Subject: Re: [PATCH] s390/ctcm: replace deprecated strncpy with strscpy

From: Kees Cook <[email-masked]>
Date: Tue, 24 Oct 2023 10:28:48 -0700

On Mon, Oct 23, 2023 at 07:35:07PM +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 chid to be NUL-terminated based on its use with format
> strings:
> 
> 	CTCM_DBF_TEXT_(SETUP, CTC_DBF_INFO, "%s(%s) %s", CTCM_FUNTAIL,
> 			chid, ok ? "OK" : "failed");
> 
> Moreover, NUL-padding is not required as it is _only_ used in this one
> instance with a format string.
> 
> 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.
> 
> We can also drop the +1 from chid's declaration as we no longer need to
> be cautious about leaving a spot for a NUL-byte. Let's use the more
> idiomatic strscpy usage of (dest, src, sizeof(dest)) as this more
> closely ties the destination buffer to the length.
> 
> 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]>

Yeah, all looks correct to me.

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

-- 
Kees Cook