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Date:   Fri, 28 Jul 2023 11:58:15 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Justin Stitt <justinstitt@google.com>
Cc:     Cezary Rojewski <cezary.rojewski@intel.com>,
        Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>,
        Liam Girdwood <liam.r.girdwood@linux.intel.com>,
        Peter Ujfalusi <peter.ujfalusi@linux.intel.com>,
        Bard Liao <yung-chuan.liao@linux.intel.com>,
        Ranjani Sridharan <ranjani.sridharan@linux.intel.com>,
        Kai Vehmanen <kai.vehmanen@linux.intel.com>,
        Mark Brown <broonie@kernel.org>,
        Jaroslav Kysela <perex@perex.cz>,
        Takashi Iwai <tiwai@suse.com>,
        Nathan Chancellor <nathan@kernel.org>,
        alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] ASoC: Intel: Skylake: replace deprecated strncpy with
 strscpy
Message-ID: <202307281156.59CC304@keescook>
References: <20230726-asoc-intel-skylake-remove-deprecated-strncpy-v1-1-020e04184c7d@google.com>
 <20230727-asoc-intel-skylake-remove-deprecated-strncpy-v2-1-152830093921@google.com>
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In-Reply-To: <20230727-asoc-intel-skylake-remove-deprecated-strncpy-v2-1-152830093921@google.com>
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On Thu, Jul 27, 2023 at 08:30:18PM +0000, 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_ the case for `strncpy`!
> 
> It was pretty difficult, in this case, to try and figure out whether or
> not the destination buffer was zero-initialized. If it is and this
> behavior is relied on then perhaps `strscpy_pad` is the preferred
> option here.
> 
> Kees was able to help me out and identify the following code snippet
> which seems to show that the destination buffer is zero-initialized.
> 
> |       skl = devm_kzalloc(&pci->dev, sizeof(*skl), GFP_KERNEL);
> 
> With this information, I opted for `strscpy` since padding is seemingly
> not required.
> 
> [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
> 
> Link: https://github.com/KSPP/linux/issues/90
> Suggested-by: Kees Cook <keescook@chromium.org>
> Signed-off-by: Justin Stitt <justinstitt@google.com>

Thanks for the updates! And based on the details from Amadeusz, it
looks safe.

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook