netdev - Re: [RESEND] net: phy: fix NULL pointer dereference in phy_polling

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Message-ID: <ywr5p6ccsbvoxronpzpbtxjqyjlwp5g6ksazbeyh47vmhta6sb@xxl6dzd2hsgg>
Date: Wed, 6 Aug 2025 16:56:58 +0800
From: Xu Yang <xu.yang_2@....com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: andrew@...n.ch, hkallweit1@...il.com, o.rempel@...gutronix.de, 
	pabeni@...hat.com, netdev@...r.kernel.org, imx@...ts.linux.dev, 
	linux-kernel@...r.kernel.org
Subject: Re: [RESEND] net: phy: fix NULL pointer dereference in
 phy_polling_mode()

Hi Russell,

On Wed, Aug 06, 2025 at 09:45:01AM +0100, Russell King (Oracle) wrote:
> On Wed, Aug 06, 2025 at 04:29:31PM +0800, Xu Yang wrote:
> > Not all phy devices have phy driver attached, so fix the NULL pointer
> > dereference issue in phy_polling_mode() which was observed on USB net
> > devices.
> 
> See my comments in response to your first posting.

Thanks for the comments!

Reproduce step is simple:

1. connect an USB to Ethernet device to USB port, I'm using "D-Link Corp.
   DUB-E100 Fast Ethernet Adapter".
2. the asix driver (drivers/net/usb/asix_devices.c) will bind to this USB
   device.

root@...95evk:~# lsusb -t
/:  Bus 001.Port 001: Dev 001, Class=root_hub, Driver=ci_hdrc/1p, 480M
    |__ Port 001: Dev 003, If 0, Class=Vendor Specific Class, Driver=asix, 480M

3. then the driver will create many mdio devices. 

root@...95evk:/sys/bus/mdio_bus# ls -d devices/usb*
devices/usb-001:005:00  devices/usb-001:005:04  devices/usb-001:005:08  devices/usb-001:005:0c  devices/usb-001:005:10  devices/usb-001:005:14  devices/usb-001:005:18  devices/usb-001:005:1c
devices/usb-001:005:01  devices/usb-001:005:05  devices/usb-001:005:09  devices/usb-001:005:0d  devices/usb-001:005:11  devices/usb-001:005:15  devices/usb-001:005:19  devices/usb-001:005:1d
devices/usb-001:005:02  devices/usb-001:005:06  devices/usb-001:005:0a  devices/usb-001:005:0e  devices/usb-001:005:12  devices/usb-001:005:16  devices/usb-001:005:1a  devices/usb-001:005:1e
devices/usb-001:005:03  devices/usb-001:005:07  devices/usb-001:005:0b  devices/usb-001:005:0f  devices/usb-001:005:13  devices/usb-001:005:17  devices/usb-001:005:1b  devices/usb-001:005:1f

4. but only usb-001:005:03 is bind to genphy drivers.

root@...95evk:/sys/bus/mdio_bus# ls drivers/'Generic PHY'/
bind  uevent  unbind  usb-001:005:03

5. just do system suspend and resume test, a lot of kernel dump happens.

Thanks,
Xu Yang

> 
> -- 
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!