netdev - Re: [PATCH net 1/2] net: phy: Avoid NPD upon phy

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Message-ID: <b33da0da-4c6a-ae11-b77e-93d014a90123@gmail.com>
Date:   Thu, 17 Sep 2020 09:32:03 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     netdev@...r.kernel.org, hkallweit1@...il.com, kuba@...nel.org,
        davem@...emloft.net
Subject: Re: [PATCH net 1/2] net: phy: Avoid NPD upon phy_detach() when driver
 is unbound



On 9/17/2020 6:15 AM, Andrew Lunn wrote:
> On Wed, Sep 16, 2020 at 08:43:09PM -0700, Florian Fainelli wrote:
>> If we have unbound the PHY driver prior to calling phy_detach() (often
>> via phy_disconnect()) then we can cause a NULL pointer de-reference
>> accessing the driver owner member. The steps to reproduce are:
>>
>> echo unimac-mdio-0:01 > /sys/class/net/eth0/phydev/driver/unbind
>> ip link set eth0 down
> 
> Hi Florian
> 
> How forceful is this unbind? Can we actually block it while the
> interface is up? Or returning -EBUSY would make sense.

It it not forceful, you can unbind the PHY driver from underneath the 
net_device and nothing bad happens, really. This is not a very realistic 
or practical use case, but several years ago, I went into making sure we 
would not create NPD if that happened.
-- 
Florian