Re: [PATCH] ethtool: don't touch the parent device of a net device being unregistered

[Alexander Popov <alex.popov@linux.com>]

On 3/24/26 01:08, Jakub Kicinski wrote:
> On Mon, 23 Mar 2026 02:08:53 +0300 Alexander Popov wrote:
>> Hello Andrew, let me describe the scenario that I see:
>>
>>    - The netdev_run_todo() function handles the net devices in net_todo_list
>>      in a loop and moves each of them into the NETREG_UNREGISTERED state:
>>        netdev_lock(dev);
>>        WRITE_ONCE(dev->reg_state, NETREG_UNREGISTERED);
>>        netdev_unlock(dev);
>>
>>    - Then netdev_run_todo() frees these net devices in another loop.
>>      On each iteration, it chooses a device for freeing:
>>        dev = netdev_wait_allrefs_any(&list);
>>
>>    - At the same time, the ethnl_set_features() function calls
>>      ethnl_parse_header_dev_get() for the child net device.
>>
>>    - If the race condition succeeds, ethnl_set_features() takes the reference
>>      to the child net device being unregistered. That makes netdev_run_todo()
>>      free the parent first.
> 
> That's not sufficient detail. ethnl_parse_header_dev_get() is under RCU
> and unregistration does an RCU sync after delisting the device. Also
> not sure you're distinguishing struct net_device and struct device.
> 
> How did you hit this issue? What are the net devices involved?

I've provided additional details about the reproducer of this vulnerability to 
Jakub and to security@kernel.org.

Best regards,
Alexander