linux-kernel - Re: Controlling devices and device namespaces

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Date:	Sun, 16 Sep 2012 08:32:01 -0500
From:	Serge Hallyn <serge@...lyn.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Aristeu Rozanski <aris@...vo.org>,
	Neil Horman <nhorman@...driver.com>,
	"Serge E. Hallyn" <serue@...ibm.com>,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, Michal Hocko <mhocko@...e.cz>,
	Thomas Graf <tgraf@...g.ch>, Paul Mackerras <paulus@...ba.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Johannes Weiner <hannes@...xchg.org>,
	Tejun Heo <tj@...nel.org>, cgroups@...r.kernel.org,
	Paul Turner <pjt@...gle.com>, Ingo Molnar <mingo@...hat.com>
Subject: Re: Controlling devices and device namespaces

On 09/16/2012 07:17 AM, Eric W. Biederman wrote:
> ebiederm@...ssion.com (Eric W. Biederman) writes:
>
>> Alan Cox <alan@...rguk.ukuu.org.uk> writes:
>>
>>>> One piece of the puzzle is that we should be able to allow unprivileged
>>>> device node creation and access for any device on any filesystem
>>>> for which it unprivileged access is safe.
>>>
>>> Which devices are "safe" is policy for all interesting and useful cases,
>>> as are file permissions, security tags, chroot considerations and the
>>> like.
>>>
>>> It's a complete non starter.
>
> Come to think of it mknod is completely unnecessary.
>
> Without mknod.  Without being able to mount filesystems containing
> device nodes.

Hm?  That sounds like it will really upset init/udev/upgrades in the 
container.

Are you saying all filesystems containing device nodes will need to be 
mounted in advance by the process setting up the container?

 > The mount namespace is sufficient to prevent all of the
> cases that the device control group prevents (open and mknod on device
> nodes).
>
> So I honestly think the device control group is superflous, and it is
> probably wise to deprecate it and move to a model where it does not
> exist.
>
> Eric
>

That's what I said a few emails ago :)  The device cgroup was meant as a 
short-term workaround for lack of user (and device) namespaces.
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