linux-kernel - Re: [PATCH v2 1/2] lib/strtox: introduce kstrtoull

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Message-ID: <ZYL3c1S7B9PHPEwI@smile.fi.intel.com>
Date: Wed, 20 Dec 2023 16:17:23 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Qu Wenruo <wqu@...e.com>
Cc: linux-btrfs@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>,
	Christophe JAILLET <christophe.jaillet@...adoo.fr>,
	David Laight <David.Laight@...lab.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] lib/strtox: introduce kstrtoull_suffix() helper

On Wed, Dec 20, 2023 at 10:40:00AM +1030, Qu Wenruo wrote:
> Just as mentioned in the comment of memparse(), the simple_stroull()
> usage can lead to overflow all by itself.
> 
> Furthermore, the suffix calculation is also super overflow prone because
> that some suffix like "E" itself would eat 60bits, leaving only 4 bits
> available.
> 
> And that suffix "E" can also lead to confusion since it's using the same
> char of hex Ox'E'.
> 
> One simple example to expose all the problem is to use memparse() on
> "25E".
> The correct value should be 28823037615171174400, but the suffix E makes
> it super simple to overflow, resulting the incorrect value
> 10376293541461622784 (9E).
> 
> So here we introduce a new helper to address the problem,
> kstrtoull_suffix():
> 
> - Enhance _kstrtoull()
>   This allow _kstrtoull() to return even if it hits an invalid char, as
>   long as the optional parameter @retptr is provided.
> 
>   If @retptr is provided, _kstrtoull() would try its best to parse the
>   valid part, and leave the remaining to be handled by the caller.
> 
>   If @retptr is not provided, the behavior is not altered.
> 
> - New kstrtoull_suffix() helper
>   This new helper utilize the new @retptr capability of _kstrtoull(),
>   and provides 2 new ability:
> 
>   * Allow certain suffixes to be chosen
>     The recommended suffix list is "KMGTP" (using the new unit_suffix
>     enum as a bitmap), excluding the overflow prone "E".
>     Undermost cases there is really no need to use "E" suffix anyway.
>     And for those who really need that exabytes suffix, they can enable
>     that suffix pretty easily.
> 
>   * Add overflow checks for the suffixes
>     If the original number string is fine, but with the extra left
>     shift overflow happens, then -EOVERFLOW is returned.

NAK. Read the v1 discussion why.

-- 
With Best Regards,
Andy Shevchenko