full-disclosure - Re: exploitation ideas under memory pressure

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Message-ID: <20130518004458.GB3199@cmpxchg8b.com>
Date: Fri, 17 May 2013 17:44:58 -0700
From: Tavis Ormandy <taviso@...xchg8b.com>
To: full-disclosure@...ts.grok.org.uk
Subject: Re: exploitation ideas under memory pressure

On Fri, May 17, 2013 at 02:26:10PM -0700, Tavis Ormandy wrote:
> 
> The question is how to get PATHALLOC() to succeed under memory pressure so we
> can make this exploitable, my first thought was have another thread
> manipulating the free pool, but I can't figure out how to synchronize
> that. Getting code execution should be trivial after this.
> 
> I guess it's possible to just race it until we win, but this seems like an
> inelegant solution. Anyone have any ideas?
> 

Ahh, I just realised a really cute trick, we can make PATHREC->next
point to the same userspace PATHREC, and EPATHOBJ::bFlatten will spin
forever traversing an infinite linked list.

i.e.

PathRecord->next = PathRecord;

While it's spinning, another thread can clean up the pool, then patch
the listnode (because it's in userspace), to break into pprFlattenRec!
Turning this into a clean write-what-where should be trivial.

Anyone want to volunteer to write it up over the weekend? :)

Tavis.

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