我对cdh4安全机制的解读

     老大让我看cdh4的安全机制的实现，说实话，没有太多的思路。然后老大说，安全认证不通过肯定会抛异常，然后我就从异常入手了。


  目测 AccessControlException比较像，然后看到他有个子类：AuthorizationException。这个受众更小，更容易做为切入点，好，就这个了。

 public void authorize(UserGroupInformation user, 
                               Class<?> protocol,
                               Configuration conf,
                               InetAddress addr
                               ) throws AuthorizationException {
    AccessControlList acl = protocolToAcl.get(protocol);
    if (acl == null) {
      throw new AuthorizationException("Protocol " + protocol + 
                                       " is not known.");
    }
    
    // get client principal key to verify (if available)
    KerberosInfo krbInfo = SecurityUtil.getKerberosInfo(protocol, conf);
    String clientPrincipal = null; 
    if (krbInfo != null) {
      String clientKey = krbInfo.clientPrincipal();
      if (clientKey != null && !clientKey.equals("")) {
        try {
          clientPrincipal = SecurityUtil.getServerPrincipal(
              conf.get(clientKey), addr);
        } catch (IOException e) {
          throw (AuthorizationException) new AuthorizationException(
              "Can't figure out Kerberos principal name for connection from "
                  + addr + " for user=" + user + " protocol=" + protocol)
              .initCause(e);
        }
      }
    }
    if((clientPrincipal != null && !clientPrincipal.equals(user.getUserName())) || 
        !acl.isUserAllowed(user)) {
      AUDITLOG.warn(AUTHZ_FAILED_FOR + user + " for protocol=" + protocol
          + ", expected client Kerberos principal is " + clientPrincipal);
      throw new AuthorizationException("User " + user + 
          " is not authorized for protocol " + protocol + 
          ", expected client Kerberos principal is " + clientPrincipal);
    }
    AUDITLOG.info(AUTHZ_SUCCESSFUL_FOR + user + " for protocol="+protocol);
  }

这里是会抛出AuthorizationException异常的。
我比较关注kerberos的部分：clientPrincipal.equals(user.getUserName()

 clientPrincipal = SecurityUtil.getServerPrincipal(
              conf.get(clientKey), addr);

KerberosInfo krbInfo = SecurityUtil.getKerberosInfo(protocol, conf);

关键是clientKey，但是clientKey需要krbInfo。所以krbInfo就是最关键的地方了。

for(SecurityInfo provider: securityInfoProviders) {
KerberosInfo result = provider.getKerberosInfo(protocol, conf);

那这里是的securityInfoProviders是怎么来的呢：

  private static ServiceLoader<SecurityInfo> securityInfoProviders = 
    ServiceLoader.load(SecurityInfo.class);

这里使用了ServiceLoader，我们看到hadoop-commom的META-INF\services文件夹，有个叫org.apache.hadoop.security.SecurityInfo的文件名，内容是

org.apache.hadoop.security.AnnotatedSecurityInfo

。

public class AnnotatedSecurityInfo extends SecurityInfo {

  @Override
  public KerberosInfo getKerberosInfo(Class<?> protocol, Configuration conf) {
    return protocol.getAnnotation(KerberosInfo.class);
  }

意思就是返回protocol对应类的注解KerberosInfo 就可以了。

protocol = getProtocolClass(protocolName, getConf());

这个类似根据protocolName反射得到的。



可以看到protocolName是从数据流中读取的，

processOneRpc(data.array());

这里的data就是protocolName的源头了。

现在能拿到clientKey，再回过头来。  

clientPrincipal = SecurityUtil.getServerPrincipal(
              conf.get(clientKey), addr);

这里就与conf扯上关系了，conf的各个key和value都是系统初始化进去的。
clientPrincipal 只是conf对应的value替换掉主机名而已。看到替换规则，这些value应该是以[/@]来分隔的，但是我看了conf的初始化过程，没有找见有这样的value.

厉害，楼主在广州哪里工作？