Re: [PATCH v2 1/2] lib/vsprintf: Fix to check field_width and precision

[David Laight <david.laight.linux@gmail.com>]

On Fri, 20 Mar 2026 12:54:48 +0900
"Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:

> From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> 
> 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.
> 
> Fixes: 938df695e98d ("vsprintf: associate the format state with the format pointer")
> Reported-by: David Laight <david.laight.linux@gmail.com>
> Closes: https://lore.kernel.org/all/20260318151250.40fef0ab@pumpkin/
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> ---
>  Changes in v2:
>   - Fix to use logical split.
> ---
>  lib/vsprintf.c |    6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 800b8ac49f53..32a164e2adf4 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -2803,7 +2803,8 @@ 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)) {
> +	if (WARN_ONCE(spec->field_width > FIELD_WIDTH_MAX || spec->field_width < -FIELD_WIDTH_MAX,

Check and update width before the assignment to spec->field_width.

	David

> +		      "field width %d too large", width)) {
>  		spec->field_width = clamp(width, -FIELD_WIDTH_MAX, FIELD_WIDTH_MAX);
>  	}
>  }
> @@ -2812,7 +2813,8 @@ static void
>  set_precision(struct printf_spec *spec, int prec)
>  {
>  	spec->precision = prec;
> -	if (WARN_ONCE(spec->precision != prec, "precision %d too large", prec)) {
> +	if (WARN_ONCE(spec->precision > PRECISION_MAX || spec->precision < 0,
> +		      "precision %d too large", prec)) {
>  		spec->precision = clamp(prec, 0, PRECISION_MAX);
>  	}
>  }
>