selftest/target/dns_hub.py

   1 #!/usr/bin/env python3
   2 #
   3 # Unix SMB/CIFS implementation.
   4 # Copyright (C) Volker Lendecke 2017
   5 #
   6 # This program is free software; you can redistribute it and/or modify
   7 # it under the terms of the GNU General Public License as published by
   8 # the Free Software Foundation; either version 3 of the License, or
   9 # (at your option) any later version.
  10 #
  11 # This program is distributed in the hope that it will be useful,
  12 # but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 # GNU General Public License for more details.
  15 #
  16 # You should have received a copy of the GNU General Public License
  17 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
  18 #
  19 # Used by selftest to proxy DNS queries to the correct testenv DC.
  20 # See selftest/target/README for more details.
  21 # Based on the EchoServer example from python docs
  22
  23 import threading
  24 import sys
  25 import select
  26 import socket
  27 import time
  28 from samba.dcerpc import dns
  29 import samba.ndr as ndr
  30
  31 if sys.version_info[0] < 3:
  32     import SocketServer
  33     sserver = SocketServer
  34 else:
  35     import socketserver
  36     sserver = socketserver
  37
  38 DNS_REQUEST_TIMEOUT = 10
  39
  40
  41 class DnsHandler(sserver.BaseRequestHandler):
  42     dns_qtype_strings = dict((v, k) for k, v in vars(dns).items() if k.startswith('DNS_QTYPE_'))
  43     def dns_qtype_string(self, qtype):
  44         "Return a readable qtype code"
  45         return self.dns_qtype_strings[qtype]
  46
  47     dns_rcode_strings = dict((v, k) for k, v in vars(dns).items() if k.startswith('DNS_RCODE_'))
  48     def dns_rcode_string(self, rcode):
  49         "Return a readable error code"
  50         return self.dns_rcode_strings[rcode]
  51
  52     def dns_transaction_udp(self, packet, host):
  53         "send a DNS query and read the reply"
  54         s = None
  55         try:
  56             send_packet = ndr.ndr_pack(packet)
  57             s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, 0)
  58             s.settimeout(DNS_REQUEST_TIMEOUT)
  59             s.connect((host, 53))
  60             s.sendall(send_packet, 0)
  61             recv_packet = s.recv(2048, 0)
  62             return ndr.ndr_unpack(dns.name_packet, recv_packet)
  63         except socket.error as err:
  64             print("Error sending to host %s for name %s: %s\n" %
  65                   (host, packet.questions[0].name, err.errno))
  66             raise
  67         finally:
  68             if s is not None:
  69                 s.close()
  70         return None
  71
  72     def get_pdc_ipv4_addr(self, lookup_name):
  73         """Maps a DNS realm to the IPv4 address of the PDC for that testenv"""
  74
  75         realm_to_ip_mappings = self.server.realm_to_ip_mappings
  76
  77         # sort the realms so we find the longest-match first
  78         testenv_realms = sorted(realm_to_ip_mappings.keys(), key=len)
  79         testenv_realms.reverse()
  80
  81         for realm in testenv_realms:
  82             if lookup_name.endswith(realm):
  83                 # return the corresponding IP address for this realm's PDC
  84                 return realm_to_ip_mappings[realm]
  85
  86         return None
  87
  88     def forwarder(self, name):
  89         lname = name.lower()
  90
  91         # check for special cases used by tests (e.g. dns_forwarder.py)
  92         if lname.endswith('an-address-that-will-not-resolve'):
  93             return 'ignore'
  94         if lname.endswith('dsfsdfs'):
  95             return 'fail'
  96         if lname.endswith("torture1", 0, len(lname)-2):
  97             # CATCH TORTURE100, TORTURE101, ...
  98             return 'torture'
  99         if lname.endswith('_none_.example.com'):
 100             return 'torture'
 101         if lname.endswith('torturedom.samba.example.com'):
 102             return 'torture'
 103
 104         # return the testenv PDC matching the realm being requested
 105         return self.get_pdc_ipv4_addr(lname)
 106
 107     def handle(self):
 108         start = time.monotonic()
 109         data, sock = self.request
 110         query = ndr.ndr_unpack(dns.name_packet, data)
 111         name = query.questions[0].name
 112         forwarder = self.forwarder(name)
 113         response = None
 114
 115         if forwarder is 'ignore':
 116             return
 117         elif forwarder is 'fail':
 118             pass
 119         elif forwarder in ['torture', None]:
 120             response = query
 121             response.operation |= dns.DNS_FLAG_REPLY
 122             response.operation |= dns.DNS_FLAG_RECURSION_AVAIL
 123             response.operation |= dns.DNS_RCODE_NXDOMAIN
 124         else:
 125             response = self.dns_transaction_udp(query, forwarder)
 126
 127         if response is None:
 128             response = query
 129             response.operation |= dns.DNS_FLAG_REPLY
 130             response.operation |= dns.DNS_FLAG_RECURSION_AVAIL
 131             response.operation |= dns.DNS_RCODE_SERVFAIL
 132
 133         send_packet = ndr.ndr_pack(response)
 134
 135         end = time.monotonic()
 136         tdiff = end - start
 137         errcode = response.operation & dns.DNS_RCODE
 138         if tdiff > (DNS_REQUEST_TIMEOUT/5):
 139             debug = True
 140         else:
 141             debug = False
 142         if debug:
 143             print("dns_hub: forwarder[%s] client[%s] name[%s][%s] %s response.operation[0x%x] tdiff[%s]\n" %
 144                 (forwarder, self.client_address, name,
 145                  self.dns_qtype_string(query.questions[0].question_type),
 146                  self.dns_rcode_string(errcode), response.operation, tdiff))
 147
 148         try:
 149             sock.sendto(send_packet, self.client_address)
 150         except socket.error as err:
 151             print("dns_hub: Error sending response to client[%s] for name[%s] tdiff[%s]: %s\n" %
 152                 (self.client_address, name, tdiff, err))
 153
 154
 155 class server_thread(threading.Thread):
 156     def __init__(self, server):
 157         threading.Thread.__init__(self)
 158         self.server = server
 159
 160     def run(self):
 161         self.server.serve_forever()
 162         print("dns_hub: after serve_forever()")
 163
 164
 165 def main():
 166     timeout = int(sys.argv[1]) * 1000
 167     timeout = min(timeout, 2**31 - 1)  # poll with 32-bit int can't take more
 168     host = sys.argv[2]
 169
 170     server = sserver.UDPServer((host, int(53)), DnsHandler)
 171
 172     # we pass in the realm-to-IP mappings as a comma-separated key=value
 173     # string. Convert this back into a dictionary that the DnsHandler can use
 174     realm_mapping = dict(kv.split('=') for kv in sys.argv[3].split(','))
 175     server.realm_to_ip_mappings = realm_mapping
 176
 177     print("dns_hub will proxy DNS requests for the following realms:")
 178     for realm, ip in server.realm_to_ip_mappings.items():
 179         print("  {0} ==> {1}".format(realm, ip))
 180
 181     t = server_thread(server)
 182     t.start()
 183     p = select.poll()
 184     stdin = sys.stdin.fileno()
 185     p.register(stdin, select.POLLIN)
 186     p.poll(timeout)
 187     print("dns_hub: after poll()")
 188     server.shutdown()
 189     t.join()
 190     print("dns_hub: before exit()")
 191     sys.exit(0)
 192
 193 main()