Re: [PATCH v2] leds: pwm: Annotate leds[] with __counted_by()

[Lee Jones <lee@kernel.org>]

On Thu, 02 Jul 2026, sashiko-bot@kernel.org wrote:

> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] The addition of the `__counted_by(num_leds)` annotation causes an unconditional out-of-bounds trap during probe.

Can you provide comment or remediation please?

> --
> 
> commit f2069ade09481403f091ed2758ef698b0c75c2cc
> Author: Mert Seftali <mertsftl@gmail.com>
> 
> leds: pwm: Annotate leds[] with __counted_by()
> 
> This commit adds the __counted_by(num_leds) attribute to the flexible array
> member leds[] in struct led_pwm_priv for bounds checking. It also updates
> led_pwm_add() to accept the led_pwm_data element directly, leaving num_leds
> to be incremented in the caller.
> 
> > diff --git a/drivers/leds/leds-pwm.c b/drivers/leds/leds-pwm.c
> > index 6c1f2f50ff854..dabdf04235826 100644
> > --- a/drivers/leds/leds-pwm.c
> > +++ b/drivers/leds/leds-pwm.c
> > @@ -36,7 +36,7 @@ struct led_pwm_data {
> >  
> >  struct led_pwm_priv {
> >  	int num_leds;
> > -	struct led_pwm_data leds[];
> > +	struct led_pwm_data leds[] __counted_by(num_leds);
> >  };
> 
> [ ... ]
> 
> > @@ -193,9 +191,10 @@ static int led_pwm_create_fwnode(struct device *dev, struct led_pwm_priv *priv)
> >  
> >  		led.default_state = led_init_default_state_get(fwnode);
> >  
> > -		ret = led_pwm_add(dev, priv, &led, fwnode);
> > +		ret = led_pwm_add(dev, &priv->leds[priv->num_leds], &led, fwnode);
> 
> [Severity: High]
> Does evaluating &priv->leds[priv->num_leds] before incrementing num_leds
> trigger an out-of-bounds trap under UBSAN_BOUNDS or FORTIFY_SOURCE?
> 
> Because leds is now annotated with __counted_by(num_leds), the compiler
> expects the valid indices to be less than num_leds. When this loop starts
> in led_pwm_create_fwnode(), priv->num_leds is initially 0. Taking the address
> of index 0 when the count is 0 will fail the bounds check and trigger a
> splat during driver probe.
> 
> >  		if (ret)
> >  			return ret;
> > +		priv->num_leds++;
> >  	}
> >  
> >  	return 0;
> 
> -- 
> Sashiko AI review · https://sashiko.dev/#/patchset/20260702155452.67594-1-mertseftali@web.de?part=1

-- 
Lee Jones