linux-hardening - Re: [PATCH v4 3/3] xfs: adjust handling of a few numerical mount options

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Message-ID: <aW-YP7wCEvRJzyfR@smile.fi.intel.com>
Date: Tue, 20 Jan 2026 16:59:11 +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>,
	Carlos Maiolino <cem@...nel.org>,
	Christoph Hellwig <hch@...radead.org>, linux-xfs@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH v4 3/3] xfs: adjust handling of a few numerical mount
 options

On Tue, Jan 20, 2026 at 05:12:29PM +0300, Dmitry Antipov wrote:
> Prefer recently introduced 'memvalue()' over an ad-hoc 'suffix_kstrtoint()'
> and 'suffix_kstrtoull()' to parse and basically validate the values passed
> via 'logbsize', 'allocsize', and 'max_atomic_write' mount options, and
> reject non-power-of-two values passed via the first and second one early
> in 'xfs_fs_parse_param()' rather than in 'xfs_fs_validate_params()'.

...

> -	if (kstrtoint(value, base, &_res))
> -		ret = -EINVAL;
> -	kfree(value);
> -	*res = _res << shift_left_factor;
> -	return ret;

_res is int, if negative the above is UB in accordance with C standard.
So, if ever this code runs to the shifting left negative numbers it goes
to a slippery slope (I think it works as intended, but...).

That said, I assume this code was never designed to get a negative value
to the _res.

With all this, I do not see the point of having a new API.
Also, where are the test cases for it?

-- 
With Best Regards,
Andy Shevchenko