[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Date: Wed, 17 Oct 2018 10:48:37 -0400
From: Rich Felker <dalias@...c.org>
To: "Perry E. Metzger" <perry@...rmont.com>
Cc: oss-security@...ts.openwall.com, Tavis Ormandy <taviso@...gle.com>,
Bob Friesenhahn <bfriesen@...ple.dallas.tx.us>
Subject: Re: ghostscript: bypassing executeonly to escape
-dSAFER sandbox (CVE-2018-17961)
On Wed, Oct 17, 2018 at 09:21:54AM -0400, Perry E. Metzger wrote:
> On Wed, 17 Oct 2018 02:09:28 -0400 Rich Felker <dalias@...c.org>
> 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.
> > >
> > > They wouldn't even support a compilation mode where if you #define
> > > the right thing those syscalls are cut out?
> > >
> > > I don't care much about upstream's desires on this if they oppose
> > > that. I'd be happy to have patches that simply cut out the
> > > dangerous syscalls entirely. It's open source, that should be
> > > feasible.
> >
> > This. It's utterly ridiculous that the interpreter even has bindings
> > for accessing the filesystem and such. But I wonder if some of its
> > library routines (e.g. font loading) are implemented in Postscript,
> > using these bindings, rather than being implemented in C outside of
> > the language interpreter. If so it might be harder to extricate.
> > But I still think it's worthwhile to try. Once there are patches I
> > would expect all reasonable distros to start shipping with them,
> > and if upstream tries to make it hard, I would expect one of the
> > big distros to just fork and abandon upstream.
>
> Does anyone other than Tavis know their way around the inside of the
> codebase? Perhaps we can collaborate on patches.
I don't, but one further idea that might appeal to upstream if they
want the fs bindings for the sake of executing ancient programs
written in postscript that operate on files: rather than binding to
actual fs operations on the host, implement a virtual filesystem
within the interpreter, and require explicit command line options to
import/export files from/to the real filesystem at entry/exit.
Rich
Powered by blists - more mailing lists
Please check out the
Open Source Software Security Wiki, which is counterpart to this
mailing list.
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
