OpenSshServerKeyDatabase.java
/*
* 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 static java.nio.charset.StandardCharsets.UTF_8;
import static java.text.MessageFormat.format;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.net.InetSocketAddress;
import java.net.SocketAddress;
import java.nio.file.Files;
import java.nio.file.InvalidPathException;
import java.nio.file.NoSuchFileException;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.security.GeneralSecurityException;
import java.security.PublicKey;
import java.security.SecureRandom;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Random;
import java.util.TreeSet;
import java.util.concurrent.ConcurrentHashMap;
import java.util.function.Supplier;
import org.apache.sshd.client.config.hosts.HostPatternsHolder;
import org.apache.sshd.client.config.hosts.KnownHostDigest;
import org.apache.sshd.client.config.hosts.KnownHostEntry;
import org.apache.sshd.client.config.hosts.KnownHostHashValue;
import org.apache.sshd.client.keyverifier.KnownHostsServerKeyVerifier.HostEntryPair;
import org.apache.sshd.client.session.ClientSession;
import org.apache.sshd.common.NamedFactory;
import org.apache.sshd.common.config.keys.AuthorizedKeyEntry;
import org.apache.sshd.common.config.keys.KeyUtils;
import org.apache.sshd.common.config.keys.PublicKeyEntry;
import org.apache.sshd.common.config.keys.PublicKeyEntryResolver;
import org.apache.sshd.common.digest.BuiltinDigests;
import org.apache.sshd.common.mac.Mac;
import org.apache.sshd.common.util.io.ModifiableFileWatcher;
import org.apache.sshd.common.util.net.SshdSocketAddress;
import org.eclipse.jgit.annotations.NonNull;
import org.eclipse.jgit.internal.storage.file.LockFile;
import org.eclipse.jgit.transport.CredentialItem;
import org.eclipse.jgit.transport.CredentialsProvider;
import org.eclipse.jgit.transport.URIish;
import org.eclipse.jgit.transport.sshd.ServerKeyDatabase;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* A sever host key verifier that honors the {@code StrictHostKeyChecking} and
* {@code UserKnownHostsFile} values from the ssh configuration.
* <p>
* The verifier can be given default known_hosts files in the constructor, which
* will be used if the ssh config does not specify a {@code UserKnownHostsFile}.
* If the ssh config <em>does</em> set {@code UserKnownHostsFile}, the verifier
* uses the given files in the order given. Non-existing or unreadable files are
* ignored.
* <p>
* {@code StrictHostKeyChecking} accepts the following values:
* </p>
* <dl>
* <dt>ask</dt>
* <dd>Ask the user whether new or changed keys shall be accepted and be added
* to the known_hosts file.</dd>
* <dt>yes/true</dt>
* <dd>Accept only keys listed in the known_hosts file.</dd>
* <dt>no/false</dt>
* <dd>Silently accept all new or changed keys, add new keys to the known_hosts
* file.</dd>
* <dt>accept-new</dt>
* <dd>Silently accept keys for new hosts and add them to the known_hosts
* file.</dd>
* </dl>
* <p>
* If {@code StrictHostKeyChecking} is not set, or set to any other value, the
* default value <b>ask</b> is active.
* </p>
* <p>
* This implementation relies on the {@link ClientSession} being a
* {@link JGitClientSession}. By default Apache MINA sshd does not forward the
* config file host entry to the session, so it would be unknown here which
* entry it was and what setting of {@code StrictHostKeyChecking} should be
* used. If used with some other session type, the implementation assumes
* "<b>ask</b>".
* <p>
* <p>
* Asking the user is done via a {@link CredentialsProvider} obtained from the
* session. If none is set, the implementation falls back to strict host key
* checking ("<b>yes</b>").
* </p>
* <p>
* Note that adding a key to the known hosts file may create the file. You can
* specify in the constructor whether the user shall be asked about that, too.
* If the user declines updating the file, but the key was otherwise
* accepted (user confirmed for "<b>ask</b>", or "no" or "accept-new" are
* active), the key is accepted for this session only.
* </p>
* <p>
* If several known hosts files are specified, a new key is always added to the
* first file (even if it doesn't exist yet; see the note about file creation
* above).
* </p>
*
* @see <a href="http://man.openbsd.org/OpenBSD-current/man5/ssh_config.5">man
* ssh-config</a>
*/
public class OpenSshServerKeyDatabase
implements ServerKeyDatabase {
// TODO: GlobalKnownHostsFile? May need some kind of LRU caching; these
// files may be large!
private static final Logger LOG = LoggerFactory
.getLogger(OpenSshServerKeyDatabase.class);
/** Can be used to mark revoked known host lines. */
private static final String MARKER_REVOKED = "revoked"; //$NON-NLS-1$
private final boolean askAboutNewFile;
private final Map<Path, HostKeyFile> knownHostsFiles = new ConcurrentHashMap<>();
private final List<HostKeyFile> defaultFiles = new ArrayList<>();
private Random prng;
/**
* Creates a new {@link OpenSshServerKeyDatabase}.
*
* @param askAboutNewFile
* whether to ask the user, if possible, about creating a new
* non-existing known_hosts file
* @param defaultFiles
* typically ~/.ssh/known_hosts and ~/.ssh/known_hosts2. May be
* empty or {@code null}, in which case no default files are
* installed. The files need not exist.
*/
public OpenSshServerKeyDatabase(boolean askAboutNewFile,
List<Path> defaultFiles) {
if (defaultFiles != null) {
for (Path file : defaultFiles) {
HostKeyFile newFile = new HostKeyFile(file);
knownHostsFiles.put(file, newFile);
this.defaultFiles.add(newFile);
}
}
this.askAboutNewFile = askAboutNewFile;
}
private List<HostKeyFile> getFilesToUse(@NonNull Configuration config) {
List<HostKeyFile> filesToUse = defaultFiles;
List<HostKeyFile> userFiles = addUserHostKeyFiles(
config.getUserKnownHostsFiles());
if (!userFiles.isEmpty()) {
filesToUse = userFiles;
}
return filesToUse;
}
@Override
public List<PublicKey> lookup(@NonNull String connectAddress,
@NonNull InetSocketAddress remoteAddress,
@NonNull Configuration config) {
List<HostKeyFile> filesToUse = getFilesToUse(config);
List<PublicKey> result = new ArrayList<>();
Collection<SshdSocketAddress> candidates = getCandidates(
connectAddress, remoteAddress);
for (HostKeyFile file : filesToUse) {
for (HostEntryPair current : file.get()) {
KnownHostEntry entry = current.getHostEntry();
if (!isRevoked(entry)) {
for (SshdSocketAddress host : candidates) {
if (entry.isHostMatch(host.getHostName(),
host.getPort())) {
result.add(current.getServerKey());
break;
}
}
}
}
}
return result;
}
@Override
public boolean accept(@NonNull String connectAddress,
@NonNull InetSocketAddress remoteAddress,
@NonNull PublicKey serverKey,
@NonNull Configuration config, CredentialsProvider provider) {
List<HostKeyFile> filesToUse = getFilesToUse(config);
AskUser ask = new AskUser(config, provider);
HostEntryPair[] modified = { null };
Path path = null;
Collection<SshdSocketAddress> candidates = getCandidates(connectAddress,
remoteAddress);
for (HostKeyFile file : filesToUse) {
try {
if (find(candidates, serverKey, file.get(), modified)) {
return true;
}
} catch (RevokedKeyException e) {
ask.revokedKey(remoteAddress, serverKey, file.getPath());
return false;
}
if (path == null && modified[0] != null) {
// Remember the file in which we might need to update the
// entry
path = file.getPath();
}
}
if (modified[0] != null) {
// We found an entry, but with a different key
AskUser.ModifiedKeyHandling toDo = ask.acceptModifiedServerKey(
remoteAddress, modified[0].getServerKey(),
serverKey, path);
if (toDo == AskUser.ModifiedKeyHandling.ALLOW_AND_STORE) {
try {
updateModifiedServerKey(serverKey, modified[0], path);
knownHostsFiles.get(path).resetReloadAttributes();
} catch (IOException e) {
LOG.warn(format(SshdText.get().knownHostsCouldNotUpdate,
path));
}
}
if (toDo == AskUser.ModifiedKeyHandling.DENY) {
return false;
}
// TODO: OpenSsh disables password and keyboard-interactive
// authentication in this case. Also agent and local port forwarding
// are switched off. (Plus a few other things such as X11 forwarding
// that are of no interest to a git client.)
return true;
} else if (ask.acceptUnknownKey(remoteAddress, serverKey)) {
if (!filesToUse.isEmpty()) {
HostKeyFile toUpdate = filesToUse.get(0);
path = toUpdate.getPath();
try {
if (Files.exists(path) || !askAboutNewFile
|| ask.createNewFile(path)) {
updateKnownHostsFile(candidates, serverKey, path,
config);
toUpdate.resetReloadAttributes();
}
} catch (Exception e) {
LOG.warn(format(SshdText.get().knownHostsCouldNotUpdate,
path), e);
}
}
return true;
}
return false;
}
private static class RevokedKeyException extends Exception {
private static final long serialVersionUID = 1L;
}
private boolean isRevoked(KnownHostEntry entry) {
return MARKER_REVOKED.equals(entry.getMarker());
}
private boolean find(Collection<SshdSocketAddress> candidates,
PublicKey serverKey, List<HostEntryPair> entries,
HostEntryPair[] modified) throws RevokedKeyException {
for (HostEntryPair current : entries) {
KnownHostEntry entry = current.getHostEntry();
for (SshdSocketAddress host : candidates) {
if (entry.isHostMatch(host.getHostName(), host.getPort())) {
boolean revoked = isRevoked(entry);
if (KeyUtils.compareKeys(serverKey,
current.getServerKey())) {
// Exact match
if (revoked) {
throw new RevokedKeyException();
}
modified[0] = null;
return true;
} else if (!revoked) {
// Server sent a different key
modified[0] = current;
// Keep going -- maybe there's another entry for this
// host
}
break;
}
}
}
return false;
}
private List<HostKeyFile> addUserHostKeyFiles(List<String> fileNames) {
if (fileNames == null || fileNames.isEmpty()) {
return Collections.emptyList();
}
List<HostKeyFile> userFiles = new ArrayList<>();
for (String name : fileNames) {
try {
Path path = Paths.get(name);
HostKeyFile file = knownHostsFiles.computeIfAbsent(path,
p -> new HostKeyFile(path));
userFiles.add(file);
} catch (InvalidPathException e) {
LOG.warn(format(SshdText.get().knownHostsInvalidPath,
name));
}
}
return userFiles;
}
private void updateKnownHostsFile(Collection<SshdSocketAddress> candidates,
PublicKey serverKey, Path path, Configuration config)
throws Exception {
String newEntry = createHostKeyLine(candidates, serverKey, config);
if (newEntry == null) {
return;
}
LockFile lock = new LockFile(path.toFile());
if (lock.lockForAppend()) {
try {
try (BufferedWriter writer = new BufferedWriter(
new OutputStreamWriter(lock.getOutputStream(),
UTF_8))) {
writer.newLine();
writer.write(newEntry);
writer.newLine();
}
lock.commit();
} catch (IOException e) {
lock.unlock();
throw e;
}
} else {
LOG.warn(format(SshdText.get().knownHostsFileLockedUpdate,
path));
}
}
private void updateModifiedServerKey(PublicKey serverKey,
HostEntryPair entry, Path path)
throws IOException {
KnownHostEntry hostEntry = entry.getHostEntry();
String oldLine = hostEntry.getConfigLine();
if (oldLine == null) {
return;
}
String newLine = updateHostKeyLine(oldLine, serverKey);
if (newLine == null || newLine.isEmpty()) {
return;
}
if (oldLine.isEmpty() || newLine.equals(oldLine)) {
// Shouldn't happen.
return;
}
LockFile lock = new LockFile(path.toFile());
if (lock.lock()) {
try {
try (BufferedWriter writer = new BufferedWriter(
new OutputStreamWriter(lock.getOutputStream(), UTF_8));
BufferedReader reader = Files.newBufferedReader(path,
UTF_8)) {
boolean done = false;
String line;
while ((line = reader.readLine()) != null) {
String toWrite = line;
if (!done) {
int pos = line.indexOf('#');
String toTest = pos < 0 ? line
: line.substring(0, pos);
if (toTest.trim().equals(oldLine)) {
toWrite = newLine;
done = true;
}
}
writer.write(toWrite);
writer.newLine();
}
}
lock.commit();
} catch (IOException e) {
lock.unlock();
throw e;
}
} else {
LOG.warn(format(SshdText.get().knownHostsFileLockedUpdate,
path));
}
}
private static class AskUser {
public enum ModifiedKeyHandling {
DENY, ALLOW, ALLOW_AND_STORE
}
private enum Check {
ASK, DENY, ALLOW;
}
private final @NonNull Configuration config;
private final CredentialsProvider provider;
public AskUser(@NonNull Configuration config,
CredentialsProvider provider) {
this.config = config;
this.provider = provider;
}
private static boolean askUser(CredentialsProvider provider, URIish uri,
String prompt, String... messages) {
List<CredentialItem> items = new ArrayList<>(messages.length + 1);
for (String message : messages) {
items.add(new CredentialItem.InformationalMessage(message));
}
if (prompt != null) {
CredentialItem.YesNoType answer = new CredentialItem.YesNoType(
prompt);
items.add(answer);
return provider.get(uri, items) && answer.getValue();
}
return provider.get(uri, items);
}
private Check checkMode(SocketAddress remoteAddress, boolean changed) {
if (!(remoteAddress instanceof InetSocketAddress)) {
return Check.DENY;
}
switch (config.getStrictHostKeyChecking()) {
case REQUIRE_MATCH:
return Check.DENY;
case ACCEPT_ANY:
return Check.ALLOW;
case ACCEPT_NEW:
return changed ? Check.DENY : Check.ALLOW;
default:
return provider == null ? Check.DENY : Check.ASK;
}
}
public void revokedKey(SocketAddress remoteAddress, PublicKey serverKey,
Path path) {
if (provider == null) {
return;
}
InetSocketAddress remote = (InetSocketAddress) remoteAddress;
URIish uri = JGitUserInteraction.toURI(config.getUsername(),
remote);
String sha256 = KeyUtils.getFingerPrint(BuiltinDigests.sha256,
serverKey);
String md5 = KeyUtils.getFingerPrint(BuiltinDigests.md5, serverKey);
String keyAlgorithm = serverKey.getAlgorithm();
askUser(provider, uri, null, //
format(SshdText.get().knownHostsRevokedKeyMsg,
remote.getHostString(), path),
format(SshdText.get().knownHostsKeyFingerprints,
keyAlgorithm),
md5, sha256);
}
public boolean acceptUnknownKey(SocketAddress remoteAddress,
PublicKey serverKey) {
Check check = checkMode(remoteAddress, false);
if (check != Check.ASK) {
return check == Check.ALLOW;
}
InetSocketAddress remote = (InetSocketAddress) remoteAddress;
// Ask the user
String sha256 = KeyUtils.getFingerPrint(BuiltinDigests.sha256,
serverKey);
String md5 = KeyUtils.getFingerPrint(BuiltinDigests.md5, serverKey);
String keyAlgorithm = serverKey.getAlgorithm();
String remoteHost = remote.getHostString();
URIish uri = JGitUserInteraction.toURI(config.getUsername(),
remote);
String prompt = SshdText.get().knownHostsUnknownKeyPrompt;
return askUser(provider, uri, prompt, //
format(SshdText.get().knownHostsUnknownKeyMsg,
remoteHost),
format(SshdText.get().knownHostsKeyFingerprints,
keyAlgorithm),
md5, sha256);
}
public ModifiedKeyHandling acceptModifiedServerKey(
InetSocketAddress remoteAddress, PublicKey expected,
PublicKey actual, Path path) {
Check check = checkMode(remoteAddress, true);
if (check == Check.ALLOW) {
// Never auto-store on CHECK.ALLOW
return ModifiedKeyHandling.ALLOW;
}
String keyAlgorithm = actual.getAlgorithm();
String remoteHost = remoteAddress.getHostString();
URIish uri = JGitUserInteraction.toURI(config.getUsername(),
remoteAddress);
List<String> messages = new ArrayList<>();
String warning = format(
SshdText.get().knownHostsModifiedKeyWarning,
keyAlgorithm, expected.getAlgorithm(), remoteHost,
KeyUtils.getFingerPrint(BuiltinDigests.md5, expected),
KeyUtils.getFingerPrint(BuiltinDigests.sha256, expected),
KeyUtils.getFingerPrint(BuiltinDigests.md5, actual),
KeyUtils.getFingerPrint(BuiltinDigests.sha256, actual));
messages.addAll(Arrays.asList(warning.split("\n"))); //$NON-NLS-1$
if (check == Check.DENY) {
if (provider != null) {
messages.add(format(
SshdText.get().knownHostsModifiedKeyDenyMsg, path));
askUser(provider, uri, null,
messages.toArray(new String[0]));
}
return ModifiedKeyHandling.DENY;
}
// ASK -- two questions: procceed? and store?
List<CredentialItem> items = new ArrayList<>(messages.size() + 2);
for (String message : messages) {
items.add(new CredentialItem.InformationalMessage(message));
}
CredentialItem.YesNoType proceed = new CredentialItem.YesNoType(
SshdText.get().knownHostsModifiedKeyAcceptPrompt);
CredentialItem.YesNoType store = new CredentialItem.YesNoType(
SshdText.get().knownHostsModifiedKeyStorePrompt);
items.add(proceed);
items.add(store);
if (provider.get(uri, items) && proceed.getValue()) {
return store.getValue() ? ModifiedKeyHandling.ALLOW_AND_STORE
: ModifiedKeyHandling.ALLOW;
}
return ModifiedKeyHandling.DENY;
}
public boolean createNewFile(Path path) {
if (provider == null) {
// We can't ask, so don't create the file
return false;
}
URIish uri = new URIish().setPath(path.toString());
return askUser(provider, uri, //
format(SshdText.get().knownHostsUserAskCreationPrompt,
path), //
format(SshdText.get().knownHostsUserAskCreationMsg, path));
}
}
private static class HostKeyFile extends ModifiableFileWatcher
implements Supplier<List<HostEntryPair>> {
private List<HostEntryPair> entries = Collections.emptyList();
public HostKeyFile(Path path) {
super(path);
}
@Override
public List<HostEntryPair> get() {
Path path = getPath();
synchronized (this) {
try {
if (checkReloadRequired()) {
entries = reload(getPath());
}
} catch (IOException e) {
LOG.warn(format(SshdText.get().knownHostsFileReadFailed,
path));
}
return Collections.unmodifiableList(entries);
}
}
private List<HostEntryPair> reload(Path path) throws IOException {
try {
List<KnownHostEntry> rawEntries = KnownHostEntryReader
.readFromFile(path);
updateReloadAttributes();
if (rawEntries == null || rawEntries.isEmpty()) {
return Collections.emptyList();
}
List<HostEntryPair> newEntries = new LinkedList<>();
for (KnownHostEntry entry : rawEntries) {
AuthorizedKeyEntry keyPart = entry.getKeyEntry();
if (keyPart == null) {
continue;
}
try {
PublicKey serverKey = keyPart.resolvePublicKey(null,
PublicKeyEntryResolver.IGNORING);
if (serverKey == null) {
LOG.warn(format(
SshdText.get().knownHostsUnknownKeyType,
path, entry.getConfigLine()));
} else {
newEntries.add(new HostEntryPair(entry, serverKey));
}
} catch (GeneralSecurityException e) {
LOG.warn(format(SshdText.get().knownHostsInvalidLine,
path, entry.getConfigLine()));
}
}
return newEntries;
} catch (FileNotFoundException | NoSuchFileException e) {
resetReloadAttributes();
return Collections.emptyList();
}
}
}
private int parsePort(String s) {
try {
return Integer.parseInt(s);
} catch (NumberFormatException e) {
return -1;
}
}
private SshdSocketAddress toSshdSocketAddress(@NonNull String address) {
String host = null;
int port = 0;
if (HostPatternsHolder.NON_STANDARD_PORT_PATTERN_ENCLOSURE_START_DELIM == address
.charAt(0)) {
int end = address.indexOf(
HostPatternsHolder.NON_STANDARD_PORT_PATTERN_ENCLOSURE_END_DELIM);
if (end <= 1) {
return null; // Invalid
}
host = address.substring(1, end);
if (end < address.length() - 1
&& HostPatternsHolder.PORT_VALUE_DELIMITER == address
.charAt(end + 1)) {
port = parsePort(address.substring(end + 2));
}
} else {
int i = address
.lastIndexOf(HostPatternsHolder.PORT_VALUE_DELIMITER);
if (i > 0) {
port = parsePort(address.substring(i + 1));
host = address.substring(0, i);
} else {
host = address;
}
}
if (port < 0 || port > 65535) {
return null;
}
return new SshdSocketAddress(host, port);
}
private Collection<SshdSocketAddress> getCandidates(
@NonNull String connectAddress,
@NonNull InetSocketAddress remoteAddress) {
Collection<SshdSocketAddress> candidates = new TreeSet<>(
SshdSocketAddress.BY_HOST_AND_PORT);
candidates.add(SshdSocketAddress.toSshdSocketAddress(remoteAddress));
SshdSocketAddress address = toSshdSocketAddress(connectAddress);
if (address != null) {
candidates.add(address);
}
return candidates;
}
private String createHostKeyLine(Collection<SshdSocketAddress> patterns,
PublicKey key, Configuration config) throws Exception {
StringBuilder result = new StringBuilder();
if (config.getHashKnownHosts()) {
// SHA1 is the only algorithm for host name hashing known to OpenSSH
// or to Apache MINA sshd.
NamedFactory<Mac> digester = KnownHostDigest.SHA1;
Mac mac = digester.create();
if (prng == null) {
prng = new SecureRandom();
}
byte[] salt = new byte[mac.getDefaultBlockSize()];
for (SshdSocketAddress address : patterns) {
if (result.length() > 0) {
result.append(',');
}
prng.nextBytes(salt);
KnownHostHashValue.append(result, digester, salt,
KnownHostHashValue.calculateHashValue(
address.getHostName(), address.getPort(), mac,
salt));
}
} else {
for (SshdSocketAddress address : patterns) {
if (result.length() > 0) {
result.append(',');
}
KnownHostHashValue.appendHostPattern(result,
address.getHostName(), address.getPort());
}
}
result.append(' ');
PublicKeyEntry.appendPublicKeyEntry(result, key);
return result.toString();
}
private String updateHostKeyLine(String line, PublicKey newKey)
throws IOException {
// Replaces an existing public key by the new key
int pos = line.indexOf(' ');
if (pos > 0 && line.charAt(0) == KnownHostEntry.MARKER_INDICATOR) {
// We're at the end of the marker. Skip ahead to the next blank.
pos = line.indexOf(' ', pos + 1);
}
if (pos < 0) {
// Don't update if bogus format
return null;
}
StringBuilder result = new StringBuilder(line.substring(0, pos + 1));
PublicKeyEntry.appendPublicKeyEntry(result, newKey);
return result.toString();
}
}