linux-kernel - Re: [PATCH v5 2/5] lib: fix memparse() to handle overflow

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Message-ID: <aYNa5ZBcA_pJqS7Y@smile.fi.intel.com>
Date: Wed, 4 Feb 2026 16:42:45 +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 v5 2/5] lib: fix memparse() to handle overflow

On Wed, Feb 04, 2026 at 04:57:14PM +0300, Dmitry Antipov wrote:
> Since '_parse_integer_limit()' (and so 'simple_strtoull()') is now
> capable to handle overflow, adjust 'memparse()' to handle overflow
> (denoted by ULLONG_MAX) returned from 'simple_strtoull()'. Also
> use 'check_shl_overflow()' to catch an overflow possibly caused
> by processing size suffix and denote it with ULLONG_MAX as well.

Do we have already test cases to cover this?

...

> unsigned long long memparse(const char *ptr, char **retptr)
>  {
>  	char *endptr;	/* local pointer to end of parsed string */

>  

Shouldn't be an empty line in the definition block.

> +	unsigned int shl = 0;
>  	unsigned long long ret = simple_strtoull(ptr, &endptr, 0);

and it would be better to preserve reversed xmas tree order (to some extent).

	char *endptr;	/* local pointer to end of parsed string */
	unsigned long long ret = simple_strtoull(ptr, &endptr, 0);
	unsigned int shl = 0;

> +	/* Consume valid suffix even in case of overflow. */
>  	switch (*endptr) {
>  	case 'E':
>  	case 'e':
> -		ret <<= 10;
> +		shl += 10;
>  		fallthrough;
>  	case 'P':
>  	case 'p':
> -		ret <<= 10;
> +		shl += 10;
>  		fallthrough;
>  	case 'T':
>  	case 't':
> -		ret <<= 10;
> +		shl += 10;
>  		fallthrough;
>  	case 'G':
>  	case 'g':
> -		ret <<= 10;
> +		shl += 10;
>  		fallthrough;
>  	case 'M':
>  	case 'm':
> -		ret <<= 10;
> +		shl += 10;
>  		fallthrough;
>  	case 'K':
>  	case 'k':
> -		ret <<= 10;
> +		shl += 10;
>  		endptr++;
>  		fallthrough;
>  	default:
>  		break;
>  	}

> +	/* If no overflow, apply suffix if any. */
> +	if (likely(ret != ULLONG_MAX) && shl) {

Do we need to check for shl? Yes, it will be an additional check below,
but do we care?

> +		unsigned long long val;

> +		ret = (unlikely(check_shl_overflow(ret, shl, &val))
> +		       ? ULLONG_MAX : val);

Unneeded parentheses, and ? should be on the previous line.
With that said, I prefer to see the regular conditional instead:

		ret = check_shl_overflow(...);
		if (unlikely(ret))
			ret = ...
		else
			ret = val;

> +	}
> +
>  	if (retptr)
>  		*retptr = endptr;

-- 
With Best Regards,
Andy Shevchenko