linux-kernel - Re: [RFC] Introduce CAP_CHECKPOINT capability and filter map

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Date:	Thu, 17 Nov 2011 15:07:13 -0600
From:	"Serge E. Hallyn" <serge.hallyn@...onical.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Cyrill Gorcunov <gorcunov@...il.com>, Tejun Heo <tj@...nel.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] Introduce CAP_CHECKPOINT capability and filter map_files/
 access

Quoting Andrew Morton (akpm@...ux-foundation.org):
> On Thu, 17 Nov 2011 09:41:05 -0600
> "Serge E. Hallyn" <serge.hallyn@...onical.com> wrote:
> 
> > >  - (not yet merged) clone-with-specified-pid, might be changed to last_pid+clone setup
> > >  - (not yet published/stabilized) prctls calls to tune up vDSO and elements
> > >    of mm_struct such as mm->start_code, mm->end_code, mm->start_data and etc
> > > 
> > > I would like to gather people opinions on such approach as a general.
> > > _ANY_ comments are highly appreciated. Would it worth it or not (since
> > > CAPs space is pretty limited one).
> > 
> > It's hard to have a specific dialogue without the full c/r patchset and
> > idea of the architecture of the exploiters (ie c/r and maybe
> > debuggers)
> > 
> > Sorry, the security implications of the in-kernel c/r syscalls were
> > pretty simple and clear to me, but those of the new approach are not.
> 
> yup.
> 
> From a development-order perspective perhaps it is better to get
> everything working and stabilized for root first.  Then as a separate
> activity start working on making it available to less-privileged users.
> 
> We would need to be confident that such a second development effort
> doesn't cause back-compatibility issues (ie: interface changes) for
> existing root users.
> 
> 
> 
> Is it possible that once everything is working for root, we realise
> that we can get it all working for non-root users via suitable setuid
> userspace tools?

Not only that, I think it's possible that by the time all the needed c/r
pieces are in, user namespaces will be as well, as will unprivileged
namespace cloning (at least when done along with CLONE_NEWUSER).  In that
case, it should be possible to do c/r of a container with no privileges
on the host (but full privileges to the user namespace of the container).

-serge
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