netdev - Re: [PATCH net] ip[6]: don't register inet[6]dev when dev is down

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Message-Id: <20170708.110234.1001958921525251511.davem@davemloft.net>
Date:   Sat, 08 Jul 2017 11:02:34 +0100 (WEST)
From:   David Miller <davem@...emloft.net>
To:     nicolas.dichtel@...nd.com
Cc:     netdev@...r.kernel.org, hongjun.li@...nd.com
Subject: Re: [PATCH net] ip[6]: don't register inet[6]dev when dev is down

From: Nicolas Dichtel <nicolas.dichtel@...nd.com>
Date: Wed,  5 Jul 2017 17:57:25 +0200

> From: Hongjun Li <hongjun.li@...nd.com>
> 
> When the netdev event NETDEV_CHANGEMTU is triggered, the inet[6]dev may be
> created even if the corresponding device is down. This may lead to a leak
> in the procfs when the device is unregistered, and finally trigger a
> backtrace:
 ...
> When a device changes from one netns to another, it's first unregistered,
> then the netns reference is updated and the dev is registered in the new
> netns. Thus, when a slave moves to another netns, it is first
> unregistered. This triggers a NETDEV_UNREGISTER event which is caught by
> the bonding driver. The driver calls bond_release(), which calls
> dev_set_mtu() and thus triggers NETDEV_CHANGEMTU (the device is still in
> the old netns).
> 
> Signed-off-by: Hongjun Li <hongjun.li@...nd.com>
> Signed-off-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>

I'm still not convinced about this.

We have lots of code which iterates ipv6 idevs, and then has a
check for IFF_UP.

So having an idev attached to a down interface is not a bug nor
illegal.

In fact, addrconf_cleanup() walks all of the init_net idevs and
calls addrconf_ifdown() with how=1 regardless of IFF_UP or not.

This entire area is quite a mess.

Can you show exactly why the procfs state isn't cleaned up for
these devices moving between namespaces?  Maybe that is the real
bug and a better place to fix this.

Thanks.