linux-kernel - Re: [patch 0/4] MAP_NOZERO v2 - VM_NOZERO/MAP

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Message-ID: <Pine.LNX.4.64.0707021537350.14774@alien.or.mcafeemobile.com>
Date:	Mon, 2 Jul 2007 15:38:53 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Andy Isaacson <adi@...apodia.org>
cc:	Kyle Moffett <mrmacman_g4@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [patch 0/4] MAP_NOZERO v2 - VM_NOZERO/MAP_NOZERO early summer
 madness

On Mon, 2 Jul 2007, Andy Isaacson wrote:

> On Sat, Jun 30, 2007 at 12:03:07PM -0700, Davide Libenzi wrote:
> > I think the focus should be to find a case where under the currently 
> > implemented policy for MAP_NOZERO, MAP_NOZERO represent a loss of security 
> > WRT no MAP_NOZERO.   I have not been able to find one yet, although Andy 
> > found a potential one in the setuid+exec/ptrace race (fixed by a patch 
> > that should IMO go in in any case).
> 
> BTW, the ptrace variant of this issue is not a problem -- PTRACE_ATTACH
> running as newuid gets EPERM when trying to attach at /* here */ below.
> 
>     setuid(newuid);
>     /* here */
>     exec(...);
>     exit(1);
> 
> sys_setuid sets current->mm->dumpable = suid_dumpable, so unless the
> admin asked for it, there is no risk WRT PTRACE_ATTACH.  However, this
> risk vector does need to be considered when implementing MAP_NOZERO.

Yes, I missed that. Ptrace is fine there. The 3 lines patch is still 
needed for MAP_NOZERO though.



- Davide


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