netdev - RE: [PATCH net] phy: fix null pointer issue in phy_attach

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Message-ID: <IA1PR11MB62896ACA123AAED81DA3FFC689E92@IA1PR11MB6289.namprd11.prod.outlook.com>
Date: Thu, 30 Jan 2025 19:18:53 +0000
From: "Joshi, Sreedevi" <sreedevi.joshi@...el.com>
To: Russell King <linux@...linux.org.uk>, sreedevi.joshi
	<joshisre@...mtp.an.intel.com>
CC: "andrew@...n.ch" <andrew@...n.ch>, "hkallweit1@...il.com"
	<hkallweit1@...il.com>, "edumazet@...gle.com" <edumazet@...gle.com>,
	"kuba@...nel.org" <kuba@...nel.org>, "pabeni@...hat.com" <pabeni@...hat.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH net] phy: fix null pointer issue in phy_attach_direct()



> -----Original Message-----
> From: Russell King <linux@...linux.org.uk>
> Sent: Wednesday, January 29, 2025 2:30 PM
> To: sreedevi.joshi <joshisre@...mtp.an.intel.com>
> Cc: andrew@...n.ch; hkallweit1@...il.com; edumazet@...gle.com; kuba@...nel.org; pabeni@...hat.com;
> netdev@...r.kernel.org; Joshi, Sreedevi <sreedevi.joshi@...el.com>
> Subject: Re: [PATCH net] phy: fix null pointer issue in phy_attach_direct()
> 
> On Wed, Jan 29, 2025 at 12:36:38PM -0600, sreedevi.joshi wrote:
> > From: Sreedevi Joshi <sreedevi.joshi@...el.com>
> >
> > When attaching a fixed phy to devices like veth, it is possible that
> > there is no parent. The logic in
> > phy_attach_direct() tries to access the driver member without checking
> > for the null. This causes segfault in the case of fixed phy.
> 
> Kernel mode doesn't segfault. That's a userspace thing. Kernel mode oopses.
You are right. My bad for using for the wrong terminology. I have attached the
Kernel Oops log in my previous reply.
> 
> I'm confused. You mention veth, which presumably is drivers/net/veth.c.
> Grepping this driver for "phy" returns nothing. So how can veth be broken by a phylib change?
Yes. There is no PHY attached to the veth. This is part of the POC we are working on. We attach a
Fixed PHY to veth so the mii_timestamper hooks can be exercised for the demo. This was uncovered 
during that and even though there is no PHY usually attached to a virtual interface, it may be good
idea to have the necessary check before accessing the member to avoid issues. Wanted to check with
community if it can be included in the upstream driver.
> 
> --
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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