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

[Kees Cook <keescook@chromium.org>]

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@vger.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@google.com>

Looks good.

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

-- 
Kees Cook