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Date: Wed, 17 Oct 2018 02:14:46 -0400
From: Rich Felker <dalias@...c.org>
To: oss-security@...ts.openwall.com
Cc: Perry Metzger <perry@...rmont.com>
Subject: Re: ghostscript: 1Policy operator gives access to
 .forceput CVE-2018-18284

On Tue, Oct 16, 2018 at 01:33:32PM -0700, Tavis Ormandy wrote:
> On Tue, Oct 16, 2018 at 12:57 PM Perry E. Metzger <perry@...rmont.com>
> wrote:
> 
> > On Tue, 16 Oct 2018 11:06:14 -0700 Tavis Ormandy <taviso@...gle.com>
> > wrote:
> > > Side note: I'm done looking at ghostscript for now, but still
> > > *strongly* recommend that we deprecate untrusted postscript and
> > > disable ghostscript coders by default in policy.xml.
> >
> > Again, given that PostScript is an archival format for a lot of
> > documents, wouldn't a version of ghostscript with all the ability to
> > do anything dangerous removed from the interpreter at compile time be
> > rational?
> >
> >
> We have to work with what we've got.
> 
> Even with the easy to exploit stuff compiled out (which upstream do not
> support), I haven't been bothering to get CVE's for all the memory
> corruption or UaF I've been reporting, because nobody can keep up with
> these operator leaks anyway.

An obvious fix for UaF's would be just removing the frees. Use of gs
as an interactive program where leaks would matter is a historical
curiosity; the only meaningful modern use is as a converter.

If someone insists there are still uses where freeing matters,
something like talloc may be a reasonable solution, removing all the
internal frees and only performing frees of the whole context.

Rich

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