linux-kernel - Re: [PATCH 4/4] cgroup/bpf: Honor cgroup NS in cgroup

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Date:   Mon, 29 Aug 2022 14:59:57 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Yosry Ahmed <yosryahmed@...gle.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Cgroups <cgroups@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Tejun Heo <tj@...nel.org>, Aditya Kali <adityakali@...gle.com>,
        Serge Hallyn <serge.hallyn@...onical.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Yonghong Song <yhs@...com>,
        Muneendra Kumar <muneendra.kumar@...adcom.com>,
        Hao Luo <haoluo@...gle.com>
Subject: Re: [PATCH 4/4] cgroup/bpf: Honor cgroup NS in cgroup_iter for
 ancestors

On Fri, Aug 26, 2022 at 10:41:37AM -0700, Yosry Ahmed <yosryahmed@...gle.com> wrote:
> I understand that currently cgroup_iter is the only user of this, but
> for future use cases, is it safe to assume that cgrp will always be
> inside ns? Would it be safer to do something like:

I preferred the simpler root_cgrp comparison to avoid pointer
arithmetics in cgroup_is_descendant. But I also made the assumption of
cgrp in ns.

Thanks, I'll likely adjust cgroup_path_ns to make it more robust for
an external cgrp.

I'd like to clarify, if a process A in a broad cgroup ns sets up a BPF
cgroup iterator, exposes it via bpffs and than a process B in a narrowed
cgroup ns (which excludes the origin cgroup) wants to traverse the
iterator, should it fail straight ahead (regardless of iter order)?
The alternative would be to allow self-dereference but prohibit any
iterator moves (regardless of order).

Thanks,
Michal

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