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

From: Tejun Heo
Date: Tue Oct 04 2016 - 15:38:47 EST

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?