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From:   Yosry Ahmed <yosryahmed@google.com>
Date:   Mon, 29 Aug 2022 10:30:45 -0700
Message-ID: <CAJD7tkZySzWgJgp4xbkpSstc_RMN_tJqt83-FFrxv6jASeg8CA@mail.gmail.com>
Subject: Re: [PATCH 4/4] cgroup/bpf: Honor cgroup NS in cgroup_iter for ancestors
To:     =?UTF-8?Q?Michal_Koutn=C3=BD?= <mkoutny@suse.com>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Cgroups <cgroups@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
        Tejun Heo <tj@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>,
        Hao Luo <haoluo@google.com>
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On Mon, Aug 29, 2022 at 6:00 AM Michal Koutn=C3=BD <mkoutny@suse.com> wrote=
:
>
> On Fri, Aug 26, 2022 at 10:41:37AM -0700, Yosry Ahmed <yosryahmed@google.=
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.
>

Great, thanks!

>
> 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).
>

imo it should fail straight ahead, but maybe others (Tejun? Hao?) have
other opinions here.

>
> Thanks,
> Michal