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Date: Mon, 21 Mar 2011 12:55:25 -0400
From: Steve Grubb <>
Cc: "Steven M. Christey" <>
Subject: Re: Local memory disclosure (was: libpurple CVE UnRequest)

On Monday, March 21, 2011 12:02:40 pm Steven M. Christey wrote:
> Doesn't memory "belong" to one process (assuming it's not shared), even in 
> heap management?  So another user couldn't access the memory while it's 
> used in the process, and (I guess?) if it's free'd, it's still only 
> accessible to that process (or, alternately, is the region cleared before 
> another program can access it?)  If this is the case, then the question 
> becomes what happens to the memory when the vulnerable process exits - is 
> the memory cleared by the kernel, or is it otherwise left alone?  What 
> happens if the memory is cached on disk?
> I did extremely limited experiments in this area a couple years ago, and 
> for the limited set of OSes I tried this on (no idea what libraries), I 
> always got "clean" memory when I ran initial malloc's from a fresh process 
> (later malloc's could contain contents of memory that was previously freed 
> in the same session).  That doesn't prove anything, of course...

Any OS that passes common criteria (Linux for example) has to meet certain 
requirements for object reuse. This is FDP_RIP in case anyone is interested. The 
granularity is at the process level. The clearing action is required at allocation 
rather than release of the object. Calls to brk() and sbrk() should show cleared 
memory when address space is increased.

So, if it were found that there is an unintended interprocess memory leak, that is a 
big problem. Within one process, there are no common criteria claims.


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