This is a followup to JDK-8193683.  

There is a bug currently in the way ServerHandshakers creates HandshakeHashes.  If we do the following valid API pattern:

    SSLServerSocket sslServerSocket =
        (SSLServerSocket) sslssf.createServerSocket(serverPort);
    SSLSocket sslSocket = (SSLSocket) sslServerSocket.accept();

    // This is *AFTER* a SSLSocketImpl was created!!!
    sslSocket.setNeedClientAuth(true);

    InputStream sslIS = sslSocket.getInputStream();
    sslIS.read();

The SSLSocketImpl is initialized with no clientauth required, which creates a ServerHandshaker with no auth, which creates a HandshakeHash(false), which only creates 3 clones.  Now return to the app's setNeedClientAuth call, which updates the ServerHandshaker to require the client auth, but it doesn't update HandshakeHash to now require 4 digests.

Actually, this bug could be updated to better calculate the exact number of HandshakeHash clones that are needed.  

 102     /**
 103      * Create a new HandshakeHash. 
 104      * The number of necessary digest clones is calculated in Handshaker
 105      */
 106     HandshakeHash(int numDigests) {
 107         clonesNeeded = numDigests;
 108     }

 228         try {
 229             finMD = CloneableDigest.getDigest(normalizeAlgName(s), 4);
 230         } catch (NoSuchAlgorithmException e) {
 231             throw new Error(e);
 232         }

and in Handshaker.java

 555         // We accumulate digests of the handshake messages so that
 556         // we can read/write CertificateVerify and Finished messages,
 557         // getting assurance against some particular active attacks.
 558         int numDigests = 2;
 559         if (needCertVerify) {
 560             numDigests++;
 561         }
 562         if (useExtendedMasterSecret) {
 563             numDigests++;
 564         }
 565         handshakeHash = new HandshakeHash(numDigests);

Note that this code also needs a way to update the HandshakeHash if clientAuth is turned on after the Handshaker has been created.