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

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Message-ID: <2b3fvsi7c47oit4p6drgjqeaxgwyzyopt7czfv3g2a74j2ay5j@qu22cohdcrjs>
Date: Thu, 7 Aug 2025 17:23:24 +0800
From: Xu Yang <xu.yang_2@....com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Andrew Lunn <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()

On Wed, Aug 06, 2025 at 05:47:53PM +0100, Russell King (Oracle) wrote:
> On Wed, Aug 06, 2025 at 05:01:22PM +0200, Andrew Lunn wrote:
> > > > > 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".
> > 
> > static const struct driver_info dlink_dub_e100_info = {
> >         .description = "DLink DUB-E100 USB Ethernet",
> >         .bind = ax88172_bind,
> >         .status = asix_status,
> >         .link_reset = ax88172_link_reset,
> >         .reset = ax88172_link_reset,
> >         .flags =  FLAG_ETHER | FLAG_LINK_INTR,
> >         .data = 0x009f9d9f,
> > };
> > 

[...]

> 
> Notice that the following return the PHY 3 register 3 value, so
> I suspect for anything that isn't PHY 3, it just returns whatever
> data was last read from PHY 3. This makes it an incredibly buggy
> USB device.
> 
> Looking at usbnet_read_cmd(), the above can be the only explanation,
> as usbnet_read_cmd() memcpy()'s the data into &res, so the value
> in the kmalloc()'d buf (which likely be poisoned on free, or if not
> unlikely to reallocate the same memory - that needs to be verified)
> must be coming from firmware on the device itself.

I confirm it's returned by the device. I capture the USB transfer with
an USB analyzer too.

> 
> asix_read_cmd() will catch a short read, and usbnet_read_cmd() will
> catch a zero-length read as invalid.
> 
> So, my conclusion is... broken firmware on this device.

The data transfer function works fine on my side. And even if something
is wrong with this device, the linux system shouldn't be broken down
because of this.

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!