On 2024/8/15 0:52, Tejun Heo wrote:
Hello,
On Wed, Aug 14, 2024 at 04:09:59PM +0800, chenridong wrote:
...
Hi，TJ， We plan to use delegation in cgroup-v2, so I am conducting some
tests.
As doc mentions 'Because the resource control interface files in a given
directory control the distribution of the parent's resources, the delegatee
shouldn't be allowed to write to them.' However I found a root can write
parent's file(cgroup.subtree_control) to change the resource limits(a
fraudulent method). I believe this could pose a risk in some scenarios where
a root enters a new cgroup ns without unmounting original cgroup system, and
it can break limitations. For instance, running a docker with --privileged,
could this be a risk?
So I sent this patch to discuss whether this case should be addressed?
That sounsd like a misconfiguration. cgroup NS doesn't make much sense if
you don't limit the actual visibility. The interface is half broken in that
situation anyway and if you're leaking filesystem visibility into a
supposedly isolated container, relaxed resource limits aren't biggest of
your problems.
While the proposed change isn't necessarily a bad idea, it's a behavior
change and I don't either modifying existing behavior or introducing a new
mount flag is justified here. Maybe just update the documentation indicating
that the ancestral cgroups shouldn't be visible in a delegated ns?
Thanks.
Thank you, TJ, I will send a patch to update comment and the documentation.
Thanks,
Ridong
