linux-kernel - Re: [RFC][PATCH 0/2] Another pass at Android style loosening of cgroup attach permissions

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Date:   Tue, 4 Oct 2016 16:26:43 -0500
From:   "Serge E. Hallyn" <serge@...lyn.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     "Serge E. Hallyn" <serge@...lyn.com>,
        John Stultz <john.stultz@...aro.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Li Zefan <lizefan@...wei.com>,
        Jonathan Corbet <corbet@....net>, 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>
Subject: Re: [RFC][PATCH 0/2] Another pass at Android style loosening of
 cgroup attach permissions

Quoting Tejun Heo (tj@...nel.org):
> Hello, Serge.
> 
> On Tue, Oct 04, 2016 at 03:18:40PM -0500, Serge E. Hallyn wrote:
> > how about changing the GLOBAL_ROOT_UID check with a targeted
> > capability check, like
> > 
> > 	if (!ns_capable(tcred->user_ns, CAP_SYS_NICE) &&
> >             !uid_eq(cred->euid, tcred->uid) &&
> >             !uid_eq(cred->euid, tcred->suid))
> > 		ret = -EACCES;
> > 
> > where the actual capability to use may require some thought.
> 
> Yeah, that's the direction I'm thinking too.  We can't use
> CAP_SYS_NICE in general tho.  Let's see if a dedicated CAP sticks.

One possibility would be to let each cgroup subsystem define
a move_caps capability mask which is required over the target
task.  And add a new CAP_CGROUP which always suffices?