8320798: Console read line with zero out should zero out underlying buffer

Reviewed-by: bpb, lancea, joehw, alanb, jpai, mbaesken

src/java.base/share/classes/jdk/internal/io/JdkConsoleImpl.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2022, 2023, 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
@@ -195,6 +195,9 @@ public final class JdkConsoleImpl implements JdkConsole {
             System.arraycopy(rcb, 0, b, 0, len);
             if (zeroOut) {
                 Arrays.fill(rcb, 0, len, ' ');
+                if (reader instanceof LineReader lr) {
+                    lr.zeroOut();
+                }
             }
         }
         return b;
@@ -228,6 +231,11 @@ public final class JdkConsoleImpl implements JdkConsole {
             nextChar = nChars = 0;
             leftoverLF = false;
         }
+        public void zeroOut() throws IOException {
+            if (in instanceof StreamDecoder sd) {
+                sd.fillZeroToPosition();
+            }
+        }
         public void close () {}
         public boolean ready() throws IOException {
             //in.ready synchronizes on readLock already

src/java.base/share/classes/sun/nio/cs/StreamDecoder.java

@@ -42,6 +42,8 @@ import java.nio.charset.CoderResult;
 import java.nio.charset.CodingErrorAction;
 import java.nio.charset.IllegalCharsetNameException;
 import java.nio.charset.UnsupportedCharsetException;
+import java.util.Arrays;
+
 import jdk.internal.misc.InternalLock;
 
 public class StreamDecoder extends Reader {
@@ -271,6 +273,25 @@ public class StreamDecoder extends Reader {
         return !closed;
     }
 
+    public void fillZeroToPosition() throws IOException {
+        Object lock = this.lock;
+        if (lock instanceof InternalLock locker) {
+            locker.lock();
+            try {
+                lockedFillZeroToPosition();
+            } finally {
+                locker.unlock();
+            }
+        } else {
+            synchronized (lock) {
+                lockedFillZeroToPosition();
+            }
+        }
+    }
+
+    private void lockedFillZeroToPosition() {
+        Arrays.fill(bb.array(), bb.arrayOffset(), bb.arrayOffset() + bb.position(), (byte)0);
+    }
 
     // -- Charset-based stream decoder impl --