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Bugtraq archives for 2nd quarter (Apr-Jun) 1999: Clarification: LD_PRELOAD issue

Clarification: LD_PRELOAD issue

David F. Skoll (dfsDOE.CARLETON.CA)
Fri, 14 May 1999 09:17:25 -0400 

Hi,

I feel I need to provide more context for the LD_PRELOAD issue.  Yes,
I'm well aware that set[ug]id programs ignore LD_PRELOAD and the other
LD_* environment variables.

The context is a software license manager.  A commercial software
organization wants to protect its software with a license manager
which relies on accurate time information.  Any user of the system,
including root, must be viewed as a potential cracker.  This is not your
usual security issue.

Now, any license manager can be spoofed, from as blunt an attack as
changing the system time to sophisticated reverse-engineering attacks
on the license manager binary.  The issue is to prevent "cheap"
attacks -- if attacking the license manager is expensive enough,
people won't bother (or they'll find other avenues of attack. :-))

Changing the system time introduces all kinds of problems, so most
potential license abusers won't do it.  A two-line shell script with a
6-line C program is a very cheap attack on a dynamically-linked
license manager daemon.  Attacking a statically-linked license manager
binary is quite a bit more expensive, and should greatly reduce the
incentive for an attack.

--
David F. Skoll