Fixing permission errors for `KERBEROS` security mode for HDFS Repository (#23439)

Added missing permissions required for authenticating with Kerberos to HDFS. Also implemented 
code to support authentication in the form of using a Kerberos keytab file. In order to support 
HDFS authentication, users must install a Kerberos keytab file on each node and transfer it to the 
configuration directory. When a user specifies a Kerberos principal in the repository settings the 
plugin automatically enables security for Hadoop and begins the login process. There will be a 
separate PR and commit for the testing infrastructure to support these changes.

5 files changed, 336 insertions, 42 deletions

diff --git a/plugins/repository-hdfs/src/main/java/org/elasticsearch/repositories/hdfs/HdfsBlobStore.java b/plugins/repository-hdfs/src/main/java/org/elasticsearch/repositories/hdfs/HdfsBlobStore.java
index 7ce5e8d3cd..8d88b7fd07 100644
--- a/plugins/repository-hdfs/src/main/java/org/elasticsearch/repositories/hdfs/HdfsBlobStore.java
+++ b/plugins/repository-hdfs/src/main/java/org/elasticsearch/repositories/hdfs/HdfsBlobStore.java
@@ -29,23 +29,21 @@ import org.elasticsearch.common.blobstore.BlobPath;
 import org.elasticsearch.common.blobstore.BlobStore;
 
 import java.io.IOException;
-import java.lang.reflect.ReflectPermission;
-import java.net.SocketPermission;
 import java.security.AccessController;
 import java.security.PrivilegedActionException;
 import java.security.PrivilegedExceptionAction;
 
-import javax.security.auth.AuthPermission;
-
 final class HdfsBlobStore implements BlobStore {
 
     private final Path root;
     private final FileContext fileContext;
+    private final HdfsSecurityContext securityContext;
     private final int bufferSize;
     private volatile boolean closed;
 
     HdfsBlobStore(FileContext fileContext, String path, int bufferSize) throws IOException {
         this.fileContext = fileContext;
+        this.securityContext = new HdfsSecurityContext(fileContext.getUgi());
         this.bufferSize = bufferSize;
         this.root = execute(fileContext1 -> fileContext1.makeQualified(new Path(path)));
         try {
@@ -107,9 +105,6 @@ final class HdfsBlobStore implements BlobStore {
     /**
      * Executes the provided operation against this store
      */
-    // we can do FS ops with only two elevated permissions:
-    // 1) hadoop dynamic proxy is messy with access rules
-    // 2) allow hadoop to add credentials to our Subject
     <V> V execute(Operation<V> operation) throws IOException {
         SpecialPermission.check();
         if (closed) {
@@ -117,8 +112,12 @@ final class HdfsBlobStore implements BlobStore {
         }
         try {
             return AccessController.doPrivileged((PrivilegedExceptionAction<V>)
-                    () -> operation.run(fileContext), null, new ReflectPermission("suppressAccessChecks"),
-                     new AuthPermission("modifyPrivateCredentials"), new SocketPermission("*", "connect"));
+                () -> {
+                    securityContext.ensureLogin();
+                    return operation.run(fileContext);
+                },
+                null,
+                securityContext.getRestrictedExecutionPermissions());
         } catch (PrivilegedActionException pae) {
             throw (IOException) pae.getException();
         }
diff --git a/plugins/repository-hdfs/src/main/java/org/elasticsearch/repositories/hdfs/HdfsPlugin.java b/plugins/repository-hdfs/src/main/java/org/elasticsearch/repositories/hdfs/HdfsPlugin.java
index 9ea53a5acf..4e51ab23b8 100644
--- a/plugins/repository-hdfs/src/main/java/org/elasticsearch/repositories/hdfs/HdfsPlugin.java
+++ b/plugins/repository-hdfs/src/main/java/org/elasticsearch/repositories/hdfs/HdfsPlugin.java
@@ -26,6 +26,9 @@ import java.security.PrivilegedAction;
 import java.util.Collections;
 import java.util.Map;
 
+import org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolPB;
+import org.apache.hadoop.security.KerberosInfo;
+import org.apache.hadoop.security.SecurityUtil;
 import org.elasticsearch.SpecialPermission;
 import org.elasticsearch.common.SuppressForbidden;
 import org.elasticsearch.common.xcontent.NamedXContentRegistry;
@@ -40,6 +43,7 @@ public final class HdfsPlugin extends Plugin implements RepositoryPlugin {
     static {
         SpecialPermission.check();
         AccessController.doPrivileged((PrivilegedAction<Void>) HdfsPlugin::evilHadoopInit);
+        AccessController.doPrivileged((PrivilegedAction<Void>) HdfsPlugin::eagerInit);
     }
 
     @SuppressForbidden(reason = "Needs a security hack for hadoop on windows, until HADOOP-XXXX is fixed")
@@ -79,6 +83,34 @@ public final class HdfsPlugin extends Plugin implements RepositoryPlugin {
         return null;
     }
 
+    private static Void eagerInit() {
+        /*
+         * Hadoop RPC wire serialization uses ProtocolBuffers. All proto classes for Hadoop
+         * come annotated with configurations that denote information about if they support
+         * certain security options like Kerberos, and how to send information with the
+         * message to support that authentication method. SecurityUtil creates a service loader
+         * in a static field during its clinit. This loader provides the implementations that
+         * pull the security information for each proto class. The service loader sources its
+         * services from the current thread's context class loader, which must contain the Hadoop
+         * jars. Since plugins don't execute with their class loaders installed as the thread's
+         * context class loader, we need to install the loader briefly, allow the util to be
+         * initialized, then restore the old loader since we don't actually own this thread.
+         */
+        ClassLoader oldCCL = Thread.currentThread().getContextClassLoader();
+        try {
+            Thread.currentThread().setContextClassLoader(HdfsRepository.class.getClassLoader());
+            KerberosInfo info = SecurityUtil.getKerberosInfo(ClientNamenodeProtocolPB.class, null);
+            // Make sure that the correct class loader was installed.
+            if (info == null) {
+                throw new RuntimeException("Could not initialize SecurityUtil: " +
+                    "Unable to find services for [org.apache.hadoop.security.SecurityInfo]");
+            }
+        } finally {
+            Thread.currentThread().setContextClassLoader(oldCCL);
+        }
+        return null;
+    }
+
     @Override
     public Map<String, Repository.Factory> getRepositories(Environment env, NamedXContentRegistry namedXContentRegistry) {
         return Collections.singletonMap("hdfs", (metadata) -> new HdfsRepository(metadata, env, namedXContentRegistry));
diff --git a/plugins/repository-hdfs/src/main/java/org/elasticsearch/repositories/hdfs/HdfsRepository.java b/plugins/repository-hdfs/src/main/java/org/elasticsearch/repositories/hdfs/HdfsRepository.java
index d784e8bf09..16ed9d06a5 100644
--- a/plugins/repository-hdfs/src/main/java/org/elasticsearch/repositories/hdfs/HdfsRepository.java
+++ b/plugins/repository-hdfs/src/main/java/org/elasticsearch/repositories/hdfs/HdfsRepository.java
@@ -19,29 +19,31 @@
 package org.elasticsearch.repositories.hdfs;
 
 import java.io.IOException;
-import java.lang.reflect.Constructor;
+import java.io.UncheckedIOException;
+import java.net.InetAddress;
 import java.net.URI;
+import java.net.UnknownHostException;
 import java.security.AccessController;
-import java.security.Principal;
 import java.security.PrivilegedAction;
-import java.util.Collections;
 import java.util.Locale;
 import java.util.Map;
 import java.util.Map.Entry;
 
-import javax.security.auth.Subject;
-
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.AbstractFileSystem;
 import org.apache.hadoop.fs.FileContext;
 import org.apache.hadoop.fs.UnsupportedFileSystemException;
-import org.elasticsearch.ElasticsearchGenerationException;
+import org.apache.hadoop.security.SecurityUtil;
+import org.apache.hadoop.security.UserGroupInformation;
+import org.apache.hadoop.security.UserGroupInformation.AuthenticationMethod;
+import org.apache.logging.log4j.Logger;
 import org.elasticsearch.SpecialPermission;
 import org.elasticsearch.cluster.metadata.RepositoryMetaData;
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.SuppressForbidden;
 import org.elasticsearch.common.blobstore.BlobPath;
 import org.elasticsearch.common.blobstore.BlobStore;
+import org.elasticsearch.common.logging.Loggers;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.unit.ByteSizeUnit;
 import org.elasticsearch.common.unit.ByteSizeValue;
@@ -51,9 +53,14 @@ import org.elasticsearch.repositories.blobstore.BlobStoreRepository;
 
 public final class HdfsRepository extends BlobStoreRepository {
 
-    private final BlobPath basePath = BlobPath.cleanPath();
+    private static final Logger LOGGER = Loggers.getLogger(HdfsRepository.class);
+
+    private static final String CONF_SECURITY_PRINCIPAL = "security.principal";
+
+    private final Environment environment;
     private final ByteSizeValue chunkSize;
     private final boolean compress;
+    private final BlobPath basePath = BlobPath.cleanPath();
 
     private HdfsBlobStore blobStore;
 
@@ -65,6 +72,7 @@ public final class HdfsRepository extends BlobStoreRepository {
                           NamedXContentRegistry namedXContentRegistry) throws IOException {
         super(metadata, environment.settings(), namedXContentRegistry);
 
+        this.environment = environment;
         this.chunkSize = metadata.settings().getAsBytesSize("chunk_size", null);
         this.compress = metadata.settings().getAsBoolean("compress", false);
     }
@@ -101,49 +109,116 @@ public final class HdfsRepository extends BlobStoreRepository {
             blobStore = new HdfsBlobStore(fileContext, pathSetting, bufferSize);
             logger.debug("Using file-system [{}] for URI [{}], path [{}]", fileContext.getDefaultFileSystem(), fileContext.getDefaultFileSystem().getUri(), pathSetting);
         } catch (IOException e) {
-            throw new ElasticsearchGenerationException(String.format(Locale.ROOT, "Cannot create HDFS repository for uri [%s]", uri), e);
+            throw new UncheckedIOException(String.format(Locale.ROOT, "Cannot create HDFS repository for uri [%s]", uri), e);
         }
         super.doStart();
     }
 
     // create hadoop filecontext
-    @SuppressForbidden(reason = "lesser of two evils (the other being a bunch of JNI/classloader nightmares)")
-    private static FileContext createContext(URI uri, Settings repositorySettings)  {
-        Configuration cfg = new Configuration(repositorySettings.getAsBoolean("load_defaults", true));
-        cfg.setClassLoader(HdfsRepository.class.getClassLoader());
-        cfg.reloadConfiguration();
+    private FileContext createContext(URI uri, Settings repositorySettings)  {
+        Configuration hadoopConfiguration = new Configuration(repositorySettings.getAsBoolean("load_defaults", true));
+        hadoopConfiguration.setClassLoader(HdfsRepository.class.getClassLoader());
+        hadoopConfiguration.reloadConfiguration();
 
         Map<String, String> map = repositorySettings.getByPrefix("conf.").getAsMap();
         for (Entry<String, String> entry : map.entrySet()) {
-            cfg.set(entry.getKey(), entry.getValue());
+            hadoopConfiguration.set(entry.getKey(), entry.getValue());
         }
 
-        // create a hadoop user. if we want some auth, it must be done different anyway, and tested.
-        Subject subject;
-        try {
-            Class<?> clazz = Class.forName("org.apache.hadoop.security.User");
-            Constructor<?> ctor = clazz.getConstructor(String.class);
-            ctor.setAccessible(true);
-            Principal principal = (Principal) ctor.newInstance(System.getProperty("user.name"));
-            subject = new Subject(false, Collections.singleton(principal), Collections.emptySet(), Collections.emptySet());
-        } catch (ReflectiveOperationException e) {
-            throw new RuntimeException(e);
-        }
+        // Create a hadoop user
+        UserGroupInformation ugi = login(hadoopConfiguration, repositorySettings);
 
-        // disable FS cache
-        cfg.setBoolean("fs.hdfs.impl.disable.cache", true);
+        // Disable FS cache
+        hadoopConfiguration.setBoolean("fs.hdfs.impl.disable.cache", true);
 
-        // create the filecontext with our user
-        return Subject.doAs(subject, (PrivilegedAction<FileContext>) () -> {
+        // Create the filecontext with our user information
+        // This will correctly configure the filecontext to have our UGI as it's internal user.
+        return ugi.doAs((PrivilegedAction<FileContext>) () -> {
             try {
-                AbstractFileSystem fs = AbstractFileSystem.get(uri, cfg);
-                return FileContext.getFileContext(fs, cfg);
+                AbstractFileSystem fs = AbstractFileSystem.get(uri, hadoopConfiguration);
+                return FileContext.getFileContext(fs, hadoopConfiguration);
             } catch (UnsupportedFileSystemException e) {
-                throw new RuntimeException(e);
+                throw new UncheckedIOException(e);
             }
         });
     }
 
+    private UserGroupInformation login(Configuration hadoopConfiguration, Settings repositorySettings) {
+        // Validate the authentication method:
+        AuthenticationMethod authMethod = SecurityUtil.getAuthenticationMethod(hadoopConfiguration);
+        if (authMethod.equals(AuthenticationMethod.SIMPLE) == false
+            && authMethod.equals(AuthenticationMethod.KERBEROS) == false) {
+            throw new RuntimeException("Unsupported authorization mode ["+authMethod+"]");
+        }
+
+        // Check if the user added a principal to use, and that there is a keytab file provided
+        String kerberosPrincipal = repositorySettings.get(CONF_SECURITY_PRINCIPAL);
+
+        // Check to see if the authentication method is compatible
+        if (kerberosPrincipal != null && authMethod.equals(AuthenticationMethod.SIMPLE)) {
+            LOGGER.warn("Hadoop authentication method is set to [SIMPLE], but a Kerberos principal is " +
+                "specified. Continuing with [KERBEROS] authentication.");
+            SecurityUtil.setAuthenticationMethod(AuthenticationMethod.KERBEROS, hadoopConfiguration);
+        } else if (kerberosPrincipal == null && authMethod.equals(AuthenticationMethod.KERBEROS)) {
+            throw new RuntimeException("HDFS Repository does not support [KERBEROS] authentication without " +
+                "a valid Kerberos principal and keytab. Please specify a principal in the repository settings with [" +
+                CONF_SECURITY_PRINCIPAL + "].");
+        }
+
+        // Now we can initialize the UGI with the configuration.
+        UserGroupInformation.setConfiguration(hadoopConfiguration);
+
+        // Debugging
+        LOGGER.debug("Hadoop security enabled: [{}]", UserGroupInformation.isSecurityEnabled());
+        LOGGER.debug("Using Hadoop authentication method: [{}]", SecurityUtil.getAuthenticationMethod(hadoopConfiguration));
+
+        // UserGroupInformation (UGI) instance is just a Hadoop specific wrapper around a Java Subject
+        try {
+            if (UserGroupInformation.isSecurityEnabled()) {
+                String principal = preparePrincipal(kerberosPrincipal);
+                String keytab = HdfsSecurityContext.locateKeytabFile(environment).toString();
+                LOGGER.debug("Using kerberos principal [{}] and keytab located at [{}]", principal, keytab);
+                return UserGroupInformation.loginUserFromKeytabAndReturnUGI(principal, keytab);
+            }
+            return UserGroupInformation.getCurrentUser();
+        } catch (IOException e) {
+            throw new UncheckedIOException("Could not retrieve the current user information", e);
+        }
+    }
+
+    // Convert principals of the format 'service/_HOST@REALM' by subbing in the local address for '_HOST'.
+    private static String preparePrincipal(String originalPrincipal) {
+        String finalPrincipal = originalPrincipal;
+        // Don't worry about host name resolution if they don't have the _HOST pattern in the name.
+        if (originalPrincipal.contains("_HOST")) {
+            try {
+                finalPrincipal = SecurityUtil.getServerPrincipal(originalPrincipal, getHostName());
+            } catch (IOException e) {
+                throw new UncheckedIOException(e);
+            }
+
+            if (originalPrincipal.equals(finalPrincipal) == false) {
+                LOGGER.debug("Found service principal. Converted original principal name [{}] to server principal [{}]",
+                    originalPrincipal, finalPrincipal);
+            }
+        }
+        return finalPrincipal;
+    }
+
+    @SuppressForbidden(reason = "InetAddress.getLocalHost(); Needed for filling in hostname for a kerberos principal name pattern.")
+    private static String getHostName() {
+        try {
+            /*
+             * This should not block since it should already be resolved via Log4J and Netty. The
+             * host information is cached by the JVM and the TTL for the cache entry is infinite
+             * when the SecurityManager is activated.
+             */
+            return InetAddress.getLocalHost().getCanonicalHostName();
+        } catch (UnknownHostException e) {
+            throw new RuntimeException("Could not locate host information", e);
+        }
+    }
+
     @Override
     protected BlobStore blobStore() {
         return blobStore;
diff --git a/plugins/repository-hdfs/src/main/java/org/elasticsearch/repositories/hdfs/HdfsSecurityContext.java b/plugins/repository-hdfs/src/main/java/org/elasticsearch/repositories/hdfs/HdfsSecurityContext.java
new file mode 100644
index 0000000000..3cd1a5a40f
--- /dev/null
+++ b/plugins/repository-hdfs/src/main/java/org/elasticsearch/repositories/hdfs/HdfsSecurityContext.java
@@ -0,0 +1,145 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.elasticsearch.repositories.hdfs;
+
+import java.io.IOException;
+import java.io.UncheckedIOException;
+import java.lang.reflect.ReflectPermission;
+import java.net.SocketPermission;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.security.Permission;
+import java.util.Arrays;
+import java.util.Locale;
+import java.util.function.Supplier;
+import javax.security.auth.AuthPermission;
+import javax.security.auth.PrivateCredentialPermission;
+import javax.security.auth.kerberos.ServicePermission;
+
+import org.apache.hadoop.security.UserGroupInformation;
+import org.apache.logging.log4j.Logger;
+import org.elasticsearch.common.logging.Loggers;
+import org.elasticsearch.env.Environment;
+
+/**
+ * Oversees all the security specific logic for the HDFS Repository plugin.
+ *
+ * Keeps track of the current user for a given repository, as well as which
+ * permissions to grant the blob store restricted execution methods.
+ */
+class HdfsSecurityContext {
+
+    private static final Logger LOGGER = Loggers.getLogger(HdfsSecurityContext.class);
+
+    private static final Permission[] SIMPLE_AUTH_PERMISSIONS;
+    private static final Permission[] KERBEROS_AUTH_PERMISSIONS;
+    static {
+        // We can do FS ops with only a few elevated permissions:
+        SIMPLE_AUTH_PERMISSIONS = new Permission[]{
+            new SocketPermission("*", "connect"),
+            // 1) hadoop dynamic proxy is messy with access rules
+            new ReflectPermission("suppressAccessChecks"),
+            // 2) allow hadoop to add credentials to our Subject
+            new AuthPermission("modifyPrivateCredentials")
+        };
+
+        // If Security is enabled, we need all the following elevated permissions:
+        KERBEROS_AUTH_PERMISSIONS = new Permission[] {
+            new SocketPermission("*", "connect"),
+            // 1) hadoop dynamic proxy is messy with access rules
+            new ReflectPermission("suppressAccessChecks"),
+            // 2) allow hadoop to add credentials to our Subject
+            new AuthPermission("modifyPrivateCredentials"),
+            // 3) allow hadoop to act as the logged in Subject
+            new AuthPermission("doAs"),
+            // 4) Listen and resolve permissions for kerberos server principals
+            new SocketPermission("localhost:0", "listen,resolve"),
+            // We add the following since hadoop requires the client to re-login when the kerberos ticket expires:
+            // 5) All the permissions needed for UGI to do its weird JAAS hack
+            new RuntimePermission("getClassLoader"),
+            new RuntimePermission("setContextClassLoader"),
+            // 6) Additional permissions for the login modules
+            new AuthPermission("modifyPrincipals"),
+            new PrivateCredentialPermission("org.apache.hadoop.security.Credentials * \"*\"", "read"),
+            new PrivateCredentialPermission("javax.security.auth.kerberos.KerberosTicket * \"*\"", "read"),
+            new PrivateCredentialPermission("javax.security.auth.kerberos.KeyTab * \"*\"", "read")
+            // Included later:
+            // 7) allow code to initiate kerberos connections as the logged in user
+            // Still far and away fewer permissions than the original full plugin policy
+        };
+    }
+
+    /**
+     * Locates the keytab file in the environment and verifies that it exists.
+     * Expects keytab file to exist at {@code $CONFIG_DIR$/repository-hdfs/krb5.keytab}
+     */
+    static Path locateKeytabFile(Environment environment) {
+        Path keytabPath = environment.configFile().resolve("repository-hdfs").resolve("krb5.keytab");
+        try {
+            if (Files.exists(keytabPath) == false) {
+                throw new RuntimeException("Could not locate keytab at [" + keytabPath + "].");
+            }
+        } catch (SecurityException se) {
+            throw new RuntimeException("Could not locate keytab at [" + keytabPath + "]", se);
+        }
+        return keytabPath;
+    }
+
+    private final UserGroupInformation ugi;
+    private final Permission[] restrictedExecutionPermissions;
+
+    HdfsSecurityContext(UserGroupInformation ugi) {
+        this.ugi = ugi;
+        this.restrictedExecutionPermissions = renderPermissions(ugi);
+    }
+
+    private Permission[] renderPermissions(UserGroupInformation ugi) {
+        Permission[] permissions;
+        if (ugi.isFromKeytab()) {
+            // KERBEROS
+            // Leave room to append one extra permission based on the logged in user's info.
+            int permlen = KERBEROS_AUTH_PERMISSIONS.length + 1;
+            permissions = new Permission[permlen];
+
+            System.arraycopy(KERBEROS_AUTH_PERMISSIONS, 0, permissions, 0, KERBEROS_AUTH_PERMISSIONS.length);
+
+            // Append a kerberos.ServicePermission to only allow initiating kerberos connections
+            // as the logged in user.
+            permissions[permissions.length - 1] = new ServicePermission(ugi.getUserName(), "initiate");
+        } else {
+            // SIMPLE
+            permissions = Arrays.copyOf(SIMPLE_AUTH_PERMISSIONS, SIMPLE_AUTH_PERMISSIONS.length);
+        }
+        return permissions;
+    }
+
+    Permission[] getRestrictedExecutionPermissions() {
+        return restrictedExecutionPermissions;
+    }
+
+    void ensureLogin() {
+        if (ugi.isFromKeytab()) {
+            try {
+                ugi.checkTGTAndReloginFromKeytab();
+            } catch (IOException ioe) {
+                throw new UncheckedIOException("Could not re-authenticate", ioe);
+            }
+        }
+    }
+}
diff --git a/plugins/repository-hdfs/src/main/plugin-metadata/plugin-security.policy b/plugins/repository-hdfs/src/main/plugin-metadata/plugin-security.policy
index b800f3eee4..f6476f290b 100644
--- a/plugins/repository-hdfs/src/main/plugin-metadata/plugin-security.policy
+++ b/plugins/repository-hdfs/src/main/plugin-metadata/plugin-security.policy
@@ -25,17 +25,60 @@ grant {
   permission java.lang.RuntimePermission "accessDeclaredMembers";
   permission java.lang.reflect.ReflectPermission "suppressAccessChecks";
 
+  // Needed so that Hadoop can load the correct classes for SPI and JAAS
+  // org.apache.hadoop.security.SecurityUtil clinit
+  // org.apache.hadoop.security.UserGroupInformation.newLoginContext()
+  permission java.lang.RuntimePermission "setContextClassLoader";
+
   // org.apache.hadoop.util.StringUtils clinit
   permission java.util.PropertyPermission "*", "read,write";
 
   // org.apache.hadoop.util.ShutdownHookManager clinit
   permission java.lang.RuntimePermission "shutdownHooks";
   
-  // JAAS is used always, we use a fake subject, hurts nobody
+  // JAAS is used by Hadoop for authentication purposes
+  // The Hadoop Login JAAS module modifies a Subject's private credentials and principals
+  // The Hadoop RPC Layer must be able to read these credentials, and initiate Kerberos connections
+
+  // org.apache.hadoop.security.UserGroupInformation.getCurrentUser()
   permission javax.security.auth.AuthPermission "getSubject";
+
+  // org.apache.hadoop.security.UserGroupInformation.doAs()
   permission javax.security.auth.AuthPermission "doAs";
+
+  // org.apache.hadoop.security.UserGroupInformation.getCredentialsInternal()
+  permission javax.security.auth.PrivateCredentialPermission "org.apache.hadoop.security.Credentials * \"*\"", "read";
+
+  // Hadoop depends on the Kerberos login module for kerberos authentication
+  // com.sun.security.auth.module.Krb5LoginModule.login()
+  permission java.lang.RuntimePermission "accessClassInPackage.sun.security.krb5";
+
+  // com.sun.security.auth.module.Krb5LoginModule.commit()
   permission javax.security.auth.AuthPermission "modifyPrivateCredentials";
+  permission javax.security.auth.AuthPermission "modifyPrincipals";
+  permission javax.security.auth.PrivateCredentialPermission "javax.security.auth.kerberos.KeyTab * \"*\"", "read";
+  permission javax.security.auth.PrivateCredentialPermission "javax.security.auth.kerberos.KerberosTicket * \"*\"", "read";
+
+  // Hadoop depends on OS level user information for simple authentication
+  // Unix: UnixLoginModule: com.sun.security.auth.module.UnixSystem.UnixSystem init
+  permission java.lang.RuntimePermission "loadLibrary.jaas_unix";
+  // Windows: NTLoginModule: com.sun.security.auth.module.NTSystem.loadNative
+  permission java.lang.RuntimePermission "loadLibrary.jaas_nt";
+  permission javax.security.auth.AuthPermission "modifyPublicCredentials";
+
+  // org.apache.hadoop.security.SaslRpcServer.init()
+  permission java.security.SecurityPermission "putProviderProperty.SaslPlainServer";
+
+  // org.apache.hadoop.security.SaslPlainServer.SecurityProvider.SecurityProvider init
+  permission java.security.SecurityPermission "insertProvider.SaslPlainServer";
+
+  // org.apache.hadoop.security.SaslRpcClient.getServerPrincipal -> KerberosPrincipal init
+  permission javax.security.auth.kerberos.ServicePermission "*", "initiate";
 
   // hdfs client opens socket connections for to access repository
   permission java.net.SocketPermission "*", "connect";
+
+  // client binds to the address returned from the host name of any principal set up as a service principal
+  // org.apache.hadoop.ipc.Client.Connection.setupConnection
+  permission java.net.SocketPermission "localhost:0", "listen,resolve";
 };