neverallow "write ops" on system_data_file from "others"

Only a few system level components should be creating and writing
these files, force a type transition for shared files.

Signed-off-by: William Roberts <william.c.roberts@linux.intel.com>
(cherry picked from commit 529a8634)

Change-Id: I9c4df4e332426e253dd6fcd4f8ea0348dc3a5f54
Bug: 21924438

domain.te

@@ -424,3 +424,22 @@ neverallow { domain -init } proc:{ file dir } mounton;
 # from a domain to a non-domain type and vice versa.
 neverallow domain ~domain:process { transition dyntransition };
 neverallow ~domain domain:process { transition dyntransition };
+
+#
+# Only system_app and system_server should be creating or writing
+# their files. The proper way to share files is to setup
+# type transitions to a more specific type or assigning a type
+# to its parent directory via a file_contexts entry.
+# Example type transition:
+#  mydomain.te:file_type_auto_trans(mydomain, system_data_file, new_file_type)
+#
+neverallow {
+  domain
+  -system_server
+  -system_app
+  -init
+  -installd # for relabelfrom and unlink, check for this in explicit neverallow
+} system_data_file:file no_w_file_perms;
+# do not grant anything greater than r_file_perms and relabelfrom unlink
+# to installd
+neverallow installd system_data_file:file ~{ r_file_perms relabelfrom unlink };