linux-kernel - Re: [PATCH v6 1/5] lib: fix _parse_integer

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Message-ID: <aYrgASJXAyoholbF@smile.fi.intel.com>
Date: Tue, 10 Feb 2026 09:36:33 +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, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 1/5] lib: fix _parse_integer_limit() to handle overflow

On Mon, Feb 09, 2026 at 07:47:53PM +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.

...

> -	unsigned long long res;
> +	unsigned long long res = 0;

>  
> -	res = 0;

We can leave this untouched.

...


> -	while (max_chars--) {
> +	for (rv = 0; max_chars--; rv++, s++) {

I don't see how max_chars is used. With that said, I would rather see the usual
way of expressing the condition in the for-loop:

	for (rv = 0; rv < max_chars; rv++, s++) {

...

> +		if (likely(res != ULLONG_MAX)) {

Have you seen David's question about these checks?
Maybe I missed your answer...

> +			if (unlikely(res & (~0ull << 60))) {
> +				/* We're close to possible overflow. */
> +				unsigned long long tmp;
> +
> +				if (check_mul_overflow(res, base, &tmp) ||
> +				    check_add_overflow(tmp, val, &res)) {
> +					res = ULLONG_MAX;
> +					rv |= KSTRTOX_OVERFLOW;
> +				}
> +			} else {
> +				res = res * base + val;
> +			}
>  		}

-- 
With Best Regards,
Andy Shevchenko