[PATCH 3.2 17/79] l2tp: ensure sessions are freed after their PPPOL2TP socket

Ben Hutchings
2018-02-11T04:33:40Z

From: Guillaume Nault <g.nault@alphalink.fr>

commit cdd10c9627496ad25c87ce6394e29752253c69d3 upstream.

If l2tp_tunnel_delete() or l2tp_tunnel_closeall() deletes a session
right after pppol2tp_release() orphaned its socket, then the 'sock'
variable of the pppol2tp_session_close() callback is NULL. Yet the
session is still used by pppol2tp_release().

Therefore we need to take an extra reference in any case, to prevent
l2tp_tunnel_delete() or l2tp_tunnel_closeall() from freeing the session.

Since the pppol2tp_session_close() callback is only set if the session
is associated to a PPPOL2TP socket and that both l2tp_tunnel_delete()
and l2tp_tunnel_closeall() hold the PPPOL2TP socket before calling
pppol2tp_session_close(), we're sure that pppol2tp_session_close() and
pppol2tp_session_destruct() are paired and called in the right order.
So the reference taken by the former will be released by the later.

Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
net/l2tp/l2tp_ppp.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

--- a/net/l2tp/l2tp_ppp.c
+++ b/net/l2tp/l2tp_ppp.c
@@ -466,11 +466,11 @@ static void pppol2tp_session_close(struc
BUG_ON(session->magic != L2TP_SESSION_MAGIC);

- if (sock) {
+ if (sock)
inet_shutdown(sock, 2);
- /* Don't let the session go away before our socket does */
- l2tp_session_inc_refcount(session);
- }
+
+ /* Don't let the session go away before our socket does */
+ l2tp_session_inc_refcount(session);
return;
}