linux-kernel - Re: [PATCH 3/5] device_cgroup: keep track of local group settings

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Date:	Mon, 3 Dec 2012 18:01:25 +0000
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	Aristeu Rozanski <aris@...hat.com>
Cc:	"Serge E. Hallyn" <serge@...lyn.com>, linux-kernel@...r.kernel.org,
	Tejun Heo <tj@...nel.org>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	cgroups@...r.kernel.org
Subject: Re: [PATCH 3/5] device_cgroup: keep track of local group settings

Quoting Aristeu Rozanski (aris@...hat.com):
> On Thu, Nov 29, 2012 at 08:26:08PM +0000, Serge E. Hallyn wrote:
> > Quoting Aristeu Rozanski (aris@...hat.com):
> > > 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
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