netdev - Re: [PATCH net] netlink: don't send unknown nsid

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Message-ID: <057303a1-5d27-1b24-c8b0-d3cf46b14825@6wind.com>
Date:   Thu, 8 Jun 2017 10:31:53 +0200
From:   Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:     Flavio Leitner <fbl@...close.org>
Cc:     davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH net] netlink: don't send unknown nsid

Le 07/06/2017 à 21:14, Flavio Leitner a écrit :
> On Mon, Jun 05, 2017 at 10:40:24AM +0200, Nicolas Dichtel wrote:
>>> Let me ask this instead: How do you think userspace should behave when
>>> netnsid allocation fails?
>>>
>> There is two ways to assign a nsid:
>>  - manually with netlink ('ip netns set'). In this case, the error is reported
>>    to userspace via netlink.
> 
> OK.
> 
>>  - automatically when a x-netns interface is created. The link-nsid is also
>>    reported to userspace. If the allocation failed, NETNSA_NSID_NOT_ASSIGNED is
>>    reported. And if you were able to create this x-netns interface, it means
>>    that you have access to this peer netns, thus you can try to assign the nsid
>>    manually.
> 
> Does that prevent the interface to be created?
No.

> 
>> So, in both cases, userland knows that something went wrong.
>> Do you have another scenario in mind?
> 
> Let's say the app is restarted, or another monitoring app is executed
> with enough perms.  How will it identify the error condition?
Your app wants to monitor a subset of netns. It means that you already have a
way to identify those netns, something like a file stored somewhere
(/var/run/netns/, /proc/<pid>/ns/net, ...). Thus, it's easy to check if those
netns have a nsid assigned in the netns where your app will open the socket.

This option was called NETLINK_F_LISTEN_ALL_NSID, because it only enables to
listen netns *with* a nsid assigned, nothing more. It's up to the user to ensure
that nsid are correctly assigned.


Regards,
Nicolas