linux-kernel - Re: [PATCH v3 2/2] mm/memfd: Use strncpy_from

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Message-ID: <Z4FOMHqlnVywZdNv@google.com>
Date: Fri, 10 Jan 2025 08:43:28 -0800
From: Isaac Manjarres <isaacmanjarres@...gle.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, kaleshsingh@...gle.com,
	jstultz@...gle.com, aliceryhl@...gle.com, surenb@...gle.com,
	kernel-team@...roid.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/2] mm/memfd: Use strncpy_from_user() to read memfd
 name

On Fri, Jan 10, 2025 at 12:48:44PM +0000, Lorenzo Stoakes wrote:
> On Thu, Jan 09, 2025 at 10:59:05AM -0800, Isaac J. Manjarres wrote:
> > The existing logic uses strnlen_user() to calculate the length of the
> > memfd name from userspace and then copies the string into a buffer using
> > copy_from_user(). This is error-prone, as the string length
> > could have changed between the time when it was calculated and when the
> > string was copied. The existing logic handles this by ensuring that the
> > last byte in the buffer is the terminating zero.
> >
> > This handling is contrived and can better be handled by using
> > strncpy_from_user(), which gets the length of the string and copies
> > it in one shot. Therefore, simplify the logic for copying the memfd
> > name by using strncpy_from_user().
> >
> > No functional change.
> >
> > Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
> > Signed-off-by: Isaac J. Manjarres <isaacmanjarres@...gle.com>
> 
> LGTM,
> 
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> 

Thank you!

--Isaac