USB: serial: xr: fix NULL-deref on disconnect

Claiming the sibling control interface is a bit more involved and
specifically requires adding support to USB-serial core for managing
either interface being unbound first, something which could otherwise
lead to a NULL-pointer dereference.

Similarly, additional infrastructure is also needed to handle suspend
properly.

Since the driver currently isn't actually using the control interface,
we can defer this for now by simply not claiming the control interface.

Fixes: c2d405aa86 ("USB: serial: add MaxLinear/Exar USB to Serial driver")
Reported-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Tested-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Manivannan Sadhasivam <mani@kernel.org>
Signed-off-by: Johan Hovold <johan@kernel.org>

drivers/usb/serial/xr_serial.c

@@ -545,37 +545,13 @@ static void xr_close(struct usb_serial_port *port)
 
 static int xr_probe(struct usb_serial *serial, const struct usb_device_id *id)
 {
-	struct usb_driver *driver = serial->type->usb_driver;
-	struct usb_interface *control_interface;
-	int ret;
-
 	/* Don't bind to control interface */
 	if (serial->interface->cur_altsetting->desc.bInterfaceNumber == 0)
 		return -ENODEV;
 
-	/* But claim the control interface during data interface probe */
-	control_interface = usb_ifnum_to_if(serial->dev, 0);
-	if (!control_interface)
-		return -ENODEV;
-
-	ret = usb_driver_claim_interface(driver, control_interface, NULL);
-	if (ret) {
-		dev_err(&serial->interface->dev, "Failed to claim control interface\n");
-		return ret;
-	}
-
 	return 0;
 }
 
-static void xr_disconnect(struct usb_serial *serial)
-{
-	struct usb_driver *driver = serial->type->usb_driver;
-	struct usb_interface *control_interface;
-
-	control_interface = usb_ifnum_to_if(serial->dev, 0);
-	usb_driver_release_interface(driver, control_interface);
-}
-
 static const struct usb_device_id id_table[] = {
 	{ USB_DEVICE(0x04e2, 0x1410) }, /* XR21V141X */
 	{ }
@@ -590,7 +566,6 @@ static struct usb_serial_driver xr_device = {
 	.id_table		= id_table,
 	.num_ports		= 1,
 	.probe			= xr_probe,
-	.disconnect		= xr_disconnect,
 	.open			= xr_open,
 	.close			= xr_close,
 	.break_ctl		= xr_break_ctl,