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Date: Thu, 16 Jul 2009 10:30:42 +0200
From: Marcus Meissner <>
Cc: "Steven M. Christey" <>
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.
> 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:
> References:


Ciao, Marcus

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