[PATCH] ASoC: fsl_micfil: refactor deprecated strncpy

[Shengjiu Wang]

On Fri, Jul 28, 2023 at 6:26 AM Justin Stitt <justinstitt at google.com> 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`!
>
> In this case, though, there was great care taken to ensure that the
> destination buffer would be NUL-terminated through the use of `len - 1`
> ensuring that the previously zero-initialized buffer would not overwrite
> the last NUL byte. This means that there's no bug here.
>
> However, `strscpy` will add a mandatory NUL byte to the destination
> buffer as promised by the following `strscpy` implementation [3]:
> |       /* Hit buffer length without finding a NUL; force NUL-termination.
> */
> |       if (res)
> |               dest[res-1] = '\0';
>
> This means we can lose the `- 1` which clears up whats happening here.
> All the while, we get one step closer to eliminating the ambiguous
> `strncpy` api in favor of its less ambiguous replacement like `strscpy`,
> `strscpy_pad`, `strtomem` and `strtomem_pad` amongst others.
>
> [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 at google.com>
>

Acked-by: Shengjiu Wang <shengjiu.wang at gmail.com>

Best regards
wang shengjiu

> ---
>  sound/soc/fsl/fsl_micfil.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/sound/soc/fsl/fsl_micfil.c b/sound/soc/fsl/fsl_micfil.c
> index 3f08082a55be..fe28b27e50d0 100644
> --- a/sound/soc/fsl/fsl_micfil.c
> +++ b/sound/soc/fsl/fsl_micfil.c
> @@ -1044,7 +1044,7 @@ static int fsl_micfil_probe(struct platform_device
> *pdev)
>                 return -ENOMEM;
>
>         micfil->pdev = pdev;
> -       strncpy(micfil->name, np->name, sizeof(micfil->name) - 1);
> +       strscpy(micfil->name, np->name, sizeof(micfil->name));
>
>         micfil->soc = of_device_get_match_data(&pdev->dev);
>
>
> ---
> base-commit: 57012c57536f8814dec92e74197ee96c3498d24e
> change-id: 20230727-sound-soc-fsl-4fc5569d771e
>
> Best regards,
> --
> Justin Stitt <justinstitt at google.com>
>
>
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