netdev - Re: [RESEND][PATCH v4] cgroup: Use CAP_SYS_RESOURCE to allow a process to migrate other tasks between cgroups

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Date:   Thu, 8 Dec 2016 21:39:38 -0800
From:   John Stultz <john.stultz@...aro.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Andy Lutomirski <luto@...nel.org>,
        Mickaël Salaün <mic@...ikod.net>,
        Daniel Mack <daniel@...que.org>,
        "David S. Miller" <davem@...emloft.net>, kafai@...com,
        Florian Westphal <fw@...len.de>,
        Harald Hoyer <harald@...hat.com>,
        Network Development <netdev@...r.kernel.org>,
        Sargun Dhillon <sargun@...gun.me>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Li Zefan <lizefan@...wei.com>,
        Jonathan Corbet <corbet@....net>,
        "open list:CONTROL GROUP (CGROUP)" <cgroups@...r.kernel.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        Rom Lemarchand <romlem@...roid.com>,
        Colin Cross <ccross@...roid.com>,
        Dmitry Shmidt <dimitrysh@...gle.com>,
        Todd Kjos <tkjos@...gle.com>,
        Christian Poetzsch <christian.potzsch@...tec.com>,
        Amit Pundir <amit.pundir@...aro.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Kees Cook <keescook@...omium.org>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [RESEND][PATCH v4] cgroup: Use CAP_SYS_RESOURCE to allow a
 process to migrate other tasks between cgroups

On Tue, Dec 6, 2016 at 10:23 AM, Tejun Heo <tj@...nel.org> wrote:
> Hello,
>
> On Tue, Dec 06, 2016 at 10:13:53AM -0800, Andy Lutomirski wrote:
>> > Delegation is an explicit operation and reflected in the ownership of
>> > the subdirectories and cgroup interface files in them.  The
>> > subhierarchy containment is achieved by requiring the user who's
>> > trying to migrate a process to have write perm on cgroup.procs on the
>> > common ancestor of the source and target in addition to the target.
>>
>> OK, I see what you're doing.  That's interesting.
>
> It's something born out of usages of cgroup v1.  People used it that
> way (chowning files and directories) and combined with the uid checksn
> it yielded something which is useful sometimes, but it always had
> issues with hierarchical behaviors, which files to chmod and the weird
> combination of uid checks.  cgroup v2 has a clear delegation model but
> the uid checks are still left in as not changing was the default.
>
> It's not necessary and I'm thinking about queueing something like the
> following in the next cycle.
>
> As for the android CAP discussion, I think it'd be nice to share an
> existing CAP but if we can't find a good one to share, let's create a
> new one.

So just to clarify the discussion for my purposes and make sure I
understood, per-cgroup CAP rules was not desired, and instead we
should either utilize an existing cap (are there still objections to
CAP_SYS_RESOURCE? - this isn't clear to me) or create a new one (ie,
bring back the older CAP_CGROUP_MIGRATE patch).

Tejun: Do you have a more finished version of your patch that I should
add my changes on top of?

thanks
-john