8224541: Better mapping of serial ENUMs

Reviewed-by: mschoene, rhalade, robm, rriggs, smarks

src/java.base/share/classes/java/io/ObjectInputStream.java

@@ -1858,6 +1858,8 @@ public class ObjectInputStream
                 break;
             case TC_REFERENCE:
                 descriptor = (ObjectStreamClass) readHandle(unshared);
+                // Should only reference initialized class descriptors
+                descriptor.checkInitialized();
                 break;
             case TC_PROXYCLASSDESC:
                 descriptor = readProxyDesc(unshared);

src/java.base/share/classes/java/io/ObjectStreamClass.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1996, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1996, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -885,6 +885,17 @@ public class ObjectStreamClass implements Serializable {
             throw new InternalError("Unexpected call when not initialized");
     }
 
+    /**
+     * Throws InvalidClassException if not initialized.
+     * To be called in cases where an uninitialized class descriptor indicates
+     * a problem in the serialization stream.
+     */
+    final void checkInitialized() throws InvalidClassException {
+        if (!initialized) {
+            throw new InvalidClassException("Class descriptor should be initialized");
+        }
+    }
+
     /**
      * Throws an InvalidClassException if object instances referencing this
      * class descriptor should not be allowed to deserialize.  This method does