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Sender: Tejun Heo <htejun@gmail.com>
Date:   Fri, 26 Aug 2022 11:08:04 -1000
From:   Tejun Heo <tj@kernel.org>
To:     Michal =?iso-8859-1?Q?Koutn=FD?= <mkoutny@suse.com>
Cc:     linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
        bpf@vger.kernel.org, Aditya Kali <adityakali@google.com>,
        Serge Hallyn <serge.hallyn@canonical.com>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Yonghong Song <yhs@fb.com>,
        Muneendra Kumar <muneendra.kumar@broadcom.com>,
        Yosry Ahmed <yosryahmed@google.com>,
        Hao Luo <haoluo@google.com>
Subject: Re: [PATCH 0/4] Honor cgroup namespace when resolving cgroup id
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Hello,

On Fri, Aug 26, 2022 at 06:52:34PM +0200, Michal Koutn? wrote:
> Cgroup id is becoming a new way for userspace how to refer to cgroups it
> wants to act upon. As opposed to cgroupfs (paths, opened FDs), the
> current approach does not reflect limited view by (non-init) cgroup
> namespaces.

Looking at the code, I'm not quite sure we're actually plugging all holes in
terms of lookup. I think cgroup_get_from_path() would allow walking up past
the ns boundary. We aren't using kernfs ns support and I don't see anything
preventing ..'ing past the boundary.

> This patches don't aim to limit what a user can do (consider an uid=0 in
> mere cgroup namespace) but to provide consistent view within a
> namespace.

Considering userns and the fact that we try to isolate two separate sub
hierarchies delegated to the same UID, I think we'd have to tighten down on
the behaviors so that visiblity scope matches the permission scope.

Thanks.

-- 
tejun