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sshd: Skip unknown keys from the SSH agent 

An SSH agent might contain keys that Apache MINA sshd cannot handle.
Pageant for instance can contain ed448 keys, which are not implemented
in OpenSSH or in Apache MINA sshd.

When an agent delivers such keys, simply skip (and log) them. That way,
we can work with the remaining keys. Otherwise a single unknown key in
the agent would break pubkey authentication.

Change-Id: I3945d932c7e64b628465004cfbaf10f4dc05f3e4
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>
This commit is contained in:
Thomas Wolf 2021-12-29 20:33:33 +01:00
parent b73548bc4c
commit f41929708e
4 changed files with 57 additions and 6 deletions
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1
org.eclipse.jgit.ssh.apache/META-INF/MANIFEST.MF
View File

@ -72,6 +72,7 @@ Import-Package: net.i2p.crypto.eddsa;version="[0.3.0,0.4.0)",
org.apache.sshd.common.signature;version="[2.8.0,2.9.0)",
org.apache.sshd.common.util;version="[2.8.0,2.9.0)",
org.apache.sshd.common.util.buffer;version="[2.8.0,2.9.0)",
org.apache.sshd.common.util.buffer.keys;version="[2.8.0,2.9.0)",
org.apache.sshd.common.util.closeable;version="[2.8.0,2.9.0)",
org.apache.sshd.common.util.io;version="[2.8.0,2.9.0)",
org.apache.sshd.common.util.io.der;version="[2.8.0,2.9.0)",

2
org.eclipse.jgit.ssh.apache/resources/org/eclipse/jgit/internal/transport/sshd/SshdText.properties
View File

@ -93,6 +93,8 @@ sshAgentPayloadLengthError=Expected {0,choice,0#no bytes|1#one byte|1<{0} bytes}
sshAgentReplyLengthError=Invalid SSH agent reply message length {0} after command {1}
sshAgentReplyUnexpected=Unexpected reply from ssh-agent: {0}
sshAgentShortReadBuffer=Short read from SSH agent
sshAgentUnknownKey=SSH agent delivered a key that cannot be handled
sshAgentWrongKeyLength=SSH agent delivered illogical key length {0} at offset {1} in buffer of length {2}
sshAgentWrongNumberOfKeys=Invalid number of SSH agent keys: {0}
sshClosingDown=Apache MINA sshd session factory is closing down; cannot create new ssh sessions on this factory
sshCommandTimeout={0} timed out after {1} seconds while opening the channel

2
org.eclipse.jgit.ssh.apache/src/org/eclipse/jgit/internal/transport/sshd/SshdText.java
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@ -114,6 +114,8 @@ public static SshdText get() {
/***/ public String sshAgentReplyLengthError;
/***/ public String sshAgentReplyUnexpected;
/***/ public String sshAgentShortReadBuffer;
/***/ public String sshAgentUnknownKey;
/***/ public String sshAgentWrongKeyLength;
/***/ public String sshAgentWrongNumberOfKeys;
/***/ public String sshClosingDown;
/***/ public String sshCommandTimeout;

58
org.eclipse.jgit.ssh.apache/src/org/eclipse/jgit/internal/transport/sshd/agent/SshAgentClient.java
View File

@ -33,6 +33,7 @@
import org.apache.sshd.common.util.buffer.BufferException;
import org.apache.sshd.common.util.buffer.BufferUtils;
import org.apache.sshd.common.util.buffer.ByteArrayBuffer;
import org.apache.sshd.common.util.buffer.keys.BufferPublicKeyParser;
import org.apache.sshd.common.util.io.der.DERParser;
import org.eclipse.jgit.internal.transport.sshd.SshdText;
import org.eclipse.jgit.transport.sshd.agent.Connector;
@ -141,14 +142,17 @@ public Iterable<? extends Map.Entry<PublicKey, String>> getIdentities()
List<Map.Entry<PublicKey, String>> keys = new ArrayList<>(
numberOfKeys);
for (int i = 0; i < numberOfKeys; i++) {
PublicKey key = reply.getPublicKey();
PublicKey key = readKey(reply);
String comment = reply.getString();
if (tracing) {
LOG.trace("Got SSH agent {} key: {} {}", //$NON-NLS-1$
KeyUtils.getKeyType(key),
KeyUtils.getFingerPrint(key), comment);
if (key != null) {
if (tracing) {
LOG.trace("Got SSH agent {} key: {} {}", //$NON-NLS-1$
KeyUtils.getKeyType(key),
KeyUtils.getFingerPrint(key), comment);
}
keys.add(new AbstractMap.SimpleImmutableEntry<>(key,
comment));
}
keys.add(new AbstractMap.SimpleImmutableEntry<>(key, comment));
}
return keys;
} catch (BufferException e) {
@ -404,6 +408,48 @@ private static byte[] asn1Parse(byte[] encoded, int n) throws IOException {
}
}
/**
* A safe version of {@link Buffer#getPublicKey()}. Upon return the
* buffers's read position is always after the key blob; any exceptions
* thrown by trying to read the key are logged and <em>not</em> propagated.
* <p>
* This is needed because an SSH agent might contain and deliver keys that
* we cannot handle (for instance ed448 keys).
* </p>
*
* @param buffer
* to read the key from
* @return the {@link PublicKey}, or {@code null} if the key could not be
* read
* @throws BufferException
* if the length of the key blob cannot be read or is corrupted
*/
private static PublicKey readKey(Buffer buffer) throws BufferException {
int endOfBuffer = buffer.wpos();
int keyLength = buffer.getInt();
int afterKey = buffer.rpos() + keyLength;
if (keyLength <= 0 || afterKey > endOfBuffer) {
throw new BufferException(
MessageFormat.format(SshdText.get().sshAgentWrongKeyLength,
Integer.toString(keyLength),
Integer.toString(buffer.rpos()),
Integer.toString(endOfBuffer)));
}
// Limit subsequent reads to the public key blob
buffer.wpos(afterKey);
try {
return buffer.getRawPublicKey(BufferPublicKeyParser.DEFAULT);
} catch (Exception e) {
LOG.warn(SshdText.get().sshAgentUnknownKey, e);
return null;
} finally {
// Restore real buffer end
buffer.wpos(endOfBuffer);
// Set the read position to after this key, even if failed
buffer.rpos(afterKey);
}
}
private Buffer rpc(byte command, byte[] message) throws IOException {
return new ByteArrayBuffer(connector.rpc(command, message));
}