linux-kernel - Re: [PATCH 4/8] gpiolib: sanitize the return value of gpio

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Message-ID: <Z7yekJ8uRh8dphKn@black.fi.intel.com>
Date: Mon, 24 Feb 2025 18:30:08 +0200
From: Andy Shevchenko <andriy.shevchenko@...el.com>
To: Bartosz Golaszewski <brgl@...ev.pl>
Cc: Linus Walleij <linus.walleij@...aro.org>, linux-gpio@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH 4/8] gpiolib: sanitize the return value of
 gpio_chip::get()

On Mon, Feb 10, 2025 at 11:51:58AM +0100, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> 
> As per the API contract, the get() callback is only allowed to return 0,
> 1 or a negative error number. Add a wrapper around the callback calls
> that filters out anything else.

...

> +static int gpiochip_get(struct gpio_chip *gc, unsigned int offset)
> +{
> +	int ret;
> +
> +	lockdep_assert_held(&gc->gpiodev->srcu);
> +
> +	if (!gc->get)
> +		return -EIO;
> +
> +	ret = gc->get(gc, offset);
> +	if (ret > 1)

Perhaps use the respective GPIO macro instead? Otherwise it's not clear what
the meaning of 1 is.

> +		ret = -EBADE;
> +
> +	return ret;
> +}
> +
>  static int gpio_chip_get_value(struct gpio_chip *gc, const struct gpio_desc *desc)
>  {
> -	return gc->get ? gc->get(gc, gpio_chip_hwgpio(desc)) : -EIO;
> +	return gpiochip_get(gc, gpio_chip_hwgpio(desc));
>  }

...

>  		for_each_set_bit(i, mask, gc->ngpio) {
> -			value = gc->get(gc, i);
> +			value = gpiochip_get(gc, i);

This will delay the function for checking every time if the get() exists. Which
must be here.

>  			if (value < 0)
>  				return value;
>  			__assign_bit(i, bits, value);

What I would expect here is something like this:

static int gpio_chip_get_value_nocheck(struct gpio_chip *gc, unsigned int offset)
{
	int ret;

	lockdep_assert_held(&gc->gpiodev->srcu);

	ret = gc->get(gc, offset);
	if (ret > GPIO_LINE_DIRECTION_IN)
		ret = -EBADE;

	return ret;
}

static int gpio_chip_get_value(struct gpio_chip *gc, const struct gpio_desc *desc)
{
	return gc->get ? gpio_chip_get_value_nocheck(gc, gpio_chip_hwgpio(desc)) : -EIO;
}

But I see the downside of it as it might lurk without RCU lock if get is not
defined. So, up to you.

-- 
With Best Regards,
Andy Shevchenko