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# By Peter V. Saveliev https://pypi.python.org/pypi/pyroute2. Dual licensed under the Apache 2 and GPLv2+ see https://github.com/svinota/pyroute2 for License details.
'''
IPv4 DHCP socket
================
'''
from pyroute2.common import AddrPool
from pyroute2.protocols import udpmsg
from pyroute2.protocols import udp4_pseudo_header
from pyroute2.protocols import ethmsg
from pyroute2.protocols import ip4msg
from pyroute2.protocols.rawsocket import RawSocket
from pyroute2.dhcp.dhcp4msg import dhcp4msg
def listen_udp_port(port=68):
# pre-scripted BPF code that matches UDP port
bpf_code = [[40, 0, 0, 12],
[21, 0, 8, 2048],
[48, 0, 0, 23],
[21, 0, 6, 17],
[40, 0, 0, 20],
[69, 4, 0, 8191],
[177, 0, 0, 14],
[72, 0, 0, 16],
[21, 0, 1, port],
[6, 0, 0, 65535],
[6, 0, 0, 0]]
return bpf_code
class DHCP4Socket(RawSocket):
'''
Parameters:
* ifname -- interface name to work on
This raw socket binds to an interface and installs BPF filter
to get only its UDP port. It can be used in poll/select and
provides also the context manager protocol, so can be used in
`with` statements.
It does not provide any DHCP state machine, and does not inspect
DHCP packets, it is totally up to you. No default values are
provided here, except `xid` -- DHCP transaction ID. If `xid` is
not provided, DHCP4Socket generates it for outgoing messages.
'''
def __init__(self, ifname, port=68):
RawSocket.__init__(self, ifname, listen_udp_port(port))
self.port = port
# Create xid pool
#
# Every allocated xid will be released automatically after 1024
# alloc() calls, there is no need to call free(). Minimal xid == 16
self.xid_pool = AddrPool(minaddr=16, release=1024)
def __enter__(self):
return self
def __exit__(self, exc_type, exc_value, traceback):
self.close()
def put(self, msg=None, dport=67):
'''
Put DHCP message. Parameters:
* msg -- dhcp4msg instance
* dport -- DHCP server port
If `msg` is not provided, it is constructed as default
BOOTREQUEST + DHCPDISCOVER.
Examples::
sock.put(dhcp4msg({'op': BOOTREQUEST,
'chaddr': 'ff:11:22:33:44:55',
'options': {'message_type': DHCPREQUEST,
'parameter_list': [1, 3, 6, 12, 15],
'requested_ip': '172.16.101.2',
'server_id': '172.16.101.1'}}))
The method returns dhcp4msg that was sent, so one can get from
there `xid` (transaction id) and other details.
'''
# DHCP layer
dhcp = msg or dhcp4msg({'chaddr': self.l2addr})
# dhcp transaction id
if dhcp['xid'] is None:
dhcp['xid'] = self.xid_pool.alloc()
data = dhcp.encode().buf
# UDP layer
udp = udpmsg({'sport': self.port,
'dport': dport,
'len': 8 + len(data)})
udph = udp4_pseudo_header({'dst': '255.255.255.255',
'len': 8 + len(data)})
udp['csum'] = self.csum(udph.encode().buf + udp.encode().buf + data)
udp.reset()
# IPv4 layer
ip4 = ip4msg({'len': 20 + 8 + len(data),
'proto': 17,
'dst': '255.255.255.255'})
ip4['csum'] = self.csum(ip4.encode().buf)
ip4.reset()
# MAC layer
eth = ethmsg({'dst': 'ff:ff:ff:ff:ff:ff',
'src': self.l2addr,
'type': 0x800})
data = eth.encode().buf +\
ip4.encode().buf +\
udp.encode().buf +\
data
self.send(data)
dhcp.reset()
return dhcp
def get(self):
'''
Get the next incoming packet from the socket and try
to decode it as IPv4 DHCP. No analysis is done here,
only MAC/IPv4/UDP headers are stripped out, and the
rest is interpreted as DHCP.
'''
(data, addr) = self.recvfrom(4096)
eth = ethmsg(buf=data).decode()
ip4 = ip4msg(buf=data, offset=eth.offset).decode()
udp = udpmsg(buf=data, offset=ip4.offset).decode()
return dhcp4msg(buf=data, offset=udp.offset).decode()
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