Re: [PATCH v2] gpio: cdev: fix kernel stack leak to user-space in error path

[Kent Gibson <warthog618@gmail.com>]

On Mon, Sep 21, 2026 at 02:56:58PM +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@vger.kernel.org
> Reported-by: Sashiko <sashiko-bot@kernel.org>
> Closes: https://sashiko.dev/#/patchset/20260912123529.7951-1-tzungbi%40kernel.org?part=3
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
> ---
> 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@oss.qualcomm.com

> @@ -2521,7 +2533,14 @@ 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);
> +		pr_err("GPIO controller that generated the line info notification was removed\n");
> +		return NOTIFY_DONE;
> +	}
> +

Does resolving a race warrant an error?

Also, compared to the kzalloc_obj() error path earlier in the function, here
you flip the order of the fput() and pr_err(). Is that significant?

Other than that, looks good to me.

Cheers,
Kent.