119 lines
4.0 KiB
Python
119 lines
4.0 KiB
Python
#!/usr/bin/env python3
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"""Temporary loopback-only OpenSSH forwarding fixture. Requires local sshd.
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No system SSH configuration or authorized_keys files are changed. Only forwarding
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is allowed; MaxSessions=0 disables shell, command and subsystem sessions.
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Pass --metadata to TERMIND_SSH_FIXTURE in SSHForwardingWireTests.
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"""
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import argparse
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import getpass
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import json
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import os
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from pathlib import Path
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import signal
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import socket
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import subprocess
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import tempfile
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import threading
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import time
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def echo_connection(connection):
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with connection:
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try:
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while data := connection.recv(65536):
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connection.sendall(data)
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except OSError:
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pass
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def echo_server(listener):
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while True:
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try:
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connection, _ = listener.accept()
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except OSError:
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return
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threading.Thread(target=echo_connection, args=(connection,), daemon=True).start()
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def main():
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parser = argparse.ArgumentParser(description=__doc__)
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parser.add_argument("--metadata", required=True)
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args = parser.parse_args()
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metadata = Path(args.metadata)
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signal.signal(signal.SIGTERM, lambda *_: (_ for _ in ()).throw(KeyboardInterrupt()))
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with tempfile.TemporaryDirectory(prefix="termind-openssh-") as directory, socket.socket() as echo:
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root = Path(directory)
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for name in ("host", "client"):
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subprocess.run(["ssh-keygen", "-q", "-t", "ed25519", "-N", "", "-f", str(root / name)], check=True)
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authorized = root / "authorized_keys"
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authorized.write_text((root / "client.pub").read_text())
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authorized.chmod(0o600)
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with socket.socket() as reservation:
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reservation.bind(("127.0.0.1", 0))
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port = reservation.getsockname()[1]
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echo.bind(("127.0.0.1", 0))
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echo.listen(128)
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echo_port = echo.getsockname()[1]
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threading.Thread(target=echo_server, args=(echo,), daemon=True).start()
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config = root / "sshd_config"
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config.write_text(f"""ListenAddress 127.0.0.1
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Port {port}
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HostKey {root / 'host'}
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PidFile {root / 'pid'}
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AuthorizedKeysFile {authorized}
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StrictModes no
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UsePAM no
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PasswordAuthentication no
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KbdInteractiveAuthentication no
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PubkeyAuthentication yes
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AuthenticationMethods publickey
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AllowUsers {getpass.getuser()}
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AllowTcpForwarding yes
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PermitOpen 127.0.0.1:{port} 127.0.0.1:{echo_port}
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PermitListen 127.0.0.1:*
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GatewayPorts no
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AllowAgentForwarding no
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X11Forwarding no
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PermitTunnel no
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MaxSessions 0
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LogLevel ERROR
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""")
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server = subprocess.Popen(["/usr/sbin/sshd", "-D", "-e", "-f", str(config)], start_new_session=True)
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created_metadata = False
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try:
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for _ in range(100):
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if server.poll() is not None:
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raise RuntimeError("sshd exited before becoming ready; see its diagnostic above")
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try:
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with socket.create_connection(("127.0.0.1", port), timeout=0.1):
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break
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except OSError:
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time.sleep(0.05)
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else:
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raise RuntimeError("sshd did not become ready")
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descriptor = os.open(metadata, os.O_WRONLY | os.O_CREAT | os.O_EXCL, 0o600)
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created_metadata = True
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with os.fdopen(descriptor, "w") as output:
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json.dump({"port": port, "echoPort": echo_port, "server": "openssh",
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"username": getpass.getuser(), "privateKey": (root / "client").read_text()}, output)
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print(f"OpenSSH forwarding fixture listening on 127.0.0.1:{port}", flush=True)
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server.wait()
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except KeyboardInterrupt:
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pass
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finally:
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if server.poll() is None:
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os.killpg(server.pid, signal.SIGTERM)
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try:
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server.wait(timeout=5)
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except subprocess.TimeoutExpired:
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os.killpg(server.pid, signal.SIGKILL)
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server.wait()
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if created_metadata:
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metadata.unlink(missing_ok=True)
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if __name__ == "__main__":
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main()
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