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

Reviewed-by: mdoerr
Backport-of: 48c847836e44aec2d5be4aaa3040dffc9d95fad5

Author: GoeLin

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

@@ -426,6 +426,10 @@ else if (rcb[len-1] == '\n') {
             System.arraycopy(rcb, 0, b, 0, len);
             if (zeroOut) {
                 Arrays.fill(rcb, 0, len, ' ');
+                if (reader instanceof LineReader) {
+                    LineReader lr = (LineReader)reader;
+                    lr.zeroOut();
+                }
             }
         }
         return b;
@@ -450,6 +454,12 @@ class LineReader extends Reader {
             nextChar = nChars = 0;
             leftoverLF = false;
         }
+        public void zeroOut() throws IOException {
+            if (in instanceof StreamDecoder) {
+                StreamDecoder sd = (StreamDecoder)in;
+                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

@@ -32,6 +32,7 @@
 import java.nio.*;
 import java.nio.channels.*;
 import java.nio.charset.*;
+import java.util.Arrays;
 
 public class StreamDecoder extends Reader
 {
@@ -199,6 +200,16 @@ private boolean isOpen() {
         return !closed;
     }
 
+    public void fillZeroToPosition() throws IOException {
+        Object lock = this.lock;
+        synchronized (lock) {
+            lockedFillZeroToPosition();
+        }
+    }
+
+    private void lockedFillZeroToPosition() {
+        Arrays.fill(bb.array(), bb.arrayOffset(), bb.arrayOffset() + bb.position(), (byte)0);
+    }
 
     // -- Charset-based stream decoder impl --