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✏️ Editing: agent.py

# Copyright (C) 2003-2007  John Rochester <john@jrochester.org>
#
# This file is part of paramiko.
#
# Paramiko is free software; you can redistribute it and/or modify it under the
# terms of the GNU Lesser General Public License as published by the Free
# Software Foundation; either version 2.1 of the License, or (at your option)
# any later version.
#
# Paramiko is distributed in the hope that it will be useful, but WITHOUT ANY
# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
# A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more
# details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with Paramiko; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA.

"""
SSH Agent interface
"""

import os
import socket
import struct
import sys
import threading
import time
import tempfile
import stat
from logging import DEBUG
from select import select
from paramiko.common import io_sleep, byte_chr

from paramiko.ssh_exception import SSHException, AuthenticationException
from paramiko.message import Message
from paramiko.pkey import PKey, UnknownKeyType
from paramiko.util import asbytes, get_logger

cSSH2_AGENTC_REQUEST_IDENTITIES = byte_chr(11)
SSH2_AGENT_IDENTITIES_ANSWER = 12
cSSH2_AGENTC_SIGN_REQUEST = byte_chr(13)
SSH2_AGENT_SIGN_RESPONSE = 14

SSH_AGENT_RSA_SHA2_256 = 2
SSH_AGENT_RSA_SHA2_512 = 4
# NOTE: RFC mildly confusing; while these flags are OR'd together, OpenSSH at
# least really treats them like "AND"s, in the sense that if it finds the
# SHA256 flag set it won't continue looking at the SHA512 one; it
# short-circuits right away.
# Thus, we never want to eg submit 6 to say "either's good".
ALGORITHM_FLAG_MAP = {
    "rsa-sha2-256": SSH_AGENT_RSA_SHA2_256,
    "rsa-sha2-512": SSH_AGENT_RSA_SHA2_512,
}
for key, value in list(ALGORITHM_FLAG_MAP.items()):
    ALGORITHM_FLAG_MAP[f"{key}-cert-v01@openssh.com"] = value

# TODO 4.0: rename all these - including making some of their methods public?
class AgentSSH:
    def __init__(self):
        self._conn = None
        self._keys = ()

def get_keys(self):
        """
        Return the list of keys available through the SSH agent, if any.  If
        no SSH agent was running (or it couldn't be contacted), an empty list
        will be returned.

This method performs no IO, just returns the list of keys retrieved
        when the connection was made.

:return:
            a tuple of `.AgentKey` objects representing keys available on the
            SSH agent
        """
        return self._keys

def _connect(self, conn):
        self._conn = conn
        ptype, result = self._send_message(cSSH2_AGENTC_REQUEST_IDENTITIES)
        if ptype != SSH2_AGENT_IDENTITIES_ANSWER:
            raise SSHException("could not get keys from ssh-agent")
        keys = []
        for i in range(result.get_int()):
            keys.append(
                AgentKey(
                    agent=self,
                    blob=result.get_binary(),
                    comment=result.get_text(),
                )
            )
        self._keys = tuple(keys)

def _close(self):
        if self._conn is not None:
            self._conn.close()
        self._conn = None
        self._keys = ()

def _send_message(self, msg):
        msg = asbytes(msg)
        self._conn.send(struct.pack(">I", len(msg)) + msg)
        data = self._read_all(4)
        msg = Message(self._read_all(struct.unpack(">I", data)[0]))
        return ord(msg.get_byte()), msg

def _read_all(self, wanted):
        result = self._conn.recv(wanted)
        while len(result) < wanted:
            if len(result) == 0:
                raise SSHException("lost ssh-agent")
            extra = self._conn.recv(wanted - len(result))
            if len(extra) == 0:
                raise SSHException("lost ssh-agent")
            result += extra
        return result

class AgentProxyThread(threading.Thread):
    """
    Class in charge of communication between two channels.
    """

def __init__(self, agent):
        threading.Thread.__init__(self, target=self.run)
        self._agent = agent
        self._exit = False

def run(self):
        try:
            (r, addr) = self.get_connection()
            # Found that r should be either
            # a socket from the socket library or None
            self.__inr = r
            # The address should be an IP address as a string? or None
            self.__addr = addr
            self._agent.connect()
            if not isinstance(self._agent, int) and (
                self._agent._conn is None
                or not hasattr(self._agent._conn, "fileno")
            ):
                raise AuthenticationException("Unable to connect to SSH agent")
            self._communicate()
        except:
            # XXX Not sure what to do here ... raise or pass ?
            raise

def _communicate(self):
        import fcntl

oldflags = fcntl.fcntl(self.__inr, fcntl.F_GETFL)
        fcntl.fcntl(self.__inr, fcntl.F_SETFL, oldflags | os.O_NONBLOCK)
        while not self._exit:
            events = select([self._agent._conn, self.__inr], [], [], 0.5)
            for fd in events[0]:
                if self._agent._conn == fd:
                    data = self._agent._conn.recv(512)
                    if len(data) != 0:
                        self.__inr.send(data)
                    else:
                        self._close()
                        break
                elif self.__inr == fd:
                    data = self.__inr.recv(512)
                    if len(data) != 0:
                        self._agent._conn.send(data)
                    else:
                        self._close()
                        break
            time.sleep(io_sleep)

def _close(self):
        self._exit = True
        self.__inr.close()
        self._agent._conn.close()

class AgentLocalProxy(AgentProxyThread):
    """
    Class to be used when wanting to ask a local SSH Agent being
    asked from a remote fake agent (so use a unix socket for ex.)
    """

def __init__(self, agent):
        AgentProxyThread.__init__(self, agent)

def get_connection(self):
        """
        Return a pair of socket object and string address.

May block!
        """
        conn = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
        try:
            conn.bind(self._agent._get_filename())
            conn.listen(1)
            (r, addr) = conn.accept()
            return r, addr
        except:
            raise

class AgentRemoteProxy(AgentProxyThread):
    """
    Class to be used when wanting to ask a remote SSH Agent
    """

def __init__(self, agent, chan):
        AgentProxyThread.__init__(self, agent)
        self.__chan = chan

def get_connection(self):
        return self.__chan, None

def get_agent_connection():
    """
    Returns some SSH agent object, or None if none were found/supported.

.. versionadded:: 2.10
    """
    if ("SSH_AUTH_SOCK" in os.environ) and (sys.platform != "win32"):
        conn = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
        try:
            conn.connect(os.environ["SSH_AUTH_SOCK"])
            return conn
        except:
            # probably a dangling env var: the ssh agent is gone
            return
    elif sys.platform == "win32":
        from . import win_pageant, win_openssh

conn = None
        if win_pageant.can_talk_to_agent():
            conn = win_pageant.PageantConnection()
        elif win_openssh.can_talk_to_agent():
            conn = win_openssh.OpenSSHAgentConnection()
        return conn
    else:
        # no agent support
        return

class AgentClientProxy:
    """
    Class proxying request as a client:

#. client ask for a request_forward_agent()
    #. server creates a proxy and a fake SSH Agent
    #. server ask for establishing a connection when needed,
       calling the forward_agent_handler at client side.
    #. the forward_agent_handler launch a thread for connecting
       the remote fake agent and the local agent
    #. Communication occurs ...
    """

def __init__(self, chanRemote):
        self._conn = None
        self.__chanR = chanRemote
        self.thread = AgentRemoteProxy(self, chanRemote)
        self.thread.start()

def __del__(self):
        self.close()

def connect(self):
        """
        Method automatically called by ``AgentProxyThread.run``.
        """
        conn = get_agent_connection()
        if not conn:
            return
        self._conn = conn

def close(self):
        """
        Close the current connection and terminate the agent
        Should be called manually
        """
        if hasattr(self, "thread"):
            self.thread._exit = True
            self.thread.join(1000)
        if self._conn is not None:
            self._conn.close()

class AgentServerProxy(AgentSSH):
    """
    Allows an SSH server to access a forwarded agent.

This also creates a unix domain socket on the system to allow external
    programs to also access the agent. For this reason, you probably only want
    to create one of these.

:meth:`connect` must be called before it is usable. This will also load the
    list of keys the agent contains. You must also call :meth:`close` in
    order to clean up the unix socket and the thread that maintains it.
    (:class:`contextlib.closing` might be helpful to you.)

:param .Transport t: Transport used for SSH Agent communication forwarding

:raises: `.SSHException` -- mostly if we lost the agent
    """

def __init__(self, t):
        AgentSSH.__init__(self)
        self.__t = t
        self._dir = tempfile.mkdtemp("sshproxy")
        os.chmod(self._dir, stat.S_IRWXU)
        self._file = self._dir + "/sshproxy.ssh"
        self.thread = AgentLocalProxy(self)
        self.thread.start()

def __del__(self):
        self.close()

def connect(self):
        conn_sock = self.__t.open_forward_agent_channel()
        if conn_sock is None:
            raise SSHException("lost ssh-agent")
        conn_sock.set_name("auth-agent")
        self._connect(conn_sock)

def close(self):
        """
        Terminate the agent, clean the files, close connections
        Should be called manually
        """
        os.remove(self._file)
        os.rmdir(self._dir)
        self.thread._exit = True
        self.thread.join(1000)
        self._close()

def get_env(self):
        """
        Helper for the environment under unix

:return:
            a dict containing the ``SSH_AUTH_SOCK`` environment variables
        """
        return {"SSH_AUTH_SOCK": self._get_filename()}

def _get_filename(self):
        return self._file

class AgentRequestHandler:
    """
    Primary/default implementation of SSH agent forwarding functionality.

Simply instantiate this class, handing it a live command-executing session
    object, and it will handle forwarding any local SSH agent processes it
    finds.

For example::

# Connect
        client = SSHClient()
        client.connect(host, port, username)
        # Obtain session
        session = client.get_transport().open_session()
        # Forward local agent
        AgentRequestHandler(session)
        # Commands executed after this point will see the forwarded agent on
        # the remote end.
        session.exec_command("git clone https://my.git.repository/")
    """

def __init__(self, chanClient):
        self._conn = None
        self.__chanC = chanClient
        chanClient.request_forward_agent(self._forward_agent_handler)
        self.__clientProxys = []

def _forward_agent_handler(self, chanRemote):
        self.__clientProxys.append(AgentClientProxy(chanRemote))

def __del__(self):
        self.close()

def close(self):
        for p in self.__clientProxys:
            p.close()

class Agent(AgentSSH):
    """
    Client interface for using private keys from an SSH agent running on the
    local machine.  If an SSH agent is running, this class can be used to
    connect to it and retrieve `.PKey` objects which can be used when
    attempting to authenticate to remote SSH servers.

Upon initialization, a session with the local machine's SSH agent is
    opened, if one is running. If no agent is running, initialization will
    succeed, but `get_keys` will return an empty tuple.

:raises: `.SSHException` --
        if an SSH agent is found, but speaks an incompatible protocol

.. versionchanged:: 2.10
        Added support for native openssh agent on windows (extending previous
        putty pageant support)
    """

def __init__(self):
        AgentSSH.__init__(self)

conn = get_agent_connection()
        if not conn:
            return
        self._connect(conn)

def close(self):
        """
        Close the SSH agent connection.
        """
        self._close()

class AgentKey(PKey):
    """
    Private key held in a local SSH agent.  This type of key can be used for
    authenticating to a remote server (signing).  Most other key operations
    work as expected.

.. versionchanged:: 3.2
        Added the ``comment`` kwarg and attribute.

.. versionchanged:: 3.2
        Added the ``.inner_key`` attribute holding a reference to the 'real'
        key instance this key is a proxy for, if one was obtainable, else None.
    """

def __init__(self, agent, blob, comment=""):
        self.agent = agent
        self.blob = blob
        self.comment = comment
        msg = Message(blob)
        self.name = msg.get_text()
        self._logger = get_logger(__file__)
        self.inner_key = None
        try:
            self.inner_key = PKey.from_type_string(
                key_type=self.name, key_bytes=blob
            )
        except UnknownKeyType:
            # Log, but don't explode, since inner_key is a best-effort thing.
            err = "Unable to derive inner_key for agent key of type {!r}"
            self.log(DEBUG, err.format(self.name))

def log(self, *args, **kwargs):
        return self._logger.log(*args, **kwargs)

def asbytes(self):
        # Prefer inner_key.asbytes, since that will differ for eg RSA-CERT
        return self.inner_key.asbytes() if self.inner_key else self.blob

def get_name(self):
        return self.name

def get_bits(self):
        # Have to work around PKey's default get_bits being crap
        if self.inner_key is not None:
            return self.inner_key.get_bits()
        return super().get_bits()

def __getattr__(self, name):
        """
        Proxy any un-implemented methods/properties to the inner_key.
        """
        if self.inner_key is None:  # nothing to proxy to
            raise AttributeError(name)
        return getattr(self.inner_key, name)

@property
    def _fields(self):
        fallback = [self.get_name(), self.blob]
        return self.inner_key._fields if self.inner_key else fallback

def sign_ssh_data(self, data, algorithm=None):
        msg = Message()
        msg.add_byte(cSSH2_AGENTC_SIGN_REQUEST)
        # NOTE: this used to be just self.blob, which is not entirely right for
        # RSA-CERT 'keys' - those end up always degrading to ssh-rsa type
        # signatures, for reasons probably internal to OpenSSH's agent code,
        # even if everything else wants SHA2 (including our flag map).
        msg.add_string(self.asbytes())
        msg.add_string(data)
        msg.add_int(ALGORITHM_FLAG_MAP.get(algorithm, 0))
        ptype, result = self.agent._send_message(msg)
        if ptype != SSH2_AGENT_SIGN_RESPONSE:
            raise SSHException("key cannot be used for signing")
        return result.get_binary()

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