linux-kernel - Re: [PATCHv1 7/8] cgroup: cgroup namespace setns support

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Message-ID: <20141016214710.GA4759@mail.hallyn.com>
Date:	Thu, 16 Oct 2014 23:47:10 +0200
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	Aditya Kali <adityakali@...gle.com>
Cc:	"Serge E. Hallyn" <serge@...lyn.com>, Tejun Heo <tj@...nel.org>,
	Li Zefan <lizefan@...wei.com>,
	Serge Hallyn <serge.hallyn@...ntu.com>,
	Andy Lutomirski <luto@...capital.net>, cgroups@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Linux Containers <containers@...ts.linux-foundation.org>,
	Rohit Jnagal <jnagal@...gle.com>
Subject: Re: [PATCHv1 7/8] cgroup: cgroup namespace setns support

Quoting Aditya Kali (adityakali@...gle.com):
> On Thu, Oct 16, 2014 at 2:12 PM, Serge E. Hallyn <serge@...lyn.com> wrote:
> > Quoting Aditya Kali (adityakali@...gle.com):
> >> setns on a cgroup namespace is allowed only if
> >> * task has CAP_SYS_ADMIN in its current user-namespace and
> >>   over the user-namespace associated with target cgroupns.
> >> * task's current cgroup is descendent of the target cgroupns-root
> >>   cgroup.
> >
> > What is the point of this?
> >
> > If I'm a user logged into
> > /lxc/c1/user.slice/user-1000.slice/session-c12.scope and I start
> > a container which is in
> > /lxc/c1/user.slice/user-1000.slice/session-c12.scope/x1
> > then I will want to be able to enter the container's cgroup.
> > The container's cgroup root is under my own (satisfying the
> > below condition0 but my cgroup is not a descendent of the
> > container's cgroup.
> >
> This condition is there because we don't want to do implicit cgroup
> changes when a process attaches to another cgroupns. cgroupns tries to
> preserve the invariant that at any point, your current cgroup is
> always under the cgroupns-root of your cgroup namespace. But in your
> example, if we allow a process in "session-c12.scope" container to
> attach to cgroupns root'ed at "session-c12.scope/x1" container
> (without implicitly moving its cgroup), then this invariant won't
> hold.

Oh, I see.  Guess that should be workable.  Thanks.

-serge
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