linux-hardening - Re: [PATCH v2 1/3] lib: fix _parse_integer

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Message-ID: <aXOcjQqvE3TNUlel@smile.fi.intel.com>
Date: Fri, 23 Jan 2026 18:06:37 +0200
From: Andy Shevchenko <andriy.shevchenko@...el.com>
To: Dmitry Antipov <dmantipov@...dex.ru>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Kees Cook <kees@...nel.org>,
	"Darrick J . Wong" <djwong@...nel.org>,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2 1/3] lib: fix _parse_integer_limit() to handle overflow

On Fri, Jan 23, 2026 at 02:46:45PM +0300, Dmitry Antipov wrote:
> In '_parse_integer_limit()', replace native integer arithmetic with
> 'check_mul_overflow()' and 'check_add_overflow()' to check whether
> an intermediate result goes out of range, and denote such a case
> with ULLONG_MAX. Adjust comment to kernel-doc style as well.

Probably you also wanted to say that this is to be aligned with libc behaviour
of strto*()?

...

>  		/*
> +		 * Accumulate result if no overflow detected.
> +		 * Otherwise just consume valid characters.
>  		 */
> +		if (res != ULLONG_MAX) {

Here I would put another comment explaining that the order operations matters
(has a side effect), id est the result of the first one is used in the second
one.

			/*
			 * Keep an eye on the order.
			 *
			 * @tmp is being used in the second operation,
			 * if the first one succeeds.
			 */

> +			if (check_mul_overflow(res, base, &tmp) ||
> +			    check_add_overflow(tmp, val, &res)) {
> +				res = ULLONG_MAX;
>  				rv |= KSTRTOX_OVERFLOW;
> +			}
>  		}

-- 
With Best Regards,
Andy Shevchenko