linux-hardening - Re: [PATCH v4 1/4] lib: fix _parse_integer

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Message-ID: <aYKJBZRwQe3llJlW@smile.fi.intel.com>
Date: Wed, 4 Feb 2026 01:47:17 +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 v4 1/4] lib: fix _parse_integer_limit() to handle overflow

On Mon, Feb 02, 2026 at 02:54:48PM +0300, Dmitry Antipov wrote:
> In '_parse_integer_limit()', adjust native integer arithmetic
> with near-to-overflow branch where 'check_mul_overflow()' and
> 'check_add_overflow()' are used to check whether an intermediate
> result goes out of range, and denote such a case with ULLONG_MAX,
> thus making the function more similar to standard C library's
> 'strtoull()'. Adjust comment to kernel-doc style as well.

This version is good enough, we may consider further optimisations later on.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@...el.com>

...

>  		/*
> -		 * Check for overflow only if we are within range of
> -		 * it in the max base we support (16)
> +		 * Accumulate result if no overflow detected.
> +		 * Otherwise just consume valid characters.
>  		 */
> -		if (unlikely(res & (~0ull << 60))) {
> -			if (res > div_u64(ULLONG_MAX - val, base))
> -				rv |= KSTRTOX_OVERFLOW;
> +		if (likely(res != ULLONG_MAX)) {
> +			if (unlikely(res & (~0ull << 60))) {
> +				/* We're close to possible overflow. */
> +				if (check_mul_overflow(res, base, &tmp) ||
> +				    check_add_overflow(tmp, val, &res)) {
> +					res = ULLONG_MAX;
> +					rv |= KSTRTOX_OVERFLOW;
> +				}
> +			} else
> +				res = res * base + val;

Formally this should be } else { ... }, but I'm not going to insist.

>  		}
> -		res = res * base + val;
>  		rv++;
>  		s++;

-- 
With Best Regards,
Andy Shevchenko