From 587de668e43486f7109a885f617b9b757d7a649e Mon Sep 17 00:00:00 2001
From: Todd Lipcon <todd@cloudera.com>
Date: Sat, 24 Apr 2010 17:33:34 -0700
Subject: [PATCH] HADOOP-6722. Workaround a TCP spec quirk by not allowing NetUtils.connect to connect to itself

Description: TCP's ephemeral port assignment results in the possibility
             that a client can connect back to its own outgoing socket,
             resulting in failed RPCs or datanode transfers.
Reason: Fixes intermittent errors in cluster testing with ephemeral
        IPC/transceiver ports on datanodes.
Author: Todd Lipcon
Ref: CDH-659
---
 src/core/org/apache/hadoop/net/NetUtils.java     |   16 ++++++
 src/test/org/apache/hadoop/net/TestNetUtils.java |   56 ++++++++++++++++++++++
 2 files changed, 72 insertions(+), 0 deletions(-)
 create mode 100644 src/test/org/apache/hadoop/net/TestNetUtils.java

diff --git a/src/core/org/apache/hadoop/net/NetUtils.java b/src/core/org/apache/hadoop/net/NetUtils.java
index 854a00a..4c33a73 100644
--- a/src/core/org/apache/hadoop/net/NetUtils.java
+++ b/src/core/org/apache/hadoop/net/NetUtils.java
@@ -26,6 +26,7 @@ import java.net.Socket;
 import java.net.SocketAddress;
 import java.net.URI;
 import java.net.UnknownHostException;
+import java.net.ConnectException;
 import java.nio.channels.SocketChannel;
 import java.util.Map.Entry;
 import java.util.*;
@@ -406,6 +407,21 @@ public class NetUtils {
     } else {
       SocketIOWithTimeout.connect(ch, endpoint, timeout);
     }
+
+    // There is a very rare case allowed by the TCP specification, such that
+    // if we are trying to connect to an endpoint on the local machine,
+    // and we end up choosing an ephemeral port equal to the destination port,
+    // we will actually end up getting connected to ourself (ie any data we
+    // send just comes right back). This is only possible if the target
+    // daemon is down, so we'll treat it like connection refused.
+    if (socket.getLocalPort() == socket.getPort() &&
+        socket.getLocalAddress().equals(socket.getInetAddress())) {
+      LOG.info("Detected a loopback TCP socket, disconnecting it");
+      socket.close();
+      throw new ConnectException(
+        "Localhost targeted connection resulted in a loopback. " +
+        "No daemon is listening on the target port.");
+    }
   }
   
   /** 
diff --git a/src/test/org/apache/hadoop/net/TestNetUtils.java b/src/test/org/apache/hadoop/net/TestNetUtils.java
new file mode 100644
index 0000000..52fb209
--- /dev/null
+++ b/src/test/org/apache/hadoop/net/TestNetUtils.java
@@ -0,0 +1,56 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.net;
+
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+import java.net.Socket;
+import java.net.ConnectException;
+import java.net.InetSocketAddress;
+import org.apache.hadoop.conf.Configuration;
+
+public class TestNetUtils {
+
+  /**
+   * Test that we can't accidentally connect back to the connecting socket due
+   * to a quirk in the TCP spec.
+   *
+   * This is a regression test for HADOOP-6722.
+   */
+  @Test
+  public void testAvoidLoopbackTcpSockets() throws Exception {
+    Configuration conf = new Configuration();
+
+    Socket socket = NetUtils.getDefaultSocketFactory(conf)
+      .createSocket();
+    socket.bind(new InetSocketAddress("127.0.0.1", 0));
+    System.err.println("local address: " + socket.getLocalAddress());
+    System.err.println("local port: " + socket.getLocalPort());
+    try {
+      NetUtils.connect(socket,
+        new InetSocketAddress(socket.getLocalAddress(), socket.getLocalPort()),
+        20000);
+      socket.close();
+      fail("Should not have connected");
+    } catch (ConnectException ce) {
+      System.err.println("Got exception: " + ce);
+      assertTrue(ce.getMessage().contains("resulted in a loopback"));
+    }
+  }
+}
-- 
1.6.0.4

