Only allow system_server to send commands to zygote.

Add neverallow rules to ensure that zygote commands are only taken from
system_server.

Also remove the zygote policy class which was removed as an object manager in
commit: ccb3424639821b5ef85264bc5836451590e8ade7

Bug: 19624279

Change-Id: I1c925d7facf19b3953b5deb85d992415344c4c9f

access_vectors

@@ -876,14 +876,6 @@ class binder
 	transfer
 }
 
-class zygote
-{
-	specifyids
-	specifyrlimits
-	specifyinvokewith
-	specifyseinfo
-}
-
 class property_service
 {
 	set

domain.te

@@ -344,6 +344,10 @@ neverallow {
   -dex2oat
 } dalvikcache_data_file:file no_w_file_perms;
 
+# Only system_server should be able to send commands via the zygote socket
+neverallow { domain -zygote -system_server } zygote:unix_stream_socket connectto;
+neverallow { domain -system_server } zygote_socket:sock_file write;
+
 # Android does not support System V IPCs.
 #
 # The reason for this is due to the fact that, by design, they lead to global

system_server.te

@@ -296,9 +296,6 @@ allow system_server wpa_socket:sock_file unlink;
 type_transition system_server system_data_file:sock_file system_ndebug_socket "ndebugsocket";
 allow system_server system_ndebug_socket:sock_file create_file_perms;
 
-# Specify any arguments to zygote.
-allow system_server self:zygote { specifyids specifyrlimits specifyseinfo };
-
 # Manage cache files.
 allow system_server cache_file:dir { relabelfrom create_dir_perms };
 allow system_server cache_file:file { relabelfrom create_file_perms };