Committed.
Gary Benson wrote:
> Hi all,
>
> The documentation for java.net.InetAddress states that it maintains a
> DNS cache in order to guard against DNS spoofing attacks. This patch
> adds this, but I wanted to float it for comments before checking it
> in as this has been an issue before: Classpath _had_ a DNS cache, but
> it was removed in January:
>
> http://permalink.gmane.org/gmane.comp.java.classpath.patches/6288
>
> The main difference between that cache and this one is that the old
> cache had its own set of rules for exipry and purging, and its own set
> of system properties for controlling those rules. This cache does
> exactly what the javadoc for InetAddress says it should, so it should
> defeat whatever attack the it was originally created for. What that
> attack _is_ exactly is not clear. One possibility is [1], though it
> seems that that would require the browser to be using the same cache
> for a fix.
>
> Of course, by doing exactly what the javadoc says we also inherit the
> same problems as other JVMs that implement this cache [2, 3, 4]. We
> do have the same solutions, however, so it's not like we'll be leaving
> people out to dry.
>
> Cheers,
> Gary
>
> [1] http://www.cs.princeton.edu/sip/news/sun-02-22-96.html
> [2] http://www.limewire.org/pipermail/codepatch/2004-February/000310.html
> [3] http://www.adobe.com/cfusion/knowledgebase/index.cfm?id=13115e61
> [4] http://www.openldap.org/lists/openldap-devel/200603/msg00007.html
Index: ChangeLog
===================================================================
RCS file: /cvsroot/classpath/classpath/ChangeLog,v
retrieving revision 1.8564
diff -u -r1.8564 ChangeLog
--- ChangeLog 19 Sep 2006 05:47:38 -0000 1.8564
+++ ChangeLog 19 Sep 2006 08:40:36 -0000
@@ -1,3 +1,9 @@
+2006-09-19 Gary Benson <[EMAIL PROTECTED]>
+
+ * java/net/ResolverCache.java: New class (a DNS cache).
+ * java/net/InetAddress.java
+ (internalGetCanonicalHostName, getAllByName): Use the above.
+
2006-09-19 Jeroen Frijters <[EMAIL PROTECTED]>
* gnu/java/nio/SocketChannelImpl.java: Removed unused import.
Index: java/net/ResolverCache.java
===================================================================
RCS file: java/net/ResolverCache.java
diff -N java/net/ResolverCache.java
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ java/net/ResolverCache.java 19 Sep 2006 08:40:36 -0000
@@ -0,0 +1,269 @@
+/* ResolverCache.java -- A cache of resolver lookups for InetAddress.
+ Copyright (C) 2006 Free Software Foundation, Inc.
+
+This file is part of GNU Classpath.
+
+GNU Classpath is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2, or (at your option)
+any later version.
+
+GNU Classpath 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 for more details.
+
+You should have received a copy of the GNU General Public License
+along with GNU Classpath; see the file COPYING. If not, write to the
+Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+02110-1301 USA.
+
+Linking this library statically or dynamically with other modules is
+making a combined work based on this library. Thus, the terms and
+conditions of the GNU General Public License cover the whole
+combination.
+
+As a special exception, the copyright holders of this library give you
+permission to link this library with independent modules to produce an
+executable, regardless of the license terms of these independent
+modules, and to copy and distribute the resulting executable under
+terms of your choice, provided that you also meet, for each linked
+independent module, the terms and conditions of the license of that
+module. An independent module is a module which is not derived from
+or based on this library. If you modify this library, you may extend
+this exception to your version of the library, but you are not
+obligated to do so. If you do not wish to do so, delete this
+exception statement from your version. */
+
+
+package java.net;
+
+import java.security.Security;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.LinkedList;
+
+/**
+ * This class provides a cache of name service resolutions. By
+ * default successful resolutions are cached forever to guard
+ * against DNS spoofing attacks and failed resolutions are cached
+ * for 10 seconds to improve performance. The length of time that
+ * results remain in the cache is determined by the following
+ * security properties:
+ * <dl>
+ * <dt><code>networkaddress.cache.ttl</code></dt>
+ * <dd>
+ * This property specifies the length of time in seconds that
+ * successful resolutions remain in the cache. The default is
+ * -1, indicating to cache forever.
+ * </dd>
+ * <dt><code>networkaddress.cache.negative.ttl</code></dt>
+ * <dd>
+ * This property specifies the length of time in seconds that
+ * unsuccessful resolutions remain in the cache. The default
+ * is 10, indicating to cache for 10 seconds.
+ * </dd>
+ * In both cases, a value of -1 indicates to cache forever and a
+ * value of 0 indicates not to cache.
+ *
+ * @author Gary Benson ([EMAIL PROTECTED])
+ */
+class ResolverCache
+{
+ /**
+ * The time in seconds for which successful lookups are cached.
+ */
+ private static final int POSITIVE_TTL =
+ getTTL("networkaddress.cache.ttl", -1);
+
+ /**
+ * The time in seconds for which unsuccessful lookups are cached.
+ */
+ private static final int NEGATIVE_TTL =
+ getTTL("networkaddress.cache.negative.ttl", 10);
+
+ /**
+ * Helper function to set the TTLs.
+ */
+ private static int getTTL(String propName, int defaultValue)
+ {
+ String propValue = Security.getProperty(propName);
+ if (propValue == null)
+ return defaultValue;
+
+ return Integer.parseInt(propValue);
+ }
+
+ /**
+ * The cache itself.
+ */
+ private static HashMap cache = new HashMap();
+
+ /**
+ * List of entries which may expire.
+ */
+ private static LinkedList killqueue = new LinkedList();
+
+ /**
+ * Return the hostname for the specified IP address.
+ *
+ * @param ip The IP address as a byte array
+ *
+ * @return The hostname
+ *
+ * @exception UnknownHostException If the reverse lookup fails
+ */
+ public static String getHostByAddr(byte[] addr) throws UnknownHostException
+ {
+ Object key = makeHashableAddress(addr);
+ Entry entry = (Entry) get(key);
+ if (entry != null)
+ {
+ if (entry.value == null)
+ throw new UnknownHostException();
+ return (String) entry.value;
+ }
+
+ try
+ {
+ String hostname = VMInetAddress.getHostByAddr(addr);
+ put(new Entry(key, hostname));
+ return hostname;
+ }
+ catch (UnknownHostException e)
+ {
+ put(new Entry(key, null));
+ throw e;
+ }
+ }
+
+ /**
+ * Return a list of all IP addresses for the specified hostname.
+ *
+ * @param hostname The hostname
+ *
+ * @return An list of IP addresses as byte arrays
+ *
+ * @exception UnknownHostException If the lookup fails
+ */
+ public static byte[][] getHostByName(String hostname)
+ throws UnknownHostException
+ {
+ Entry entry = (Entry) get(hostname);
+ if (entry != null)
+ {
+ if (entry.value == null)
+ throw new UnknownHostException();
+ return (byte[][]) entry.value;
+ }
+
+ try
+ {
+ byte[][] addrs = VMInetAddress.getHostByName(hostname);
+ put(new Entry(hostname, addrs));
+ return addrs;
+ }
+ catch (UnknownHostException e)
+ {
+ put(new Entry(hostname, null));
+ throw e;
+ }
+ }
+
+ /**
+ * Convert an IP address expressed as a byte array into something
+ * we can use as a hashtable key.
+ */
+ private static Object makeHashableAddress(byte[] addr)
+ {
+ char[] chars = new char[addr.length];
+ for (int i = 0; i < addr.length; i++)
+ chars[i] = (char) addr[i];
+ return new String(chars);
+ }
+
+ /**
+ * Return the entry in the cache associated with the supplied key,
+ * or <code>null</code> if the cache does not contain an entry
+ * associated with this key.
+ */
+ private static synchronized Entry get(Object key)
+ {
+ reap();
+ return (Entry) cache.get(key);
+ }
+
+ /**
+ * Insert the supplied entry into the cache.
+ */
+ private static synchronized void put(Entry entry)
+ {
+ reap();
+ if (entry.expires != 0)
+ {
+ if (entry.expires != -1)
+ killqueue.add(entry);
+ cache.put(entry.key, entry);
+ }
+ }
+
+ /**
+ * Clear expired entries. This method is not synchronized, so
+ * it must only be called by methods that are.
+ */
+ private static void reap()
+ {
+ if (!killqueue.isEmpty())
+ {
+ long now = System.currentTimeMillis();
+
+ Iterator iter = killqueue.iterator();
+ while (iter.hasNext())
+ {
+ Entry entry = (Entry) iter.next();
+ if (entry.expires > now)
+ break;
+ cache.remove(entry.key);
+ iter.remove();
+ }
+ }
+ }
+
+ /**
+ * An entry in the cache.
+ */
+ private static class Entry
+ {
+ /**
+ * The key by which this entry is referenced.
+ */
+ public final Object key;
+
+ /**
+ * The entry itself. A null value indicates a failed lookup.
+ */
+ public final Object value;
+
+ /**
+ * The time when this cache entry expires. If set to -1 then
+ * this entry will never expire. If set to 0 then this entry
+ * expires immediately and will not be inserted into the cache.
+ */
+ public final long expires;
+
+ /**
+ * Constructor.
+ */
+ public Entry(Object key, Object value)
+ {
+ this.key = key;
+ this.value = value;
+
+ int ttl = value != null ? POSITIVE_TTL : NEGATIVE_TTL;
+ if (ttl < 1)
+ expires = ttl;
+ else
+ expires = System.currentTimeMillis() + ttl * 1000;
+ }
+ }
+}
Index: java/net/InetAddress.java
===================================================================
RCS file: /cvsroot/classpath/classpath/java/net/InetAddress.java,v
retrieving revision 1.51
diff -u -r1.51 InetAddress.java
--- java/net/InetAddress.java 14 Sep 2006 13:43:40 -0000 1.51
+++ java/net/InetAddress.java 19 Sep 2006 08:40:36 -0000
@@ -316,7 +316,7 @@
{
try
{
- return VMInetAddress.getHostByAddr(addr);
+ return ResolverCache.getHostByAddr(addr);
}
catch (UnknownHostException e)
{
@@ -587,7 +587,7 @@
sm.checkConnect(hostname, -1);
// Resolve the hostname
- byte[][] iplist = VMInetAddress.getHostByName(hostname);
+ byte[][] iplist = ResolverCache.getHostByName(hostname);
if (iplist.length == 0)
throw new UnknownHostException(hostname);
