vsock: cope with memory allocation failure at socket creation time

In the unlikely event that the kmalloc call in vmci_transport_socket_init()
fails, we end-up calling vmci_transport_destruct() with a NULL vmci_trans()
and oopsing.

This change addresses the above explicitly checking for zero vmci_trans()
at destruction time.
Reported-by: Xiumei Mu <xmu@redhat.com>
Fixes: d021c344 ("VSOCK: Introduce VM Sockets")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Jorgen Hansen <jhansen@vmware.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/vmw_vsock/vmci_transport.c

@@ -1651,6 +1651,10 @@ static void vmci_transport_cleanup(struct work_struct *work)
 
 static void vmci_transport_destruct(struct vsock_sock *vsk)
 {
+	/* transport can be NULL if we hit a failure at init() time */
+	if (!vmci_trans(vsk))
+		return;
+
 	/* Ensure that the detach callback doesn't use the sk/vsk
 	 * we are about to destruct.
 	 */