priv_app: allow safetynet to read exec_type on /system

Bug: 27545805
Change-Id: I6281dd64c51f74b467deb7acd5cd4403696dcff2

priv_app.te

@@ -70,9 +70,8 @@ userdebug_or_eng(`
   allow priv_app perfprofd_data_file:dir r_dir_perms;
 ')
 
-# Allow GMS core to stat files and executables on
-# the system partition
-allow priv_app exec_type:file getattr;
+# Allow GMS core to scan executables on the system partition
+allow priv_app exec_type:file { getattr read open };
 
 # For AppFuse.
 allow priv_app vold:fd use;