Fix security hole in GateKeeperResponse

GateKeeperResponse has inconsistent writeToParcel() and
createFromParcel() methods, making it possible for a malicious app to
create a Bundle that changes contents after reserialization. Such
Bundles can be used to execute Intents with system privileges.

We fixed related issues previously for GateKeeperResponse class, but
one of the case was remaining when payload is byte array of size 0,
Fixing this case now.

Bug: 220303465
Test: With the POC provided in the bug.
Change-Id: Ida28d611edd674e76ed39dd8037f52abcba82586

core/java/android/service/gatekeeper/GateKeeperResponse.java

@@ -105,7 +105,7 @@ public final class GateKeeperResponse implements Parcelable {
             dest.writeInt(mTimeout);
         } else if (mResponseCode == RESPONSE_OK) {
             dest.writeInt(mShouldReEnroll ? 1 : 0);
-            if (mPayload != null) {
+            if (mPayload != null && mPayload.length > 0) {
                 dest.writeInt(mPayload.length);
                 dest.writeByteArray(mPayload);
             } else {