linux-kernel - Re: c/r: broken locking when executing map

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Date:	Fri, 11 May 2012 21:56:40 +0400
From:	Vasiliy Kulikov <segoon@...nwall.com>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
Cc:	Sasha Levin <levinsasha928@...il.com>, khlebnikov@...nvz.org,
	xemul@...allels.com, Dave Jones <davej@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: c/r: broken locking when executing map_files

On Mon, May 07, 2012 at 00:49 +0400, Cyrill Gorcunov wrote:
> On Mon, May 07, 2012 at 12:21:32AM +0400, Vasiliy Kulikov wrote:
> > On Sat, May 05, 2012 at 23:32 +0400, Cyrill Gorcunov wrote:
> > > On Sat, May 05, 2012 at 10:53:06PM +0400, Cyrill Gorcunov wrote:
> > >  | [root@...tune ~]# /proc/self/map_files/400000-419000
> > > 
> > > it sleeps forever until killed, which is not good I think. Vasiliy, could
> > > you remind me what exactly is problem if we use unlocked ptrace_may_access
> > > here?
> > 
> > There is a race between ptrace_may_access() and dname_to_vma_addr().
> > The target task may do exec() between these calls and
> > dname_to_vma_addr() will be called against a privileged task.  This may
> > lead to a leak of task maps.
> 
> Wait, the proc_map_files_lookup requires the caller to be cap-sysadmin
> granted, would not this be enough?

Yes :-) You can also remove additional checks after capable() in
readdir and revalidate functions.

-- 
Vasily Kulikov
http://www.openwall.com - bringing security into open computing environments
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