Re: [PATCH v3] gpio: cdev: fix kernel stack leak to user-space in error path

[Kent Gibson]

On Tue, Sep 22, 2026 at 10:52:28AM +0200, Bartosz Golaszewski wrote:
> If we fail to acquire the GPIO chip guard in gpio_desc_to_lineinfo(), we
> return immediately before zeroing the info struct we'll end up passing
> to the user-space later in lineinfo_get_v1(). This may leak the kernel
> stack contents. Make gpio_desc_to_lineinfo() return int so that the
> -ENODEV returned on failure to acquire the guard can be propagated to
> the callers.
> 
> While not strictly necessary: move the memset() before trying to acquire
> the SRCU read lock too for good measure.
> 
> Fixes: d83cee3d2bb1 ("gpio: protect the pointer to gpio_chip in gpio_device with SRCU")
> Cc: stable@xxxxxxxxxxxxxxx
> Reported-by: Sashiko <sashiko-bot@xxxxxxxxxx>
> Closes: https://sashiko.dev/#/patchset/20260912123529.7951-1-tzungbi%40kernel.org?part=3
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxxxxxxxx>
> ---
> Changes in v3:
> - Don't emit an error log message from the line info notifier if we fail
>   to acquire the chip guard
> - Link to v2: https://patch.msgid.link/20260921-gpio-cdev-stack-leak-fixes-v2-1-3307c4320352@xxxxxxxxxxxxxxxx
> 
> Changes in v2:
> - Make gpio_desc_to_lineinfo() return an integer return value so that
>   the error code returned in case of a failure to acquire the guard can
>   be propagated down the stack
> - Link to v1: https://patch.msgid.link/20260917-gpio-cdev-stack-leak-fixes-v1-1-2bb52879e49c@xxxxxxxxxxxxxxxx
> ---
>  drivers/gpio/gpiolib-cdev.c | 32 +++++++++++++++++++++++++-------
>  1 file changed, 25 insertions(+), 7 deletions(-)
> 

> @@ -2491,6 +2502,7 @@ static int lineinfo_changed_notify(struct notifier_block *nb,
>  	struct lineinfo_changed_ctx *ctx;
>  	struct gpio_desc *desc = data;
>  	struct file *fp;
> +	int ret;
>  
>  	if (!test_bit(gpiod_hwgpio(desc), cdev->watched_lines))
>  		return NOTIFY_DONE;
> @@ -2521,7 +2533,13 @@ static int lineinfo_changed_notify(struct notifier_block *nb,
>  
>  	ctx->chg.event_type = action;
>  	ctx->chg.timestamp_ns = ktime_get_ns();
> -	gpio_desc_to_lineinfo(desc, &ctx->chg.info, true);
> +
> +	ret = gpio_desc_to_lineinfo(desc, &ctx->chg.info, true);
> +	if (ret) {
> +		fput(fp);
> +		return NOTIFY_DONE;
> +	}
> +

Drop the ret and just test the return directly?

Sorry - should've picked that up in the previous version.

Cheers,
Kent.