnel_inc_refcount(tunnel);
 
 		/* Ensure tunnel socket isn't deleted */