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From:   Justin Stitt <justinstitt@google.com>
Date:   Tue, 10 Oct 2023 10:36:36 -0700
Message-ID: <CAFhGd8pgGij4BXNzrB5fqk_2CNPDBTgf-3nN0i6cJak6vye_bA@mail.gmail.com>
Subject: Re: [PATCH] net: dsa: realtek: rtl8365mb: replace deprecated strncpy
 with ethtool_sprintf
To:     Vladimir Oltean <olteanv@gmail.com>
Cc:     Linus Walleij <linus.walleij@linaro.org>,
        =?UTF-8?Q?Alvin_=C5=A0ipraga?= <alsi@bang-olufsen.dk>,
        Andrew Lunn <andrew@lunn.ch>,
        Florian Fainelli <f.fainelli@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
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On Tue, Oct 10, 2023 at 4:07=E2=80=AFAM Vladimir Oltean <olteanv@gmail.com>=
 wrote:
>
> Hello Justin,
>
> On Mon, Oct 09, 2023 at 10:43:59PM +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#st=
rncpy-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/realtek/rtl8365mb.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/dsa/realtek/rtl8365mb.c b/drivers/net/dsa/real=
tek/rtl8365mb.c
> > index 41ea3b5a42b1..d171c18dd354 100644
> > --- a/drivers/net/dsa/realtek/rtl8365mb.c
> > +++ b/drivers/net/dsa/realtek/rtl8365mb.c
> > @@ -1303,8 +1303,7 @@ static void rtl8365mb_get_strings(struct dsa_swit=
ch *ds, int port, u32 stringset
> >
> >       for (i =3D 0; i < RTL8365MB_MIB_END; i++) {
> >               struct rtl8365mb_mib_counter *mib =3D &rtl8365mb_mib_coun=
ters[i];
> > -
> > -             strncpy(data + i * ETH_GSTRING_LEN, mib->name, ETH_GSTRIN=
G_LEN);
> > +             ethtool_sprintf(&data, "%s", mib->name);
>
> Is there any particular reason why you opted for the "%s" printf format
> specifier when you could have simply given mib->name as the single
> argument? This comment applies to all the ethtool_sprintf() patches
> you've submitted.

Yeah, it causes a -Wformat-security warning for me. I briefly mentioned it
in one of my first patches like this [1].

[1]: https://lore.kernel.org/all/20231005-strncpy-drivers-net-dsa-lan9303-c=
ore-c-v2-1-feb452a532db@google.com/