throw Baloo in jail

[Detlef Eppers]

File indexing tools encounter all different types of files, both of 
trusted and untrusted origin, and last November it was demonstrated by 
Chris Evans how this can potentially be exploited*. In order to provide 
a means for mitigation, I have written a Firejail profile** for Baloo 
recently (Firejail is a SUID sandboxing tool, modeled after the Chromium 
sandbox).

However, almost all the stuff I do now with Firejail (seccomp filter, 
dropping capabilities, namespaces, file system restrictions) could 
equally be done through a systemd unit file, providing better security 
for all Plasma users. So my question number one is if for Baloo, 
switching to a systemd user unit could be considered a viable option 
(versus the current autostart mechanism).

Question number two: I would like to restrict Baloo's access to the file 
system through Firejail. But if I bind-mount the home directory 
write-protected and only ~/.local/share/baloo as writable, baloo_file 
will fail to launch, printing:

Failed to create database, removing corrupted database.
Failed to create database after deleting corrupted one.

If the whole ~/.local/share is writable however, everything works as 
expected.

Similarly, baloo_file won't write to its configuration file 
~/.config/baloofilerc if it is remounted writable. Only if the whole 
~/.config folder is writable everything works as expected. To me this 
looks like Baloo wants to create write-locks, and the question is if one 
could conceive an alternative mechanism. This would not only help to 
write tighter Firejail profiles, but also in restricting baloo_file as 
much as possible through a systemd execution environment.

Thank you for your thoughts and any insight.

Cheers,
Detlef

*Link to Chris Evans blog post: 
https://scarybeastsecurity.blogspot.de/2016/11/0day-poc-risky-design-decisions-in.html
**Link to the Firejail profile in question: 
https://github.com/netblue30/firejail/blob/master/etc/baloo_file.profile
Back then the profile used to work with last lines uncommented, now it 
doesn't any more.