linux-kernel - [PATCH] ASoC: 88pm860x: refactor deprecated strncpy

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Date:   Thu, 27 Jul 2023 22:46:13 +0000
From:   Justin Stitt <justinstitt@...gle.com>
To:     Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>
Cc:     alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        Kees Cook <keescook@...omium.org>,
        Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH] ASoC: 88pm860x: refactor deprecated strncpy

`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`!

In this case, though, there was care taken to ensure that the
destination buffer would be NUL-terminated. The destination buffer is
zero-initialized and each `pm860x->name[i]` has a size of
`MAX_NAME_LENGTH + 1`. This means that there is unlikely to be a bug
here.

However, in an attempt to eliminate the usage of the `strncpy` API as
well as disambiguate implementations, replacements such as: `strscpy`,
`strscpy_pad`, `strtomem` and `strtomem_pad` should be preferred.

We are able to eliminate the need for `len + 1` since `strscpy`
guarantees NUL-termination for its destination buffer as per its
implementation [3]:

|       /* Hit buffer length without finding a NUL; force NUL-termination. */
|       if (res)
| 	        dest[res-1] = '\0';

[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://elixir.bootlin.com/linux/v6.3/source/lib/string.c#L183

Link: https://github.com/KSPP/linux/issues/90
Signed-off-by: Justin Stitt <justinstitt@...gle.com>
---
 sound/soc/codecs/88pm860x-codec.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/sound/soc/codecs/88pm860x-codec.c b/sound/soc/codecs/88pm860x-codec.c
index 3574c68e0dda..d99b674d574b 100644
--- a/sound/soc/codecs/88pm860x-codec.c
+++ b/sound/soc/codecs/88pm860x-codec.c
@@ -143,7 +143,7 @@ struct pm860x_priv {
 	struct pm860x_det	det;
 
 	int			irq[4];
-	unsigned char		name[4][MAX_NAME_LEN+1];
+	unsigned char		name[4][MAX_NAME_LEN];
 };
 
 /* -9450dB to 0dB in 150dB steps ( mute instead of -9450dB) */
@@ -1373,7 +1373,7 @@ static int pm860x_codec_probe(struct platform_device *pdev)
 			return -EINVAL;
 		}
 		pm860x->irq[i] = res->start + chip->irq_base;
-		strncpy(pm860x->name[i], res->name, MAX_NAME_LEN);
+		strscpy(pm860x->name[i], res->name, MAX_NAME_LEN);
 	}
 
 	ret = devm_snd_soc_register_component(&pdev->dev,

---
base-commit: 57012c57536f8814dec92e74197ee96c3498d24e
change-id: 20230727-sound-soc-codecs-947fcb9536a7

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