Re: [PATCH net v2 2/2] net: usb: asix: ax88772: Increase phy_name size

[Andy Shevchenko]

On Wed, Mar 19, 2025 at 02:43:40PM +0000, Russell King (Oracle) wrote:
> On Wed, Mar 19, 2025 at 12:54:34PM +0200, Andy Shevchenko wrote:

> > GCC compiler (Debian 14.2.0-17) is not happy about printing
> > into a short buffer (when build with `make W=1`):
> > 
> >  drivers/net/usb/ax88172a.c: In function ‘ax88172a_reset’:
> >  include/linux/phy.h:312:20: error: ‘%s’ directive output may be truncated writing up to 60 bytes into a region of size 20 [-Werror=format-truncation=]
> 
> GCC reckons this can be up to 60 bytes...

It has two complains, but they a bit differ, first one was about %s, as you see
above, the other one which I missed to add here is about %02x:

drivers/net/usb/ax88172a.c:311:9: note: ‘snprintf’ output between 4 and 66 bytes into a destination of size 20

...

> > -	char phy_name[20];
> > +	char phy_name[MII_BUS_ID_SIZE + 3];
> 
> MII_BUS_ID_SIZE is sized to 61, and is what is used in struct
> mii_bus::id. Why there a +3 here, which seems like a random constant to
> make it 64-bit aligned in size. If we have need to increase
> MII_BUS_ID_SIZE in the future, this kind of alignment then goes
> wrong...
> 
> If the intention is to align it to 64-bit then there's surely a better
> and future-proof ways to do that.

Nope, intention is to cover the rest after %s.

...

> I'm also surprised that the +3 randomness wasn't described in the
> commit message.

It was referred in the cover letter and previous discussion, but I agree that
it has to be clarified here, it's ':%02x', the %s case, i.e. MII_BUS_ID_SIZE
covers 60 characters + NUL.

...

> > +	if (ret >= PHY_MAX_ADDR) {
> > +		netdev_err(dev->net, "Invalid PHY ID %x\n", ret);
> 
> An address is not a "PHY ID". "Invalid PHY address %d\n" probably makes
> more sense, but if you want to keep the hex, then it really should be
> %#x or 0x%x to make it clear that e.g. "20" is hex and not decimal.

Sure, I fix it locally, but we need to understand how to go with the
+3/+whatever fix, so format specifier won't hit us back.

...

Thank you for the review!

-- 
With Best Regards,
Andy Shevchenko