l2tp: device MTU setup, tunnel socket needs a lock 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>

diff --git a/include/linux/net.h b/include/linux/net.h
index 2c8b092..54270c4 100644
--- a/include/linux/net.h
+++ b/include/linux/net.h

@@ -298,7 +298,7 @@ int kernel_sendpage(struct socket *sock, struct page *page, int offset,
 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) \

diff --git a/net/l2tp/l2tp_eth.c b/net/l2tp/l2tp_eth.c
index 60764ac..8b8fc23 100644
--- a/net/l2tp/l2tp_eth.c
+++ b/net/l2tp/l2tp_eth.c

@@ -240,7 +240,9 @@ static void l2tp_eth_adjust_mtu(struct l2tp_tunnel *tunnel,
 		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

diff --git a/net/socket.c b/net/socket.c
index 4892719..88abc72 100644
--- 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)
 {