Coalesce shared_app, media_app, release_app into untrusted_app.

This change folds the shared_app, media_app, and release_app
domains into untrusted_app, reducing the set of app domains down
to just distinct domains for the fixed UID apps (e.g. system_app, bluetooth,
nfc, radio), a single domain for apps signed by the platform key
(platform_app), and a single domain for all other apps (untrusted_app).
Thus, SELinux only distinguishes when already distinguished by a predefined
Android ID (AID) or by the platform certificate (which get the signature-only
Android permissions and thus may require special OS-level accesses).

It is still possible to introduce specific app domains for specific
apps by adding signer and package stanzas to mac_permissions.xml,
but this can be done on an as-needed basis for specialized apps that
require particular OS-level permissions outside the usual set.

As there is now only a single platform app domains, get rid of the
platformappdomain attribute and platform_app_domain() macro.  We used
to add mlstrustedsubject to those domains but drop this since we are not
using MLS in AOSP presently; we can revisit which domains need it if/when
we use MLS.

Since we are dropping the shared, media, and release seinfo entries from
seapp_contexts, drop them from mac_permissions.xml as well.  However,
we leave the keys.conf entries in case someone wants to add a signer
entry in the future for specific apps signed by those keys to
mac_permissions.xml.

Change-Id: I877192cca07360c4a3c0ef475f016cc273e1d968
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>

1 files changed, 17 insertions, 1 deletions

diff --git a/untrusted_app.te b/untrusted_app.te
index e60bfff..ebde0eb 100644
--- a/untrusted_app.te
+++ b/untrusted_app.te
@@ -10,7 +10,7 @@
 ### and AID_ISOLATED_START (99000) if the app has no specific seinfo
 ### value as determined from mac_permissions.xml.  In current AOSP, this
 ### domain is assigned to all non-system apps as well as to any system apps
-### that are not signed by one of the four platform keys.  To move
+### that are not signed by the platform key.  To move
 ### a system app into a specific domain, add a signer entry for it to
 ### mac_permissions.xml and assign it one of the pre-existing seinfo values
 ### or define and use a new seinfo value in both mac_permissions.xml and
@@ -48,3 +48,19 @@ create_pty(untrusted_app)
 # Figure out a way to remove these rules.
 allow untrusted_app shell_data_file:file r_file_perms;
 allow untrusted_app shell_data_file:dir r_dir_perms;
+
+#
+# Rules migrated from old app domains coalesced into untrusted_app.
+# This includes what used to be media_app, shared_app, and release_app.
+#
+
+# Access /dev/mtp_usb.
+allow untrusted_app mtp_device:chr_file rw_file_perms;
+
+# Access to /data/media.
+allow untrusted_app media_rw_data_file:dir create_dir_perms;
+allow untrusted_app media_rw_data_file:file create_file_perms;
+
+# Write to /cache.
+allow untrusted_app cache_file:dir create_dir_perms;
+allow untrusted_app cache_file:file create_file_perms;