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

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Date:   Sat, 8 Jul 2017 11:44:14 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Hongjun Li <hongjun.li@...nd.com>
Subject: Re: [PATCH net] ip[6]: don't register inet[6]dev when dev is down

On Sat, Jul 8, 2017 at 3:02 AM, David Miller <davem@...emloft.net> wrote:
> 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.

+1. I fixed a nasty bug with how=1 for loopback before...

>
> 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.
>

It is because the ipv6_add_dev() adds these proc files back after
NETDEV_UNREGISTER event.