USB: serial: mxuport: fix use-after-free in probe error path

The interface read and event URBs are submitted in attach, but were
never explicitly unlinked by the driver. Instead the URBs would have
been killed by usb-serial core on disconnect.

In case of a late probe error (e.g. due to failed minor allocation),
disconnect is never called and we could end up with active URBs for an
unbound interface. This in turn could lead to deallocated memory being
dereferenced in the completion callbacks.

Fixes: ee467a1f2066 ("USB: serial: add Moxa UPORT 12XX/14XX/16XX
driver")
Cc: stable <stable@vger.kernel.org>	# v3.14
Signed-off-by: Johan Hovold <johan@kernel.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/serial/mxuport.c

@@ -1259,6 +1259,15 @@ static int mxuport_attach(struct usb_serial *serial)
 	return 0;
 }
 
+static void mxuport_release(struct usb_serial *serial)
+{
+	struct usb_serial_port *port0 = serial->port[0];
+	struct usb_serial_port *port1 = serial->port[1];
+
+	usb_serial_generic_close(port1);
+	usb_serial_generic_close(port0);
+}
+
 static int mxuport_open(struct tty_struct *tty, struct usb_serial_port *port)
 {
 	struct mxuport_port *mxport = usb_get_serial_port_data(port);
@@ -1361,6 +1370,7 @@ static struct usb_serial_driver mxuport_device = {
 	.probe			= mxuport_probe,
 	.port_probe		= mxuport_port_probe,
 	.attach			= mxuport_attach,
+	.release		= mxuport_release,
 	.calc_num_ports		= mxuport_calc_num_ports,
 	.open			= mxuport_open,
 	.close			= mxuport_close,