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Date: Tue, 1 Dec 2020 20:37:07 -0500
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: [PATCH] harden against unauthorized writes to the atexit
function lists
On Tue, Dec 01, 2020 at 05:55:39PM -0700, Ariadne Conill wrote:
> previously, the first atexit list block was stored in BSS, which means an
> attacker could potentially ascertain its location and modify it, allowing
> for its abuse as a code execution mechanism.
>
> by moving the atexit list into a series of anonymous mmaped pages, we can
> use mprotect to protect the atexit lists by keeping them readonly when they
> are not being mutated by the __cxa_atexit() function.
This is a non-starter. atexit is specifically required by the standard
to succeed when called no more than 32 times, which is why we have 32
built-in slots that always exist. If you really want to pursue
something here it should probably just be protecting the pointers with
some secret...
Rich
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