Quoting Tejun Heo (tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org):

Hello, Serge.

On Tue, Oct 04, 2016 at 03:18:40PM -0500, Serge E. Hallyn wrote:

quoted

how about changing the GLOBAL_ROOT_UID check with a targeted
capability check, like

	if (!ns_capable(tcred->user_ns, CAP_SYS_NICE) &&
            !uid_eq(cred->euid, tcred->uid) &&
            !uid_eq(cred->euid, tcred->suid))
		ret = -EACCES;

where the actual capability to use may require some thought.

Yeah, that's the direction I'm thinking too.  We can't use
CAP_SYS_NICE in general tho.  Let's see if a dedicated CAP sticks.

One possibility would be to let each cgroup subsystem define
a move_caps capability mask which is required over the target
task.  And add a new CAP_CGROUP which always suffices?