Re: [PATCH v5] cgroup: Add new capability to allow a process to migrate other tasks between cgroups

From: John Stultz
Date: Tue Dec 13 2016 - 12:34:31 EST

On Tue, Dec 13, 2016 at 9:17 AM, Casey Schaufler <casey@xxxxxxxxxxxxxxxx> wrote:
> On 12/13/2016 8:49 AM, John Stultz wrote:
>> On Tue, Dec 13, 2016 at 8:39 AM, Casey Schaufler <casey@xxxxxxxxxxxxxxxx> wrote:
>>> On 12/13/2016 1:47 AM, Michael Kerrisk (man-pages) wrote:
>>>> How about CAP_CGROUP_CONTROL or some such, with the idea that this
>>>> might be a capability that allows the holder to step outside usual
>>>> cgroup rules? At the moment, that capability would allow only one such
>>>> step, but maybe there would be others in the future.
>>> I agree, but want to put it more strongly. The granularity of
>>> capabilities can never be fine enough for some people, and this
>>> is an example of a case where you're going a bit too far. If the
>>> use case is Android as you say, you don't need this. As my friends
>>> on the far side of the aisle would say, "just write SELinux policy"
>>> to correctly control access as required.
>> So.. The trouble is that while selinux is good for restricting
>> permissions, the in-kernel permission checks here are already too
>> restrictive.
> Why did the original authors of cgroups make it that restrictive?
> If there isn't a good reason, loosen it up. If there is a good
> reason, then pay heed to it.

That's what this patch is proposing. And I agree with Michael that the
newly proposed cap was a bit to narrowly focused on my immediate use
case, and broadening it to CGROUP_CONTROL is smart. Then that
capability could be further restricted w/ selinux policy, as you