netdev - Re: [BUG] rtnl_newlink: Rogue MOVE event delivered on netns change

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Date: Sat, 14 Oct 2023 10:58:20 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Daniel Gröber <dxld@...kboxed.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	netdev@...r.kernel.org, Richard Weinberger <richard@....at>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [BUG] rtnl_newlink: Rogue MOVE event delivered on netns change

On Fri, Oct 13, 2023 at 03:43:02PM -0700, Jakub Kicinski wrote:
> On Fri, 13 Oct 2023 15:36:05 -0700 Jakub Kicinski wrote:
> >    kobject_uevent(&dev->dev.kobj, KOBJ_REMOVE);
> >    dev_net_set(dev, net);
> >    kobject_uevent(&dev->dev.kobj, KOBJ_ADD);
> 
> Greg, we seem to have a problem in networking with combined
> netns move and name change.
> 
> We have this code in __dev_change_net_namespace():
> 
> 	kobject_uevent(&dev->dev.kobj, KOBJ_REMOVE);
> 	dev_net_set(dev, net);
> 	kobject_uevent(&dev->dev.kobj, KOBJ_ADD);
> 
> 	err = device_rename(&dev->dev, dev->name);
> 
> Is there any way we can only get the REMOVE (old name) and ADD
> (new name) events, without the move? I.e. silence the rename? 
> 
> Daniel is reporting that with current code target netns sees an 
> add of an interface with the old (duplicated) name. And then a rename.

But that's how this has always been, right?  What problems is this
causing?

> Without a silent move best we can do is probably:
> 
> 	kobject_uevent(&dev->dev.kobj, KOBJ_REMOVE);
> 	dev_net_set(dev, net);
> 	err = device_rename(&dev->dev, dev->name);
> 	kobject_uevent(&dev->dev.kobj, KOBJ_ADD);
> 
> which will give us:
> 
> 	MOVE new-name
> 	ADD new-name
> 
> in target netns, which, hm.

That wouldn't make much sense.

What is the real problem here?  What changed to cause a problem?

thanks,

greg k-h