netdev - Re: [PATCH] net: clear iflink when moving to a new netns

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Date:	Wed, 12 Feb 2014 18:00:47 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Cong Wang <cwang@...pensource.com>
Cc:	Nicolas Dichtel <nicolas.dichtel@...nd.com>,
	Cong Wang <xiyou.wangcong@...il.com>,
	netdev <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>
Subject: Re: [PATCH] net: clear iflink when moving to a new netns

Cong Wang <cwang@...pensource.com> writes:

> On Wed, Feb 12, 2014 at 7:43 AM, Nicolas Dichtel
> <nicolas.dichtel@...nd.com> wrote:
>> Le 12/02/2014 00:51, Cong Wang a écrit :
>>
>>> From: Cong Wang <cwang@...pensource.com>
>>>
>>> BZ: https://bugzilla.kernel.org/show_bug.cgi?id=66691
>>>
>>> macvlan and vlan both use iflink to identify its lower device,
>>> however, after such device is moved to the new netns, its iflink
>>> would become meaningless as ifindex is per netns. So, instead of
>>> forbid them moving to another netns, just clear this field so that
>>> it will not be dumped at least.
>>>
>>> Cc: David S. Miller <davem@...emloft.net>
>>> Cc: Eric W. Biederman <ebiederm@...ssion.com>
>>> Cc: Eric Dumazet <eric.dumazet@...il.com>
>>> Cc: Hannes Frederic Sowa <hannes@...essinduktion.org>,
>>> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
>>> Signed-off-by: Cong Wang <cwang@...pensource.com>
>>
>> I wonder if this patch breaks things in ip tunnels.
>> For example, ip6_tunnel uses iflink to find tunnels that are bound to an
>> interface.
>> If you reset this field, ipip6_tunnel_lookup() will fail when the tunnel
>> moves
>> to another netns.
>
> Most tunnels set NETIF_F_NETNS_LOCAL, ip6_tunnel should set it too
> (need a patch). So this is not a problem.

There was an effort not long ago to make tunnels safe to pass between
namespaces.  NETIF_F_NETNS_LOCAL was removed from ip6_tunnel in that
effort.  Apparently something was overlooked.

Making iflink a netdevice reference or finding a way to remove it
entirely seems better that masking the problem.

Eric
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