Re: [PATCH 5.4 106/434] media: flexcop-usb: fix NULL-ptr deref in flexcop_usb_transfer_init()

[Johan Hovold]

On Sun, Dec 29, 2019 at 06:22:39PM +0100, Greg Kroah-Hartman wrote:
> From: Yang Yingliang <yangyingliang@xxxxxxxxxx>
> 
> [ Upstream commit 649cd16c438f51d4cd777e71ca1f47f6e0c5e65d ]
> 
> If usb_set_interface() failed, iface->cur_altsetting will
> not be assigned and it will be used in flexcop_usb_transfer_init()
> It may lead a NULL pointer dereference.
> 
> Check usb_set_interface() return value in flexcop_usb_init()
> and return failed to avoid using this NULL pointer.
> 
> Signed-off-by: Yang Yingliang <yangyingliang@xxxxxxxxxx>
> Signed-off-by: Sean Young <sean@xxxxxxxx>
> Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@xxxxxxxxxx>
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

This commit is bogus and should be dropped from all stable queues.

Contrary to what the commit message claims, iface->cur_altsetting will
never be NULL so there's no risk for a NULL-pointer dereference here.

Even though the change itself is benign, we shouldn't spread this
confusion further.

> ---
>  drivers/media/usb/b2c2/flexcop-usb.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/usb/b2c2/flexcop-usb.c b/drivers/media/usb/b2c2/flexcop-usb.c
> index 1a801dc286f8..d1331f828108 100644
> --- a/drivers/media/usb/b2c2/flexcop-usb.c
> +++ b/drivers/media/usb/b2c2/flexcop-usb.c
> @@ -504,7 +504,13 @@ urb_error:
>  static int flexcop_usb_init(struct flexcop_usb *fc_usb)
>  {
>  	/* use the alternate setting with the larges buffer */
> -	usb_set_interface(fc_usb->udev,0,1);
> +	int ret = usb_set_interface(fc_usb->udev, 0, 1);
> +
> +	if (ret) {
> +		err("set interface failed.");
> +		return ret;
> +	}
> +
>  	switch (fc_usb->udev->speed) {
>  	case USB_SPEED_LOW:
>  		err("cannot handle USB speed because it is too slow.");

Johan