Re: [PATCH] USB: serial: xr: fix NULL-deref on disconnect

[Manivannan Sadhasivam <mani@kernel.org>]

On Fri, Feb 26, 2021 at 11:08:26AM +0100, Johan Hovold wrote:
> 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: c2d405aa86b4 ("USB: serial: add MaxLinear/Exar USB to Serial driver")
> Reported-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
> Cc: Manivannan Sadhasivam <mani@kernel.org>
> Signed-off-by: Johan Hovold <johan@kernel.org>

Reviewed-by: Manivannan Sadhasivam <mani@kernel.org>

Thanks,
Mani

> ---
>  drivers/usb/serial/xr_serial.c | 25 -------------------------
>  1 file changed, 25 deletions(-)
> 
> diff --git a/drivers/usb/serial/xr_serial.c b/drivers/usb/serial/xr_serial.c
> index 483d07dee19d..0ca04906da4b 100644
> --- a/drivers/usb/serial/xr_serial.c
> +++ b/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,
> -- 
> 2.26.2
>