DO NOT MERGE Check caller for sending media key to telephony service

Prevent sending media key events from the non-system app to the
telephony service through the AudioManager.dispatchMediaKeyEvent()
or sending media key broadcast directly.

Bug: 29833954
Tested: Installed malicious apps and confirmed that they don't work.
Tested: Run CtsTelecomTestCases and CtsMediaTestCases
Change-Id: I2a9e78196ba7455324e485f098f095d03b47ee15
(cherry picked from commit d1641e8)

media/java/android/media/MediaFocusControl.java

@@ -40,6 +40,7 @@
 import android.os.Looper;
 import android.os.Message;
 import android.os.PowerManager;
+import android.os.Process;
 import android.os.RemoteException;
 import android.os.UserHandle;
 import android.os.IBinder.DeathRecipient;
@@ -750,7 +751,13 @@ private void filterMediaKeyEvent(KeyEvent keyEvent, boolean needWakeLock) {
             synchronized(mRCStack) {
                 if ((mMediaReceiverForCalls != null) &&
                         (mIsRinging || (mAudioService.getMode() == AudioSystem.MODE_IN_CALL))) {
-                    dispatchMediaKeyEventForCalls(keyEvent, needWakeLock);
+                    if (Binder.getCallingUid() != Process.SYSTEM_UID) {
+                        // Prevent dispatching key event to the global priority session.
+                        Slog.i(TAG, "Only the system can dispatch media key event "
+                                + "to the global priority session.");
+                    } else {
+                        dispatchMediaKeyEventForCalls(keyEvent, needWakeLock);
+                    }
                     return;
                 }
             }

policy/src/com/android/internal/policy/impl/PhoneWindowManager.java

@@ -4044,6 +4044,18 @@ public int interceptKeyBeforeQueueing(KeyEvent event, int policyFlags, boolean i
             case KeyEvent.KEYCODE_MEDIA_RECORD:
             case KeyEvent.KEYCODE_MEDIA_FAST_FORWARD:
             case KeyEvent.KEYCODE_MEDIA_AUDIO_TRACK: {
+                ITelephony telephonyService = getTelephonyService();
+                if (telephonyService != null) {
+                    try {
+                        if (!telephonyService.isIdle()) {
+                            // When phone is ringing or in-call, pass all media keys to it.
+                            result &= ~ACTION_PASS_TO_USER;
+                        }
+                    } catch (RemoteException ex) {
+                        Log.w(TAG, "ITelephony threw RemoteException", ex);
+                    }
+                }
+
                 if ((result & ACTION_PASS_TO_USER) == 0) {
                     // Only do this if we would otherwise not pass it to the user. In that
                     // case, the PhoneWindow class will do the same thing, except it will