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Message-ID: <20161004201840.GA27018@mail.hallyn.com>
Date: Tue, 4 Oct 2016 15:18:40 -0500
From: "Serge E. Hallyn" <serge@...lyn.com>
To: Tejun Heo <tj@...nel.org>
Cc: 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, John.
>
> On Tue, Oct 04, 2016 at 11:01:12AM -0700, John Stultz wrote:
> > So to make sure I understand your suggestion, you're suggesting the
> > cgroupfs files like:
> > cpuctrl/tasks,
> > cpuctrl/bg_non_interactive/tasks,
> > cpuset/foreground/tasks,
> > cpuset/background/tasks,
> > etc
> > use ACL permissions to specify the specific uids that can write to
> > them? I guess this would be conceptually similar to just setting the
> > owner to the system task, no? Though I'm not sure that would be
>
> Yeah, finer grained but essentially just giving write perms.
>
> > sufficient since it would still fail the
> > cgroup_procs_write_permission() checks. Or are you suggesting we add
> > extra logic to make the file owner uid as sufficient to change other
> > tasks?
>
> Hah, now I'm not sure how this is supposed to work inside a userns as
> it's checking against GLOBAL_ROOT_UID. cc'ing Serge. Serge, can you
> please have a look?
Hi, thanks for the cc,
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.
> But back on subject, yeah, I think a capability based approach is
> better here too. No idea how difficult it is to add a new CAP but I
> think it's worth trying. Can you please spin up a patch?
>
> Thanks!
>
> --
> tejun
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