netdev - Re: [PATCH net-next] netlink: include netnsid only when netns differs.

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Date:   Wed, 31 May 2017 15:48:06 +0200
From:   Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:     Flavio Leitner <fbl@...close.org>
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH net-next] netlink: include netnsid only when netns
 differs.

Le 31/05/2017 à 14:28, Flavio Leitner a écrit :
> On Wed, May 31, 2017 at 10:38:21AM +0200, Nicolas Dichtel wrote:
>> Le 30/05/2017 à 23:33, Flavio Leitner a écrit :
>>> Don't include netns id for notifications broadcasts when the
>>> socket and the skb are in the same netns because it will be
>>> an error which can't be distinguished from a peer netns failing
>>> to allocate an id.
>> I don't understand the problem. peernet2id() doesn't allocate ids, it only do a
>> lookup. If you need an id for the current netns, you have to allocate one.
> 
> The issue is that if you query an interface on the same netns, the
> error is returned, then we cannot tell if the iface is on the same
> netns or if there was an error while allocating the ID and the
> iface is on another netns.
If the returned id is NETNSA_NSID_NOT_ASSIGNED, then the netns is the same.

Some lines before your patch, we call peernet_has_id() when the netns differ,
thus we ensure that the id is available.

The principle was that netlink messages of other netns can be sent only if an id
is assigned.

> 
>> This patch changes the metadata exported to the userland and will break existing
>> tools.
> 
> It should not break because it changes only for interfaces on
> the same netns where there is no ID and that value wasn't
> exported until recently.
> 
It was exported since the initial patch (59324cf35aba ("netlink: allow to listen
"all" netns"). Am I wrong?


Regards,
Nicolas