linux-kernel - Re: [PATCH 2/2] net: Implement SO

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Date:	Thu, 13 Mar 2014 14:21:40 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Simo Sorce <ssorce@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	cgroups@...r.kernel.org,
	Network Development <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>, Tejun Heo <tj@...nel.org>,
	jkaluza@...hat.com, lpoetter@...hat.com, kay@...hat.com
Subject: Re: [PATCH 2/2] net: Implement SO_PEERCGROUP

On Thu, Mar 13, 2014 at 1:06 PM, Vivek Goyal <vgoyal@...hat.com> wrote:
> On Thu, Mar 13, 2014 at 12:58:14PM -0700, Andy Lutomirski wrote:
>> On Thu, Mar 13, 2014 at 12:53 PM, Vivek Goyal <vgoyal@...hat.com> wrote:
>> > On Thu, Mar 13, 2014 at 10:55:16AM -0700, Andy Lutomirski wrote:
>> >
>> > [..]
>> >> >> 2. Docker is a container system, so use the "container" (aka
>> >> >> namespace) APIs.  There are probably several clever things that could
>> >> >> be done with /proc/<pid>/ns.
>> >> >
>> >> > pid is racy, if it weren't I would simply go straight
>> >> > to /proc/<pid>/cgroups ...
>> >>
>> >> How about:
>> >>
>> >> open("/proc/self/ns/ipc", O_RDONLY);
>> >> send the result over SCM_RIGHTS?
>> >
>> > As I don't know I will ask. So what will server now do with this file
>> > descriptor of client's ipc namespace.
>> >
>> > IOW, what information/identifier does it contain which can be
>> > used to map to pre-configrued per container/per namespace policies.
>>
>> Inode number, which will match that assigned to the container at runtime.
>>
>
> But what would I do with this inode number. I am assuming this is
> generated dynamically when respective namespace was created. To me
> this is like assigning a pid dynamically and one does not create
> policies in user space based on pid. Similarly I will not be able
> to create policies based on an inode number which is generated
> dynamically.
>
> For it to be useful, it should map to something more static which
> user space understands.

Like what?  I imagine that, at best, sssd will be hardcoding some
understanding of Docker's cgroup names.  As an alternative, it could
ask Docker for a uid or an inode number of something else -- it's
hardcoding an understanding of Docker anyway.  And Docker needs to
cooperate regardless, since otherwise it could change its cgroup
naming or stop using cgroups entirely.

--Andy
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