| Current Path : /usr/share/nmap/nselib/ |
| Current File : //usr/share/nmap/nselib/dhcp.lua |
---Implement a Dynamic Host Configuration Protocol (DHCP) client.
--
-- DHCP, defined in rfc2132 and rfc2131, is a protocol for hosts to automatically
-- configure themselves on a network (that is, obtain an ip address). This library,
-- which have a trivial one-function interface, can send out DHCP packets of many
-- types and parse the responses.
--
module(... or "dhcp", package.seeall)
require 'bin'
require 'bit'
require 'ipOps'
require 'stdnse'
request_types =
{
DHCPDISCOVER = 1,
DHCPOFFER = 2,
DHCPREQUEST = 3,
DHCPDECLINE = 4,
DHCPACK = 5,
DHCPNAK = 6,
DHCPRELEASE = 7,
DHCPINFORM = 8
}
request_types_str = {}
request_types_str[1] = "DHCPDISCOVER"
request_types_str[2] = "DHCPOFFER"
request_types_str[3] = "DHCPREQUEST"
request_types_str[4] = "DHCPDECLINE"
request_types_str[5] = "DHCPACK"
request_types_str[6] = "DHCPNAK"
request_types_str[7] = "DHCPRELEASE"
request_types_str[8] = "DHCPINFORM"
---Read an IP address or a list of IP addresses. Print an error if the length isn't a multiple of 4.
--
--@param data The packet.
--@param pos The position in the packet.
--@param length The length that the server claims the field is.
--@return The new position (will always be pos + length, no matter what we think it should be)
--@return The value of the field, or nil if the field length was wrong.
local function read_ip(data, pos, length)
if(length ~= 4) then
if((length % 4) ~= 0) then
stdnse.print_debug(1, "dhcp-discover: Invalid length for an ip address (%d)", length)
pos = pos + length
return pos, nil
else
local results = {}
for i=1, length, 4 do
local value
pos, value = bin.unpack("<I", data, pos)
table.insert(results, ipOps.fromdword(value))
end
return pos, results
end
else
local value
pos, value = bin.unpack("<I", data, pos)
return pos, ipOps.fromdword(value)
end
end
---Read a string. The length of the string is given by the length field.
--
--@param data The packet.
--@param pos The position in the packet.
--@param length The length that the server claims the field is.
--@return The new position (will always be pos + length, no matter what we think it should be)
--@return The value of the field, or nil if the field length was wrong.
local function read_string(data, pos, length)
return bin.unpack(string.format("A%d", length), data, pos)
end
---Read a single byte. Print an error if the length isn't 1.
--
--@param data The packet.
--@param pos The position in the packet.
--@param length The length that the server claims the field is.
--@return The new position (will always be pos + length, no matter what we think it should be)
--@return The value of the field, or nil if the field length was wrong.
local function read_1_byte(data, pos, length)
if(length ~= 1) then
stdnse.print_debug(1, "dhcp-discover: Invalid length for data (%d; should be %d)", length, 1)
pos = pos + length
return pos, nil
end
return bin.unpack("C", data, pos)
end
---Read a message type. This is a single-byte value that's looked up in the <code>request_types_str</code>
-- table. Print an error if the length isn't 1.
--
--@param data The packet.
--@param pos The position in the packet.
--@param length The length that the server claims the field is.
--@return The new position (will always be pos + length, no matter what we think it should be)
--@return The value of the field, or nil if the field length was wrong.
local function read_message_type(data, pos, length)
local value
pos, value = read_1_byte(data, pos, length)
if(value == nil) then
stdnse.print_debug(1, "dhcp-discover: Couldn't read the 1-byte message type")
return pos, nil
end
return pos, request_types_str[value]
end
---Read a single byte, and return 'false' if it's 0, or 'true' if it's non-zero. Print an error if the
-- length isn't 1.
--
--@param data The packet.
--@param pos The position in the packet.
--@param length The length that the server claims the field is.
--@return The new position (will always be pos + length, no matter what we think it should be)
--@return The value of the field, or nil if the field length was wrong.
local function read_boolean(data, pos, length)
local result
pos, result = read_1_byte(data, pos, length)
if(result == nil) then
stdnse.print_debug(1, "dhcp-discover: Couldn't read the 1-byte boolean")
return pos, nil
elseif(result == 0) then
return pos, "false"
else
return pos, "true"
end
end
---Read a 2-byte unsigned little endian value. Print an error if the length isn't 2.
--
--@param data The packet.
--@param pos The position in the packet.
--@param length The length that the server claims the field is.
--@return The new position (will always be pos + length, no matter what we think it should be)
--@return The value of the field, or nil if the field length was wrong.
local function read_2_bytes(data, pos, length)
if(length ~= 2) then
stdnse.print_debug(1, "dhcp-discover: Invalid length for data (%d; should be %d)", length, 2)
pos = pos + length
return pos, nil
end
return bin.unpack(">S", data, pos)
end
---Read a list of 2-byte unsigned little endian values. Print an error if the length isn't a multiple
-- of 2.
--
--@param data The packet.
--@param pos The position in the packet.
--@param length The length that the server claims the field is.
--@return The new position (will always be pos + length, no matter what we think it should be)
--@return The value of the field, or nil if the field length was wrong.
local function read_2_bytes_list(data, pos, length)
if((length % 2) ~= 0) then
stdnse.print_debug(1, "dhcp-discover: Invalid length for data (%d; should be multiple of %d)", length, 2)
pos = pos + length
return pos, nil
else
local results = {}
for i=1, length, 2 do
local value
pos, value = bin.unpack(">S", data, pos)
table.insert(results, value)
end
return pos, results
end
end
---Read a 4-byte unsigned little endian value. Print an error if the length isn't 4.
--
--@param data The packet.
--@param pos The position in the packet.
--@param length The length that the server claims the field is.
--@return The new position (will always be pos + length, no matter what we think it should be)
--@return The value of the field, or nil if the field length was wrong.
local function read_4_bytes(data, pos, length)
if(length ~= 4) then
stdnse.print_debug(1, "dhcp-discover: Invalid length for data (%d; should be %d)", length, 4)
pos = pos + length
return pos, nil
end
return bin.unpack(">I", data, pos)
end
---Read a 4-byte unsigned little endian value, and interpret it as a time offset value. Print an
-- error if the length isn't 4.
--
--@param data The packet.
--@param pos The position in the packet.
--@param length The length that the server claims the field is.
--@return The new position (will always be pos + length, no matter what we think it should be)
--@return The value of the field, or nil if the field length was wrong.
local function read_time(data, pos, length)
local result
if(length ~= 4) then
stdnse.print_debug(1, "dhcp-discover: Invalid length for data (%d; should be %d)", length, 4)
pos = pos + length
return pos, nil
end
pos, result = bin.unpack(">I", data, pos)
-- This code was mostly taken from snmp-sysdescr.nse. It should probably be abstracted into stdnse.lua [TODO]
local days, hours, minutes, seconds, htime, mtime, stime
days = math.floor(result / 86400)
htime = math.fmod(result, 86400)
hours = math.floor(htime / 3600)
mtime = math.fmod(htime, 3600)
minutes = math.floor(mtime / 60)
seconds = math.fmod(mtime, 60)
local dayLabel
if days == 1 then
dayLabel = "day"
else
dayLabel = "days"
end
return pos, string.format("%d %s, %d:%02d:%02d", days, dayLabel, hours, minutes, seconds)
end
---Read a list of static routes. Each of them are a pair of IP addresses, a destination and a
-- router. Print an error if the length isn't a multiple of 8.
--
--@param data The packet.
--@param pos The position in the packet.
--@param length The length that the server claims the field is.
--@return The new position (will always be pos + length, no matter what we think it should be)
--@return The value of the field, or nil if the field length was wrong.
local function read_static_route(data, pos, length)
if((length % 8) ~= 0) then
stdnse.print_debug(1, "dhcp-discover: Invalid length for data (%d; should be multiple of %d)", length, 8)
pos = pos + length
return pos, nil
else
local results = {}
for i=1, length, 8 do
local destination, router
pos, destination = read_ip(data, pos, 4)
pos, router = read_ip(data, pos, 4)
table.insert(results, {destination=destination, router=router})
end
return pos, results
end
end
---Read a list of policy filters. Each of them are a pair of IP addresses, an address and a
-- mask. Print an error if the length isn't a multiple of 8.
--
--@param data The packet.
--@param pos The position in the packet.
--@param length The length that the server claims the field is.
--@return The new position (will always be pos + length, no matter what we think it should be)
--@return The value of the field, or nil if the field length was wrong.
local function read_policy_filter(data, pos, length)
if((length % 8) ~= 0) then
stdnse.print_debug(1, "dhcp-discover: Invalid length for data (%d; should be multiple of %d)", length, 8)
pos = pos + length
return pos, nil
else
local results = {}
for i=1, length, 8 do
local address, router, mask
pos, address = read_ip(data, pos, 4)
pos, mask = read_ip(data, pos, 4)
table.insert(results, {address=address, mask=mask})
end
return pos, results
end
end
---These are the different fields for DHCP. These have to come after the read_* function
-- definitions.
local actions = {}
actions[1] = {name="Subnet Mask", func=read_ip, default=true}
actions[2] = {name="Time Offset", func=read_4_bytes, default=false}
actions[3] = {name="Router", func=read_ip, default=true}
actions[4] = {name="Time Server", func=read_ip, default=true}
actions[5] = {name="Name Server", func=read_ip, default=true}
actions[6] = {name="Domain Name Server", func=read_ip, default=true}
actions[7] = {name="Log Server", func=read_ip, default=true}
actions[8] = {name="Cookie Server", func=read_ip, default=true}
actions[9] = {name="LPR Server", func=read_ip, default=true}
actions[10] = {name="Impress Server", func=read_ip, default=true}
actions[11] = {name="Resource Location Server", func=read_ip, default=true}
actions[12] = {name="Hostname", func=read_string, default=true}
actions[13] = {name="Boot File Size", func=read_2_bytes, default=false}
actions[14] = {name="Merit Dump File", func=read_string, default=false}
actions[15] = {name="Domain Name", func=read_string, default=true}
actions[16] = {name="Swap Server", func=read_ip, default=true}
actions[17] = {name="Root Path", func=read_string, default=false}
actions[18] = {name="Extensions Path", func=read_string, default=false}
actions[19] = {name="IP Forwarding", func=read_boolean, default=false}
actions[20] = {name="Non-local Source Routing", func=read_boolean, default=true}
actions[21] = {name="Policy Filter", func=read_policy_filter, default=false}
actions[22] = {name="Maximum Datagram Reassembly Size",func=read_2_bytes, default=false}
actions[23] = {name="Default IP TTL", func=read_1_byte, default=false}
actions[24] = {name="Path MTU Aging Timeout", func=read_time, default=false}
actions[25] = {name="Path MTU Plateau", func=read_2_bytes_list, default=false}
actions[26] = {name="Interface MTU", func=read_2_bytes, default=false}
actions[27] = {name="All Subnets are Local", func=read_boolean, default=false}
actions[28] = {name="Broadcast Address", func=read_ip, default=true}
actions[29] = {name="Perform Mask Discovery", func=read_boolean, default=false}
actions[30] = {name="Mask Supplier", func=read_boolean, default=false}
actions[31] = {name="Perform Router Discovery", func=read_boolean, default=false}
actions[32] = {name="Router Solicitation Address", func=read_ip, default=true}
actions[33] = {name="Static Route", func=read_static_route, default=true}
actions[34] = {name="Trailer Encapsulation", func=read_boolean, default=false}
actions[35] = {name="ARP Cache Timeout", func=read_time, default=false}
actions[36] = {name="Ethernet Encapsulation", func=read_boolean, default=false}
actions[37] = {name="TCP Default TTL", func=read_1_byte, default=false}
actions[38] = {name="TCP Keepalive Interval", func=read_4_bytes, default=false}
actions[39] = {name="TCP Keepalive Garbage", func=read_boolean, default=false}
actions[40] = {name="NIS Domain", func=read_string, default=true}
actions[41] = {name="NIS Servers", func=read_ip, default=true}
actions[42] = {name="NTP Servers", func=read_ip, default=true}
actions[43] = {name="Vendor Specific Information", func=read_string, default=false}
actions[44] = {name="NetBIOS Name Server", func=read_ip, default=true}
actions[45] = {name="NetBIOS Datagram Server", func=read_ip, default=true}
actions[46] = {name="NetBIOS Node Type", func=read_1_byte, default=false}
actions[47] = {name="NetBIOS Scope", func=read_string, default=false}
actions[48] = {name="X Window Font Server", func=read_ip, default=true}
actions[49] = {name="X Window Display Manager", func=read_ip, default=true}
actions[50] = {name="Requested IP Address (client)", func=read_ip, default=false}
actions[51] = {name="IP Address Lease Time", func=read_time, default=false}
actions[52] = {name="Option Overload", func=read_1_byte, default=false}
actions[53] = {name="DHCP Message Type", func=read_message_type, default=false}
actions[54] = {name="Server Identifier", func=read_ip, default=true}
actions[55] = {name="Parameter Request List (client)", func=read_string, default=false}
actions[56] = {name="Error Message", func=read_string, default=true}
actions[57] = {name="Maximum DHCP Message Size", func=read_2_bytes, default=false}
actions[58] = {name="Renewal Time Value", func=read_time, default=false}
actions[59] = {name="Rebinding Time Value", func=read_time, default=false}
actions[60] = {name="Class Identifier", func=read_string, default=false}
actions[61] = {name="Client Identifier (client)", func=read_string, default=false}
--- Does the send/receive, doesn't build/parse anything.
local function dhcp_send(interface, host, packet, transaction_id)
local socket
local status, err, data
local result
local results = {}
local bind_socket = nmap.new_socket("udp")
bind_socket:bind(nil, 68)
bind_socket:set_timeout(5000)
stdnse.print_debug(1, "dhcp: Starting listener")
-- Create the UDP socket (TODO: enable SO_BROADCAST if we need to)
socket = nmap.new_socket()
status, err = socket:connect(host, 67, "udp")
if(status == false) then
return false, "Couldn't create socket: " .. err
end
stdnse.print_debug(1, "dhcp: Created UDP socket")
-- Send out the packet
socket:send(packet)
-- Read the response
local status, data = bind_socket:receive()
-- This pulls back 4 bytes in the packet that correspond to the transaction id. This should be randomly
-- generated and different for every instance of a script (to prevent collisions)
while status and data:sub(5, 8) ~= transaction_id do
local status, data = bind_socket:receive()
end
if(status == false) then
stdnse.print_debug(1, "dhcp: Error calling bind_socket:receive(): %s", err)
return false, "Error calling bind_socket:receive(): " .. err
end
-- If no data was captured (ie, a timeout), return an error
if(data == nil) then
stdnse.print_debug(1, "dhcp: Error calling pcap_receive(): TIMEOUT")
return false, "TIMEOUT"
end
-- Close our sockets
socket:close()
bind_socket:close()
-- Finally, return the data
return true, data
end
local function dhcp_build(request_type, ip_address, mac_address, request_options, overrides, lease_time, transaction_id)
local packet = ''
-- Set up the default overrides
if(overrides == nil) then
overrides = {}
end
if(request_options == nil) then
-- Request the defaults, or there's no verbosity; otherwise, request everything!
request_options = ''
for i = 1, 61, 1 do
if(nmap.verbosity() > 0) then
request_options = request_options .. string.char(i)
else
if(actions[i] and actions[i].default) then
request_options = request_options .. string.char(i)
end
end
end
end
-- Header
packet = packet .. bin.pack(">CCCC", overrides['op'] or 1, overrides['htype'] or 1, overrides['hlen'] or 6, overrides['hops'] or 0) -- BOOTREQUEST, 10mb ethernet, 6 bytes long, 0 hops
packet = packet .. transaction_id -- Transaction ID
packet = packet .. bin.pack(">SS", overrides['secs'] or 0, overrides['flags'] or 0x0000) -- Secs, flags
packet = packet .. bin.pack("A", ip_address) -- Client address
packet = packet .. bin.pack("<I", overrides['yiaddr'] or 0) -- yiaddr
packet = packet .. bin.pack("<I", overrides['siaddr'] or 0) -- siaddr
packet = packet .. bin.pack("<I", overrides['giaddr'] or 0) -- giaddr
packet = packet .. mac_address .. string.rep(string.char(0), 16 - #mac_address) -- chaddr (MAC address)
packet = packet .. (overrides['sname'] or string.rep(string.char(0), 64)) -- sname
packet = packet .. (overrides['file'] or string.rep(string.char(0), 128)) -- file
packet = packet .. bin.pack(">I", overrides['cookie'] or 0x63825363) -- Magic cookie
-- Options
packet = packet .. bin.pack(">CCC", 0x35, 1, request_type) -- Request type
packet = packet .. bin.pack(">CCA", 0x37, #request_options, request_options) -- Request options
packet = packet .. bin.pack(">CCI", 0x33, 4, lease_time or 1) -- Lease time
packet = packet .. bin.pack(">C", 0xFF) -- Termination
return true, packet
end
---Parse a DHCP packet (either a request or a response) and return the results as a table. The
-- table at the top of this function (<code>actions</code>) defines the name of each field, as
-- laid out in rfc2132, and the function that parses it.
--
-- In theory, this should be able to parse any valid DHCP packet.
--
--@param data The DHCP packet data. Any padding at the end of the packet will be ignored (by default,
-- DHCP packets are padded with \x00 bytes).
local function dhcp_parse(data, transaction_id)
local pos = 1
local result = {}
-- Receive the first bit and make sure we got the correct operation back
pos, result['op'], result['htype'], result['hlen'], result['hops'] = bin.unpack(">CCCC", data, pos)
if(result['op'] ~= 2) then
return false, string.format("DHCP server returned invalid reply ('op' wasn't BOOTREPLY (it was 0x%02x))", result['op'])
end
-- Confirm the transaction id
pos, result['xid'] = bin.unpack("A4", data, pos)
if(result['xid'] ~= transaction_id) then
return false, string.format("DHCP server returned invalid reply (transaction id didn't match (%s != %s))", result['xid'], transaction_id)
end
-- Unpack the secs, flags, addresses, sname, and file
pos, result['secs'], result['flags'] = bin.unpack(">SS", data, pos)
pos, result['ciaddr'] = bin.unpack("<I", data, pos)
pos, result['yiaddr'] = bin.unpack("<I", data, pos)
pos, result['siaddr'] = bin.unpack("<I", data, pos)
pos, result['giaddr'] = bin.unpack("<I", data, pos)
pos, result['chaddr'] = bin.unpack("A16", data, pos)
pos, result['sname'] = bin.unpack("A64", data, pos)
pos, result['file'] = bin.unpack("A128", data, pos)
-- Convert the addresses to strings
result['ciaddr_str'] = ipOps.fromdword(result['ciaddr'])
result['yiaddr_str'] = ipOps.fromdword(result['yiaddr'])
result['siaddr_str'] = ipOps.fromdword(result['siaddr'])
result['giaddr_str'] = ipOps.fromdword(result['giaddr'])
-- Confirm the cookie
pos, result['cookie'] = bin.unpack(">I", data, pos)
if(result['cookie'] ~= 0x63825363) then
return false, "DHCP server returned invalid reply (the magic cookie was invalid)"
end
-- Parse the options
result['options'] = {}
while true do
local option, length
pos, option, length = bin.unpack(">CC", data, pos)
-- Check for termination condition
if(option == 0xFF) then
break;
end
-- Get the action from the array, based on the code
local action = actions[option]
-- Verify we got a valid code (if we didn't, we're probably in big trouble)
local value
if(action == nil) then
stdnse.print_debug(1, "dhcp-discover: Unknown option: %d", option)
pos = pos + length
else
-- Call the function to parse the option, and insert the result into our results table
stdnse.print_debug(2, "dhcp-discover: Attempting to parse %s", action['name'])
pos, value = action['func'](data, pos, length)
if(nmap.verbosity() == 0 and action.default == false) then
stdnse.print_debug(1, "dhcp-discover: Server returned unrequested option (%s => %s)", action['name'], value)
else
if(value) then
table.insert(result['options'], {name=action['name'], value=value})
else
stdnse.print_debug(1, "dhcp-discover: Couldn't determine value for %s", action['name']);
end
end
end
-- Handle the 'Option Overload' option specially -- if it's set, it tells us to use the file and/or sname values after we
-- run out of data.
if(option == 52) then
if(value == 1) then
data = data .. result['file']
elseif(value == 2) then
data = data .. result['sname']
elseif(value == 3) then
data = data .. result['file'] .. result['sname']
else
stdnse.print_debug(1, "dhcp-discover: Warning: 'Option Overload' gave an unsupported value: %d", value)
end
end
end
return true, result
end
---Build and send any kind of DHCP packet, and parse the response. This is the only interface
-- to the DHCP library, and should be the only one necessary.
--
-- All DHCP packet have the same structure, but different fields. It is therefore easy to build
-- any of the possible request types:
-- * DHCPDISCOVER
-- * DHCPOFFER
-- * DHCPREQUEST
-- * DHCPDECLINE
-- * DHCPACK
-- * DHCPNAK
-- * DHCPRELEASE
-- * DHCPINFORM
--
-- Although these will all build a valid packet with any option, and the default options (that can be
-- overridden with the <code>overrides</code> argument) won't necessarily work with every request
-- type. If you're going to build some DHCP code on your own, I recommend reading rfc2131.
--
--@param request_type The type of request as an integer (use the <code>request_types</code> table at the
-- top of this file).
--@param ip_address Your ip address (as a dotted-decimal string). This tells the DHCP server where to
-- send the response. Setting it to "255.255.255.255" or "0.0.0.0" is generally acceptable (if not,
-- host.ip_src can work).
--@param mac_address Your mac address (as a string up to 16 bytes) where the server will send the response. Like
-- <code>ip_address</code>, setting to the broadcast address (FF:FF:FF:FF:FF:FF) is
-- common (host.mac_addr_src works).
--@param request_options [optional] The options to request from the server, as an array of integers. For the
-- acceptable options, see the <code>actions</code> table above or have a look at rfc2132.
-- Some DHCP servers (such as my Linksys WRT54g) will ignore this list and send whichever
-- information it wants. Default: all options marked as 'default' in the <code>actions</code>
-- table above are requested (the typical interesting ones) if no verbosity is given.
-- If any level of verbosity is on, get all types.
--@param overrides [optional] A table of overrides. If a field in the table matches a field in the DHCP
-- packet (see rfc2131 section 2 for a list of possible fields), the value in the table
-- will be sent instead of the default value.
--@param lease_time [optional] The lease time used when requestint an IP. Default: 1 second.
--@return status (true or false)
--@return The parsed response, as a table.
function make_request(target, interface, request_type, ip_address, mac_address, request_options, overrides, lease_time)
-- A unique id that identifies this particular session (and lets us filter out what we don't want to see)
local transaction_id = bin.pack("<I", math.random(0, 0x7FFFFFFF))
-- Generate the packet
local status, packet = dhcp_build(request_type, bin.pack(">I", ipOps.todword(ip_address)), mac_address, request_options, overrides, lease_time, transaction_id)
if(not(status)) then
stdnse.print_debug(1, "dhcp: Couldn't build packet: " .. packet)
return false, "Couldn't build packet: " .. packet
end
-- Send the packet and get the response
local status, response = dhcp_send(interface, target, packet, transaction_id)
if(not(status)) then
stdnse.print_debug(1, "dhcp: Couldn't send packet: " .. response)
return false, "Couldn't send packet: " .. response
end
-- Parse the response
local status, parsed = dhcp_parse(response, transaction_id)
if(not(status)) then
stdnse.print_debug(1, "dhcp: Couldn't parse response: " .. parsed)
return false, "Couldn't parse response: " .. parsed
end
return true, parsed
end
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