Pass targetSdkVersion specifier for SELinux labeling

Motivation:
Provide the ability to phase in new security policies by
applying them to apps with a minimum targetSdkVersion

Test: Marlin builds and boots. Apps targeting targetSdkVersion<=25
run in untrusted_app_25 domain. Apps targeting the current development
build >=26 run in the untrusted_app domain with fewer permissions. No
new denials observed during testing.
Bug: 34115651
Change-Id: Ib9f6ded9bd2f426861a6d843861b4074084253b0
diff --git a/services/core/java/com/android/server/pm/SELinuxMMAC.java b/services/core/java/com/android/server/pm/SELinuxMMAC.java
index 2781150..7e7de21 100644
--- a/services/core/java/com/android/server/pm/SELinuxMMAC.java
+++ b/services/core/java/com/android/server/pm/SELinuxMMAC.java
@@ -72,6 +72,9 @@
     // Append ephemeral to existing seinfo label
     private static final String EPHEMERAL_APP_STR = ":ephemeralapp";
 
+    // Append targetSdkVersion=n to existing seinfo label where n is the app's targetSdkVersion
+    private static final String TARGETSDKVERSION_STR = ":targetSdkVersion=";
+
     /**
      * Load the mac_permissions.xml file containing all seinfo assignments used to
      * label apps. The loaded mac_permissions.xml file is determined by the
@@ -296,6 +299,8 @@
         if (pkg.applicationInfo.isPrivilegedApp())
             pkg.applicationInfo.seinfo += PRIVILEGED_APP_STR;
 
+        pkg.applicationInfo.seinfo += TARGETSDKVERSION_STR + pkg.applicationInfo.targetSdkVersion;
+
         if (DEBUG_POLICY_INSTALL) {
             Slog.i(TAG, "package (" + pkg.packageName + ") labeled with " +
                     "seinfo=" + pkg.applicationInfo.seinfo);