Subject: Re: [PATCH] isdn: replace deprecated strncpy with strscpy

From: Kees Cook <[email-masked]>
Date: Sat, 23 Sep 2023 20:37:00 -0700

On Fri, Sep 22, 2023 at 11:58:06AM +0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings
> [1] and as such we should prefer more robust and less ambiguous string
> interfaces.
> 
> We expect `iclock->name` to be NUL-terminated based on its use within
> printk:
> |	printk(KERN_DEBUG "%s: %s %d\n", __func__, iclock->name,
> |	       iclock->pri);
> 
> `iclock` is zero-initialized and as such is already NUL-padded which
> means strncpy is doing extra work here by eagerly NUL-padding the
> destination buffer.
> 
> Considering the above, a suitable replacement is `strscpy` [2] due to
> the fact that it guarantees NUL-termination on the destination buffer
> without unnecessarily NUL-padding.
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: [email-masked]
> Signed-off-by: Justin Stitt <[email-masked]>

Yup, looks like a clean replacement.

Reviewed-by: Kees Cook <[email-masked]>

-- 
Kees Cook