linux-kernel - Re: [PATCH] devpts: Add ptmx_uid and ptmx

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Date:	Tue, 31 Mar 2015 06:12:29 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	James Bottomley <James.Bottomley@...senpartnership.com>
Cc:	Alexander Larsson <alexl@...hat.com>, gnome-os-list@...me.org,
	Linux Containers <containers@...ts.linux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	mclasen@...hat.com, "Eric W. Biederman" <ebiederm@...ssion.com>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] devpts: Add ptmx_uid and ptmx_gid options

On Tue, Mar 31, 2015 at 6:07 AM, James Bottomley
<James.Bottomley@...senpartnership.com> wrote:
> On Tue, 2015-03-31 at 09:57 +0200, Alexander Larsson wrote:
>> On fre, 2015-03-27 at 10:03 +0100, James Bottomley
>> >
>> > > On Fri, Feb 20, 2015 at 5:04 PM, Andy Lutomirski <luto@...capital.net> wrote:
>> > > > It's currently impossible to mount devpts in a user namespace that
>> > > > has no root user, since ptmx can't be created.
>> >
>> > This is where I stopped reading because it's not true ... because it is
>> > possible, you just do it from the host as real root.
>>
>> The point is being able to set up a container as a user, not requiring
>> the setup to be run as root at all. In my case container is a desktop
>> application which will be started by the user, and will run as the user.
>> There is no root involved in the call chain at all.
>
> I don't really like that use case:  Most container setups are under the
> control of an orchestration system (like LXC, OpenVZ or even Docker).
> You typically get the orchestration system to do the dangerous
> operations (mount being one of the bigger dangers) because it has the
> capacity to vet them.  I can see the value in allowing a user to set up
> a container without an oversight system, but at the same time you're
> increasing the security vulnerability of the system.  Security is often
> a result of policy, so now this embeds policy into the kernel.  I
> strongly feel we should define the list of things we expect an
> unsupervised (as in with no orchestration system) container to do and
> then revisit this once we've given it some thought.

Try thinking "sandbox", not "container".  The ability to create
sandboxes without some root-installed orchestration is incredibly
valuable.

In any event, this ship sailed quite awhile ago.  devpts is one of the
smallish number of important missing features.

--Andy
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