249 lines
9.6 KiB
Python
Executable File
249 lines
9.6 KiB
Python
Executable File
#!/usr/bin/env python
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# Copyright 2017 Red Hat, Inc.
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# All Rights Reserved.
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#
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# Licensed under the Apache License, Version 2.0 (the "License"); you may
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# not use this file except in compliance with the License. You may obtain
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# a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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# License for the specific language governing permissions and limitations
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# under the License.
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import fcntl
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import six
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import socket
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import struct
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import sys
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import threading
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import time
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ETH_P_IP = 0x0800
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SIOCGIFHWADDR = 0x8927
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dhcp_servers = []
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interfaces_addresses = {}
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class DHCPDiscover(object):
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def __init__(self, interface):
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self.interface = interface
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self.mac = interfaces_addresses[interface]
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self.socket = socket.socket(socket.AF_PACKET, socket.SOCK_RAW)
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def bind(self):
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self.socket.bind((self.interface, 0))
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def send(self):
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packet = self.packet()
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self.bind()
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self.socket.send(packet)
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def close_socket(self):
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self.socket.close()
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def packet(self):
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return self.ethernet_header() \
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+ self.ip_header() \
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+ self.udp_header() \
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+ self.dhcp_discover_payload()
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def ethernet_header(self):
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return struct.pack('!6s6sH',
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b'\xff\xff\xff\xff\xff\xff', # Dest HW address
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self.mac, # Source HW address
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ETH_P_IP) # EtherType - IPv4
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def ip_header(self, checksum=None):
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# 0 1 2 3
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# 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
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# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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# |Version| IHL |Type of Service| Total Length |
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# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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# | Identification |Flags| Fragment Offset |
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# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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# | Time to Live | Protocol | Header Checksum |
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# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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# | Source Address |
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# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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# | Destination Address |
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# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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# | Options | Padding |
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# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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if checksum is None:
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checksum = self.ip_checksum()
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return struct.pack('!BBHHHBBHI4s',
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(4 << 4) + 5, # IPv4 + 20 bytes header length
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0, # TOS
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272, # Total Length
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1, # Id
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0, # Flags & Fragment Offset
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64, # TTL
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socket.IPPROTO_UDP,
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checksum,
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0, # Source
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socket.inet_aton('255.255.255.255')) # Destination
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def ip_checksum(self):
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generated_checksum = self._checksum(self.ip_header(checksum=0))
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return socket.htons(generated_checksum)
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def udp_header(self, checksum=None):
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# 0 7 8 15 16 23 24 31
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# +--------+--------+--------+--------+
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# | Source | Destination |
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# | Port | Port |
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# +--------+--------+--------+--------+
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# | | |
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# | Length | Checksum |
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# +--------+--------+--------+--------+
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if checksum is None:
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checksum = self.udp_checksum()
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return struct.pack('!HHHH',
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68,
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67,
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252,
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checksum)
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def udp_checksum(self):
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pseudo_header = self.ip_pseudo_header()
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generated_checksum = self._checksum(pseudo_header + self.udp_header(
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checksum=0) + self.dhcp_discover_payload())
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return socket.htons(generated_checksum)
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def ip_pseudo_header(self):
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# 0 7 8 15 16 23 24 31
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# +--------+--------+--------+--------+
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# | source address |
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# +--------+--------+--------+--------+
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# | destination address |
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# +--------+--------+--------+--------+
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# | zero |protocol| UDP length |
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# +--------+--------+--------+--------+
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return struct.pack('!I4sBBH',
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0,
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socket.inet_aton('255.255.255.255'),
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0,
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socket.IPPROTO_UDP,
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252) # Length
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def dhcp_discover_payload(self):
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return struct.pack('!BBBBIHHIIII6s10s67s125s4s3s1s',
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1, # Message Type - Boot Request
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1, # Hardware Type - Ethernet
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6, # HW Address Length
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0, # Hops
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0, # Transaction ID
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0, # Seconds elapsed
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0, # Bootp flags
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0, # Client IP Address
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0, # Your IP Address
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0, # Next server IP Address
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0, # Relay Agent IP Address
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self.mac, # Client MAC address
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b'\x00' * 10, # Client HW address padding
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b'\x00' * 67, # Server host name not given
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b'\x00' * 125, # Boot file name not given
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b'\x63\x82\x53\x63', # Magic Cookie
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b'\x35\x01\x01', # DHCP Message Type = Discover
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b'\xff' # Option End
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)
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def _checksum(self, msg):
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s = 0
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for i in range(0, len(msg), 2):
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if six.PY3:
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w = msg[i] + (msg[i + 1] << 8)
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else:
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w = ord(msg[i]) + (ord(msg[i + 1]) << 8)
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s = s + w
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s = (s >> 16) + (s & 0xffff)
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s = s + (s >> 16)
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s = ~s & 0xffff
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return s
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def get_hw_addresses(interfaces):
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s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
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for interface in interfaces:
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info = fcntl.ioctl(s.fileno(),
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SIOCGIFHWADDR,
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struct.pack('256s', interface[:15].encode('utf-8')))
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interfaces_addresses[interface] = info[18:24]
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s.close()
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def inspect_frame(data):
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eth_type = struct.unpack('!H', data[12:14])[0]
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protocol = data[23] if six.PY3 else ord(data[23])
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src_port = struct.unpack('!H', data[34:36])[0]
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dst_port = struct.unpack('!H', data[36:38])[0]
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msg_type = data[42] if six.PY3 else ord(data[42])
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# Make sure we got a DHCP Offer
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if eth_type == ETH_P_IP \
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and protocol == socket.IPPROTO_UDP \
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and src_port == 67 \
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and dst_port == 68 \
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and msg_type == 2: # DHCP Boot Reply
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if six.PY3:
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server_ip_address = '.'.join(["%s" % m for m in
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data[26:30]])
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server_hw_address = ":".join(["%02x" % m for m in
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data[6:12]])
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else:
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server_ip_address = '.'.join(["%s" % ord(m) for m in
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data[26:30]])
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server_hw_address = ":".join(["%02x" % ord(m) for m in
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data[6:12]])
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dhcp_servers.append([server_ip_address, server_hw_address])
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def wait_for_dhcp_offers(interfaces, timeout):
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listening_socket = socket.socket(socket.PF_PACKET, socket.SOCK_RAW,
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socket.htons(ETH_P_IP))
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listening_socket.settimeout(timeout)
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allowed_macs = interfaces_addresses.values()
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end_of_time = time.time() + timeout
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try:
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while time.time() < end_of_time:
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data = listening_socket.recv(1024)
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dst_mac = struct.unpack('!6s', data[0:6])[0]
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if dst_mac in allowed_macs:
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inspect_frame(data)
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except socket.timeout:
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pass
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listening_socket.close()
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def main():
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interfaces = sys.argv[1:]
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timeout = 5
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get_hw_addresses(interfaces)
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listening_thread = threading.Thread(target=wait_for_dhcp_offers,
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args=[interfaces, timeout])
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listening_thread.start()
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for interface in interfaces:
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dhcp_discover = DHCPDiscover(interface)
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dhcp_discover.send()
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dhcp_discover.close_socket()
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listening_thread.join()
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if dhcp_servers:
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sys.stderr.write('Found {} DHCP servers:'.format(len(dhcp_servers)))
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for ip, mac in dhcp_servers:
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sys.stderr.write("\n* {} ({})".format(ip, mac))
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sys.exit(1)
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else:
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print("No DHCP servers found.")
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if __name__ == '__main__':
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main()
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