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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;

import sun.misc.SharedSecrets;

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 static final boolean DEBUG = Krb5.DEBUG; 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 final 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). final 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 = SharedSecrets.getJavaSecurityAccess().doPrivileged (new PrivilegedExceptionAction<Attributes>() { public Attributes run() throws Exception { return ((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) { final 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). final 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 = SharedSecrets.getJavaSecurityAccess().doPrivileged (new PrivilegedExceptionAction<Attributes>() { public Attributes run() throws Exception { return ((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 } } } }