linux-kernel - Re: [PATCH v2 0/4] Checkpoint/Restore: Show in proc IDs of objects that can be shared between tasks

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Message-Id: <20111118123728.554b45e7.akpm@linux-foundation.org>
Date:	Fri, 18 Nov 2011 12:37:28 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Pavel Emelyanov <xemul@...allels.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Glauber Costa <glommer@...allels.com>,
	Andi Kleen <andi@...stfloor.org>, Tejun Heo <tj@...nel.org>,
	Matt Helsley <matthltc@...ibm.com>,
	Pekka Enberg <penberg@...nel.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Vasiliy Kulikov <segoon@...nwall.com>
Subject: Re: [PATCH v2 0/4] Checkpoint/Restore: Show in proc IDs of objects
 that can be shared between tasks

On Sat, 19 Nov 2011 00:03:42 +0400
Cyrill Gorcunov <gorcunov@...il.com> wrote:

> On Fri, Nov 18, 2011 at 11:07:16AM -0800, Andrew Morton wrote:
> ...
> > 
> > OK.  Using the object's kernel virtual address is certainly very
> > attractive.
> > 
> > It is the case that we're causing difficulty with this longer-term plan
> > to make c/r available to unprivileged processes?  Because it's OK to
> > expose kernel addresses to CAP_SYS_ADMIN (or similar) tasks (isn't it?).
> > 
> 
> Actually the address is not exposed in open-form but rather xor'ed with
> a random number, still from security pov it's not clear if it's really useful
> for attacker to obtain inverted low bits of the former random number (which
> might happen on aligned addresses).
> 

Of course.  But

a) I'm not sure that this scheme actually protects the kernel
   addresses - there may be way in which cunning userspace can work out
   the random mask.

b) If we can export these addresses only to CAP_SYS_ADMIN tasks then
   we don't need to obfuscate them anyway.

   Which takes me back to again asking: why not make c/r root-only? 
   And provide non-root access via a carefully-written setuid
   front-end?


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