Re: [PATCH v3 1/2] lib/vsprintf: Fix to check field_width and precision

[Andy Shevchenko]

On Sat, Mar 21, 2026 at 11:41:12PM +0900, Masami Hiramatsu (Google) wrote:

> Check the field_width and presition correctly. Previously it depends
> on the bitfield conversion from int to check out-of-range error.
> However, commit 938df695e98d ("vsprintf: associate the format state
> with the format pointer") changed those fields to int.
> We need to check the out-of-range correctly without bitfield
> conversion.

...

>  static void
>  set_field_width(struct printf_spec *spec, int width)
>  {
> -	spec->field_width = width;
> -	if (WARN_ONCE(spec->field_width != width, "field width %d too large", width)) {
> -		spec->field_width = clamp(width, -FIELD_WIDTH_MAX, FIELD_WIDTH_MAX);
> +	if (WARN_ONCE(width > FIELD_WIDTH_MAX || width < -FIELD_WIDTH_MAX,
> +		      "field width %d too large", width)) {
> +		width = clamp(width, -FIELD_WIDTH_MAX, FIELD_WIDTH_MAX);
>  	}
> +	spec->field_width = width;
>  }
>  
>  static void
>  set_precision(struct printf_spec *spec, int prec)
>  {
> -	spec->precision = prec;
> -	if (WARN_ONCE(spec->precision != prec, "precision %d too large", prec)) {
> -		spec->precision = clamp(prec, 0, PRECISION_MAX);
> +	if (WARN_ONCE(prec > PRECISION_MAX || prec < 0,
> +		      "precision %d too large", prec)) {
> +		prec = clamp(prec, 0, PRECISION_MAX);
>  	}
> +	spec->precision = prec;
>  }

Looking at this, perhaps

#define clamp_WARN_*(...)
	...

Potential users besides these two:

arch/powerpc/platforms/pseries/papr-sysparm.c-39-
drivers/gpu/drm/drm_color_mgmt.c-142-
drivers/gpu/drm/i915/display/intel_backlight.c-48-
drivers/media/i2c/vgxy61.c-952-

-- 
With Best Regards,
Andy Shevchenko