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

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Date:	Mon, 2 Jul 2007 11:38:35 -0700
From:	Andy Isaacson <adi@...apodia.org>
To:	Davide Libenzi <davidel@...ilserver.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 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.

-andy
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