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KrbServiceLocator
/*
* Copyright (c) 2006, 2011, 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
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package sun.security.krb5;
import sun.security.krb5.internal.Krb5;
import java.security.AccessController;
import java.security.PrivilegedActionException;
import java.security.PrivilegedExceptionAction;
import java.util.Arrays;
import java.util.Hashtable;
import java.util.Random;
import java.util.StringTokenizer;
import javax.naming.*;
import javax.naming.directory.*;
import javax.naming.spi.NamingManager;
This class discovers the location of Kerberos services by querying DNS,
as defined in RFC 4120.
Author: Seema Malkani Since: 1.7
/**
* This class discovers the location of Kerberos services by querying DNS,
* as defined in RFC 4120.
*
* @author Seema Malkani
* @since 1.7
*/
class KrbServiceLocator {
private static final String SRV_RR = "SRV";
private static final String[] SRV_RR_ATTR = new String[] {SRV_RR};
private static final String SRV_TXT = "TXT";
private static final String[] SRV_TXT_ATTR = new String[] {SRV_TXT};
private static final Random random = new Random();
private KrbServiceLocator() {
}
Locates the KERBEROS service for a given domain.
Queries DNS for a list of KERBEROS Service Text Records (TXT) for a
given domain name.
Information on the mapping of DNS hostnames and domain names
to Kerberos realms is stored using DNS TXT records
Params: - realmName – A string realm name.
Returns: An ordered list of hostports for the Kerberos service or null if
the service has not been located.
/**
* Locates the KERBEROS service for a given domain.
* Queries DNS for a list of KERBEROS Service Text Records (TXT) for a
* given domain name.
* Information on the mapping of DNS hostnames and domain names
* to Kerberos realms is stored using DNS TXT records
*
* @param realmName A string realm name.
* @return An ordered list of hostports for the Kerberos service or null if
* the service has not been located.
*/
static String[] getKerberosService(String realmName) {
// search realm in SRV TXT records
String dnsUrl = "dns:///_kerberos." + realmName;
String[] records = null;
try {
// Create the DNS context using NamingManager rather than using
// the initial context constructor. This avoids having the initial
// context constructor call itself (when processing the URL
// argument in the getAttributes call).
Context ctx = NamingManager.getURLContext("dns", new Hashtable<>(0));
if (!(ctx instanceof DirContext)) {
return null; // cannot create a DNS context
}
Attributes attrs = null;
try {
// both connect and accept are needed since DNS is thru UDP
attrs = AccessController.doPrivileged(
(PrivilegedExceptionAction<Attributes>)
() -> ((DirContext)ctx).getAttributes(
dnsUrl, SRV_TXT_ATTR),
null,
new java.net.SocketPermission("*", "connect,accept"));
} catch (PrivilegedActionException e) {
throw (NamingException)e.getCause();
}
Attribute attr;
if (attrs != null && ((attr = attrs.get(SRV_TXT)) != null)) {
int numValues = attr.size();
int numRecords = 0;
String[] txtRecords = new String[numValues];
// gather the text records
int i = 0;
int j = 0;
while (i < numValues) {
try {
txtRecords[j] = (String)attr.get(i);
j++;
} catch (Exception e) {
// ignore bad value
}
i++;
}
numRecords = j;
// trim
if (numRecords < numValues) {
String[] trimmed = new String[numRecords];
System.arraycopy(txtRecords, 0, trimmed, 0, numRecords);
records = trimmed;
} else {
records = txtRecords;
}
}
} catch (NamingException e) {
// ignore
}
return records;
}
Locates the KERBEROS service for a given domain.
Queries DNS for a list of KERBEROS Service Location Records (SRV) for a
given domain name.
Params: - realmName – A string realm name.
- protocol – the protocol string, can be "_udp" or "_tcp"
Returns: An ordered list of hostports for the Kerberos service or null if
the service has not been located.
/**
* Locates the KERBEROS service for a given domain.
* Queries DNS for a list of KERBEROS Service Location Records (SRV) for a
* given domain name.
*
* @param realmName A string realm name.
* @param protocol the protocol string, can be "_udp" or "_tcp"
* @return An ordered list of hostports for the Kerberos service or null if
* the service has not been located.
*/
static String[] getKerberosService(String realmName, String protocol) {
String dnsUrl = "dns:///_kerberos." + protocol + "." + realmName;
String[] hostports = null;
try {
// Create the DNS context using NamingManager rather than using
// the initial context constructor. This avoids having the initial
// context constructor call itself (when processing the URL
// argument in the getAttributes call).
Context ctx = NamingManager.getURLContext("dns", new Hashtable<>(0));
if (!(ctx instanceof DirContext)) {
return null; // cannot create a DNS context
}
Attributes attrs = null;
try {
// both connect and accept are needed since DNS is thru UDP
attrs = AccessController.doPrivileged(
(PrivilegedExceptionAction<Attributes>)
() -> ((DirContext)ctx).getAttributes(
dnsUrl, SRV_RR_ATTR),
null,
new java.net.SocketPermission("*", "connect,accept"));
} catch (PrivilegedActionException e) {
throw (NamingException)e.getCause();
}
Attribute attr;
if (attrs != null && ((attr = attrs.get(SRV_RR)) != null)) {
int numValues = attr.size();
int numRecords = 0;
SrvRecord[] srvRecords = new SrvRecord[numValues];
// create the service records
int i = 0;
int j = 0;
while (i < numValues) {
try {
srvRecords[j] = new SrvRecord((String) attr.get(i));
j++;
} catch (Exception e) {
// ignore bad value
}
i++;
}
numRecords = j;
// trim
if (numRecords < numValues) {
SrvRecord[] trimmed = new SrvRecord[numRecords];
System.arraycopy(srvRecords, 0, trimmed, 0, numRecords);
srvRecords = trimmed;
}
// Sort the service records in ascending order of their
// priority value. For records with equal priority, move
// those with weight 0 to the top of the list.
if (numRecords > 1) {
Arrays.sort(srvRecords);
}
// extract the host and port number from each service record
hostports = extractHostports(srvRecords);
}
} catch (NamingException e) {
// e.printStackTrace();
// ignore
}
return hostports;
}
Extract hosts and port numbers from a list of SRV records.
An array of hostports is returned or null if none were found.
/**
* Extract hosts and port numbers from a list of SRV records.
* An array of hostports is returned or null if none were found.
*/
private static String[] extractHostports(SrvRecord[] srvRecords) {
String[] hostports = null;
int head = 0;
int tail = 0;
int sublistLength = 0;
int k = 0;
for (int i = 0; i < srvRecords.length; i++) {
if (hostports == null) {
hostports = new String[srvRecords.length];
}
// find the head and tail of the list of records having the same
// priority value.
head = i;
while (i < srvRecords.length - 1 &&
srvRecords[i].priority == srvRecords[i + 1].priority) {
i++;
}
tail = i;
// select hostports from the sublist
sublistLength = (tail - head) + 1;
for (int j = 0; j < sublistLength; j++) {
hostports[k++] = selectHostport(srvRecords, head, tail);
}
}
return hostports;
}
/*
* Randomly select a service record in the range [head, tail] and return
* its hostport value. Follows the algorithm in RFC 2782.
*/
private static String selectHostport(SrvRecord[] srvRecords, int head,
int tail) {
if (head == tail) {
return srvRecords[head].hostport;
}
// compute the running sum for records between head and tail
int sum = 0;
for (int i = head; i <= tail; i++) {
if (srvRecords[i] != null) {
sum += srvRecords[i].weight;
srvRecords[i].sum = sum;
}
}
String hostport = null;
// If all records have zero weight, select first available one;
// otherwise, randomly select a record according to its weight
int target = (sum == 0 ? 0 : random.nextInt(sum + 1));
for (int i = head; i <= tail; i++) {
if (srvRecords[i] != null && srvRecords[i].sum >= target) {
hostport = srvRecords[i].hostport;
srvRecords[i] = null; // make this record unavailable
break;
}
}
return hostport;
}
This class holds a DNS service (SRV) record.
See http://www.ietf.org/rfc/rfc2782.txt
/**
* This class holds a DNS service (SRV) record.
* See http://www.ietf.org/rfc/rfc2782.txt
*/
static class SrvRecord implements Comparable<SrvRecord> {
int priority;
int weight;
int sum;
String hostport;
Creates a service record object from a string record.
DNS supplies the string record in the following format:
" " " " " "
/**
* Creates a service record object from a string record.
* DNS supplies the string record in the following format:
* <pre>
* <Priority> " " <Weight> " " <Port> " " <Host>
* </pre>
*/
SrvRecord(String srvRecord) throws Exception {
StringTokenizer tokenizer = new StringTokenizer(srvRecord, " ");
String port;
if (tokenizer.countTokens() == 4) {
priority = Integer.parseInt(tokenizer.nextToken());
weight = Integer.parseInt(tokenizer.nextToken());
port = tokenizer.nextToken();
hostport = tokenizer.nextToken() + ":" + port;
} else {
throw new IllegalArgumentException();
}
}
/*
* Sort records in ascending order of priority value. For records with
* equal priority move those with weight 0 to the top of the list.
*/
public int compareTo(SrvRecord that) {
if (priority > that.priority) {
return 1; // this > that
} else if (priority < that.priority) {
return -1; // this < that
} else if (weight == 0 && that.weight != 0) {
return -1; // this < that
} else if (weight != 0 && that.weight == 0) {
return 1; // this > that
} else {
return 0; // this == that
}
}
}
}