Quoting Aristeu Rozanski (aris-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org):

On Thu, Nov 29, 2012 at 08:26:08PM +0000, Serge E. Hallyn wrote:

quoted

Quoting Aristeu Rozanski (aris-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org):

quoted

I see your point. it's indeed a problem. in dev_exception_add(), it
needs to check for permissions before actually adding to
devcgroup->exceptions.

actually, checked again, it's done correctly. when adding an exception
that will allow extra device access (DEVCG_ALLOW), it does check it
before. It means that you can't add local exceptions unless at a certain
point of the time it was allowed to do so.

Thanks.

...

git://github.com/aristeu/linux-2.6.git

please use branch devcg_hiearchy_review

Thanks!

I have a few remaining concerns.

First, generally, I don't think 'allows' added to parent should be 
automatically propagated to descendents.

In devcgroup_update_access: (around line 625)
	there is a period of time where cgroup members have
	default allow without the parent's exceptions.

propagate_behavior (line 505):
	1. doesn't follow the same ordering as devcgroup_update_access(), in
	particular cleaning exceptions before setting behavior.
	2. When changing a parent from deny to allow, I don't think children
	should be updated.

propagate_exception:
	1. the WARN_ONCE doesn't seem helpful.
	2. Again, I don't think allows to a parent should be propagated, only
	denies.

-serge