src/twisted/conch/unix.py

# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.

"""
A UNIX SSH server.
"""

from __future__ import annotations

import fcntl
import grp
import os
import pty
import pwd
import socket
import struct
import time
import tty
from typing import Callable, Dict, Tuple

from zope.interface import implementer

from twisted.conch import ttymodes
from twisted.conch.avatar import ConchUser
from twisted.conch.error import ConchError
from twisted.conch.interfaces import ISession, ISFTPFile, ISFTPServer
from twisted.conch.ls import lsLine
from twisted.conch.ssh import filetransfer, forwarding, session
from twisted.conch.ssh.filetransfer import (
    FXF_APPEND,
    FXF_CREAT,
    FXF_EXCL,
    FXF_READ,
    FXF_TRUNC,
    FXF_WRITE,
)
from twisted.cred import portal
from twisted.cred.error import LoginDenied
from twisted.internet.error import ProcessExitedAlready
from twisted.internet.interfaces import IListeningPort
from twisted.logger import Logger
from twisted.python import components
from twisted.python.compat import nativeString

try:
    import utmp
except ImportError:
    utmp = None


@implementer(portal.IRealm)
class UnixSSHRealm:
    def requestAvatar(
        self,
        username: bytes | Tuple[()],
        mind: object,
        *interfaces: portal._InterfaceItself,
    ) -> Tuple[portal._InterfaceItself, UnixConchUser, Callable[[], None]]:
        if not isinstance(username, bytes):
            raise LoginDenied("UNIX SSH realm does not authorize anonymous sessions.")
        user = UnixConchUser(username.decode())
        return interfaces[0], user, user.logout


class UnixConchUser(ConchUser):
    def __init__(self, username: str) -> None:
        ConchUser.__init__(self)
        self.username = username
        self.pwdData = pwd.getpwnam(self.username)
        l = [self.pwdData[3]]
        for groupname, password, gid, userlist in grp.getgrall():
            if username in userlist:
                l.append(gid)
        self.otherGroups = l
        self.listeners: Dict[
            str, IListeningPort
        ] = {}  # Dict mapping (interface, port) -> listener
        self.channelLookup.update(
            {
                b"session": session.SSHSession,
                b"direct-tcpip": forwarding.openConnectForwardingClient,
            }
        )

        self.subsystemLookup.update({b"sftp": filetransfer.FileTransferServer})

    def getUserGroupId(self):
        return self.pwdData[2:4]

    def getOtherGroups(self):
        return self.otherGroups

    def getHomeDir(self):
        return self.pwdData[5]

    def getShell(self):
        return self.pwdData[6]

    def global_tcpip_forward(self, data):
        hostToBind, portToBind = forwarding.unpackGlobal_tcpip_forward(data)
        from twisted.internet import reactor

        try:
            listener = self._runAsUser(
                reactor.listenTCP,
                portToBind,
                forwarding.SSHListenForwardingFactory(
                    self.conn,
                    (hostToBind, portToBind),
                    forwarding.SSHListenServerForwardingChannel,
                ),
                interface=hostToBind,
            )
        except BaseException:
            return 0
        else:
            self.listeners[(hostToBind, portToBind)] = listener
            if portToBind == 0:
                portToBind = listener.getHost()[2]  # The port
                return 1, struct.pack(">L", portToBind)
            else:
                return 1

    def global_cancel_tcpip_forward(self, data):
        hostToBind, portToBind = forwarding.unpackGlobal_tcpip_forward(data)
        listener = self.listeners.get((hostToBind, portToBind), None)
        if not listener:
            return 0
        del self.listeners[(hostToBind, portToBind)]
        self._runAsUser(listener.stopListening)
        return 1

    def logout(self) -> None:
        # Remove all listeners.
        for listener in self.listeners.values():
            self._runAsUser(listener.stopListening)
        self._log.info(
            "avatar {username} logging out ({nlisteners})",
            username=self.username,
            nlisteners=len(self.listeners),
        )

    def _runAsUser(self, f, *args, **kw):
        euid = os.geteuid()
        egid = os.getegid()
        groups = os.getgroups()
        uid, gid = self.getUserGroupId()
        os.setegid(0)
        os.seteuid(0)
        os.setgroups(self.getOtherGroups())
        os.setegid(gid)
        os.seteuid(uid)
        try:
            f = iter(f)
        except TypeError:
            f = [(f, args, kw)]
        try:
            for i in f:
                func = i[0]
                args = len(i) > 1 and i[1] or ()
                kw = len(i) > 2 and i[2] or {}
                r = func(*args, **kw)
        finally:
            os.setegid(0)
            os.seteuid(0)
            os.setgroups(groups)
            os.setegid(egid)
            os.seteuid(euid)
        return r


@implementer(ISession)
class SSHSessionForUnixConchUser:
    _log = Logger()

    def __init__(self, avatar, reactor=None):
        """
        Construct an C{SSHSessionForUnixConchUser}.

        @param avatar: The L{UnixConchUser} for whom this is an SSH session.
        @param reactor: An L{IReactorProcess} used to handle shell and exec
            requests. Uses the default reactor if None.
        """
        if reactor is None:
            from twisted.internet import reactor
        self._reactor = reactor
        self.avatar = avatar
        self.environ = {"PATH": "/bin:/usr/bin:/usr/local/bin"}
        self.pty = None
        self.ptyTuple = 0

    def addUTMPEntry(self, loggedIn=1):
        if not utmp:
            return
        ipAddress = self.avatar.conn.transport.transport.getPeer().host
        (packedIp,) = struct.unpack("L", socket.inet_aton(ipAddress))
        ttyName = self.ptyTuple[2][5:]
        t = time.time()
        t1 = int(t)
        t2 = int((t - t1) * 1e6)
        entry = utmp.UtmpEntry()
        entry.ut_type = loggedIn and utmp.USER_PROCESS or utmp.DEAD_PROCESS
        entry.ut_pid = self.pty.pid
        entry.ut_line = ttyName
        entry.ut_id = ttyName[-4:]
        entry.ut_tv = (t1, t2)
        if loggedIn:
            entry.ut_user = self.avatar.username
            entry.ut_host = socket.gethostbyaddr(ipAddress)[0]
            entry.ut_addr_v6 = (packedIp, 0, 0, 0)
        a = utmp.UtmpRecord(utmp.UTMP_FILE)
        a.pututline(entry)
        a.endutent()
        b = utmp.UtmpRecord(utmp.WTMP_FILE)
        b.pututline(entry)
        b.endutent()

    def getPty(self, term, windowSize, modes):
        self.environ["TERM"] = term
        self.winSize = windowSize
        self.modes = modes
        master, slave = pty.openpty()
        ttyname = os.ttyname(slave)
        self.environ["SSH_TTY"] = ttyname
        self.ptyTuple = (master, slave, ttyname)

    def openShell(self, proto):
        if not self.ptyTuple:  # We didn't get a pty-req.
            self._log.error("tried to get shell without pty, failing")
            raise ConchError("no pty")
        uid, gid = self.avatar.getUserGroupId()
        homeDir = self.avatar.getHomeDir()
        shell = self.avatar.getShell()
        self.environ["USER"] = self.avatar.username
        self.environ["HOME"] = homeDir
        self.environ["SHELL"] = shell
        shellExec = os.path.basename(shell)
        peer = self.avatar.conn.transport.transport.getPeer()
        host = self.avatar.conn.transport.transport.getHost()
        self.environ["SSH_CLIENT"] = f"{peer.host} {peer.port} {host.port}"
        self.getPtyOwnership()
        self.pty = self._reactor.spawnProcess(
            proto,
            shell,
            [f"-{shellExec}"],
            self.environ,
            homeDir,
            uid,
            gid,
            usePTY=self.ptyTuple,
        )
        self.addUTMPEntry()
        fcntl.ioctl(self.pty.fileno(), tty.TIOCSWINSZ, struct.pack("4H", *self.winSize))
        if self.modes:
            self.setModes()
        self.oldWrite = proto.transport.write
        proto.transport.write = self._writeHack
        self.avatar.conn.transport.transport.setTcpNoDelay(1)

    def execCommand(self, proto, cmd):
        uid, gid = self.avatar.getUserGroupId()
        homeDir = self.avatar.getHomeDir()
        shell = self.avatar.getShell() or "/bin/sh"
        self.environ["HOME"] = homeDir
        command = (shell, "-c", cmd)
        peer = self.avatar.conn.transport.transport.getPeer()
        host = self.avatar.conn.transport.transport.getHost()
        self.environ["SSH_CLIENT"] = f"{peer.host} {peer.port} {host.port}"
        if self.ptyTuple:
            self.getPtyOwnership()
        self.pty = self._reactor.spawnProcess(
            proto,
            shell,
            command,
            self.environ,
            homeDir,
            uid,
            gid,
            usePTY=self.ptyTuple or 0,
        )
        if self.ptyTuple:
            self.addUTMPEntry()
            if self.modes:
                self.setModes()
        self.avatar.conn.transport.transport.setTcpNoDelay(1)

    def getPtyOwnership(self):
        ttyGid = os.stat(self.ptyTuple[2])[5]
        uid, gid = self.avatar.getUserGroupId()
        euid, egid = os.geteuid(), os.getegid()
        os.setegid(0)
        os.seteuid(0)
        try:
            os.chown(self.ptyTuple[2], uid, ttyGid)
        finally:
            os.setegid(egid)
            os.seteuid(euid)

    def setModes(self):
        pty = self.pty
        attr = tty.tcgetattr(pty.fileno())
        for mode, modeValue in self.modes:
            if mode not in ttymodes.TTYMODES:
                continue
            ttyMode = ttymodes.TTYMODES[mode]
            if len(ttyMode) == 2:  # Flag.
                flag, ttyAttr = ttyMode
                if not hasattr(tty, ttyAttr):
                    continue
                ttyval = getattr(tty, ttyAttr)
                if modeValue:
                    attr[flag] = attr[flag] | ttyval
                else:
                    attr[flag] = attr[flag] & ~ttyval
            elif ttyMode == "OSPEED":
                attr[tty.OSPEED] = getattr(tty, f"B{modeValue}")
            elif ttyMode == "ISPEED":
                attr[tty.ISPEED] = getattr(tty, f"B{modeValue}")
            else:
                if not hasattr(tty, ttyMode):
                    continue
                ttyval = getattr(tty, ttyMode)
                attr[tty.CC][ttyval] = bytes((modeValue,))
        tty.tcsetattr(pty.fileno(), tty.TCSANOW, attr)

    def eofReceived(self):
        if self.pty:
            self.pty.closeStdin()

    def closed(self):
        if self.ptyTuple and os.path.exists(self.ptyTuple[2]):
            ttyGID = os.stat(self.ptyTuple[2])[5]
            os.chown(self.ptyTuple[2], 0, ttyGID)
        if self.pty:
            try:
                self.pty.signalProcess("HUP")
            except (OSError, ProcessExitedAlready):
                pass
            self.pty.loseConnection()
            self.addUTMPEntry(0)
        self._log.info("shell closed")

    def windowChanged(self, winSize):
        self.winSize = winSize
        fcntl.ioctl(self.pty.fileno(), tty.TIOCSWINSZ, struct.pack("4H", *self.winSize))

    def _writeHack(self, data):
        """
        Hack to send ignore messages when we aren't echoing.
        """
        if self.pty is not None:
            attr = tty.tcgetattr(self.pty.fileno())[3]
            if not attr & tty.ECHO and attr & tty.ICANON:  # No echo.
                self.avatar.conn.transport.sendIgnore("\x00" * (8 + len(data)))
        self.oldWrite(data)


@implementer(ISFTPServer)
class SFTPServerForUnixConchUser:
    def __init__(self, avatar):
        self.avatar = avatar

    def _setAttrs(self, path, attrs):
        """
        NOTE: this function assumes it runs as the logged-in user:
        i.e. under _runAsUser()
        """
        if "uid" in attrs and "gid" in attrs:
            os.chown(path, attrs["uid"], attrs["gid"])
        if "permissions" in attrs:
            os.chmod(path, attrs["permissions"])
        if "atime" in attrs and "mtime" in attrs:
            os.utime(path, (attrs["atime"], attrs["mtime"]))

    def _getAttrs(self, s):
        return {
            "size": s.st_size,
            "uid": s.st_uid,
            "gid": s.st_gid,
            "permissions": s.st_mode,
            "atime": int(s.st_atime),
            "mtime": int(s.st_mtime),
        }

    def _absPath(self, path):
        home = self.avatar.getHomeDir()
        return os.path.join(nativeString(home.path), nativeString(path))

    def gotVersion(self, otherVersion, extData):
        return {}

    def openFile(self, filename, flags, attrs):
        return UnixSFTPFile(self, self._absPath(filename), flags, attrs)

    def removeFile(self, filename):
        filename = self._absPath(filename)
        return self.avatar._runAsUser(os.remove, filename)

    def renameFile(self, oldpath, newpath):
        oldpath = self._absPath(oldpath)
        newpath = self._absPath(newpath)
        return self.avatar._runAsUser(os.rename, oldpath, newpath)

    def makeDirectory(self, path, attrs):
        path = self._absPath(path)
        return self.avatar._runAsUser(
            [(os.mkdir, (path,)), (self._setAttrs, (path, attrs))]
        )

    def removeDirectory(self, path):
        path = self._absPath(path)
        self.avatar._runAsUser(os.rmdir, path)

    def openDirectory(self, path):
        return UnixSFTPDirectory(self, self._absPath(path))

    def getAttrs(self, path, followLinks):
        path = self._absPath(path)
        if followLinks:
            s = self.avatar._runAsUser(os.stat, path)
        else:
            s = self.avatar._runAsUser(os.lstat, path)
        return self._getAttrs(s)

    def setAttrs(self, path, attrs):
        path = self._absPath(path)
        self.avatar._runAsUser(self._setAttrs, path, attrs)

    def readLink(self, path):
        path = self._absPath(path)
        return self.avatar._runAsUser(os.readlink, path)

    def makeLink(self, linkPath, targetPath):
        linkPath = self._absPath(linkPath)
        targetPath = self._absPath(targetPath)
        return self.avatar._runAsUser(os.symlink, targetPath, linkPath)

    def realPath(self, path):
        return os.path.realpath(self._absPath(path))

    def extendedRequest(self, extName, extData):
        raise NotImplementedError


@implementer(ISFTPFile)
class UnixSFTPFile:
    def __init__(self, server, filename, flags, attrs):
        self.server = server
        openFlags = 0
        if flags & FXF_READ == FXF_READ and flags & FXF_WRITE == 0:
            openFlags = os.O_RDONLY
        if flags & FXF_WRITE == FXF_WRITE and flags & FXF_READ == 0:
            openFlags = os.O_WRONLY
        if flags & FXF_WRITE == FXF_WRITE and flags & FXF_READ == FXF_READ:
            openFlags = os.O_RDWR
        if flags & FXF_APPEND == FXF_APPEND:
            openFlags |= os.O_APPEND
        if flags & FXF_CREAT == FXF_CREAT:
            openFlags |= os.O_CREAT
        if flags & FXF_TRUNC == FXF_TRUNC:
            openFlags |= os.O_TRUNC
        if flags & FXF_EXCL == FXF_EXCL:
            openFlags |= os.O_EXCL
        if "permissions" in attrs:
            mode = attrs["permissions"]
            del attrs["permissions"]
        else:
            mode = 0o777
        fd = server.avatar._runAsUser(os.open, filename, openFlags, mode)
        if attrs:
            server.avatar._runAsUser(server._setAttrs, filename, attrs)
        self.fd = fd

    def close(self):
        return self.server.avatar._runAsUser(os.close, self.fd)

    def readChunk(self, offset, length):
        return self.server.avatar._runAsUser(
            [(os.lseek, (self.fd, offset, 0)), (os.read, (self.fd, length))]
        )

    def writeChunk(self, offset, data):
        return self.server.avatar._runAsUser(
            [(os.lseek, (self.fd, offset, 0)), (os.write, (self.fd, data))]
        )

    def getAttrs(self):
        s = self.server.avatar._runAsUser(os.fstat, self.fd)
        return self.server._getAttrs(s)

    def setAttrs(self, attrs):
        raise NotImplementedError


class UnixSFTPDirectory:
    def __init__(self, server, directory):
        self.server = server
        self.files = server.avatar._runAsUser(os.listdir, directory)
        self.dir = directory

    def __iter__(self):
        return self

    def __next__(self):
        try:
            f = self.files.pop(0)
        except IndexError:
            raise StopIteration
        else:
            s = self.server.avatar._runAsUser(os.lstat, os.path.join(self.dir, f))
            longname = lsLine(f, s)
            attrs = self.server._getAttrs(s)
            return (f, longname, attrs)

    next = __next__

    def close(self):
        self.files = []


components.registerAdapter(
    SFTPServerForUnixConchUser, UnixConchUser, filetransfer.ISFTPServer
)
components.registerAdapter(SSHSessionForUnixConchUser, UnixConchUser, session.ISession)