neverallow write access to /data/dalvik-cache directories.

Prohibit all but a specific set of whitelisted domains
from writing to /data/dalvik-cache.  This is to prevent
code injection into apps, zygote, or system_server.

Inspired by:
https://www.nowsecure.com/blog/2015/06/16/remote-code-execution-as-system-user-on-samsung-phones/


which depended on system UID apps having write access to
/data/dalvik-cache (not allowed in AOSP policy but evidently
in those device policies).  Prevent this from recurring.

Change-Id: I282c7bf998421d794883e432b091ad1dcf9da67e
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>

domain.te

@@ -354,6 +354,14 @@ neverallow {
   -dex2oat
 } dalvikcache_data_file:file no_w_file_perms;
 
+neverallow {
+  domain
+  -init
+  -installd
+  -dex2oat
+  -zygote
+} dalvikcache_data_file:dir no_w_dir_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;