linux-kernel - Re: [PATCH] ALSA: xen-front: refactor deprecated strncpy

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Message-ID: <87mszfc4gp.wl-tiwai@suse.de>
Date:   Sat, 29 Jul 2023 14:00:38 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Justin Stitt <justinstitt@...gle.com>
Cc:     Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, xen-devel@...ts.xenproject.org,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] ALSA: xen-front: refactor deprecated strncpy

On Thu, 27 Jul 2023 23:53:24 +0200,
Justin Stitt wrote:
> 
> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> 
> A suitable replacement is `strscpy` [2] due to the fact that it
> guarantees NUL-termination on its destination buffer argument which is
> _not_ always the case for `strncpy`!
> 
> It should be noted that, in this case, the destination buffer has a
> length strictly greater than the source string. Moreover, the source
> string is NUL-terminated (and so is the destination) which means there
> was no real bug happening here. Nonetheless, this patch would get us one
> step closer to eliminating the `strncpy` API in the kernel, as its use
> is too ambiguous. We need to favor less ambiguous replacements such as:
> strscpy, strscpy_pad, strtomem and strtomem_pad (amongst others).
> 
> Technically, my patch yields subtly different behavior. The original
> implementation with `strncpy` would fill the entire destination buffer
> with null bytes [3] while `strscpy` will leave the junk, uninitialized
> bytes trailing after the _mandatory_ NUL-termination. So, if somehow
> `pcm->name` or `card->driver/shortname/longname` require this
> NUL-padding behavior then `strscpy_pad` should be used. My
> interpretation, though, is that the aforementioned fields are just fine
> as NUL-terminated strings. Please correct my assumptions if needed and
> I'll send in a v2.
> 
> [1]: www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
> [2]: manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html
> [3]: https://linux.die.net/man/3/strncpy
> 
> Link: https://github.com/KSPP/linux/issues/90
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>

Applied now.  Thanks.


Takashi