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#!/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 time
from samba.dcerpc import dns
import samba.ndr as ndr
if sys.version_info[0] < 3:
import SocketServer
sserver = SocketServer
else:
import socketserver
sserver = socketserver
DNS_REQUEST_TIMEOUT = 10
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
try:
send_packet = ndr.ndr_pack(packet)
s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, 0)
s.settimeout(DNS_REQUEST_TIMEOUT)
s.connect((host, 53))
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()
return None
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 is 'ignore':
return
elif forwarder is '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:
response = self.dns_transaction_udp(query, forwarder)
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):
threading.Thread.__init__(self)
self.server = server
def run(self):
self.server.serve_forever()
print("dns_hub: after serve_forever()")
def main():
if len(sys.argv) < 4:
print("Usage: dns_hub.py TIMEOUT HOST 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
host = sys.argv[2]
server = sserver.UDPServer((host, int(53)), 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
realm_mapping = dict(kv.split('=') for kv in sys.argv[3].split(','))
server.realm_to_ip_mappings = realm_mapping
print("dns_hub will proxy DNS requests for the following realms:")
for realm, ip in server.realm_to_ip_mappings.items():
print(" {0} ==> {1}".format(realm, ip))
t = server_thread(server)
t.start()
p = select.poll()
stdin = sys.stdin.fileno()
p.register(stdin, select.POLLIN)
p.poll(timeout)
print("dns_hub: after poll()")
server.shutdown()
t.join()
print("dns_hub: before exit()")
sys.exit(0)
main()
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