--- /dev/null
+From 94d7ee0baa8b764cf64ad91ed69464c1a6a0066b Mon Sep 17 00:00:00 2001
+From: Guillaume Nault <g.nault@alphalink.fr>
+Date: Wed, 29 Mar 2017 08:44:59 +0200
+Subject: l2tp: hold tunnel socket when handling control frames in l2tp_ip and l2tp_ip6
+
+From: Guillaume Nault <g.nault@alphalink.fr>
+
+commit 94d7ee0baa8b764cf64ad91ed69464c1a6a0066b upstream.
+
+The code following l2tp_tunnel_find() expects that a new reference is
+held on sk. Either sk_receive_skb() or the discard_put error path will
+drop a reference from the tunnel's socket.
+
+This issue exists in both l2tp_ip and l2tp_ip6.
+
+Fixes: a3c18422a4b4 ("l2tp: hold socket before dropping lock in l2tp_ip{, 6}_recv()")
+Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+
+---
+ net/l2tp/l2tp_ip.c | 5 +++--
+ net/l2tp/l2tp_ip6.c | 5 +++--
+ 2 files changed, 6 insertions(+), 4 deletions(-)
+
+--- a/net/l2tp/l2tp_ip.c
++++ b/net/l2tp/l2tp_ip.c
+@@ -177,9 +177,10 @@ pass_up:
+
+ tunnel_id = ntohl(*(__be32 *) &skb->data[4]);
+ tunnel = l2tp_tunnel_find(net, tunnel_id);
+- if (tunnel != NULL)
++ if (tunnel) {
+ sk = tunnel->sock;
+- else {
++ sock_hold(sk);
++ } else {
+ struct iphdr *iph = (struct iphdr *) skb_network_header(skb);
+
+ read_lock_bh(&l2tp_ip_lock);
+--- a/net/l2tp/l2tp_ip6.c
++++ b/net/l2tp/l2tp_ip6.c
+@@ -188,9 +188,10 @@ pass_up:
+
+ tunnel_id = ntohl(*(__be32 *) &skb->data[4]);
+ tunnel = l2tp_tunnel_find(&init_net, tunnel_id);
+- if (tunnel != NULL)
++ if (tunnel) {
+ sk = tunnel->sock;
+- else {
++ sock_hold(sk);
++ } else {
+ struct ipv6hdr *iph = ipv6_hdr(skb);
+
+ read_lock_bh(&l2tp_ip6_lock);