l2tp: initialise session's refcount before making it reachable

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@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index b0c2d4a..f363669 100644 (file)
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -1844,6 +1844,8 @@ struct l2tp_session *l2tp_session_create(int priv_size, struct l2tp_tunnel *tunn
 
                l2tp_session_set_header_len(session, tunnel->version);
 
+               refcount_set(&session->ref_count, 1);
+
                err = l2tp_session_add_to_tunnel(tunnel, session);
                if (err) {
                        kfree(session);
@@ -1851,10 +1853,6 @@ struct l2tp_session *l2tp_session_create(int priv_size, struct l2tp_tunnel *tunn
                        return ERR_PTR(err);
                }
 
-               /* Bump the reference count. The session context is deleted
-                * only when this drops to zero.
-                */
-               refcount_set(&session->ref_count, 1);
                l2tp_tunnel_inc_refcount(tunnel);
 
                /* Ensure tunnel socket isn't deleted */