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Re: Buffer overflow prevention
From: Crispin Cowan <crispin () immunix com>
Date: Mon, 18 Aug 2003 13:43:05 -0700

Mark Tinberg wrote:

Thank you for bringing up this point.  ISTM that expecting all
security-critical userspace code to be audited to perfection as a
prerequisite to system security is foolish.  No one, not even the most
intelligent and knowledgeable security guru can write every program to be
perfectly secure all the time without fail.

I agree whole heartedly. It is interesting to see OpenBSD transition from a stance of "audit is the only way" to actually employing access control and intrusion prevention technologies. It is tough to change your mind on big issues when you have a big public record to live down, so I don't particularly want to abuse Theo for making this policy change. I just want to tease him for choosing ProPolice instead of StackGuard without so much as talking to me :)

Again, ISTM that the only way to get close to a reasonably secure system
is to only rely on the smallest, most audited codebase possible to enforce
security policy.  To me this means something enforced by the kernel
itself, like standard POSIX permissions and capabilities, NSA Flask,
Systrace, SubDomain, LIDS, GRSecurity, etc. (note that this is not a
particularly accurate list).  For example one thing that could be done is
to automatically build bare-bones systrace profiles at compile time so
that any attempt to use a syscall not specified in the source causes the
program to immediately abort.  Not a catch-all, but something that raises
the bar.

David Wagner and Drew Dean had a very nice paper at Oakland 2001 on that. Their static analyzer constructed an automata of valid states the program could be in, and a run-time monitor watched the program execute. If the program ever did a state transition that the automata didn't like, the automata would kill the program. The effect is to enforce that the program only execute compliant with its source code, effectively blocking all but the most subtle malcode insertion.

   Intrusion Detection via Static Analysis
   <http://www.cs.berkeley.edu/%7Edaw/papers/ids-oakland01.ps>
       David Wagner and Drew Dean. 2001 IEEE Symposium on Security and
       Privacy <http://www.ieee-security.org/TC/sp2001.html>. [pdf
       <http://www.cs.berkeley.edu/%7Edaw/papers/ids-oakland01.pdf>,
       slides
<http://www.cs.berkeley.edu/%7Edaw/papers/ids-oakland01-slides.ps>]
Crispin

--
Crispin Cowan, Ph.D.           http://immunix.com/~crispin/
Chief Scientist, Immunix       http://immunix.com
           http://www.immunix.com/shop/



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