Re: [PATCH 1/2] gpio: fix NULL-deref-on-deregistration regression

[Saravana Kannan]

On Fri, Feb 26, 2021 at 6:55 AM Johan Hovold <johan@xxxxxxxxxx> wrote:
>
> Fix a NULL-pointer deference when deregistering the gpio character
> device that was introduced by the recent stub-driver hack. When the new
> "driver" is unbound as part of deregistration, driver core clears the
> driver-data pointer which is used to retrieve the struct gpio_device in
> its release callback.
>
> Fix this by using container_of() in the release callback as should have
> been done all along.
>
> Fixes: 4731210c09f5 ("gpiolib: Bind gpio_device to a driver to enable fw_devlink=on by default")
> Cc: Saravana Kannan <saravanak@xxxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Reported-by: syzbot+d27b4c8adbbff70fbfde@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Johan Hovold <johan@xxxxxxxxxx>
> ---
>  drivers/gpio/gpiolib.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index adf55db080d8..e1016bc8cf14 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -474,7 +474,7 @@ EXPORT_SYMBOL_GPL(gpiochip_line_is_valid);
>
>  static void gpiodevice_release(struct device *dev)
>  {
> -       struct gpio_device *gdev = dev_get_drvdata(dev);
> +       struct gpio_device *gdev = container_of(dev, struct gpio_device, dev);

Can you also delete the dev_set_drvdata() in
gpiochip_add_data_with_key() if the drvdata is not used
elsewhere anymore? I skimmed the code and it doesn't look like it, but
I could be wrong.

-Saravana