[PATCH] lib/vsprintf: Fix to check field_width and precision

[PATCH] lib/vsprintf: Fix to check field_width and precision

[Masami Hiramatsu (Google)]

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>
---
 lib/vsprintf.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 800b8ac49f53..054c9758118e 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, "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);
 	}
 }

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

[Andy Shevchenko]

On Thu, Mar 19, 2026 at 09:26:59AM +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.

...

>  	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, "field width %d too large", width)) {

Also use logical split as below:

	if (WARN_ONCE(spec->field_width > FIELD_WIDTH_MAX || spec->field_width < -FIELD_WIDTH_MAX,
		      "field width %d too large", width)) {

>  		spec->field_width = clamp(width, -FIELD_WIDTH_MAX, FIELD_WIDTH_MAX);
>  	}
>  }

...

>  	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);
>  	}

-- 
With Best Regards,
Andy Shevchenko

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

[Masami Hiramatsu]

On Thu, 19 Mar 2026 09:11:21 +0200
Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote:

> On Thu, Mar 19, 2026 at 09:26:59AM +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.
> 
> ...
> 
> >  	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, "field width %d too large", width)) {
> 
> Also use logical split as below:
> 
> 	if (WARN_ONCE(spec->field_width > FIELD_WIDTH_MAX || spec->field_width < -FIELD_WIDTH_MAX,
> 		      "field width %d too large", width)) {

OK, let me update it.

Thanks,

> 
> >  		spec->field_width = clamp(width, -FIELD_WIDTH_MAX, FIELD_WIDTH_MAX);
> >  	}
> >  }
> 
> ...
> 
> >  	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);
> >  	}
> 
> -- 
> With Best Regards,
> Andy Shevchenko
> 
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>