full-disclosure - Re: The GNU C library dynamic linker expands $ORIGIN in setuid library search path

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Message-ID: <20101018194206.307F.0@argo.troja.mff.cuni.cz>
Date: Mon, 18 Oct 2010 20:43:01 +0200 (MET DST)
From: Pavel Kankovsky <peak@...o.troja.mff.cuni.cz>
To: full-disclosure@...ts.grok.org.uk
Subject: Re: The GNU C library dynamic linker expands
 $ORIGIN in setuid library search path

On Mon, 18 Oct 2010, Tavis Ormandy wrote:

> LD_AUDIT is intended for use with the linker auditing api (see the
> rtld-audit manual), and has the usual restrictions for setuid programs
> as LD_PRELOAD does.

*facepalm*

<rant>

The only sensible restriction for LD_* environment variables (as well as
many other env. vars.) when a setuid or setgid program is executed is to
erase all traces of them at the first opportunity.

Those two or three guys who might ever need to execute a set*id program
with LD_PRELOAD or LD_AUDIT or whatever in order to do something other
than exploit a vulnerability are free to rebuild Glibc with
-DI_WANT_TO_PLAY_RUSSIAN_ROULETTE. Or perhaps it can be controlled by
a configuration file in /etc. But it is pretty silly to enable it for 
everyone and trade convenience for a very small minority of users
for extra risk for ALL users.

(To be honest, I would go as far as to propose to erase ANY environment
variable upon the execution of set*id program. At least unless it is
allowed EXPLICITLY.)

</rant>

-- 
Pavel Kankovsky aka Peak                          / Jeremiah 9:21        \
"For death is come up into our MS Windows(tm)..." \ 21st century edition /

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