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Re: [PATCH 2/2] cgroup: Add a allow_attach policy for Android

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On Wed, Oct 05, 2016 at 12:18:17PM -0700, John Stultz wrote:
> On Wed, Oct 5, 2016 at 12:10 PM, Dmitry Torokhov
> <dmitry.torokhov@gmail.com> wrote:
> > On Mon, Oct 03, 2016 at 09:41:30PM -0700, John Stultz wrote:
> >> +#ifdef CONFIG_CGROUP_NICE_ATTACH
> >> +int cgroup_nice_allow_attach(struct cgroup_taskset *tset)
> >> +{
> >> +     const struct cred *cred = current_cred(), *tcred;
> >> +     struct task_struct *task;
> >> +     struct cgroup_subsys_state *css;
> >> +
> >> +     if (capable(CAP_SYS_NICE))
> >> +             return 0;
> >> +
> >> +     cgroup_taskset_for_each(task, css, tset) {
> >> +             tcred = __task_cred(task);
> >
> > __task_cred() requires RCU lock (courtesy Ricky Z).
> 
> Again, hopefully this isn't an issue with the new approach, but for
> the short term I'll see if we can get this fixed in the android tree.
> 

Actually, it should all be simply removed from there right away, as this
ends up being basically noop (but with all the locking violations and
races):

cgroup_taskset_for_each() needs tasks to be placed on cset->mg_tasks
list, but nobody does this in the ->allow_access() code path, so this
loops always executes exactly 0 times and the whole thing is exactly
equivalent of doing

	return capable(CAP_SYS_NICE) ? 0 : -EACESS;

which can be done right in cgroup_procs_write_permission().

Thanks.

-- 
Dmitry

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[RFC][PATCH 0/2] Another pass at Android style loosening of cgroup attach permissions John Stultz <john.stultz@linaro.org> - 2016-10-04 06:50 +0200
  [PATCH 2/2] cgroup: Add a allow_attach policy for Android John Stultz <john.stultz@linaro.org> - 2016-10-04 06:50 +0200
    Re: [PATCH 2/2] cgroup: Add a allow_attach policy for Android John Stultz <john.stultz@linaro.org> - 2016-10-05 21:20 +0200
      Re: [PATCH 2/2] cgroup: Add a allow_attach policy for Android Dmitry Torokhov <dmitry.torokhov@gmail.com> - 2016-10-07 00:50 +0200
        Re: [PATCH 2/2] cgroup: Add a allow_attach policy for Android Dmitry Torokhov <dmitry.torokhov@gmail.com> - 2016-10-07 01:00 +0200
    Re: [PATCH 2/2] cgroup: Add a allow_attach policy for Android Dmitry Torokhov <dmitry.torokhov@gmail.com> - 2016-10-05 21:20 +0200
  [PATCH 1/2] cgroup: Add generic cgroup subsystem permission checks John Stultz <john.stultz@linaro.org> - 2016-10-04 06:50 +0200
    Re: [PATCH 1/2] cgroup: Add generic cgroup subsystem permission  checks Dmitry Torokhov <dmitry.torokhov@gmail.com> - 2016-10-05 21:10 +0200
      Re: [PATCH 1/2] cgroup: Add generic cgroup subsystem permission checks John Stultz <john.stultz@linaro.org> - 2016-10-05 21:20 +0200
        Re: [PATCH 1/2] cgroup: Add generic cgroup subsystem permission checks Dmitry Torokhov <dmitry.torokhov@gmail.com> - 2016-10-05 21:30 +0200
  Re: [RFC][PATCH 0/2] Another pass at Android style loosening of  cgroup attach permissions Tejun Heo <tj@kernel.org> - 2016-10-04 18:20 +0200
    Re: [RFC][PATCH 0/2] Another pass at Android style loosening of  cgroup attach permissions John Stultz <john.stultz@linaro.org> - 2016-10-04 20:10 +0200
    Re: [RFC][PATCH 0/2] Another pass at Android style loosening of  cgroup attach permissions John Stultz <john.stultz@linaro.org> - 2016-10-04 20:10 +0200
      Re: [RFC][PATCH 0/2] Another pass at Android style loosening of  cgroup attach permissions Tejun Heo <tj@kernel.org> - 2016-10-04 21:40 +0200
        Re: [RFC][PATCH 0/2] Another pass at Android style loosening of  cgroup attach permissions Tejun Heo <tj@kernel.org> - 2016-10-04 21:50 +0200
        Re: [RFC][PATCH 0/2] Another pass at Android style loosening of  cgroup attach permissions John Stultz <john.stultz@linaro.org> - 2016-10-04 21:50 +0200
        Re: [RFC][PATCH 0/2] Another pass at Android style loosening of  cgroup attach permissions "Serge E. Hallyn" <serge@hallyn.com> - 2016-10-04 22:20 +0200
          Re: [RFC][PATCH 0/2] Another pass at Android style loosening of  cgroup attach permissions Tejun Heo <tj@kernel.org> - 2016-10-04 22:40 +0200
            Re: [RFC][PATCH 0/2] Another pass at Android style loosening of  cgroup attach permissions "Serge E. Hallyn" <serge@hallyn.com> - 2016-10-04 23:30 +0200
              Re: [RFC][PATCH 0/2] Another pass at Android style loosening of  cgroup attach permissions Tejun Heo <tj@kernel.org> - 2016-10-04 23:40 +0200

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