Re: [PATCH] net: dsa: mt7530: replace deprecated strncpy with ethtool_sprintf

Kees Cook
2023-10-09T18:56:41Z

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