From: Guillaume Nault <g.nault@alphalink.fr>
Date: Fri, 3 Aug 2018 17:00:11 +0200
Subject: l2tp: fix missing refcount drop in pppol2tp_tunnel_ioctl()

commit f664e37dcc525768280cb94321424a09beb1c992 upstream.

If 'session' is not NULL and is not a PPP pseudo-wire, then we fail to
drop the reference taken by l2tp_session_get().

Fixes: ecd012e45ab5 ("l2tp: filter out non-PPP sessions in pppol2tp_tunnel_ioctl()")
Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.16: Also call session->deref in both cases]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 net/l2tp/l2tp_ppp.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

--- a/net/l2tp/l2tp_ppp.c
+++ b/net/l2tp/l2tp_ppp.c
@@ -1231,15 +1231,22 @@ static int pppol2tp_tunnel_ioctl(struct
 				l2tp_session_get(sock_net(sk), tunnel,
 						 stats.session_id, true);
 
-			if (session && session->pwtype == L2TP_PWTYPE_PPP) {
-				err = pppol2tp_session_ioctl(session, cmd,
-							     arg);
+			if (!session) {
+				err = -EBADR;
+				break;
+			}
+			if (session->pwtype != L2TP_PWTYPE_PPP) {
 				if (session->deref)
 					session->deref(session);
 				l2tp_session_dec_refcount(session);
-			} else {
 				err = -EBADR;
+				break;
 			}
+
+			err = pppol2tp_session_ioctl(session, cmd, arg);
+			if (session->deref)
+				session->deref(session);
+			l2tp_session_dec_refcount(session);
 			break;
 		}
 #ifdef CONFIG_XFRM