linux-hardening - Re: [PATCH] net: dsa: mt7530: replace deprecated strncpy with ethtool

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Message-ID: <202310091155.3E4328DC1B@keescook>
Date: Mon, 9 Oct 2023 11:56:33 -0700
From: Kees Cook <keescook@...omium.org>
To: Justin Stitt <justinstitt@...gle.com>
Cc: Arınç ÜNAL <arinc.unal@...nc9.com>,
	Daniel Golle <daniel@...rotopia.org>,
	Landen Chao <Landen.Chao@...iatek.com>,
	DENG Qingfang <dqfext@...il.com>,
	Sean Wang <sean.wang@...iatek.com>, Andrew Lunn <andrew@...n.ch>,
	Florian Fainelli <f.fainelli@...il.com>,
	Vladimir Oltean <olteanv@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] net: dsa: mt7530: replace deprecated strncpy with
 ethtool_sprintf

On Mon, Oct 09, 2023 at 11:31:46AM -0700, Kees Cook wrote:
> On Mon, Oct 09, 2023 at 06:29:19PM +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@...r.kernel.org
> > Signed-off-by: Justin Stitt <justinstitt@...gle.com>
> > ---
> > Note: build-tested only.
> > ---
> >  drivers/net/dsa/mt7530.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> > 
> > diff --git a/drivers/net/dsa/mt7530.c b/drivers/net/dsa/mt7530.c
> > index 035a34b50f31..e00126af8318 100644
> > --- a/drivers/net/dsa/mt7530.c
> > +++ b/drivers/net/dsa/mt7530.c
> > @@ -836,8 +836,7 @@ mt7530_get_strings(struct dsa_switch *ds, int port, u32 stringset,
> >  		return;
> >  
> >  	for (i = 0; i < ARRAY_SIZE(mt7530_mib); i++)
> > -		strncpy(data + i * ETH_GSTRING_LEN, mt7530_mib[i].name,
> > -			ETH_GSTRING_LEN);
> > +		ethtool_sprintf(&data, "%s", mt7530_mib[i].name);
> 
> Err, wait, I spoke too soon. Shouldn't this be "data" and not "&data"?

Ugh, ignore me. I keep forgetting that ethtool_sprintf() updates the
"data" pointer. My original Reviewed-by is fine. :)

-Kees

-- 
Kees Cook