USB: serial: whiteheat: fix potential slab corruption

Fix a user-controlled slab buffer overflow due to a missing sanity check
on the bulk-out transfer buffer used for control requests.

Fixes: 1da177e ("Linux-2.6.12-rc2")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20191029102354.2733-2-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/serial/whiteheat.c

@@ -559,6 +559,10 @@ static int firm_send_command(struct usb_serial_port *port, __u8 command,
 
 	command_port = port->serial->port[COMMAND_PORT];
 	command_info = usb_get_serial_port_data(command_port);
+
+	if (command_port->bulk_out_size < datasize + 1)
+		return -EIO;
+
 	mutex_lock(&command_info->mutex);
 	command_info->command_finished = false;