Re: [PATCH v3 1/2] cgroup: apply common ancestor cgroup.procs restriction in cgroupv1

[Tejun Heo <tj@kernel.org>]

On Tue, May 03, 2016 at 12:01:20AM +1000, Aleksa Sarai wrote:
> The common ancestor restriction for moving tasks between cgroups (the
> process moving the task must have the right to write to cgroup.procs in
> both the destination and common ancestor cgroup) only applied for
> cgroupv2 (cgroups in the default hierarchy). This meant that there was a
> different policy for unprivileged users in the different cgroup
> hierarchies.
> 
> Update cgroup_procs_write_permission() to apply the cgroup.procs
> restriction regardless of the cgroup root of the destination cgroup.
> However, if the task doesn't have any association with the destination
> hierarchy, there's no permission check to be done. In addition, if the
> destination cgroup is a descendant of the task's current cgroup then
> there are no further permission checks. This is important for
> unprivileged processes creating subtrees.

So, you can't apply a new restriction like this retro-actively to
cgroup v1 hierarchies.

Thanks.

-- 
tejun