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

From: [email-masked] (Eric W. Biederman)
Date: Wed, 12 Feb 2014 18:00:47 -0800

Cong Wang <[email-masked]> writes:

> On Wed, Feb 12, 2014 at 7:43 AM, Nicolas Dichtel
> <[email-masked]> wrote:
>> Le 12/02/2014 00:51, Cong Wang a écrit :
>>
>>> From: Cong Wang <[email-masked]>
>>>
>>> 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 <[email-masked]>
>>> Cc: Eric W. Biederman <[email-masked]>
>>> Cc: Eric Dumazet <[email-masked]>
>>> Cc: Hannes Frederic Sowa <[email-masked]>,
>>> Signed-off-by: Cong Wang <[email-masked]>
>>> Signed-off-by: Cong Wang <[email-masked]>
>>
>> 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