sshd: try all configured signature algorithms for a key
For RSA keys, there may be several configured signature algorithms:
rsa-sha2-512, rsa-sha2-256, and ssh-rsa. Upstream sshd has bug
SSHD-1105 [1] and always and unconditionally uses only the first
configured algorithm. With the default order, this means that it cannot
connect to a server that knows only ssh-rsa, like for instance Apache
MINA sshd servers older than 2.6.0.
This affects for instance bitbucket.org or also AWS Code Commit.
Re-introduce our own pubkey authenticator that fixes this.
Note that a server may impose a penalty (back-off delay) for subsequent
authentication attempts with signature algorithms unknown to the server.
In such cases, users can re-order the signature algorithm list via the
PubkeyAcceptedAlgorithms (formerly PubkeyAcceptedKeyTypes) ssh config.
[1] https://issues.apache.org/jira/browse/SSHD-1105
Bug: 572056
Change-Id: I7fb9c759ab6532e5f3b6524e9084085ddb2f30d6
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>
diff --git a/org.eclipse.jgit.ssh.apache.test/tst/org/eclipse/jgit/transport/sshd/ApacheSshTest.java b/org.eclipse.jgit.ssh.apache.test/tst/org/eclipse/jgit/transport/sshd/ApacheSshTest.java
index 09d048b..c56d230 100644
--- a/org.eclipse.jgit.ssh.apache.test/tst/org/eclipse/jgit/transport/sshd/ApacheSshTest.java
+++ b/org.eclipse.jgit.ssh.apache.test/tst/org/eclipse/jgit/transport/sshd/ApacheSshTest.java
@@ -664,4 +664,42 @@
session.disconnect();
}
}
+
+ /**
+ * Tests that one can log in to an old server that knows only the ssh-rsa
+ * signature algorithm. The client has by default the list of signature
+ * algorithms for RSA as "rsa-sha2-512,rsa-sha2-256,ssh-rsa". It should try
+ * all three with the single key configured, and finally succeed.
+ * <p>
+ * The re-ordering mechanism (see
+ * {@link #testConnectAuthSshRsaPubkeyAcceptedAlgorithms()}) is still
+ * important; servers may impose a penalty (back-off delay) for subsequent
+ * attempts with signature algorithms unknown to the server. So a user
+ * connecting to such a server and noticing delays may still want to put
+ * ssh-rsa first in the list for that host.
+ * </p>
+ *
+ * @see <a href="https://bugs.eclipse.org/bugs/show_bug.cgi?id=572056">bug
+ * 572056</a>
+ * @throws Exception
+ * on failure
+ */
+ @Test
+ public void testConnectAuthSshRsa() throws Exception {
+ try (SshServer oldServer = createServer(TEST_USER, publicKey1)) {
+ oldServer.setSignatureFactoriesNames("ssh-rsa");
+ oldServer.start();
+ registerServer(oldServer);
+ installConfig("Host server", //
+ "HostName localhost", //
+ "Port " + oldServer.getPort(), //
+ "User " + TEST_USER, //
+ "IdentityFile " + privateKey1.getAbsolutePath());
+ RemoteSession session = getSessionFactory().getSession(
+ new URIish("ssh://server/doesntmatter"), null, FS.DETECTED,
+ 10000);
+ assertNotNull(session);
+ session.disconnect();
+ }
+ }
}
diff --git a/org.eclipse.jgit.ssh.apache/src/org/eclipse/jgit/internal/transport/sshd/JGitPublicKeyAuthFactory.java b/org.eclipse.jgit.ssh.apache/src/org/eclipse/jgit/internal/transport/sshd/JGitPublicKeyAuthFactory.java
new file mode 100644
index 0000000..0e3e24d
--- /dev/null
+++ b/org.eclipse.jgit.ssh.apache/src/org/eclipse/jgit/internal/transport/sshd/JGitPublicKeyAuthFactory.java
@@ -0,0 +1,35 @@
+/*
+ * Copyright (C) 2018, 2021 Thomas Wolf <thomas.wolf@paranor.ch> and others
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+package org.eclipse.jgit.internal.transport.sshd;
+
+import java.io.IOException;
+
+import org.apache.sshd.client.auth.pubkey.UserAuthPublicKey;
+import org.apache.sshd.client.auth.pubkey.UserAuthPublicKeyFactory;
+import org.apache.sshd.client.session.ClientSession;
+
+/**
+ * A customized authentication factory for public key user authentication.
+ */
+public class JGitPublicKeyAuthFactory extends UserAuthPublicKeyFactory {
+
+ /** The singleton {@link JGitPublicKeyAuthFactory}. */
+ public static final JGitPublicKeyAuthFactory FACTORY = new JGitPublicKeyAuthFactory();
+
+ private JGitPublicKeyAuthFactory() {
+ super();
+ }
+
+ @Override
+ public UserAuthPublicKey createUserAuth(ClientSession session)
+ throws IOException {
+ return new JGitPublicKeyAuthentication(getSignatureFactories());
+ }
+}
diff --git a/org.eclipse.jgit.ssh.apache/src/org/eclipse/jgit/internal/transport/sshd/JGitPublicKeyAuthentication.java b/org.eclipse.jgit.ssh.apache/src/org/eclipse/jgit/internal/transport/sshd/JGitPublicKeyAuthentication.java
new file mode 100644
index 0000000..297b456
--- /dev/null
+++ b/org.eclipse.jgit.ssh.apache/src/org/eclipse/jgit/internal/transport/sshd/JGitPublicKeyAuthentication.java
@@ -0,0 +1,133 @@
+/*
+ * Copyright (C) 2018, 2021 Thomas Wolf <thomas.wolf@paranor.ch> and others
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+package org.eclipse.jgit.internal.transport.sshd;
+
+import java.io.IOException;
+import java.security.PublicKey;
+import java.util.HashSet;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Set;
+
+import org.apache.sshd.client.auth.pubkey.UserAuthPublicKey;
+import org.apache.sshd.client.session.ClientSession;
+import org.apache.sshd.common.NamedFactory;
+import org.apache.sshd.common.RuntimeSshException;
+import org.apache.sshd.common.SshConstants;
+import org.apache.sshd.common.config.keys.KeyUtils;
+import org.apache.sshd.common.signature.Signature;
+import org.apache.sshd.common.signature.SignatureFactoriesHolder;
+import org.apache.sshd.common.util.buffer.Buffer;
+
+/**
+ * Custom {@link UserAuthPublicKey} implementation fixing SSHD-1105: if there
+ * are several signature algorithms applicable for a public key type, we must
+ * try them all, in the correct order.
+ *
+ * @see <a href="https://issues.apache.org/jira/browse/SSHD-1105">SSHD-1105</a>
+ * @see <a href="https://bugs.eclipse.org/bugs/show_bug.cgi?id=572056">Bug
+ * 572056</a>
+ */
+public class JGitPublicKeyAuthentication extends UserAuthPublicKey {
+
+ private final List<String> algorithms = new LinkedList<>();
+
+ JGitPublicKeyAuthentication(List<NamedFactory<Signature>> factories) {
+ super(factories);
+ }
+
+ @Override
+ protected boolean sendAuthDataRequest(ClientSession session, String service)
+ throws Exception {
+ if (current == null) {
+ algorithms.clear();
+ }
+ String currentAlgorithm = null;
+ if (current != null && !algorithms.isEmpty()) {
+ currentAlgorithm = algorithms.remove(0);
+ }
+ if (currentAlgorithm == null) {
+ try {
+ if (keys == null || !keys.hasNext()) {
+ if (log.isDebugEnabled()) {
+ log.debug(
+ "sendAuthDataRequest({})[{}] no more keys to send", //$NON-NLS-1$
+ session, service);
+ }
+ return false;
+ }
+ current = keys.next();
+ algorithms.clear();
+ } catch (Error e) { // Copied from superclass
+ warn("sendAuthDataRequest({})[{}] failed ({}) to get next key: {}", //$NON-NLS-1$
+ session, service, e.getClass().getSimpleName(),
+ e.getMessage(), e);
+ throw new RuntimeSshException(e);
+ }
+ }
+ PublicKey key;
+ try {
+ key = current.getPublicKey();
+ } catch (Error e) { // Copied from superclass
+ warn("sendAuthDataRequest({})[{}] failed ({}) to retrieve public key: {}", //$NON-NLS-1$
+ session, service, e.getClass().getSimpleName(),
+ e.getMessage(), e);
+ throw new RuntimeSshException(e);
+ }
+ if (currentAlgorithm == null) {
+ String keyType = KeyUtils.getKeyType(key);
+ Set<String> aliases = new HashSet<>(
+ KeyUtils.getAllEquivalentKeyTypes(keyType));
+ aliases.add(keyType);
+ List<NamedFactory<Signature>> existingFactories;
+ if (current instanceof SignatureFactoriesHolder) {
+ existingFactories = ((SignatureFactoriesHolder) current)
+ .getSignatureFactories();
+ } else {
+ existingFactories = getSignatureFactories();
+ }
+ if (existingFactories != null) {
+ // Select the factories by name and in order
+ existingFactories.forEach(f -> {
+ if (aliases.contains(f.getName())) {
+ algorithms.add(f.getName());
+ }
+ });
+ }
+ currentAlgorithm = algorithms.isEmpty() ? keyType
+ : algorithms.remove(0);
+ }
+ String name = getName();
+ if (log.isDebugEnabled()) {
+ log.debug(
+ "sendAuthDataRequest({})[{}] send SSH_MSG_USERAUTH_REQUEST request {} type={} - fingerprint={}", //$NON-NLS-1$
+ session, service, name, currentAlgorithm,
+ KeyUtils.getFingerPrint(key));
+ }
+
+ Buffer buffer = session
+ .createBuffer(SshConstants.SSH_MSG_USERAUTH_REQUEST);
+ buffer.putString(session.getUsername());
+ buffer.putString(service);
+ buffer.putString(name);
+ buffer.putBoolean(false);
+ buffer.putString(currentAlgorithm);
+ buffer.putPublicKey(key);
+ session.writePacket(buffer);
+ return true;
+ }
+
+ @Override
+ protected void releaseKeys() throws IOException {
+ algorithms.clear();
+ current = null;
+ super.releaseKeys();
+ }
+}
diff --git a/org.eclipse.jgit.ssh.apache/src/org/eclipse/jgit/transport/sshd/SshdSessionFactory.java b/org.eclipse.jgit.ssh.apache/src/org/eclipse/jgit/transport/sshd/SshdSessionFactory.java
index 357994d..cad959c 100644
--- a/org.eclipse.jgit.ssh.apache/src/org/eclipse/jgit/transport/sshd/SshdSessionFactory.java
+++ b/org.eclipse.jgit.ssh.apache/src/org/eclipse/jgit/transport/sshd/SshdSessionFactory.java
@@ -32,10 +32,9 @@
import org.apache.sshd.client.SshClient;
import org.apache.sshd.client.auth.UserAuthFactory;
import org.apache.sshd.client.auth.keyboard.UserAuthKeyboardInteractiveFactory;
-import org.apache.sshd.client.auth.pubkey.UserAuthPublicKeyFactory;
import org.apache.sshd.client.config.hosts.HostConfigEntryResolver;
-import org.apache.sshd.common.SshException;
import org.apache.sshd.common.NamedFactory;
+import org.apache.sshd.common.SshException;
import org.apache.sshd.common.compression.BuiltinCompressions;
import org.apache.sshd.common.config.keys.FilePasswordProvider;
import org.apache.sshd.common.config.keys.loader.openssh.kdf.BCryptKdfOptions;
@@ -49,6 +48,7 @@
import org.eclipse.jgit.internal.transport.sshd.CachingKeyPairProvider;
import org.eclipse.jgit.internal.transport.sshd.GssApiWithMicAuthFactory;
import org.eclipse.jgit.internal.transport.sshd.JGitPasswordAuthFactory;
+import org.eclipse.jgit.internal.transport.sshd.JGitPublicKeyAuthFactory;
import org.eclipse.jgit.internal.transport.sshd.JGitServerKeyVerifier;
import org.eclipse.jgit.internal.transport.sshd.JGitSshClient;
import org.eclipse.jgit.internal.transport.sshd.JGitSshConfig;
@@ -577,7 +577,7 @@
// Password auth doesn't have this problem.
return Collections.unmodifiableList(
Arrays.asList(GssApiWithMicAuthFactory.INSTANCE,
- UserAuthPublicKeyFactory.INSTANCE,
+ JGitPublicKeyAuthFactory.FACTORY,
JGitPasswordAuthFactory.INSTANCE,
UserAuthKeyboardInteractiveFactory.INSTANCE));
}
