vsock: prevent transport modules unloading

This patch adds 'module' member in the 'struct vsock_transport'
in order to get/put the transport module. This prevents the
module unloading while sockets are assigned to it.

We increase the module refcnt when a socket is assigned to a
transport, and we decrease the module refcnt when the socket
is destructed.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Jorgen Hansen <jhansen@vmware.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 16 insertions, 4 deletions

diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index 5357714b6104..5cb0ae42d916 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -380,6 +380,16 @@ void vsock_enqueue_accept(struct sock *listener, struct sock *connected)
 }
 EXPORT_SYMBOL_GPL(vsock_enqueue_accept);
 
+static void vsock_deassign_transport(struct vsock_sock *vsk)
+{
+	if (!vsk->transport)
+		return;
+
+	vsk->transport->destruct(vsk);
+	module_put(vsk->transport->module);
+	vsk->transport = NULL;
+}
+
 /* Assign a transport to a socket and call the .init transport callback.
  *
  * Note: for stream socket this must be called when vsk->remote_addr is set
@@ -418,10 +428,13 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk)
 			return 0;
 
 		vsk->transport->release(vsk);
-		vsk->transport->destruct(vsk);
+		vsock_deassign_transport(vsk);
 	}
 
-	if (!new_transport)
+	/* We increase the module refcnt to prevent the transport unloading
+	 * while there are open sockets assigned to it.
+	 */
+	if (!new_transport || !try_module_get(new_transport->module))
 		return -ENODEV;
 
 	vsk->transport = new_transport;
@@ -741,8 +754,7 @@ static void vsock_sk_destruct(struct sock *sk)
 {
 	struct vsock_sock *vsk = vsock_sk(sk);
 
-	if (vsk->transport)
-		vsk->transport->destruct(vsk);
+	vsock_deassign_transport(vsk);
 
 	/* When clearing these addresses, there's no need to set the family and
 	 * possibly register the address family with the kernel.