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From:   Justin Stitt <justinstitt@google.com>
Date:   Tue, 10 Oct 2023 14:48:07 -0700
Message-ID: <CAFhGd8oriABD+Vob3pwXi3fQ7W3XOzp8a48mX_TYxJHDW+aBuA@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 10:36=E2=80=AFAM Justin Stitt <justinstitt@google.c=
om> wrote:
>
> On Tue, Oct 10, 2023 at 4:07=E2=80=AFAM Vladimir Oltean <olteanv@gmail.co=
m> 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 strin=
g
> > > 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/realtek/rtl8365mb.c | 3 +--
> > >  1 file changed, 1 insertion(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/net/dsa/realtek/rtl8365mb.c b/drivers/net/dsa/re=
altek/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_sw=
itch *ds, int port, u32 stringset
> > >
> > >       for (i =3D 0; i < RTL8365MB_MIB_END; i++) {
> > >               struct rtl8365mb_mib_counter *mib =3D &rtl8365mb_mib_co=
unters[i];
> > > -
> > > -             strncpy(data + i * ETH_GSTRING_LEN, mib->name, ETH_GSTR=
ING_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 i=
t
> in one of my first patches like this [1].

For more context, here's some warnings in the wild:
https://lore.kernel.org/netdev/20231003183603.3887546-3-jesse.brandeburg@in=
tel.com/

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