netdev - Re: [RFC PATCH net-next v2 0/5] netns: allow to identify peer netns

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Date:	Fri, 26 Sep 2014 15:38:57 +0200
From:	Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:	Cong Wang <cwang@...pensource.com>
CC:	netdev <netdev@...r.kernel.org>,
	containers@...ts.linux-foundation.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-api@...r.kernel.org, David Miller <davem@...emloft.net>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Stephen Hemminger <stephen@...workplumber.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>
Subject: Re: [RFC PATCH net-next v2 0/5] netns: allow to identify peer netns

Le 26/09/2014 03:58, Cong Wang a écrit :
> On Thu, Sep 25, 2014 at 1:53 AM, Nicolas Dichtel
> <nicolas.dichtel@...nd.com> wrote:
>> Le 24/09/2014 18:48, Cong Wang a écrit :
>>
>>> On Wed, Sep 24, 2014 at 9:31 AM, Nicolas Dichtel
>>> <nicolas.dichtel@...nd.com> wrote:
>>>>>
>>>>> I think in this case your ID's are still available, but aren't you
>>>>> providing a new way
>>>>> for the inner netns device to escape which we are trying to avoid?
>>>>
>>>>
>>>> It's why the ids depend on user ns. Only if user ns are the same we allow
>>>> to
>>>> get an id for a peer netns.
>>>
>>>
>>> Too late, userns is relatively new, relying on it breaks our existing
>>> assumption.
>>>
>> I don't get your point. netns has been added in kernel after user ns:
>> acce292c82d4 user namespace: add the framework => 2.6.23
>> 5f256becd868 [NET]: Basic network namespace infrastructure. => 2.6.24
>
> Was it complete on 2.6.x? I doubt...
>
> https://lkml.org/lkml/2014/8/20/826
>
>     As at Linux 3.8, most relevant subsystems supported  user  names‐
>         paces,  but  a number of filesystems did not have the infrastruc‐
>         ture needed to map user and group IDs  between  user  namespaces.
>         Linux  3.9  added the required infrastructure support for many of
>         the remaining unsupported filesystems (Plan 9 (9P),  Andrew  File
>         System  (AFS),  Ceph,  CIFS,  CODA,  NFS, and OCFS2).  Linux 3.11
>         added support the last of the unsupported major filesystems, XFS.
>
>
>>
>> In the kernel, each netns is linked with a user ns.
>
> Are you saying every time we create a netns we have a new userns?
> This doesn't make sense for me.
>
No. I mean that each netns depends on a userns.
See include/net/net_namespace.h:
struct net {
[snip]
         struct user_namespace   *user_ns;       /* Owning user namespace */
[snip]
}
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