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Date:   Tue, 24 Oct 2023 10:28:48 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Justin Stitt <justinstitt@google.com>
Cc:     Alexandra Winter <wintera@linux.ibm.com>,
        Wenjia Zhang <wenjia@linux.ibm.com>,
        Heiko Carstens <hca@linux.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        Sven Schnelle <svens@linux.ibm.com>,
        linux-s390@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH] s390/ctcm: replace deprecated strncpy with strscpy
Message-ID: <202310241027.516C46AA@keescook>
References: <20231023-strncpy-drivers-s390-net-ctcm_main-c-v1-1-265db6e78165@google.com>
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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: linux-hardening@vger.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@google.com>

Yeah, all looks correct to me.

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook