linux-kernel - Re: [RFC][PATCH 0/2] Another pass at Android style loosening of cgroup attach permissions

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Date:   Tue, 4 Oct 2016 15:38:38 -0400
From:   Tejun Heo <tj@...nel.org>
To:     John Stultz <john.stultz@...aro.org>
Cc:     lkml <linux-kernel@...r.kernel.org>, Li Zefan <lizefan@...wei.com>,
        Jonathan Corbet <corbet@....net>, cgroups@...r.kernel.org,
        Android Kernel Team <kernel-team@...roid.com>,
        Rom Lemarchand <romlem@...roid.com>,
        Colin Cross <ccross@...roid.com>,
        Dmitry Shmidt <dimitrysh@...gle.com>,
        Todd Kjos <tkjos@...gle.com>,
        Christian Poetzsch <christian.potzsch@...tec.com>,
        Amit Pundir <amit.pundir@...aro.org>,
        Serge Hallyn <serge.hallyn@...onical.com>
Subject: Re: [RFC][PATCH 0/2] Another pass at Android style loosening of
 cgroup attach permissions

Hello, John.

On Tue, Oct 04, 2016 at 11:01:12AM -0700, John Stultz wrote:
> So to make sure I understand your suggestion, you're suggesting the
> cgroupfs files like:
> cpuctrl/tasks,
> cpuctrl/bg_non_interactive/tasks,
> cpuset/foreground/tasks,
> cpuset/background/tasks,
> etc
> use ACL permissions to specify the specific uids that can write to
> them? I guess this would be conceptually similar to just setting the
> owner to the system task, no?  Though I'm not sure that would be

Yeah, finer grained but essentially just giving write perms.

> sufficient since it would still fail the
> cgroup_procs_write_permission() checks. Or are you suggesting we add
> extra logic to make the file owner uid as sufficient to change other
> tasks?

Hah, now I'm not sure how this is supposed to work inside a userns as
it's checking against GLOBAL_ROOT_UID.  cc'ing Serge.  Serge, can you
please have a look?

But back on subject, yeah, I think a capability based approach is
better here too.  No idea how difficult it is to add a new CAP but I
think it's worth trying.  Can you please spin up a patch?

Thanks!

-- 
tejun