samba-mirror/selftest/target/dns_hub.py

#!/usr/bin/env python3
#
# Unix SMB/CIFS implementation.
# Copyright (C) Volker Lendecke 2017
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3 of the License, or
# (at your option) any later version.
#
# This program 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 General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
#
# Used by selftest to proxy DNS queries to the correct testenv DC.
# See selftest/target/README for more details.
# Based on the EchoServer example from python docs

import threading
import sys
import select
import socket
import collections
import time
from samba.dcerpc import dns
import samba.ndr as ndr

import socketserver
sserver = socketserver

DNS_REQUEST_TIMEOUT = 10

# make sure the script dies immediately when hitting control-C,
# rather than raising KeyboardInterrupt. As we do all database
# operations using transactions, this is safe.
import signal
signal.signal(signal.SIGINT, signal.SIG_DFL)

class DnsHandler(sserver.BaseRequestHandler):
    dns_qtype_strings = dict((v, k) for k, v in vars(dns).items() if k.startswith('DNS_QTYPE_'))
    def dns_qtype_string(self, qtype):
        "Return a readable qtype code"
        return self.dns_qtype_strings[qtype]

    dns_rcode_strings = dict((v, k) for k, v in vars(dns).items() if k.startswith('DNS_RCODE_'))
    def dns_rcode_string(self, rcode):
        "Return a readable error code"
        return self.dns_rcode_strings[rcode]

    def dns_transaction_udp(self, packet, host):
        "send a DNS query and read the reply"
        s = None
        flags = socket.AddressInfo.AI_NUMERICHOST
        flags |= socket.AddressInfo.AI_NUMERICSERV
        flags |= socket.AddressInfo.AI_PASSIVE
        addr_info = socket.getaddrinfo(host, int(53),
                                       type=socket.SocketKind.SOCK_DGRAM,
                                       flags=flags)
        assert len(addr_info) == 1
        try:
            send_packet = ndr.ndr_pack(packet)
            s = socket.socket(addr_info[0][0], addr_info[0][1], 0)
            s.settimeout(DNS_REQUEST_TIMEOUT)
            s.connect(addr_info[0][4])
            s.sendall(send_packet, 0)
            recv_packet = s.recv(2048, 0)
            return ndr.ndr_unpack(dns.name_packet, recv_packet)
        except socket.error as err:
            print("Error sending to host %s for name %s: %s\n" %
                  (host, packet.questions[0].name, err.errno))
            raise
        finally:
            if s is not None:
                s.close()

    def get_pdc_ipv4_addr(self, lookup_name):
        """Maps a DNS realm to the IPv4 address of the PDC for that testenv"""

        realm_to_ip_mappings = self.server.realm_to_ip_mappings

        # sort the realms so we find the longest-match first
        testenv_realms = sorted(realm_to_ip_mappings.keys(), key=len)
        testenv_realms.reverse()

        for realm in testenv_realms:
            if lookup_name.endswith(realm):
                # return the corresponding IP address for this realm's PDC
                return realm_to_ip_mappings[realm]

        return None

    def forwarder(self, name):
        lname = name.lower()

        # check for special cases used by tests (e.g. dns_forwarder.py)
        if lname.endswith('an-address-that-will-not-resolve'):
            return 'ignore'
        if lname.endswith('dsfsdfs'):
            return 'fail'
        if lname.endswith("torture1", 0, len(lname)-2):
            # CATCH TORTURE100, TORTURE101, ...
            return 'torture'
        if lname.endswith('_none_.example.com'):
            return 'torture'
        if lname.endswith('torturedom.samba.example.com'):
            return 'torture'

        # return the testenv PDC matching the realm being requested
        return self.get_pdc_ipv4_addr(lname)

    def handle(self):
        start = time.monotonic()
        data, sock = self.request
        query = ndr.ndr_unpack(dns.name_packet, data)
        name = query.questions[0].name
        forwarder = self.forwarder(name)
        response = None

        if forwarder == 'ignore':
            return
        elif forwarder == 'fail':
            pass
        elif forwarder in ['torture', None]:
            response = query
            response.operation |= dns.DNS_FLAG_REPLY
            response.operation |= dns.DNS_FLAG_RECURSION_AVAIL
            response.operation |= dns.DNS_RCODE_NXDOMAIN
        else:
            try:
                response = self.dns_transaction_udp(query, forwarder)
            except OSError as err:
                print("dns_hub: Error sending dns query to forwarder[%s] for name[%s]: %s" %
                      (forwarder, name, err))

        if response is None:
            response = query
            response.operation |= dns.DNS_FLAG_REPLY
            response.operation |= dns.DNS_FLAG_RECURSION_AVAIL
            response.operation |= dns.DNS_RCODE_SERVFAIL

        send_packet = ndr.ndr_pack(response)

        end = time.monotonic()
        tdiff = end - start
        errcode = response.operation & dns.DNS_RCODE
        if tdiff > (DNS_REQUEST_TIMEOUT/5):
            debug = True
        else:
            debug = False
        if debug:
            print("dns_hub: forwarder[%s] client[%s] name[%s][%s] %s response.operation[0x%x] tdiff[%s]\n" %
                (forwarder, self.client_address, name,
                 self.dns_qtype_string(query.questions[0].question_type),
                 self.dns_rcode_string(errcode), response.operation, tdiff))

        try:
            sock.sendto(send_packet, self.client_address)
        except socket.error as err:
            print("dns_hub: Error sending response to client[%s] for name[%s] tdiff[%s]: %s\n" %
                (self.client_address, name, tdiff, err))


class server_thread(threading.Thread):
    def __init__(self, server, name):
        threading.Thread.__init__(self, name=name)
        self.server = server

    def run(self):
        print("dns_hub[%s]: before serve_forever()" % self.name)
        self.server.serve_forever()
        print("dns_hub[%s]: after serve_forever()" % self.name)

    def stop(self):
        print("dns_hub[%s]: before shutdown()" % self.name)
        self.server.shutdown()
        print("dns_hub[%s]: after shutdown()" % self.name)
        self.server.server_close()

class UDPV4Server(sserver.UDPServer):
    address_family = socket.AF_INET

class UDPV6Server(sserver.UDPServer):
    address_family = socket.AF_INET6

def main():
    if len(sys.argv) < 4:
        print("Usage: dns_hub.py TIMEOUT LISTENADDRESS[,LISTENADDRESS,...] MAPPING[,MAPPING,...]")
        sys.exit(1)

    timeout = int(sys.argv[1]) * 1000
    timeout = min(timeout, 2**31 - 1)  # poll with 32-bit int can't take more
    # we pass in the listen addresses as a comma-separated string.
    listenaddresses = sys.argv[2].split(',')
    # we pass in the realm-to-IP mappings as a comma-separated key=value
    # string. Convert this back into a dictionary that the DnsHandler can use
    realm_mappings = collections.OrderedDict(kv.split('=') for kv in sys.argv[3].split(','))

    def prepare_server_thread(listenaddress, realm_mappings):

        flags = socket.AddressInfo.AI_NUMERICHOST
        flags |= socket.AddressInfo.AI_NUMERICSERV
        flags |= socket.AddressInfo.AI_PASSIVE
        addr_info = socket.getaddrinfo(listenaddress, int(53),
                                       type=socket.SocketKind.SOCK_DGRAM,
                                       flags=flags)
        assert len(addr_info) == 1
        if addr_info[0][0] == socket.AddressFamily.AF_INET6:
            server = UDPV6Server(addr_info[0][4], DnsHandler)
        else:
            server = UDPV4Server(addr_info[0][4], DnsHandler)

        # we pass in the realm-to-IP mappings as a comma-separated key=value
        # string. Convert this back into a dictionary that the DnsHandler can use
        server.realm_to_ip_mappings = realm_mappings
        t = server_thread(server, name="UDP[%s]" % listenaddress)
        return t

    print("dns_hub will proxy DNS requests for the following realms:")
    for realm, ip in realm_mappings.items():
        print("  {0} ==> {1}".format(realm, ip))

    print("dns_hub will listen on the following UDP addresses:")
    threads = []
    for listenaddress in listenaddresses:
        print("  %s" % listenaddress)
        t = prepare_server_thread(listenaddress, realm_mappings)
        threads.append(t)

    for t in threads:
        t.start()
    p = select.poll()
    stdin = sys.stdin.fileno()
    p.register(stdin, select.POLLIN)
    p.poll(timeout)
    print("dns_hub: after poll()")
    for t in threads:
        t.stop()
    for t in threads:
        t.join()
    print("dns_hub: before exit()")
    sys.exit(0)

main()