[Gammaray-interest] LD_PRELOAD and secure-execution

[Christian Gagneraud]

Hi there,

We ran into a tricky problem at run-time (embedded Linux).
The app i want to introspect has Linux capabilities  bits set. This
put ld.so in a `secure-execution` mode.
For the preload to work, we need to meet these 3 conditions (from man page):
              In secure-execution mode, preload pathnames containing slashes
              are ignored.  Furthermore, shared objects are preloaded only
              from the standard search directories and only if they have
              set-user-ID mode bit enabled (which is not typical).

So we need Gammaray to use LD_PRELOAD=gammaray_probe.so and chmod u+s it.
This break the "multi ABI" installation, which in our case we don't
need as we only have a single Qt installed on our embedded devices.

We currently monkey patch PreloadInjector::launch() to strip the path
off, and we "ln -s /usr/lib/gammaray/2.10/qt5_6-arm/gammaray_probe.so
/usr/lib".

I first wanted to report the issue and the solution, as we spent quite
some time to understand the problem and find the solution.

But it would be nice to have a proper fix, so what about making the
preload probe honors the `--injector-override` command line parameter?
In our case we would run gammaray with "--injector-override
gammaray_probe.so" and keep the link hack. This at least would allow
us to not patch gammaray.

Chris