linux-kernel - Re: [PATCH v3 1/3] selftests/mm/write_to_hugetlbfs: parse -s as size

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Message-ID: <20251222094828.2783d9e5@pumpkin>
Date: Mon, 22 Dec 2025 09:48:28 +0000
From: David Laight <david.laight.linux@...il.com>
To: Li Wang <liwang@...hat.com>
Cc: akpm@...ux-foundation.org, linux-kselftest@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org, David Hildenbrand
 <david@...nel.org>, Mark Brown <broonie@...nel.org>, Shuah Khan
 <shuah@...nel.org>, Waiman Long <longman@...hat.com>
Subject: Re: [PATCH v3 1/3] selftests/mm/write_to_hugetlbfs: parse -s as
 size_t

On Mon, 22 Dec 2025 09:45:41 +0800
Li Wang <liwang@...hat.com> wrote:

> On Mon, Dec 22, 2025 at 6:11 AM David Laight <david.laight.linux@...il.com>
> wrote:
> 
> > On Sun, 21 Dec 2025 20:26:37 +0800
> > Li Wang <liwang@...hat.com> wrote:
> >  
> > > write_to_hugetlbfs currently parses the -s size argument with atoi()
> > > into an int. This silently accepts malformed input, cannot report  
> > overflow,  
> > > and can truncate large sizes.  
> >
> > And sscanf() will just ignore invalid trailing characters.
> > Probably much the same as atoi() apart from a leading '-'.
> >
> > Maybe you could use "%zu%c" and check the count is 1 - but I bet
> > some static checker won't like that.
> >  
> 
> Yes, that would be stronger, since it would reject trailing garbage.
> But for a selftest this is probably sufficient: switching to size_t and
> parsing with "%zu" already avoids the int truncation issue.

Have you checked at what does sscanf() does with an overlong digit string?
I'd guess that it just processes all the digits and then masks the result
to fix (like the kernel one does).

It reality scanf() is 'not the function you are lookign for'.

IIRC the 'SUS' (used to) say that this was absolutely fine for command
line parsing for 'standard utilities'.

It is best to use strtoul() and check the 'end' character is '\0'.

	David

> 
> @Andrew Morton <akpm@...ux-foundation.org>,
> 
> Hi Andrew, I noticed you have addedthe patches to your mm-new branch,
> Let me know if you prefer the "%zu%c" enhancement in a new version.
> 
>