Merge "Enable Kerberos authentication for SSH interaction"

Documentation/config-gerrit.txt

@@ -2403,6 +2403,34 @@ Supported MACs: hmac-md5, hmac-md5-96, hmac-sha1, hmac-sha1-96.
 +
 By default, all supported MACs are available.
 
+[[sshd.kerberosKeytab]]sshd.kerberosKeytab::
++
+Enable kerberos authentication for SSH connections.  To permit
+kerberos authentication, the server must have a host principal
+(see `sshd.kerberosPrincipal`) which is acquired from a keytab.
+This must be provisioned by the kerberos administrators, and is
+typically installed into `/etc/krb5.keytab` on host machines.
++
+The keytab must contain at least one `host/` principal, typically
+using the host's canonical name. If it does not use the
+canonical name, the `sshd.kerberosPrincipal` should be configured
+with the correct name.
++
+By default, not set and so kerberos authentication is not enabled.
+
+[[sshd.kerberosPrincipal]]sshd.kerberosPrincipal::
++
+If kerberos authentication is enabled with `sshd.kerberosKeytab`,
+instead use the given principal name instead of the default.
+If the principal does not begin with `host/` a warning message is
+printed and may prevent successful authentication.
++
+This may be useful if the host is behind an IP load balancer or
+other SSH forwarding systems, since the principal name is constructed
+by the client and must match for kerberos authentication to work.
++
+By default, `host/canonical.host.name`
+
 [[suggest]] Section suggest
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
 

gerrit-sshd/src/main/java/com/google/gerrit/sshd/GerritGSSAuthenticator.java

@@ -0,0 +1,68 @@
+// Copyright (C) 2013 Goldman Sachs
+//
+// Licensed 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 com.google.gerrit.sshd;
+
+import com.google.gerrit.reviewdb.client.Account;
+import com.google.gerrit.server.IdentifiedUser;
+import com.google.gerrit.server.IdentifiedUser.GenericFactory;
+import com.google.gerrit.server.account.AccountCache;
+import com.google.gerrit.server.account.AccountState;
+import com.google.inject.Inject;
+import com.google.inject.Singleton;
+
+import org.apache.sshd.server.auth.gss.GSSAuthenticator;
+import org.apache.sshd.server.session.ServerSession;
+
+/**
+ * Authenticates users with kerberos (gssapi-with-mic).
+ */
+@Singleton
+class GerritGSSAuthenticator extends GSSAuthenticator {
+  private final AccountCache accounts;
+  private final SshScope sshScope;
+  private final SshLog sshLog;
+  private final GenericFactory userFactory;
+
+  @Inject
+  GerritGSSAuthenticator(final AccountCache accounts, final SshScope sshScope,
+      final SshLog sshLog, final IdentifiedUser.GenericFactory userFactory) {
+    this.accounts = accounts;
+    this.sshScope = sshScope;
+    this.sshLog = sshLog;
+    this.userFactory = userFactory;
+  }
+
+  @Override
+  public boolean validateIdentity(final ServerSession session,
+      final String identity) {
+    final SshSession sd = session.getAttribute(SshSession.KEY);
+    int at = identity.indexOf('@');
+    String username;
+    if (at == -1) {
+      username = identity;
+    } else {
+      username = identity.substring(0, at);
+    }
+    AccountState state = accounts.getByUsername(username);
+    Account account = state == null ? null : state.getAccount();
+    boolean active = account != null && account.isActive();
+    if (active) {
+      return SshUtil.success(username, session, sshScope, sshLog, sd,
+          SshUtil.createUser(sd, userFactory, account.getId()));
+    } else {
+      return false;
+    }
+  }
+}

gerrit-sshd/src/main/java/com/google/gerrit/sshd/SshDaemon.java

@@ -19,6 +19,7 @@ import static com.google.gerrit.server.ssh.SshAddressesModule.IANA_SSH_PORT;
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
 import static java.util.concurrent.TimeUnit.SECONDS;
 
+import com.google.common.collect.Lists;
 import com.google.gerrit.common.Version;
 import com.google.gerrit.extensions.events.LifecycleListener;
 import com.google.gerrit.server.config.ConfigUtil;
@@ -75,6 +76,8 @@ import org.apache.sshd.server.PublickeyAuthenticator;
 import org.apache.sshd.server.SshFile;
 import org.apache.sshd.server.UserAuth;
 import org.apache.sshd.server.auth.UserAuthPublicKey;
+import org.apache.sshd.server.auth.gss.GSSAuthenticator;
+import org.apache.sshd.server.auth.gss.UserAuthGSS;
 import org.apache.sshd.server.channel.ChannelDirectTcpip;
 import org.apache.sshd.server.channel.ChannelSession;
 import org.apache.sshd.server.kex.DHG1;
@@ -85,9 +88,12 @@ import org.eclipse.jgit.lib.Config;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import java.io.File;
 import java.io.IOException;
+import java.net.InetAddress;
 import java.net.InetSocketAddress;
 import java.net.SocketAddress;
+import java.net.UnknownHostException;
 import java.security.InvalidKeyException;
 import java.security.KeyPair;
 import java.security.PublicKey;
@@ -129,6 +135,7 @@ public class SshDaemon extends SshServer implements SshInfo, LifecycleListener {
   @Inject
   SshDaemon(final CommandFactory commandFactory, final NoShell noShell,
       final PublickeyAuthenticator userAuth,
+      final GerritGSSAuthenticator kerberosAuth,
       final KeyPairProvider hostKeyProvider, final IdGenerator idGenerator,
       @GerritServerConfig final Config cfg, final SshLog sshLog,
       @SshListenAddresses final List<SocketAddress> listen,
@@ -159,6 +166,11 @@ public class SshDaemon extends SshServer implements SshInfo, LifecycleListener {
           String.valueOf(maxConnectionsPerUser));
     }
 
+    final String kerberosKeytab = cfg.getString(
+        "sshd", null, "kerberosKeytab");
+    final String kerberosPrincipal = cfg.getString(
+        "sshd", null, "kerberosPrincipal");
+
     if (SecurityUtils.isBouncyCastleRegistered()) {
       initProviderBouncyCastle();
     } else {
@@ -172,7 +184,7 @@ public class SshDaemon extends SshServer implements SshInfo, LifecycleListener {
     initFileSystemFactory();
     initSubsystems();
     initCompression();
-    initUserAuth(userAuth);
+    initUserAuth(userAuth, kerberosAuth, kerberosKeytab, kerberosPrincipal);
     setKeyPairProvider(hostKeyProvider);
     setCommandFactory(commandFactory);
     setShellFactory(noShell);
@@ -457,10 +469,36 @@ public class SshDaemon extends SshServer implements SshInfo, LifecycleListener {
     setSubsystemFactories(Collections.<NamedFactory<Command>> emptyList());
   }
 
-  @SuppressWarnings("unchecked")
-  private void initUserAuth(final PublickeyAuthenticator pubkey) {
-    setUserAuthFactories(Arrays
-        .<NamedFactory<UserAuth>> asList(new UserAuthPublicKey.Factory()));
+  private void initUserAuth(final PublickeyAuthenticator pubkey,
+      final GSSAuthenticator kerberosAuthenticator,
+      String kerberosKeytab, String kerberosPrincipal) {
+    List<NamedFactory<UserAuth>> authFactories = Lists.newArrayList();
+    if (kerberosKeytab != null) {
+      authFactories.add(new UserAuthGSS.Factory());
+      log.info("Enabling kerberos with keytab " + kerberosKeytab);
+      if (!new File(kerberosKeytab).canRead()) {
+        log.error("Keytab " + kerberosKeytab +
+            " does not exist or is not readable; further errors are possible");
+      }
+      kerberosAuthenticator.setKeytabFile(kerberosKeytab);
+      if (kerberosPrincipal == null) {
+        try {
+          kerberosPrincipal = "host/" +
+              InetAddress.getLocalHost().getCanonicalHostName();
+        } catch(UnknownHostException e) {
+          kerberosPrincipal = "host/localhost";
+        }
+      }
+      log.info("Using kerberos principal " + kerberosPrincipal);
+      if (!kerberosPrincipal.startsWith("host/")) {
+        log.warn("Host principal does not start with host/ " +
+            "which most SSH clients will supply automatically");
+      }
+      kerberosAuthenticator.setServicePrincipalName(kerberosPrincipal);
+      setGSSAuthenticator(kerberosAuthenticator);
+    }
+    authFactories.add(new UserAuthPublicKey.Factory());
+    setUserAuthFactories(authFactories);
     setPublickeyAuthenticator(pubkey);
   }
 

gerrit-sshd/src/main/java/com/google/gerrit/sshd/SshModule.java

@@ -42,6 +42,7 @@ import com.google.inject.servlet.RequestScoped;
 import org.apache.sshd.common.KeyPairProvider;
 import org.apache.sshd.server.CommandFactory;
 import org.apache.sshd.server.PublickeyAuthenticator;
+import org.apache.sshd.server.auth.gss.GSSAuthenticator;
 import org.eclipse.jgit.lib.Config;
 
 import java.net.SocketAddress;
@@ -84,6 +85,7 @@ public class SshModule extends FactoryModule {
         .toProvider(StreamCommandExecutorProvider.class).in(SINGLETON);
     bind(QueueProvider.class).to(CommandExecutorQueueProvider.class).in(SINGLETON);
 
+    bind(GSSAuthenticator.class).to(GerritGSSAuthenticator.class);
     bind(PublickeyAuthenticator.class).to(DatabasePubKeyAuth.class);
     bind(KeyPairProvider.class).toProvider(HostKeyProvider.class).in(SINGLETON);