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Date:   Mon, 9 Oct 2023 11:57:19 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Justin Stitt <justinstitt@google.com>
Cc:     Hauke Mehrtens <hauke@hauke-m.de>, Andrew Lunn <andrew@lunn.ch>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Vladimir Oltean <olteanv@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH] net: dsa: lantiq_gswip: replace deprecated strncpy with
 ethtool_sprintf
Message-ID: <202310091156.978D4E1@keescook>
References: <20231009-strncpy-drivers-net-dsa-lantiq_gswip-c-v1-1-d55a986a14cc@google.com>
 <202310091134.67A4236E@keescook>
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On Mon, Oct 09, 2023 at 11:34:27AM -0700, Kees Cook wrote:
> On Mon, Oct 09, 2023 at 06:24:20PM +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.
> > 
> > ethtool_sprintf() is designed specifically for get_strings() usage.
> > Let's replace strncpy in favor of this more robust and easier to
> > understand interface.
> > 
> > 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>
> > ---
> > Note: build-tested only.
> > ---
> >  drivers/net/dsa/lantiq_gswip.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> > 
> > diff --git a/drivers/net/dsa/lantiq_gswip.c b/drivers/net/dsa/lantiq_gswip.c
> > index 3c76a1a14aee..d60bc2e37701 100644
> > --- a/drivers/net/dsa/lantiq_gswip.c
> > +++ b/drivers/net/dsa/lantiq_gswip.c
> > @@ -1759,8 +1759,7 @@ static void gswip_get_strings(struct dsa_switch *ds, int port, u32 stringset,
> >  		return;
> >  
> >  	for (i = 0; i < ARRAY_SIZE(gswip_rmon_cnt); i++)
> > -		strncpy(data + i * ETH_GSTRING_LEN, gswip_rmon_cnt[i].name,
> > -			ETH_GSTRING_LEN);
> > +		ethtool_sprintf(&data, "%s", gswip_rmon_cnt[i].name);
> 
> Sorry, I read too fast: this should be "data", not "&data", yeah?

As I said in the other email, please ignore me. &data is correct. I'm
not used to ethtool_sprintf(), clearly. :) My original Reviewed-by
stands. Sorry for the noise!

-Kees

-- 
Kees Cook