Re: [libgpiod][PATCH] core: ignore positive values returned by the GPIO_V2_GET_LINE ioctl()

[Kent Gibson <warthog618@gmail.com>]

On Wed, Jan 24, 2024 at 11:39:29AM +0100, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
>
> If the kernel GPIO driver (erroneously) returns a positive value from one
> of its callbacks, it may end up being propagated to user space as
> a positive value returned by the call to ioctl(). Let's treat all
> non-zero values as errors as GPIO uAPI ioctl()s are not expected to ever
> return positive values. This should be addressed in the kernel but will
> remain a problem on older or unpatched versions so we need to sanitize it
> in user-space too.
>
> Reported-by: José Guilherme de Castro Rodrigues <joseguilhermebh@hotmail.com>
> Fixes: b7ba732e6a93 ("treewide: libgpiod v2 implementation")
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
> ---
>  lib/chip.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/lib/chip.c b/lib/chip.c
> index 7c05e53..7bf40c6 100644
> --- a/lib/chip.c
> +++ b/lib/chip.c
> @@ -239,7 +239,7 @@ gpiod_chip_request_lines(struct gpiod_chip *chip,
>  		return NULL;
>
>  	ret = ioctl(chip->fd, GPIO_V2_GET_LINE_IOCTL, &uapi_req);
> -	if (ret < 0)
> +	if (ret)
>  		return NULL;
>

What is errno going to be here?
Is errno set if the ioctl returns positive?

Cheers,
Kent.