linux-kernel - Re: [PATCH] fs/xfs: replace strncpy with strscpy

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Message-ID: <20250701145736.GE10009@frogsfrogsfrogs>
Date: Tue, 1 Jul 2025 07:57:36 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: Pranav Tyagi <pranav.tyagi03@...il.com>
Cc: Brahmajit Das <listout@...tout.xyz>, Carlos Maiolino <cem@...nel.org>,
	skhan@...uxfoundation.org, linux-kernel-mentees@...ts.linux.dev,
	linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs/xfs: replace strncpy with strscpy

On Tue, Jul 01, 2025 at 02:18:12PM +0530, Pranav Tyagi wrote:
> On Mon, Jun 30, 2025 at 7:48 PM Brahmajit Das <listout@...tout.xyz> wrote:
> >
> > On 30.06.2025 14:36, Pranav Tyagi wrote:
> > ... snip ...
> > > > >       spin_unlock(&mp->m_sb_lock);
> > > > >
> > > > >       if (copy_to_user(user_label, label, sizeof(label)))
> > > > > --
> > > > > 2.49.0
> > > > >
> > >
> > > Hi,
> > >
> > > Thank you for the feedback. I understand that my patch is incorrect and
> > > it causes a buffer overrun. The destination buffer is indeed, already, null
> > > terminated. Would you like me to send a corrected patch which uses
> > > strscpy() (as strncpy() is deprecated)?
> > >
> > If the destination buffer is already NUL terminated, you can use either
> > strtomem or strtomem_pad [0].
> >
> > [0]: https://docs.kernel.org/core-api/kernel-api.html#c.strncpy
> > (Description)
> 
> Thank you for the suggestion. On going through [0], I see that,
> both, strtomem and strscpy require the src to be null
> terminated. As far as I know, sb_fname buffer has a size of
> XFSLABEL_MAX (12 bytes). This means no terminating NULL
> for the src. So shouldn't memcpy() be the right function to use here?

memtostr_pad?

--D

> > > Regret the inconvenience.
> > >
> > > Regards
> > > Pranav Tyagi
> > >
> >
> > --
> > Regards,
> > listout
>