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# Copyright (C) Internet Systems Consortium, Inc. ("ISC")
#
# SPDX-License-Identifier: MPL-2.0
#
# This Source Code Form is subject to the terms of the Mozilla Public
# License, v. 2.0. If a copy of the MPL was not distributed with this
# file, you can obtain one at https://mozilla.org/MPL/2.0/.
#
# See the COPYRIGHT file distributed with this work for additional
# information regarding copyright ownership.
from __future__ import print_function
import os
import sys
import signal
import socket
import select
import struct
import dns, dns.message
from dns.rcode import *
modes = [
b"silent", # Do not respond
b"close", # UDP: same as silent; TCP: also close the connection
b"servfail", # Always respond with SERVFAIL
b"unstable", # Constantly switch between "silent" and "servfail"
]
mode = modes[0]
n = 0
def ctrl_channel(msg):
global modes, mode, n
msg = msg.splitlines().pop(0)
print("Received control message: %s" % msg)
if msg in modes:
mode = msg
n = 0
print("New mode: %s" % str(mode))
def create_servfail(msg):
m = dns.message.from_wire(msg)
qname = m.question[0].name.to_text()
rrtype = m.question[0].rdtype
typename = dns.rdatatype.to_text(rrtype)
with open("query.log", "a") as f:
f.write("%s %s\n" % (typename, qname))
print("%s %s" % (typename, qname), end=" ")
r = dns.message.make_response(m)
r.set_rcode(SERVFAIL)
return r
def sigterm(signum, frame):
print("Shutting down now...")
os.remove("ans.pid")
running = False
sys.exit(0)
ip4 = "10.53.0.8"
try:
port = int(os.environ["PORT"])
except:
port = 5300
try:
ctrlport = int(os.environ["EXTRAPORT1"])
except:
ctrlport = 5300
query4_udp = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
query4_udp.bind((ip4, port))
query4_tcp = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
query4_tcp.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
query4_tcp.bind((ip4, port))
query4_tcp.listen(100)
ctrl4_tcp = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
ctrl4_tcp.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
ctrl4_tcp.bind((ip4, ctrlport))
ctrl4_tcp.listen(100)
signal.signal(signal.SIGTERM, sigterm)
f = open("ans.pid", "w")
pid = os.getpid()
print(pid, file=f)
f.close()
running = True
print("Listening on %s port %d" % (ip4, port))
print("Listening on %s port %d" % (ip4, ctrlport))
print("Ctrl-c to quit")
input = [query4_udp, query4_tcp, ctrl4_tcp]
hung_conns = []
while running:
try:
inputready, outputready, exceptready = select.select(input, [], [])
except select.error as e:
break
except socket.error as e:
break
except KeyboardInterrupt:
break
for s in inputready:
if s == query4_udp:
n = n + 1
print("UDP query received on %s" % ip4, end=" ")
msg = s.recvfrom(65535)
if (
mode == b"silent"
or mode == b"close"
or (mode == b"unstable" and n % 2 == 1)
):
# Do not respond.
print("NO RESPONSE (%s)" % str(mode))
continue
elif mode == b"servfail" or (mode == b"unstable" and n % 2 == 0):
rsp = create_servfail(msg[0])
if rsp:
print(dns.rcode.to_text(rsp.rcode()))
s.sendto(rsp.to_wire(), msg[1])
else:
print("NO RESPONSE (can not create a response)")
else:
raise (Exception("unsupported mode: %s" % mode))
elif s == query4_tcp:
n = n + 1
print("TCP query received on %s" % ip4, end=" ")
conn = None
try:
if mode == b"silent" or (mode == b"unstable" and n % 2 == 1):
conn, addr = s.accept()
# Do not respond and hang the connection.
print("NO RESPONSE (%s)" % str(mode))
hung_conns.append(conn)
continue
elif mode == b"close":
conn, addr = s.accept()
# Do not respond and close the connection.
print("NO RESPONSE (%s)" % str(mode))
conn.close()
continue
elif mode == b"servfail" or (mode == b"unstable" and n % 2 == 0):
conn, addr = s.accept()
# get TCP message length
msg = conn.recv(2)
if len(msg) != 2:
print("NO RESPONSE (can not read the message length)")
conn.close()
continue
length = struct.unpack(">H", msg[:2])[0]
msg = conn.recv(length)
if len(msg) != length:
print("NO RESPONSE (can not read the message)")
conn.close()
continue
rsp = create_servfail(msg)
if rsp:
print(dns.rcode.to_text(rsp.rcode()))
wire = rsp.to_wire()
conn.send(struct.pack(">H", len(wire)))
conn.send(wire)
else:
print("NO RESPONSE (can not create a response)")
else:
raise (Exception("unsupported mode: %s" % mode))
except socket.error as e:
print("NO RESPONSE (error: %s)" % str(e))
if conn:
conn.close()
elif s == ctrl4_tcp:
print("Control channel connected")
conn = None
try:
# Handle control channel input
conn, addr = s.accept()
msg = conn.recv(1024)
if msg:
ctrl_channel(msg)
conn.close()
except s.timeout:
pass
if conn:
conn.close()
if not running:
break
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