l2tp: device MTU setup, tunnel socket needs a lock

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>

1 files changed, 2 insertions, 0 deletions

diff --git a/net/l2tp/l2tp_eth.c b/net/l2tp/l2tp_eth.c
index 138566a63123..b722d559c544 100644
--- a/net/l2tp/l2tp_eth.c
+++ b/net/l2tp/l2tp_eth.c
@@ -225,7 +225,9 @@ 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