oss-security - Re: CVE-2009-1895 kernel: personality: fix PER_CLEAR_ON

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Date: Thu, 16 Jul 2009 10:30:42 +0200
From: Marcus Meissner <meissner@...e.de>
To: oss-security@...ts.openwall.com
Cc: "Steven M. Christey" <coley@...us.mitre.org>
Subject: Re: CVE-2009-1895 kernel: personality: fix PER_CLEAR_ON_SETID

On Thu, Jul 16, 2009 at 02:49:02PM +0800, Eugene Teo wrote:
> Reported by Julien Tinnes.
> 
> "We have found that the current PER_CLEAR_ON_SETID mask on Linux doesn't
> include neither ADDR_COMPAT_LAYOUT, nor MMAP_PAGE_ZERO.
> 
> The current mask is READ_IMPLIES_EXEC|ADDR_NO_RANDOMIZE.
> 
> We believe it is important to add MMAP_PAGE_ZERO, because by using this
> personality it is possible to have the first page mapped inside a
> process running as setuid root.  This could be used in those scenarios:
> 
> - Exploiting a NULL pointer dereference issue in a setuid root binary
> - Bypassing the mmap_min_addr restrictions of the Linux kernel: by
> running a setuid binary that would drop privileges before giving us
> control back (for instance by loading a user-supplied library), we could
> get the first page mapped in a process we control.  By further using
> mremap and mprotect on this mapping, we can then completely bypass the
> mmap_min_addr restrictions.
> 
> Less importantly, we believe ADDR_COMPAT_LAYOUT should also be added
> since on x86 32bits it will in practice disable most of the address
> space layout randomization (only the stack will remain randomized)."
> 
> Upstream commit:
> http://git.kernel.org/linus/f9fabcb58a6d26d6efde842d1703ac7cfa9427b6
> 
> References:
> https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2009-1895
> http://blog.cr0.org/2009/06/bypassing-linux-null-pointer.html
> http://patchwork.kernel.org/patch/32598/
> http://marc.info/?l=linux-security-module&m=124724852000951&w=2

Also http://www.securityfocus.com/bid/35647

Ciao, Marcus

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