linux-kernel - [PATCH] ASoC: Intel: Skylake: replace deprecated strncpy with strscpy

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Message-ID: <20230726-asoc-intel-skylake-remove-deprecated-strncpy-v1-1-020e04184c7d@google.com>
Date:   Wed, 26 Jul 2023 21:12:18 +0000
From:   justinstitt@...gle.com
To:     Cezary Rojewski <cezary.rojewski@...el.com>,
        Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        Liam Girdwood <liam.r.girdwood@...ux.intel.com>,
        Peter Ujfalusi <peter.ujfalusi@...ux.intel.com>,
        Bard Liao <yung-chuan.liao@...ux.intel.com>,
        Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
        Kai Vehmanen <kai.vehmanen@...ux.intel.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Nathan Chancellor <nathan@...nel.org>,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH] ASoC: Intel: Skylake: replace deprecated strncpy with strscpy

`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.

Also within this patch is a change to an instance of  `x > y - 1` to `x >= y`
which tends to be more robust and readable. Consider, for instance, if `y` was
somehow `INT_MIN`.

[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@...omium.org>
Signed-off-by: Justin Stitt <justinstitt@...gle.com>
---
 sound/soc/intel/skylake/skl-topology.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/sound/soc/intel/skylake/skl-topology.c b/sound/soc/intel/skylake/skl-topology.c
index 96cfebded072..67f08ec3a2ea 100644
--- a/sound/soc/intel/skylake/skl-topology.c
+++ b/sound/soc/intel/skylake/skl-topology.c
@@ -3154,12 +3154,12 @@ static int skl_tplg_fill_str_mfest_tkn(struct device *dev,
 
 	switch (str_elem->token) {
 	case SKL_TKN_STR_LIB_NAME:
-		if (ref_count > skl->lib_count - 1) {
+		if (ref_count >= skl->lib_count) {
 			ref_count = 0;
 			return -EINVAL;
 		}
 
-		strncpy(skl->lib_info[ref_count].name,
+		strscpy(skl->lib_info[ref_count].name,
 			str_elem->string,
 			ARRAY_SIZE(skl->lib_info[ref_count].name));
 		ref_count++;

---
base-commit: 0b4a9fdc9317440a71d4d4c264a5650bf4a90f3c
change-id: 20230726-asoc-intel-skylake-remove-deprecated-strncpy-9dbcfc26040c

Best regards,
-- 
Justin Stitt <justinstitt@...gle.com>