netdev - Re: [PATCH 1/4] net: fix uninitialised access in mii_nway

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Message-ID: <Z_qxTN9_xJuEd2op@qasdev.system>
Date: Sat, 12 Apr 2025 19:30:36 +0100
From: Qasim Ijaz <qasdev00@...il.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: Jakub Kicinski <kuba@...nel.org>, andrew+netdev@...n.ch,
	davem@...emloft.net, edumazet@...gle.com, pabeni@...hat.com,
	horms@...nel.org, linux-usb@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	syzbot <syzbot+3361c2d6f78a3e0892f9@...kaller.appspotmail.com>
Subject: Re: [PATCH 1/4] net: fix uninitialised access in mii_nway_restart()

On Fri, Apr 11, 2025 at 03:12:06AM +0200, Andrew Lunn wrote:
> On Thu, Apr 10, 2025 at 11:15:23PM +0100, Qasim Ijaz wrote:
> > On Tue, Mar 25, 2025 at 06:33:07AM -0700, Jakub Kicinski wrote:
> > > On Wed, 19 Mar 2025 11:21:53 +0000 Qasim Ijaz wrote:
> > > > --- a/drivers/net/mii.c
> > > > +++ b/drivers/net/mii.c
> > > > @@ -464,6 +464,8 @@ int mii_nway_restart (struct mii_if_info *mii)
> > > >  
> > > >  	/* if autoneg is off, it's an error */
> > > >  	bmcr = mii->mdio_read(mii->dev, mii->phy_id, MII_BMCR);
> > > > +	if (bmcr < 0)
> > > > +		return bmcr;
> > > >  
> > > >  	if (bmcr & BMCR_ANENABLE) {
> > > >  		bmcr |= BMCR_ANRESTART;
> > > 
> > > We error check just one mdio_read() but there's a whole bunch of them
> > > in this file. What's the expected behavior then? Are all of them buggy?
> > >
> >  
> > Hi Jakub
> >     
> > Apologies for my delayed response, I had another look at this and I
> > think my patch may be off a bit. You are correct that there are multiple
> > mdio_read() calls and looking at the mii.c file we can see that calls to
> > functions like mdio_read (and a lot of others) dont check return values.
> >   
> > So in light of this I think a better patch would be to not edit the 
> > mii.c file at all and just make ch9200_mdio_read return 0 on     
> > error.
> 
> Do you actually have one of these devices? If you do have, an even
> better change would be to throwaway the mii code and swap to phylib
> and an MDIO bus. You can probably follow smsc95xx.c.
> 

Hi Andrew,

Thanks for the suggestion. I don't have one of these devices at the moment.
If in the future if I do I will definitely explore the suggestion more.

Regards,
Qasim

> 	Andrew