netdev - Re: [PATCH net] ethtool: do not perform operations on net devices being unregistered

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Message-ID: <20211206071520.1fe7e18b@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Mon, 6 Dec 2021 07:15:20 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Julian Wiedmann <jwi@...ux.ibm.com>
Cc:     Antoine Tenart <atenart@...nel.org>, davem@...emloft.net,
        alexander.duyck@...il.com, mkubecek@...e.cz, netdev@...r.kernel.org
Subject: Re: [PATCH net] ethtool: do not perform operations on net devices
 being unregistered

On Mon, 6 Dec 2021 11:46:35 +0200 Julian Wiedmann wrote:
> On 03.12.21 12:13, Antoine Tenart wrote:
> > There is a short period between a net device starts to be unregistered
> > and when it is actually gone. In that time frame ethtool operations
> > could still be performed, which might end up in unwanted or undefined
> > behaviours[1].
> > 
> > Do not allow ethtool operations after a net device starts its
> > unregistration. This patch targets the netlink part as the ioctl one
> > isn't affected: the reference to the net device is taken and the
> > operation is executed within an rtnl lock section and the net device
> > won't be found after unregister.
> > [...]
> > +++ b/net/ethtool/netlink.c
> > @@ -40,7 +40,8 @@ int ethnl_ops_begin(struct net_device *dev)
> >  	if (dev->dev.parent)
> >  		pm_runtime_get_sync(dev->dev.parent);
> >  
> > -	if (!netif_device_present(dev)) {
> > +	if (!netif_device_present(dev) ||
> > +	    dev->reg_state == NETREG_UNREGISTERING) {
> >  		ret = -ENODEV;
> >  		goto err;
> >  	}
> >   
> 
> Wondering if other places would also benefit from a netif_device_detach()
> in the unregistration sequence ...

Sounds like a good idea but maybe as a follow up to net-next? 
The likelihood of that breaking things is low, but non-zero.