linux-kernel - Re: [PATCH] gpiolib: fix a NULL-pointer dereference when setting direction

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Message-ID: <bcaa681e-7ea2-40b0-8f9f-0bcba5010b11@gmail.com>
Date: Thu, 24 Oct 2024 15:44:44 +0200
From: Klara Modin <klarasmodin@...il.com>
To: Bartosz Golaszewski <brgl@...ev.pl>,
 Linus Walleij <linus.walleij@...aro.org>, Kent Gibson
 <warthog618@...il.com>, Mark Brown <broonie@...nel.org>
Cc: linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
 Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH] gpiolib: fix a NULL-pointer dereference when setting
 direction

On 2024-10-24 15:38, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> 
> For optional GPIOs we may pass NULL to gpiod_direction_(input|output)().
> With the call to the notifier chain added by commit 07c61d4da43f
> ("gpiolib: notify user-space about in-kernel line state changes") we
> will now dereference a NULL pointer in this case. The reason for that is
> the fact that the expansion of the VALIDATE_DESC() macro (which returns
> 0 for NULL descriptors) was moved into the nonotify variants of the
> direction setters.
> 
> Move them back to the top-level interfaces as the nonotify ones are only
> ever called from inside the GPIO core and are always passed valid GPIO
> descriptors. This way we'll never call the line_state notifier chain
> with non-valid descs.
> 
> Fixes: 07c61d4da43f ("gpiolib: notify user-space about in-kernel line state changes")
> Reported-by: Mark Brown <broonie@...nel.org>
> Closes: https://lore.kernel.org/all/d6601a31-7685-4b21-9271-1b76116cc483@sirena.org.uk/
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> ---
>   drivers/gpio/gpiolib.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index ae758ba6dc3d1..6001ec96693c5 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -2695,6 +2695,8 @@ int gpiod_direction_input(struct gpio_desc *desc)
>   {
>   	int ret;
>   
> +	VALIDATE_DESC(desc);
> +
>   	ret = gpiod_direction_input_nonotify(desc);
>   	if (ret == 0)
>   		gpiod_line_state_notify(desc, GPIO_V2_LINE_CHANGED_CONFIG);
> @@ -2707,8 +2709,6 @@ int gpiod_direction_input_nonotify(struct gpio_desc *desc)
>   {
>   	int ret = 0;
>   
> -	VALIDATE_DESC(desc);
> -
>   	CLASS(gpio_chip_guard, guard)(desc);
>   	if (!guard.gc)
>   		return -ENODEV;
> @@ -2841,6 +2841,8 @@ int gpiod_direction_output(struct gpio_desc *desc, int value)
>   {
>   	int ret;
>   
> +	VALIDATE_DESC(desc);
> +
>   	ret = gpiod_direction_output_nonotify(desc, value);
>   	if (ret == 0)
>   		gpiod_line_state_notify(desc, GPIO_V2_LINE_CHANGED_CONFIG);
> @@ -2854,8 +2856,6 @@ int gpiod_direction_output_nonotify(struct gpio_desc *desc, int value)
>   	unsigned long flags;
>   	int ret;
>   
> -	VALIDATE_DESC(desc);
> -
>   	flags = READ_ONCE(desc->flags);
>   
>   	if (test_bit(FLAG_ACTIVE_LOW, &flags))

This patch fixes the issue for me, thanks!

Tested-by: Klara Modin <klarasmodin@...il.com>