Re: [PATCH] gpio: cdev: fix a NULL-pointer dereference with DEBUG enabled

[Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>]

On 16.02.2024 11:59, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
>
> We are actually passing the gc pointer to chip_dbg() so we have to
> srcu_dereference() it.
>
> Fixes: 8574b5b47610 ("gpio: cdev: use correct pointer accessors with SRCU")
> Reported-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> Closes: https://lore.kernel.org/lkml/179caa10-5f86-4707-8bb0-fe1b316326d6@xxxxxxxxxxx/
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
Tested-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> ---
>   drivers/gpio/gpiolib-cdev.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib-cdev.c b/drivers/gpio/gpiolib-cdev.c
> index 85037fa4925e..f384fa278764 100644
> --- a/drivers/gpio/gpiolib-cdev.c
> +++ b/drivers/gpio/gpiolib-cdev.c
> @@ -2795,8 +2795,8 @@ int gpiolib_cdev_register(struct gpio_device *gdev, dev_t devt)
>   		return ret;
>   
>   	guard(srcu)(&gdev->srcu);
> -
> -	if (!rcu_access_pointer(gdev->chip))
> +	gc = srcu_dereference(gdev->chip, &gdev->srcu);
> +	if (!gc)
>   		return -ENODEV;
>   
>   	chip_dbg(gc, "added GPIO chardev (%d:%d)\n", MAJOR(devt), gdev->id);

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland