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

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Date:   Thu, 1 Jun 2017 09:57:14 +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 20:34, Flavio Leitner a écrit :
> On Wed, May 31, 2017 at 03:48:06PM +0200, Nicolas Dichtel wrote:
>> 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.
> 
> Right, but that's internal to the kernel.
Sure, but a good example exists in iproute2:
https://git.kernel.org/pub/scm/linux/kernel/git/shemminger/iproute2.git/tree/ip/ipmonitor.c#n45

> 
>> The principle was that netlink messages of other netns can be sent only if an id
>> is assigned.
> 
> OK, could you please update include/uapi/linux/net_namespace.h to reflect that?
> It says NETNSA_NSID_NOT_ASSIGNED are attributes for RTM_NEWNSID or RTM_GETNSID
> which makes sense, but NOT_ASSIGNED sounds little like SAME_NSID for other
> message types.
I agree, it's confusing. I will send a patch.