Date: Wed, 17 Oct 2018 02:09:28 -0400 From: Rich Felker <dalias@...c.org> To: oss-security@...ts.openwall.com Cc: 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 10, 2018 at 03:26:05PM -0400, Perry E. Metzger wrote: > On Tue, 9 Oct 2018 15:32:02 -0700 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. > > 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. Rich
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