linux-kernel - Re: [PATCH] System Wide Capability Bounding Set

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Date:	Fri, 28 Jan 2011 13:19:27 -0500
From:	Eric Paris <eparis@...hat.com>
To:	Steve Grubb <sgrubb@...hat.com>
Cc:	"Andrew G. Morgan" <morgan@...nel.org>,
	linux-kernel@...r.kernel.org,
	"Serge E. Hallyn" <serge@...onical.com>,
	"Serge E. Hallyn" <serge.hallyn@...onical.com>,
	linux-security-module@...r.kernel.org
Subject: Re: [PATCH] System Wide Capability Bounding Set

On Thu, 2011-01-27 at 11:50 -0500, Steve Grubb wrote:
> On Thursday, January 27, 2011 11:35:13 am Andrew G. Morgan wrote:
> > > Today, people want to have multi-tenant hosting using virtual
> > > machines whereby they give away root control of the guest VM.
> > > If you were renting system space, you would expect root access.
> > > That would make a nice juicy hacking target because you don't know
> > > who else is sharing the physical machine with you and they might
> > > have something in their VM worth stealing.
> > 
> > Which root filesystem (/) do kernel helpers run in in such a virtual setup?
> 
> I would assume that root in the VM could umount and mount anything. Or bind mount over 
> it. We really want any change to a global bounding set done before initrd finishes 
> doing its thing. This way there is no chance for mischief by the time control is 
> turned over to /sbin/init - which root controls.

I feel like we are all starting to understand the problem.  It still
leaves me with the belief that the only 2 known ways to solve it are

1) global bounding set which bounds the pP = fI & pI rule, unlike the
per process bset

2) a mechanism to drop caps from the bset and pI of the kthread which
runs helper apps

Do others see another way?

-Eric

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