Re: Tracker as a security risks

[Carlos Garnacho <carlosg gnome org>]

Hi,

On Mon, Dec 5, 2016 at 3:01 PM, Hanno Böck <hanno hboeck de> wrote:
> On Mon, 5 Dec 2016 13:44:40 +0000
> Sam Thursfield <ssssam gmail com> wrote:
>
> > The design of Tracker takes the risks into account. Metadata
> > extraction is isolated in its own process (tracker-extract) which can
> > crash without (theoretically) causing any harm.
>
> I don't see how that helps against security vulnerabilities.
>
> Having an isolated process probably helps in a way that a crash won't
> cause the whole tracker service to malfunction. Thus parsing broken
> files won't cause a service disruption. But as long as this process
> runs with normal user rights this doesn't protect in a security sense.
>
> > > I think there needs to be a wider discussion about this and the
> > > fundamental design choices done here need to be questioned.
> >
> > What questions do you have in particular?
>
> Quite frankly, I don't claim to have all the answers here, that's why I
> formulated it in an open "needs discussion" way.
>
> I think sandboxing the tracker parser (which you already indicated
> in your mail) is probably the most reasonable way to go forward. This
> isn't exactly my area of expertise, so I can't comment on which
> technique here is most promising.

It indeed sounds possible to lift extraction into a separate process
with limited access to the filesystem, we essentially need to pass an
fd to mmap() and an output one to receive sparql back. There's just
two things to consider:

- The extraction process sometimes needs access to misc files (eg. CUE
files, XMP sidecar files, ...), those might be passed along too, but
then we need detecting those cases beforehand.

- Ideally we wouldn't spawn one process per file being extracted,
although if we go to defcon 1 level of paranoia, that's probably what
should happen.

Anyway, this goes IMHO too much on the technical side for this ML, we
already have https://bugzilla.gnome.org/show_bug.cgi?id=764786 filed
to Tracker, and it's already high in my list for fixing on 1.12, feel
free to join there.

And I should add... Tracker is not alone here, if it's not Tracker
stumbling on infected content, with varying but still rather low
levels of interaction it may be a thumbnailer, a previewer like sushi,
or the web browser itself streaming content which hit this. So there's
more places in need of further isolation when dealing with untrusted
content.

And still, the chain is only as strong as its weakest link, as soon as
there is anything opening that file with wide enough permissions to
cause any harm, you're essentially screwed. This might sound like an
argument to running every app through flatpak, although I think the
long term answer always is "fix the vulnerability!".

> The other issue I think is that the quality of huge parts of the foss
> ecosystem needs to be improved. The good news here is that we got some
> powerful tools in terms of fuzzing (afl, libfuzzer) and memory safety
> bug detection (asan) in the past years. Ideally all free software devs
> should be aware of those tools and use them in their development
> process. I'm trying to help here where I can, see e.g. also my recent
> post on this list [1]. If our libraries would be better tested we could
> be more comfortable feeding it with untrusted inputs.

I agree some more active prevention would be positive, sounds like
something to tackle in the libraries dealing with file formats though,
Tracker is a strawman here, in the sense that filesystem extraction
it's only exploitable through its tracker-extract's modules, and those
are for the most part implemented using external libraries.

Cheers,
  Carlos