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 a0c6c00ac1664a1d0fa1fa67089c390ab5408282..6de18ead3dfe7264b2ae78ecf26f193fe6a4b37a 100644 (file)
--- a/include/linux/net.h
+++ b/include/linux/net.h
@@ -291,7 +291,7 @@ 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 facc180d163592edfa917ec58d74286152c1837a..e0a65ee1e83064ed20e5f61a29b659e0ea4325d6 100644 (file)
--- 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 1a2a7320554bd876688ff809b46a9658230daa9c..88086d18c20860770ab65bb823bca681f2fba0fe 100644 (file)
--- a/net/socket.c
+++ b/net/socket.c
@@ -3308,7 +3308,7 @@ 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)
 {