sshuttle/sshuttle/server.py

import re
import struct
import socket
import traceback
import time
import sys
import os
import platform
from shutil import which

import sshuttle.ssnet as ssnet
import sshuttle.helpers as helpers
import sshuttle.hostwatch as hostwatch
import subprocess as ssubprocess
from sshuttle.ssnet import Handler, Proxy, Mux, MuxWrapper
from sshuttle.helpers import b, log, debug1, debug2, debug3, Fatal, \
    resolvconf_random_nameserver


def _ipmatch(ipstr):
    # FIXME: IPv4 only
    if ipstr == 'default':
        ipstr = '0.0.0.0/0'
    m = re.match(r'^(\d+(\.\d+(\.\d+(\.\d+)?)?)?)(?:/(\d+))?$', ipstr)
    if m:
        g = m.groups()
        ips = g[0]
        width = int(g[4] or 32)
        if g[1] is None:
            ips += '.0.0.0'
            width = min(width, 8)
        elif g[2] is None:
            ips += '.0.0'
            width = min(width, 16)
        elif g[3] is None:
            ips += '.0'
            width = min(width, 24)
        ips = ips
        return (struct.unpack('!I', socket.inet_aton(ips))[0], width)


def _ipstr(ip, width):
    # FIXME: IPv4 only
    if width >= 32:
        return ip
    else:
        return "%s/%d" % (ip, width)


def _maskbits(netmask):
    # FIXME: IPv4 only
    if not netmask:
        return 32
    for i in range(32):
        if netmask[0] & _shl(1, i):
            return 32 - i
    return 0


def _shl(n, bits):
    return n * int(2 ** bits)


def _route_netstat(line):
    cols = line.split(None)
    if len(cols) < 3:
        return None, None
    ipw = _ipmatch(cols[0])
    maskw = _ipmatch(cols[2])  # linux only
    mask = _maskbits(maskw)   # returns 32 if maskw is null
    return ipw, mask


def _route_iproute(line):
    ipm = line.split(None, 1)[0]
    if '/' not in ipm:
        return None, None
    ip, mask = ipm.split('/')
    ipw = _ipmatch(ip)
    return ipw, int(mask)


def _list_routes(argv, extract_route):
    # FIXME: IPv4 only
    env = {
        'PATH': os.environ['PATH'],
        'LC_ALL': "C",
    }
    p = ssubprocess.Popen(argv, stdout=ssubprocess.PIPE, env=env)
    routes = []
    for line in p.stdout:
        if not line.strip():
            continue
        ipw, mask = extract_route(line.decode("ASCII"))
        if not ipw:
            continue
        width = min(ipw[1], mask)
        ip = ipw[0] & _shl(_shl(1, width) - 1, 32 - width)
        routes.append(
            (socket.AF_INET, socket.inet_ntoa(struct.pack('!I', ip)), width))
    rv = p.wait()
    if rv != 0:
        log('WARNING: %r returned %d\n' % (argv, rv))
        log('WARNING: That prevents --auto-nets from working.\n')

    return routes


def list_routes():
    if which('ip'):
        routes = _list_routes(['ip', 'route'], _route_iproute)
    elif which('netstat'):
        routes = _list_routes(['netstat', '-rn'], _route_netstat)
    else:
        log('WARNING: Neither ip nor netstat were found on the server.\n')
        routes = []

    for (family, ip, width) in routes:
        if not ip.startswith('0.') and not ip.startswith('127.'):
            yield (family, ip, width)


def _exc_dump():
    exc_info = sys.exc_info()
    return ''.join(traceback.format_exception(*exc_info))


def start_hostwatch(seed_hosts, auto_hosts):
    s1, s2 = socket.socketpair()
    pid = os.fork()
    if not pid:
        # child
        rv = 99
        try:
            try:
                s2.close()
                os.dup2(s1.fileno(), 1)
                os.dup2(s1.fileno(), 0)
                s1.close()
                rv = hostwatch.hw_main(seed_hosts, auto_hosts) or 0
            except Exception:
                log('%s\n' % _exc_dump())
                rv = 98
        finally:
            os._exit(rv)
    s1.close()
    return pid, s2


class Hostwatch:

    def __init__(self):
        self.pid = 0
        self.sock = None


class DnsProxy(Handler):

    def __init__(self, mux, chan, request, to_nameserver):
        Handler.__init__(self, [])
        self.timeout = time.time() + 30
        self.mux = mux
        self.chan = chan
        self.tries = 0
        self.request = request
        self.peers = {}
        self.to_ns_peer = None
        self.to_ns_port = None
        if to_nameserver is None:
            self.to_nameserver = None
        else:
            self.to_ns_peer, self.to_ns_port = to_nameserver.split("@")
            self.to_nameserver = self._addrinfo(self.to_ns_peer,
                                                self.to_ns_port)
        self.try_send()

    @staticmethod
    def _addrinfo(peer, port):
        if int(port) == 0:
            port = 53
        family, _, _, _, sockaddr = socket.getaddrinfo(peer, port)[0]
        return (family, sockaddr)

    def try_send(self):
        if self.tries >= 3:
            return
        self.tries += 1

        if self.to_nameserver is None:
            _, peer = resolvconf_random_nameserver()
            port = 53
        else:
            peer = self.to_ns_peer
            port = int(self.to_ns_port)

        family, sockaddr = self._addrinfo(peer, port)
        sock = socket.socket(family, socket.SOCK_DGRAM)
        sock.setsockopt(socket.SOL_IP, socket.IP_TTL, 63)
        sock.connect(sockaddr)

        self.peers[sock] = peer

        debug2('DNS: sending to %r:%d (try %d)\n' % (peer, port, self.tries))
        try:
            sock.send(self.request)
            self.socks.append(sock)
        except socket.error:
            _, e = sys.exc_info()[:2]
            if e.args[0] in ssnet.NET_ERRS:
                # might have been spurious; try again.
                # Note: these errors sometimes are reported by recv(),
                # and sometimes by send().  We have to catch both.
                debug2('DNS send to %r: %s\n' % (peer, e))
                self.try_send()
                return
            else:
                log('DNS send to %r: %s\n' % (peer, e))
                return

    def callback(self, sock):
        peer = self.peers[sock]

        try:
            data = sock.recv(4096)
        except socket.error:
            _, e = sys.exc_info()[:2]
            self.socks.remove(sock)
            del self.peers[sock]

            if e.args[0] in ssnet.NET_ERRS:
                # might have been spurious; try again.
                # Note: these errors sometimes are reported by recv(),
                # and sometimes by send().  We have to catch both.
                debug2('DNS recv from %r: %s\n' % (peer, e))
                self.try_send()
                return
            else:
                log('DNS recv from %r: %s\n' % (peer, e))
                return
        debug2('DNS response: %d bytes\n' % len(data))
        self.mux.send(self.chan, ssnet.CMD_DNS_RESPONSE, data)
        self.ok = False


class UdpProxy(Handler):

    def __init__(self, mux, chan, family):
        sock = socket.socket(family, socket.SOCK_DGRAM)
        Handler.__init__(self, [sock])
        self.timeout = time.time() + 30
        self.mux = mux
        self.chan = chan
        self.sock = sock
        if family == socket.AF_INET:
            self.sock.setsockopt(socket.SOL_IP, socket.IP_TTL, 63)

    def send(self, dstip, data):
        debug2('UDP: sending to %r port %d\n' % dstip)
        try:
            self.sock.sendto(data, dstip)
        except socket.error:
            _, e = sys.exc_info()[:2]
            log('UDP send to %r port %d: %s\n' % (dstip[0], dstip[1], e))
            return

    def callback(self, sock):
        try:
            data, peer = sock.recvfrom(4096)
        except socket.error:
            _, e = sys.exc_info()[:2]
            log('UDP recv from %r port %d: %s\n' % (peer[0], peer[1], e))
            return
        debug2('UDP response: %d bytes\n' % len(data))
        hdr = b("%s,%r," % (peer[0], peer[1]))
        self.mux.send(self.chan, ssnet.CMD_UDP_DATA, hdr + data)


def main(latency_control, auto_hosts, to_nameserver, auto_nets):
    debug1('Starting server with Python version %s\n'
           % platform.python_version())

    if helpers.verbose >= 1:
        helpers.logprefix = ' s: '
    else:
        helpers.logprefix = 'server: '
    debug1('latency control setting = %r\n' % latency_control)

    # synchronization header
    sys.stdout.write('\0\0SSHUTTLE0001')
    sys.stdout.flush()

    handlers = []
    mux = Mux(sys.stdin, sys.stdout)
    handlers.append(mux)

    debug1('auto-nets:' + str(auto_nets) + '\n')
    if auto_nets:
        routes = list(list_routes())
        debug1('available routes:\n')
        for r in routes:
            debug1('  %d/%s/%d\n' % r)
    else:
        routes = []

    routepkt = ''
    for r in routes:
        routepkt += '%d,%s,%d\n' % r
    mux.send(0, ssnet.CMD_ROUTES, b(routepkt))

    hw = Hostwatch()
    hw.leftover = b('')

    def hostwatch_ready(sock):
        assert(hw.pid)
        content = hw.sock.recv(4096)
        if content:
            lines = (hw.leftover + content).split(b('\n'))
            if lines[-1]:
                # no terminating newline: entry isn't complete yet!
                hw.leftover = lines.pop()
                lines.append(b(''))
            else:
                hw.leftover = b('')
            mux.send(0, ssnet.CMD_HOST_LIST, b('\n').join(lines))
        else:
            raise Fatal('hostwatch process died')

    def got_host_req(data):
        if not hw.pid:
            (hw.pid, hw.sock) = start_hostwatch(
                    data.decode("ASCII").strip().split(), auto_hosts)
            handlers.append(Handler(socks=[hw.sock],
                                    callback=hostwatch_ready))
    mux.got_host_req = got_host_req

    def new_channel(channel, data):
        (family, dstip, dstport) = data.decode("ASCII").split(',', 2)
        family = int(family)
        # AF_INET is the same constant on Linux and BSD but AF_INET6
        # is different. As the client and server can be running on
        # different platforms we can not just set the socket family
        # to what comes in the wire.
        if family != socket.AF_INET:
            family = socket.AF_INET6
        dstport = int(dstport)
        outwrap = ssnet.connect_dst(family, dstip, dstport)
        handlers.append(Proxy(MuxWrapper(mux, channel), outwrap))
    mux.new_channel = new_channel

    dnshandlers = {}

    def dns_req(channel, data):
        debug2('Incoming DNS request channel=%d.\n' % channel)
        h = DnsProxy(mux, channel, data, to_nameserver)
        handlers.append(h)
        dnshandlers[channel] = h
    mux.got_dns_req = dns_req

    udphandlers = {}

    def udp_req(channel, cmd, data):
        debug2('Incoming UDP request channel=%d, cmd=%d\n' % (channel, cmd))
        if cmd == ssnet.CMD_UDP_DATA:
            (dstip, dstport, data) = data.split(b(','), 2)
            dstport = int(dstport)
            debug2('is incoming UDP data. %r %d.\n' % (dstip, dstport))
            h = udphandlers[channel]
            h.send((dstip, dstport), data)
        elif cmd == ssnet.CMD_UDP_CLOSE:
            debug2('is incoming UDP close\n')
            h = udphandlers[channel]
            h.ok = False
            del mux.channels[channel]

    def udp_open(channel, data):
        debug2('Incoming UDP open.\n')
        family = int(data)
        mux.channels[channel] = lambda cmd, data: udp_req(channel, cmd, data)
        if channel in udphandlers:
            raise Fatal('UDP connection channel %d already open' % channel)
        else:
            h = UdpProxy(mux, channel, family)
            handlers.append(h)
            udphandlers[channel] = h
    mux.got_udp_open = udp_open

    while mux.ok:
        if hw.pid:
            assert(hw.pid > 0)
            (rpid, rv) = os.waitpid(hw.pid, os.WNOHANG)
            if rpid:
                raise Fatal(
                    'hostwatch exited unexpectedly: code 0x%04x\n' % rv)

        ssnet.runonce(handlers, mux)
        if latency_control:
            mux.check_fullness()

        if dnshandlers:
            now = time.time()
            remove = []
            for channel, h in dnshandlers.items():
                if h.timeout < now or not h.ok:
                    debug3('expiring dnsreqs channel=%d\n' % channel)
                    remove.append(channel)
                    h.ok = False
            for channel in remove:
                del dnshandlers[channel]
        if udphandlers:
            remove = []
            for channel, h in udphandlers.items():
                if not h.ok:
                    debug3('expiring UDP channel=%d\n' % channel)
                    remove.append(channel)
                    h.ok = False
            for channel in remove:
                del udphandlers[channel]