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os-ken/os_ken/lib/packet/dhcp.py

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# Copyright (C) 2013 Nippon Telegraph and Telephone Corporation.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
# implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""
DHCP packet parser/serializer
"""
# RFC 2131
# DHCP packet format
# 0 1 2 3
# 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
# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
# | op (1) | htype (1) | hlen (1) | hops (1) |
# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
# | xid (4) |
# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
# | secs (2) | flags (2) |
# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
# | ciaddr (4) |
# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
# | yiaddr (4) |
# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
# | siaddr (4) |
# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
# | giaddr (4) |
# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
# | |
# | chaddr (16) |
# | |
# | |
# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
# | |
# | sname (64) |
# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
# | |
# | file (128) |
# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
# | |
# | options (variable) |
# +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
import random
import struct
import netaddr
from os_ken.lib import addrconv
from os_ken.lib import stringify
from . import packet_base
DHCP_BOOT_REQUEST = 1
DHCP_BOOT_REPLY = 2
# DHCP message type code
DHCP_DISCOVER = 1
DHCP_OFFER = 2
DHCP_REQUEST = 3
DHCP_ACK = 5
# DHCP options tag code
DHCP_PAD_OPT = 0
DHCP_SUBNET_MASK_OPT = 1
DHCP_GATEWAY_ADDR_OPT = 3
DHCP_DNS_SERVER_ADDR_OPT = 6
DHCP_HOST_NAME_OPT = 12
DHCP_DOMAIN_NAME_OPT = 15
DHCP_INTERFACE_MTU_OPT = 26
DHCP_REQUESTED_IP_ADDR_OPT = 50
DHCP_IP_ADDR_LEASE_TIME_OPT = 51
DHCP_MESSAGE_TYPE_OPT = 53
DHCP_SERVER_IDENTIFIER_OPT = 54
DHCP_PARAMETER_REQUEST_LIST_OPT = 55
DHCP_RENEWAL_TIME_OPT = 58
DHCP_REBINDING_TIME_OPT = 59
DHCP_CLASSLESS_ROUTE_OPT = 121
DHCP_END_OPT = 255
class dhcp(packet_base.PacketBase):
"""DHCP (RFC 2131) header encoder/decoder class.
The serialized packet would looks like the ones described
in the following sections.
* RFC 2131 DHCP packet format
An instance has the following attributes at least.
Most of them are same to the on-wire counterparts but in host byte order.
__init__ takes the corresponding args in this order.
.. tabularcolumns:: |l|L|
============== ====================
Attribute Description
============== ====================
op Message op code / message type.\
1 = BOOTREQUEST, 2 = BOOTREPLY
htype Hardware address type (e.g. '1' = 10mb ethernet).
hlen Hardware address length (e.g. '6' = 10mb ethernet).
hops Client sets to zero, optionally used by relay agent\
when booting via a relay agent.
xid Transaction ID, a random number chosen by the client,\
used by the client and serverto associate messages\
and responses between a client and a server.
secs Filled in by client, seconds elapsed since client\
began address acquisition or renewal process.
flags Flags.
ciaddr Client IP address; only filled in if client is in\
BOUND, RENEW or REBINDING state and can respond\
to ARP requests.
yiaddr 'your' (client) IP address.
siaddr IP address of next server to use in bootstrap;\
returned in DHCPOFFER, DHCPACK by server.
giaddr Relay agent IP address, used in booting via a\
relay agent.
chaddr Client hardware address.
sname Optional server host name, null terminated string.
boot_file Boot file name, null terminated string; "generic"\
name or null in DHCPDISCOVER, fully qualified\
directory-path name in DHCPOFFER.
options Optional parameters field\
('DHCP message type' option must be included in\
every DHCP message).
============== ====================
"""
_DHCP_PACK_STR = '!BBBBIHH4s4s4s4s16s64s128s'
_MIN_LEN = struct.calcsize(_DHCP_PACK_STR)
_MAC_ADDRESS_LEN = 6
_HARDWARE_TYPE_ETHERNET = 1
_class_prefixes = ['options']
_TYPE = {
'ascii': [
'ciaddr', 'yiaddr', 'siaddr', 'giaddr', 'chaddr',
'sname', 'boot_file'
]
}
def __init__(self, op, chaddr, options=None, htype=_HARDWARE_TYPE_ETHERNET,
hlen=0, hops=0, xid=None, secs=0, flags=0,
ciaddr='0.0.0.0', yiaddr='0.0.0.0', siaddr='0.0.0.0',
giaddr='0.0.0.0', sname='', boot_file=''):
super(dhcp, self).__init__()
self.op = op
self.htype = htype
self.hlen = hlen
self.hops = hops
if xid is None:
self.xid = random.randint(0, 0xffffffff)
else:
self.xid = xid
self.secs = secs
self.flags = flags
self.ciaddr = ciaddr
self.yiaddr = yiaddr
self.siaddr = siaddr
self.giaddr = giaddr
self.chaddr = chaddr
self.sname = sname
self.boot_file = boot_file
self.options = options
@classmethod
def parser(cls, buf):
(op, htype, hlen, hops, xid, secs, flags,
ciaddr, yiaddr, siaddr, giaddr, chaddr, sname,
boot_file) = struct.unpack_from(cls._DHCP_PACK_STR, buf)
if hlen == cls._MAC_ADDRESS_LEN:
chaddr = addrconv.mac.bin_to_text(chaddr[:cls._MAC_ADDRESS_LEN])
length = cls._MIN_LEN
parse_opt = None
if len(buf) > length:
parse_opt = options.parser(buf[length:])
length += parse_opt.options_len
return (cls(op, chaddr, parse_opt,
htype, hlen, hops, xid, secs, flags,
addrconv.ipv4.bin_to_text(ciaddr),
addrconv.ipv4.bin_to_text(yiaddr),
addrconv.ipv4.bin_to_text(siaddr),
addrconv.ipv4.bin_to_text(giaddr),
sname.decode('ascii'), boot_file.decode('ascii')),
None, buf[length:])
def serialize(self, _payload=None, _prev=None):
opt_buf = bytearray()
if self.options is not None:
opt_buf = self.options.serialize()
if netaddr.valid_mac(self.chaddr):
chaddr = addrconv.mac.text_to_bin(self.chaddr)
else:
chaddr = self.chaddr
self.hlen = len(chaddr)
return struct.pack(self._DHCP_PACK_STR, self.op, self.htype, self.hlen,
self.hops, self.xid, self.secs, self.flags,
addrconv.ipv4.text_to_bin(self.ciaddr),
addrconv.ipv4.text_to_bin(self.yiaddr),
addrconv.ipv4.text_to_bin(self.siaddr),
addrconv.ipv4.text_to_bin(self.giaddr),
chaddr,
self.sname.encode('ascii'),
self.boot_file.encode('ascii')) + opt_buf
class options(stringify.StringifyMixin):
"""DHCP (RFC 2132) options encoder/decoder class.
This is used with os_ken.lib.packet.dhcp.dhcp.
An instance has the following attributes at least.
Most of them are same to the on-wire counterparts but in host byte order.
__init__ takes the corresponding args in this order.
.. tabularcolumns:: |l|L|
============== ====================
Attribute Description
============== ====================
option_list 'end option' and 'pad option' are added automatically\
after the option class is stored in array.
options_len Option's byte length.\
('magic cookie', 'end option' and 'pad option'\
length including.)
magic_cookie The first four octets contain the decimal values\
99, 130, 83 and 99.
============== ====================
"""
_MAGIC_COOKIE_UNPACK_STR = '!4s'
# same magic cookie as is defined in RFC 1497
_MAGIC_COOKIE = '99.130.83.99'
_OPT_TAG_LEN_BYTE = 2
_class_prefixes = ['option']
_TYPE = {
'ascii': [
'magic_cookie'
]
}
def __init__(self, option_list=None, options_len=0,
magic_cookie=_MAGIC_COOKIE):
super(options, self).__init__()
self.option_list = option_list or []
self.options_len = options_len
self.magic_cookie = magic_cookie
@classmethod
def parser(cls, buf):
opt_parse_list = []
offset = struct.calcsize(cls._MAGIC_COOKIE_UNPACK_STR)
magic_cookie = struct.unpack_from(cls._MAGIC_COOKIE_UNPACK_STR, buf)[0]
while len(buf) > offset:
opt_buf = buf[offset:]
try:
opt = option.parser(opt_buf)
except struct.error:
opt_parse_list.append(opt_buf)
break
if opt is None:
break
opt_parse_list.append(opt)
offset += opt.length + cls._OPT_TAG_LEN_BYTE
return cls(opt_parse_list, len(buf),
addrconv.ipv4.bin_to_text(magic_cookie))
def serialize(self):
seri_opt = addrconv.ipv4.text_to_bin(self.magic_cookie)
for opt in self.option_list:
if isinstance(opt, option):
seri_opt += opt.serialize()
else:
seri_opt += opt
if isinstance(self.option_list[-1], option):
seri_opt += b'\xff'
self.options_len = len(seri_opt)
return seri_opt
class option(stringify.StringifyMixin):
"""DHCP (RFC 2132) options encoder/decoder class.
This is used with os_ken.lib.packet.dhcp.dhcp.options.
An instance has the following attributes at least.
Most of them are same to the on-wire counterparts but in host byte order.
__init__ takes the corresponding args in this order.
============== ====================
Attribute Description
============== ====================
tag Option type.\
(except for the 'magic cookie', 'pad option'\
and 'end option'.)
value Option's value.\
(set the value that has been converted to hexadecimal.)
length Option's value length.\
(calculated automatically from the length of value.)
============== ====================
"""
_UNPACK_STR = '!B'
_MIN_LEN = struct.calcsize(_UNPACK_STR)
def __init__(self, tag, value, length=0):
super(option, self).__init__()
self.tag = tag
self.value = value
self.length = length
@classmethod
def parser(cls, buf):
tag = struct.unpack_from(cls._UNPACK_STR, buf)[0]
if tag == DHCP_END_OPT or tag == DHCP_PAD_OPT:
return None
buf = buf[cls._MIN_LEN:]
length = struct.unpack_from(cls._UNPACK_STR, buf)[0]
buf = buf[cls._MIN_LEN:]
value_unpack_str = '%ds' % length
value = struct.unpack_from(value_unpack_str, buf)[0]
return cls(tag, value, length)
def serialize(self):
self.length = len(self.value)
options_pack_str = '!BB%ds' % self.length
return struct.pack(options_pack_str, self.tag, self.length, self.value)
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