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Date:   Tue, 24 Oct 2023 16:58:50 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Justin Stitt <justinstitt@...gle.com>
Cc:     Vineeth Vijayan <vneethv@...ux.ibm.com>,
        Peter Oberparleiter <oberpar@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] s390/cio: replace deprecated strncpy with strscpy

On Mon, Oct 23, 2023 at 07:24:38PM +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 both `params` and `id` to be NUL-terminated based on their
> usage with format strings:
> 
> 	format_node_data(iuparams, iunodeid, &lir->incident_node);
> 	format_node_data(auparams, aunodeid, &lir->attached_node);
> 
> 	switch (lir->iq.class) {
> 	case LIR_IQ_CLASS_DEGRADED:
> 		pr_warn("Link degraded: RS=%02x RSID=%04x IC=%02x "
> 			"IUPARAMS=%s IUNODEID=%s AUPARAMS=%s AUNODEID=%s\n",
> 			sei_area->rs, sei_area->rsid, lir->ic, iuparams,
> 			iunodeid, auparams, aunodeid);
> 
> NUL-padding is not required as both `params` and `id` have been memset
> to 0:
> 
> 	memset(params, 0, PARAMS_LEN);
> 	memset(id, 0, NODEID_LEN);
> 
> 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.
> 
> Note that there's no overread bugs in the current implementation as the
> string literal "n/a" has a size much smaller than PARAMS_LEN or
> NODEID_LEN. Nonetheless, let's favor strscpy().
> 
> 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@...r.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>

Looks good.

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

-- 
Kees Cook

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