Kerberos认证代码分析Can't get Kerberos realm

1. Can't get Kerberos realm

原因分析：

原始代码为：

1 2	`org.apache.hadoop.security.UserGroupInformation.setConfiguration(conf)` `sun.security.krb5.Config.refresh()`

首先根据传进来的Hadoop配置conf，去设置UserGroupInformation(UGI)，方法的调用关系如下(删除了部分不相关代码):

public static void setConfiguration(Configuration conf) {

initialize(conf, true);

}

initialize方法如下

private static synchronized void initialize(Configuration conf, boolean overrideNameRules) {

authenticationMethod = SecurityUtil.getAuthenticationMethod(conf);

if (overrideNameRules || !HadoopKerberosName.hasRulesBeenSet()) {

try {

HadoopKerberosName.setConfiguration(conf);

} catch (IOException ioe) {

throw new RuntimeException(

"Problem with Kerberos auth_to_local name configuration", ioe);

}

......

}

setConfiguration方法如下

public static void setConfiguration(Configuration conf) throws IOException {

final String defaultRule;

switch (SecurityUtil.getAuthenticationMethod(conf)) {

case KERBEROS:

case KERBEROS_SSL:

try {

KerberosUtil.getDefaultRealm();

} catch (Exception ke) {

throw new IllegalArgumentException("Can't get Kerberos realm", ke);

}

......

}

......

}

getDefaultRealm使用了反射，目的是为了兼容两套jdk，即IBM(com.ibm.security.krb5.internal.Config) 和 Oracle(sun.security.krb5.Config)

public static String getDefaultRealm()

throws ClassNotFoundException, NoSuchMethodException,

IllegalArgumentException, IllegalAccessException,

InvocationTargetException {

Object kerbConf;

Class<?> classRef;

Method getInstanceMethod;

Method getDefaultRealmMethod;

if (System.getProperty("java.vendor").contains("IBM")) {

classRef = Class.forName("com.ibm.security.krb5.internal.Config"); // 获取IBM jdk的类引用

} else {

classRef = Class.forName("sun.security.krb5.Config"); // 获取Oracle jdk的类引用

}

getInstanceMethod = classRef.getMethod("getInstance", new Class[0]);

kerbConf = getInstanceMethod.invoke(classRef, new Object[0]);

getDefaultRealmMethod = classRef.getDeclaredMethod("getDefaultRealm", new Class[0]);

return (String)getDefaultRealmMethod.invoke(kerbConf, new Object[0]);

}

从上述代码来看，先获取Config类引用，然后getInstanceMethod是获得getInstance方法，再次getDefaultRealmMethod是获得getDefaultRealm方法。

因此，假设我们是使用的Oracle的JDK，那么最后是调用的sun.security.krb5.getDefaultRealm()。接下来看一下sun.security.krb5.getDefaultRealm()是如何实现的。

public String getDefaultRealm() throws KrbException {

if(this.defaultRealm != null) { // 如果defaultRealm不为空，直接返回defaultRealm

return this.defaultRealm;

} else { // 如果defaultRealm为null，获取defaultRealm

KrbException var1 = null;

String var2 = this.getDefault("default_realm", "libdefaults");

if(var2 == null && this.useDNS_Realm()) {

try {

var2 = this.getRealmFromDNS();

} catch (KrbException var4) {

var1 = var4;

}

......

}

我们假设defaultRealm = null，看一下如何从var2 = this.getRealmFromDNS();来获取defaultRealm

private String getRealmFromDNS() throws KrbException {

String var1 = null;

String var2 = null;

try {

var2 = InetAddress.getLocalHost().getCanonicalHostName(); // 1. 获取local host name

} catch (UnknownHostException var7) {

KrbException var4 = new KrbException(60, "Unable to locate Kerberos realm: " + var7.getMessage());

var4.initCause(var7);

throw var4;

}

String var3 = PrincipalName.mapHostToRealm(var2); // 2. 根据local host name获取realm

....

}

mapHostToRealm()方法如下：

static String mapHostToRealm(String var0) {

String var1 = null;

try {

String var2 = null;

Config var3 = Config.getInstance(); // 获取Config的单例对象

if((var1 = var3.getDefault(var0, "domain_realm")) != null) {

return var1;

}

.......

} catch (KrbException var5) {

;

}

return var1;

}

这里会获取Config的单例对象，

public static synchronized Config getInstance() throws KrbException {

if(singleton == null) {

singleton = new Config();

}

return singleton;

}

再看Config.getInstance();的具体动作就是判断单例对象是否为null，不为null直接返回，为null重新new一个Config对象。

同时，Config类中还有一个方法refresh，其代码如下：

public static synchronized void refresh() throws KrbException {

singleton = new Config();

KdcComm.initStatic();

}

从refresh的代码看，只要调用refresh()方法，就会重新生成Config的单例对象。这个refresh()方法，也是我们代码里面要调用的。

再回顾一下我们的原始代码：

1 2	`org.apache.hadoop.security.UserGroupInformation.setConfiguration(conf)` `sun.security.krb5.Config.refresh()`

回到getInstance()方法，假设singleton单例是null，会生成Config的单例对象。以后，再次调用getInstance方法都会直接返回这个单例对象了，没有再new的机会了。有人开始质疑没有机会new Config()对象了？调用Config.refresh()方法不是可以new吗？答案是可以new，但是如果我们的UserGroupInformation.setConfiguration(conf)会抛出异常，是不是Config.refresh()方法就不会被调用了！我们的错误就是出现在这里，后面分析UserGroupInformation.setConfiguration(conf)怎么抛出异常了。

在我们来看一下new Config()具体做了什么事情。

private Config() throws KrbException {

String var1 = getProperty("java.security.krb5.kdc"); // 从系统变量获取kdc地址，假设我们启动JVM时没有设置该变量

if(var1 != null) {

this.defaultKDC = var1.replace(':', ' ');

} else {

this.defaultKDC = null;

}

this.defaultRealm = getProperty("java.security.krb5.realm"); // 从系统变量获取realm，假设我们启动JVM时也没有设置该变量

if((this.defaultKDC != null || this.defaultRealm == null) && (this.defaultRealm != null || this.defaultKDC == null)) {

try {

String var3 = this.getJavaFileName(); // 该方法会从JVM参数java.security.krb5.conf以及<java-home>/lib/security/krb5.conf获取到krb5.conf文件

Vector var2;

if(var3 != null) {

var2 = this.loadConfigFile(var3);

this.stanzaTable = this.parseStanzaTable(var2);

if(DEBUG) {

System.out.println("Loaded from Java config");

}

} else { // 假设JVM参数java.security.krb5.conf以及<java-home>/lib/security/krb5.conf都没有获取到krb5.conf文件

boolean var4 = false;

if(isMacosLionOrBetter()) {

try {

this.stanzaTable = SCDynamicStoreConfig.getConfig();

if(DEBUG) {

System.out.println("Loaded from SCDynamicStoreConfig");

}

var4 = true;

} catch (IOException var6) {

;

}

if(!var4) {

var3 = this.getNativeFileName(); // 我们是centos机器，会拿到/etc/krb5.conf

var2 = this.loadConfigFile(var3); // 加载/etc/krb5.conf文件

this.stanzaTable = this.parseStanzaTable(var2);

if(DEBUG) {

System.out.println("Loaded from native config");

}

} catch (IOException var7) {

;

}

} else {

throw new KrbException("System property java.security.krb5.kdc and java.security.krb5.realm both must be set or neither must be set.");

}

我们的问题就出在var2 = this.loadConfigFile(var3); 位置，因为加载/etc/krb5.conf文件的时候，恰好/etc/krb5.conf文件不存在，因为我们会把修改的krb5.conf去替换/etc/krb5.conf文件，在替换的时间内，恰好去loadConfigFile()，该方法就报了FileNotFoundException的异常。这个异常一直throw到UserGroupInformation.setConfiguration(conf)调用的地方，导致我们永远调用不到Config.refresh()方法。

2. 报错com.google.common.util.concurrent.UncheckedTimeoutException: java.util.concurrent.TimeoutException

原因分析：首先这个异常是因为调试上述报错产生的，所以顺便分析下原因。

上述报错是Can't get Kerberos realm，网上查一下，大概是因为拿不到kdc和realm。

因此，我在JVM启动参数中添加了如下3个参数:

-Djava.security.krb5.conf=/etc/krb5.conf \

-Djava.security.krb5.kdc=node1:8080 \

-Djava.security.krb5.realm=KFC.com \

指定了krb5.conf文件，kdc地址，realm值。然后重启程序，发现可以正常使用，然后把/etc/krb5.conf文件删除了（上个错误其实猜想到了是因为读不到krb5.conf造成的）。

程序竟然报错 java.util.concurrent.TimeoutException，打jstack

TimeoutException 的jstack如下:

"builtin-checker-serviceId-58" prio=10 tid=0x00007f678800e800 nid=0x4084 waiting for monitor entry [0x00007f672fffe000]

java.lang.Thread.State: BLOCKED (on object monitor)

at org.apache.hadoop.security.UserGroupInformation.loginUserFromKeytabAndReturnUGI(UserGroupInformation.java:1074)

- waiting to lock <0x00000000a8b940d0> (a java.lang.Class for org.apache.hadoop.security.UserGroupInformation)

......

at java.util.concurrent.FutureTask.run(FutureTask.java:262)

at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)

at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)

at java.lang.Thread.run(Thread.java:745)

调用UserGroupInformation.loginUserFromKeytabAndReturnUGI被block了

往上找jstack，

"builtin-checker-serviceId-59" prio=10 tid=0x00007f67680b3800 nid=0x4097 runnable [0x00007f672f2ee000]

java.lang.Thread.State: RUNNABLE

at java.net.PlainDatagramSocketImpl.receive0(Native Method)

- locked <0x000000009a0076e0> (a java.net.PlainDatagramSocketImpl)

at java.net.AbstractPlainDatagramSocketImpl.receive(AbstractPlainDatagramSocketImpl.java:146)

- locked <0x000000009a0076e0> (a java.net.PlainDatagramSocketImpl)

at java.net.DatagramSocket.receive(DatagramSocket.java:816)

- locked <0x000000009a017848> (a java.net.DatagramPacket)

- locked <0x000000009a0076a0> (a java.net.DatagramSocket)

at sun.security.krb5.internal.UDPClient.receive(NetClient.java:207) // 卡主了

at sun.security.krb5.KdcComm$KdcCommunication.run(KdcComm.java:390)

at sun.security.krb5.KdcComm$KdcCommunication.run(KdcComm.java:343)

at java.security.AccessController.doPrivileged(Native Method)

at sun.security.krb5.KdcComm.send(KdcComm.java:327)

at sun.security.krb5.KdcComm.send(KdcComm.java:219)

at sun.security.krb5.KdcComm.send(KdcComm.java:191)

at sun.security.krb5.KrbAsReqBuilder.send(KrbAsReqBuilder.java:319)

at sun.security.krb5.KrbAsReqBuilder.action(KrbAsReqBuilder.java:364)

at com.sun.security.auth.module.Krb5LoginModule.attemptAuthentication(Krb5LoginModule.java:735)

at com.sun.security.auth.module.Krb5LoginModule.login(Krb5LoginModule.java:584)

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

at java.lang.reflect.Method.invoke(Method.java:606)

at javax.security.auth.login.LoginContext.invoke(LoginContext.java:762)

at javax.security.auth.login.LoginContext.access$000(LoginContext.java:203)

at javax.security.auth.login.LoginContext$4.run(LoginContext.java:690)

at javax.security.auth.login.LoginContext$4.run(LoginContext.java:688)

at java.security.AccessController.doPrivileged(Native Method)

at javax.security.auth.login.LoginContext.invokePriv(LoginContext.java:687)

at javax.security.auth.login.LoginContext.login(LoginContext.java:595)

at org.apache.hadoop.security.UserGroupInformation.loginUserFromKeytabAndReturnUGI(UserGroupInformation.java:1092)

- locked <0x00000000a8b940d0> (a java.lang.Class for org.apache.hadoop.security.UserGroupInformation)

........

at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)

at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)

at java.lang.Thread.run(Thread.java:745)

从jstack中看到UDPClient.receive卡主了，为什么卡主了，不知道！问大神，大神说加入JVM调试参数-Dsun.security.krb5.debug=true，可以打印日志到console中。在console中看到如下日志：

Ordering keys wrt default_tkt_enctypes list

default etypes for default_tkt_enctypes: 3 1 16.

>>> KrbAsReq creating message

>>> KrbKdcReq send: kdc=node1 UDP:88, timeout=30000, number of retries =3, #bytes=134

>>> KDCCommunication: kdc=node1 UDP:88, timeout=30000,Attempt =1, #bytes=134

SocketTimeOutException with attempt: 1

>>> KDCCommunication: kdc=node1 UDP:88, timeout=30000,Attempt =2, #bytes=134

SocketTimeOutException with attempt: 2

>>> KDCCommunication: kdc=node1 UDP:88, timeout=30000,Attempt =3, #bytes=134

SocketTimeOutException with attempt: 3

>>> KrbKdcReq send: error trying node1

java.net.SocketTimeoutException: Receive timed out

at java.net.PlainDatagramSocketImpl.receive0(Native Method)

at java.net.AbstractPlainDatagramSocketImpl.receive(AbstractPlainDatagramSocketImpl.java:146)

at java.net.DatagramSocket.receive(DatagramSocket.java:816)

at sun.security.krb5.internal.UDPClient.receive(NetClient.java:207)