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Date: Wed, 10 Oct 2018 02:55:17 +0000
From: Doran Moppert <dmoppert@...hat.com>
To: oss-security@...ts.openwall.com
Cc: Bob Friesenhahn <bfriesen@...ple.dallas.tx.us>
Subject: Re: ghostscript: bypassing executeonly to escape
-dSAFER sandbox (CVE-2018-17961)
Given the number of eyes & hours on these issues my question has to be
naive, so I apologise, but couldn't seccomp provide a safe "safe mode"
relatively easily? What syscalls does legit ghostscript need once the
input and output streams are open?
On Tue, Oct 09, 2018 at 06:34:23PM -0400, Alex Gaynor wrote:
>Would they consider making a build-time "safe PS only" flag that ensured it
>was compiled without things like shell-invocation? Then we could just try
>to convince Linux distros to package it that way :-)
>
>Alex
>
>On Tue, Oct 9, 2018 at 6:33 PM Tavis Ormandy <taviso@...gle.com> wrote:
>
>> On Tue, Oct 9, 2018 at 3:27 PM Perry E. Metzger <perry@...rmont.com>
>> wrote:
>>
>> > I keep wondering if there isn't a way to fully remove the dangerous
>> > bits from a postscript interpreter so it can _only_ be used to view
>> > the document and literally has no file system access compiled in at
>> > all, so there's no way to touch the fs etc. regardless of what flags
>> > the interpreter is invoked with.
>> >
>> > (I, too, find removing the ability to look at historical postscript
>> > documents a bit more draconian than I like.)
>> >
>> >
>> I've discussed it with upstream, it's a hard no because they feel it would
>> make ghostscript non-conforming (i.e. non-conforming with the Adobe
>> PostScript Language Reference Manual)
>>
>> We probably have similar thoughts on this, but that is the final word from
>> upstream.
>>
>> Tavis.
--
Doran Moppert
Red Hat Product Security
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