Prevent isolated_app from searching system_data_file.

There should be no need for this, and it allows probing for file existence.

Access to /data and more specifically labeled directories under it
(e.g. /data/app) is not affected.

Bug: 158088415
Test: Builds
Change-Id: Iac39629b1c7322dc2fd9a57c9f034cb2ba73793f
diff --git a/private/isolated_app.te b/private/isolated_app.te
index 4c6c5aa..33b5219 100644
--- a/private/isolated_app.te
+++ b/private/isolated_app.te
@@ -74,6 +74,9 @@
 # Isolated apps should not directly open app data files themselves.
 neverallow isolated_app { app_data_file privapp_data_file }:file open;
 
+# Isolated aps should not be directly accessing system directories
+neverallow isolated_app system_data_file:dir search;
+
 # Only allow appending to /data/anr/traces.txt (b/27853304, b/18340553)
 # TODO: are there situations where isolated_apps write to this file?
 # TODO: should we tighten these restrictions further?