Enable hidepid=2 on /proc

Add the following mount options to the /proc filesystem:

  hidepid=2,gid=3009

This change blocks /proc access unless you're in group 3009
(aka AID_READPROC).

Please see
  https://github.com/torvalds/linux/blob/master/Documentation/filesystems/proc.txt
for documentation on the hidepid option.

hidepid=2 is preferred over hidepid=1 since it leaks less information
and doesn't generate SELinux ptrace denials when trying to access
/proc without being in the proper group.

Add AID_READPROC to processes which need to access /proc entries for
other UIDs.

Bug: 23310674
Change-Id: I22bb55ff7b80ff722945e224845215196f09dafa
diff --git a/rootdir/init.rc b/rootdir/init.rc
index b80c454..17e87da 100644
--- a/rootdir/init.rc
+++ b/rootdir/init.rc
@@ -556,7 +556,7 @@
     console
     disabled
     user shell
-    group shell log
+    group shell log readproc
     seclabel u:r:shell:s0
 
 on property:ro.debuggable=1