--- /dev/null
+From 57240d007816486131bee88cd474c2a71f0fe224 Mon Sep 17 00:00:00 2001
+From: "R. Parameswaran" <parameswaran.r7@gmail.com>
+Date: Wed, 12 Apr 2017 18:31:04 -0700
+Subject: l2tp: device MTU setup, tunnel socket needs a lock
+
+From: R. Parameswaran <parameswaran.r7@gmail.com>
+
+commit 57240d007816486131bee88cd474c2a71f0fe224 upstream.
+
+The MTU overhead calculation in L2TP device set-up
+merged via commit b784e7ebfce8cfb16c6f95e14e8532d0768ab7ff
+needs to be adjusted to lock the tunnel socket while
+referencing the sub-data structures to derive the
+socket's IP overhead.
+
+Reported-by: Guillaume Nault <g.nault@alphalink.fr>
+Tested-by: Guillaume Nault <g.nault@alphalink.fr>
+Signed-off-by: R. Parameswaran <rparames@brocade.com>
+Signed-off-by: David S. Miller <davem@davemloft.net>
+Cc: Giuliano Procida <gprocida@google.com>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+
+---
+ include/linux/net.h | 2 +-
+ net/l2tp/l2tp_eth.c | 2 ++
+ net/socket.c | 2 +-
+ 3 files changed, 4 insertions(+), 2 deletions(-)
+
+--- a/include/linux/net.h
++++ b/include/linux/net.h
+@@ -298,7 +298,7 @@ int kernel_sendpage(struct socket *sock,
+ int kernel_sock_ioctl(struct socket *sock, int cmd, unsigned long arg);
+ int kernel_sock_shutdown(struct socket *sock, enum sock_shutdown_cmd how);
+
+-/* Following routine returns the IP overhead imposed by a socket. */
++/* Routine returns the IP overhead imposed by a (caller-protected) socket. */
+ u32 kernel_sock_ip_overhead(struct sock *sk);
+
+ #define MODULE_ALIAS_NETPROTO(proto) \
+--- a/net/l2tp/l2tp_eth.c
++++ b/net/l2tp/l2tp_eth.c
+@@ -240,7 +240,9 @@ static void l2tp_eth_adjust_mtu(struct l
+ dev->needed_headroom += session->hdr_len;
+ return;
+ }
++ lock_sock(tunnel->sock);
+ l3_overhead = kernel_sock_ip_overhead(tunnel->sock);
++ release_sock(tunnel->sock);
+ if (l3_overhead == 0) {
+ /* L3 Overhead couldn't be identified, this could be
+ * because tunnel->sock was NULL or the socket's
+--- a/net/socket.c
++++ b/net/socket.c
+@@ -3325,7 +3325,7 @@ EXPORT_SYMBOL(kernel_sock_shutdown);
+ /* This routine returns the IP overhead imposed by a socket i.e.
+ * the length of the underlying IP header, depending on whether
+ * this is an IPv4 or IPv6 socket and the length from IP options turned
+- * on at the socket.
++ * on at the socket. Assumes that the caller has a lock on the socket.
+ */
+ u32 kernel_sock_ip_overhead(struct sock *sk)
+ {