8182125: Improve reliability of DNS lookups

Reviewed-by: chegar, rriggs, dfuchs

src/share/classes/com/sun/jndi/dns/DNSDatagramSocketFactory.java

+/*
+ * Copyright (c) 2017, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+package com.sun.jndi.dns;
+
+import java.io.IOException;
+import java.net.DatagramSocket;
+import java.net.ProtocolFamily;
+import java.net.SocketException;
+import java.net.InetSocketAddress;
+import java.nio.channels.DatagramChannel;
+import java.util.Objects;
+import java.util.Random;
+
+class DNSDatagramSocketFactory {
+    static final int DEVIATION = 3;
+    static final int THRESHOLD = 6;
+    static final int BIT_DEVIATION = 2;
+    static final int HISTORY = 32;
+    static final int MAX_RANDOM_TRIES = 5;
+    /**
+     * The dynamic allocation port range (aka ephemeral ports), as configured
+     * on the system. Use nested class for lazy evaluation.
+     */
+    static final class EphemeralPortRange {
+        private EphemeralPortRange() {}
+        static final int LOWER = sun.net.PortConfig.getLower();
+        static final int UPPER = sun.net.PortConfig.getUpper();
+        static final int RANGE = UPPER - LOWER + 1;
+    }
+
+    // Records a subset of max {@code capacity} previously used ports
+    static final class PortHistory {
+        final int capacity;
+        final int[] ports;
+        final Random random;
+        int index;
+        PortHistory(int capacity, Random random) {
+            this.random = random;
+            this.capacity = capacity;
+            this.ports = new int[capacity];
+        }
+        // returns true if the history contains the specified port.
+        public boolean contains(int port) {
+            int p = 0;
+            for (int i=0; i<capacity; i++) {
+                if ((p = ports[i]) == 0 || p == port) break;
+            }
+            return p == port;
+        }
+        // Adds the port to the history - doesn't check whether the port
+        // is already present. Always adds the port and always return true.
+        public boolean add(int port) {
+            if (ports[index] != 0) { // at max capacity
+                // remove one port at random and store the new port there
+                ports[random.nextInt(capacity)] = port;
+            } else { // there's a free slot
+                ports[index] = port;
+            }
+            if (++index == capacity) index = 0;
+            return true;
+        }
+        // Adds the port to the history if not already present.
+        // Return true if the port was added, false if the port was already
+        // present.
+        public boolean offer(int port) {
+            if (contains(port)) return false;
+            else return add(port);
+        }
+    }
+
+    int lastport = 0;
+    int suitablePortCount;
+    int unsuitablePortCount;
+    final ProtocolFamily family; // null (default) means dual stack
+    final int thresholdCount; // decision point
+    final int deviation;
+    final Random random;
+    final PortHistory history;
+
+    DNSDatagramSocketFactory() {
+        this(new Random());
+    }
+
+    DNSDatagramSocketFactory(Random random) {
+        this(Objects.requireNonNull(random), null, DEVIATION, THRESHOLD);
+    }
+    DNSDatagramSocketFactory(Random random,
+                             ProtocolFamily family,
+                             int deviation,
+                             int threshold) {
+        this.random = Objects.requireNonNull(random);
+        this.history = new PortHistory(HISTORY, random);
+        this.family = family;
+        this.deviation = Math.max(1, deviation);
+        this.thresholdCount = Math.max(2, threshold);
+    }
+
+    /**
+     * Opens a datagram socket listening to the wildcard address on a
+     * random port. If the underlying OS supports UDP port randomization
+     * out of the box (if binding a socket to port 0 binds it to a random
+     * port) then the underlying OS implementation is used. Otherwise, this
+     * method will allocate and bind a socket on a randomly selected ephemeral
+     * port in the dynamic range.
+     * @return A new DatagramSocket bound to a random port.
+     * @throws SocketException if the socket cannot be created.
+     */
+    public synchronized DatagramSocket open() throws SocketException {
+        int lastseen = lastport;
+        DatagramSocket s;
+
+        boolean thresholdCrossed = unsuitablePortCount > thresholdCount;
+        if (thresholdCrossed) {
+            // Underlying stack does not support random UDP port out of the box.
+            // Use our own algorithm to allocate a random UDP port
+            s = openRandom();
+            if (s != null) return s;
+
+            // couldn't allocate a random port: reset all counters and fall
+            // through.
+            unsuitablePortCount = 0; suitablePortCount = 0; lastseen = 0;
+        }
+
+        // Allocate an ephemeral port (port 0)
+        s = openDefault();
+        lastport = s.getLocalPort();
+        if (lastseen == 0) {
+            history.offer(lastport);
+            return s;
+        }
+
+        thresholdCrossed = suitablePortCount > thresholdCount;
+        boolean farEnough = Integer.bitCount(lastseen ^ lastport) > BIT_DEVIATION
+                            && Math.abs(lastport - lastseen) > deviation;
+        boolean recycled = history.contains(lastport);
+        boolean suitable = (thresholdCrossed || farEnough && !recycled);
+        if (suitable && !recycled) history.add(lastport);
+
+        if (suitable) {
+            if (!thresholdCrossed) {
+                suitablePortCount++;
+            } else if (!farEnough || recycled) {
+                unsuitablePortCount = 1;
+                suitablePortCount = thresholdCount/2;
+            }
+            // Either the underlying stack supports random UDP port allocation,
+            // or the new port is sufficiently distant from last port to make
+            // it look like it is. Let's use it.
+            return s;
+        }
+
+        // Undecided... the new port was too close. Let's allocate a random
+        // port using our own algorithm
+        assert !thresholdCrossed;
+        DatagramSocket ss = openRandom();
+        if (ss == null) return s;
+        unsuitablePortCount++;
+        s.close();
+        return ss;
+    }
+
+    private DatagramSocket openDefault() throws SocketException {
+        if (family != null) {
+            try {
+                DatagramChannel c = DatagramChannel.open(family);
+                try {
+                    DatagramSocket s = c.socket();
+                    s.bind(null);
+                    return s;
+                } catch (Throwable x) {
+                    c.close();
+                    throw x;
+                }
+            } catch (SocketException x) {
+                throw x;
+            } catch (IOException x) {
+                SocketException e = new SocketException(x.getMessage());
+                e.initCause(x);
+                throw e;
+            }
+        }
+        return new DatagramSocket();
+    }
+
+    synchronized boolean isUsingNativePortRandomization() {
+        return  unsuitablePortCount <= thresholdCount
+                && suitablePortCount > thresholdCount;
+    }
+
+    synchronized boolean isUsingJavaPortRandomization() {
+        return unsuitablePortCount > thresholdCount ;
+    }
+
+    synchronized boolean isUndecided() {
+        return !isUsingJavaPortRandomization()
+                && !isUsingNativePortRandomization();
+    }
+
+    private DatagramSocket openRandom() {
+        int maxtries = MAX_RANDOM_TRIES;
+        while (maxtries-- > 0) {
+            int port = EphemeralPortRange.LOWER
+                    + random.nextInt(EphemeralPortRange.RANGE);
+            try {
+                if (family != null) {
+                    DatagramChannel c = DatagramChannel.open(family);
+                    try {
+                        DatagramSocket s = c.socket();
+                        s.bind(new InetSocketAddress(port));
+                        return s;
+                    } catch (Throwable x) {
+                        c.close();
+                        throw x;
+                    }
+                }
+                return new DatagramSocket(port);
+            } catch (IOException x) {
+                // try again until maxtries == 0;
+            }
+        }
+        return null;
+    }
+
+}

src/share/classes/com/sun/jndi/dns/DnsClient.java

@@ -85,7 +85,9 @@ public class DnsClient {
     private int timeout;                // initial timeout on UDP queries in ms
     private int retries;                // number of UDP retries
 
-    private DatagramSocket udpSocket;
+    private final Object udpSocketLock = new Object();
+    private static final DNSDatagramSocketFactory factory =
+            new DNSDatagramSocketFactory(random);
 
     // Requests sent
     private Map<Integer, ResourceRecord> reqs;
@@ -105,14 +107,6 @@ public class DnsClient {
             throws NamingException {
         this.timeout = timeout;
         this.retries = retries;
-        try {
-            udpSocket = new DatagramSocket();
-        } catch (java.net.SocketException e) {
-            NamingException ne = new ConfigurationException();
-            ne.setRootCause(e);
-            throw ne;
-        }
-
         this.servers = new InetAddress[servers.length];
         serverPorts = new int[servers.length];
 
@@ -142,6 +136,16 @@ public class DnsClient {
         resps = Collections.synchronizedMap(new HashMap<Integer, byte[]>());
     }
 
+    DatagramSocket getDatagramSocket() throws NamingException {
+        try {
+            return factory.open();
+        } catch (java.net.SocketException e) {
+            NamingException ne = new ConfigurationException();
+            ne.setRootCause(e);
+            throw ne;
+        }
+    }
+
     protected void finalize() {
         close();
     }
@@ -150,7 +154,6 @@ public class DnsClient {
     private Object queuesLock = new Object();
 
     public void close() {
-        udpSocket.close();
         synchronized (queuesLock) {
             reqs.clear();
             resps.clear();
@@ -392,7 +395,8 @@ public class DnsClient {
 
         int minTimeout = 50; // msec after which there are no retries.
 
-        synchronized (udpSocket) {
+        synchronized (udpSocketLock) {
+            try (DatagramSocket udpSocket = getDatagramSocket()) {
                 DatagramPacket opkt = new DatagramPacket(
                         pkt.getData(), pkt.length(), server, port);
                 DatagramPacket ipkt = new DatagramPacket(new byte[8000], 8000);
@@ -431,6 +435,7 @@ public class DnsClient {
                 return null; // no matching packet received within the timeout
             }
         }
+    }
 
     /*
      * Sends a TCP query, and returns the first DNS message in the response.

src/share/classes/com/sun/jndi/dns/ResourceRecord.java

 /*
- * Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2000, 2017, 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
@@ -355,8 +355,19 @@ public class ResourceRecord {
                     pos += typeAndLen;
                 } else if ((typeAndLen & 0xC0) == 0xC0) { // name compression
                     ++level;
-                    endPos = pos + 2;
+                    // cater for the case where the name pointed to is itself
+                    // compressed: we don't want endPos to be reset by the second
+                    // compression level.
+                    int ppos = pos;
+                    if (endPos == -1) endPos = pos + 2;
                     pos = getUShort(pos) & 0x3FFF;
+                    if (debug) {
+                        dprint("decode: name compression at " + ppos
+                                + " -> " + pos + " endPos=" + endPos);
+                        assert endPos > 0;
+                        assert pos < ppos;
+                        assert pos >= Header.HEADER_SIZE;
+                    }
                 } else
                     throw new IOException("Invalid label type: " + typeAndLen);
             }
@@ -405,6 +416,11 @@ public class ResourceRecord {
             }
         }
         // Unknown RR type/class
+        if (debug) {
+            dprint("Unknown RR type for RR data: " + rrtype + " rdlen=" + rdlen
+                   + ", pos=" + pos +", msglen=" + msg.length + ", remaining="
+                   + (msg.length-pos));
+        }
         byte[] rd = new byte[rdlen];
         System.arraycopy(msg, pos, rd, 0, rdlen);
         return rd;
@@ -613,4 +629,15 @@ public class ResourceRecord {
 
         return buf.toString();
     }
+
+    //-------------------------------------------------------------------------
+
+    private static final boolean debug = false;
+
+    private static void dprint(String mess) {
+        if (debug) {
+            System.err.println("DNS: " + mess);
+        }
+    }
+
 }