packet.lua

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-- license = "See nmaps COPYING for license"
module("packet" ,package.seeall)

-- Raw package parsing functions. Used with raw sockets
-- in nse.
-- Author: Marek Majkowski <[e-mail]>

--[[
--]]


require "bit"


----------------------------------------------------------------------------------------------------------------
-- extract number from binary string
function u8(b, i)
        return string.byte(b, i+1)
end
function u16(b, i)
        local b1,b2
        b1, b2 = string.byte(b, i+1), string.byte(b, i+2)
        --        2^8     2^0
        return b1*256 + b2
end
function u32(b,i)
        local b1,b2,b3,b4
        b1, b2 = string.byte(b, i+1), string.byte(b, i+2)
        b3, b4 = string.byte(b, i+3), string.byte(b, i+4)
        --        2^24          2^16       2^8     2^0
        return b1*16777216 + b2*65536 + b3*256 + b4
end

-- insert number to binary string
function set_u8(b, i, num)
	local s = string.char(bit.band(num, 0xff))
	return b:sub(0+1, i+1-1) .. s .. b:sub(i+1+1)
end
function set_u16(b, i, num)
	local s = string.char(bit.band(bit.rshift(num, 8), 0xff)) .. string.char(bit.band(num, 0xff))
	return b:sub(0+1, i+1-1) .. s .. b:sub(i+1+2)
end
function set_u32(b,i, num)
	local s = string.char(bit.band(bit.rshift(num,24), 0xff)) ..
		string.char(bit.band(bit.rshift(num,16), 0xff)) ..
		string.char(bit.band(bit.rshift(num,8), 0xff)) ..
		string.char(bit.band(num, 0xff))
	return b:sub(0+1, i+1-1) .. s .. b:sub(i+1+4)
end


-- Checksum
----  Standard BSD internet checksum routine  check nmap/tcpip.cc
function in_cksum(b)
	local sum = 0
	local c
	local x = b

	while x:len() > 1 do
		c = x:sub(1,2)
		x = x:sub(3)
		sum = sum + u16(c, 0)
	end

	sum = bit.rshift(sum, 16) + bit.band(sum, 0xffff)
	sum = sum + bit.rshift(sum, 16)
	sum = bit.bnot(sum)
	sum = bit.band(sum, 0xffff) -- trunctate to 16 bits
	return sum
end

-- ip protocol field
IPPROTO_IP   = 0               	--  Dummy protocol for TCP
IPPROTO_ICMP = 1             	--  Internet Control Message Protocol
IPPROTO_IGMP = 2             	--  Internet Group Management Protocol
IPPROTO_IPIP = 4             	--  IPIP tunnels (older KA9Q tunnels use 94)
IPPROTO_TCP  = 6              	--  Transmission Control Protocol
IPPROTO_EGP  = 8              	--  Exterior Gateway Protocol
IPPROTO_PUP  = 12             	--  PUP protocol
IPPROTO_UDP  = 17             	--  User Datagram Protocol
IPPROTO_IDP  = 22             	--  XNS IDP protocol
IPPROTO_DCCP = 33            	--  Datagram Congestion Control Protocol
IPPROTO_RSVP = 46            	--  RSVP protocol
IPPROTO_GRE  = 47             	--  Cisco GRE tunnels (rfc 1701,1702)
IPPROTO_IPV6 = 41          	--  IPv6-in-IPv4 tunnelling

IPPROTO_ESP  = 50            	--  Encapsulation Security Payload protocol
IPPROTO_AH   = 51             	--  Authentication Header protocol
IPPROTO_BEETPH  = 94         	--  IP option pseudo header for BEET
IPPROTO_PIM     = 103         	--  Protocol Independent Multicast

IPPROTO_COMP    = 108        	--  Compression Header protocol
IPPROTO_SCTP    = 132         	--  Stream Control Transport Protocol
IPPROTO_UDPLITE = 136        	--  UDP-Lite (RFC 3828)


----------------------------------------------------------------------------------------------------------------
-- Packet is a class
Packet = {}
-- Constructor
-- packet          - binary string with packet data
-- packet_len      - packet length, it could be more than string.len(packet)
-- force_continue  - whether error in parsing headers should be fatal or not.
--                   especially usefull at parsing icmp packets, where on small icmp payload
--                   could be tcp header. The problem is that parsing this payload normally
--                   would fail (broken packet, because tcp header is too small)
--                   The basic question is if too short tcp header should be treated as fatal error.
function Packet:new(packet, packet_len, force_continue)
	local o = setmetatable({}, {__index = Packet})
	o.buf		= packet
	o.packet_len	= packet_len
	if not o:ip_parse(force_continue) then
		return nil
	end
	if o.ip_p == IPPROTO_TCP then
		if not o:tcp_parse(force_continue) then
			io.write("Error while parsing TCP packet\n")
		end
	elseif o.ip_p == IPPROTO_ICMP then
		if not o:icmp_parse(force_continue) then
			io.write("Error while parsing ICMP packet\n")
		end
	end
	return o
end

-- Helpers


-- from ip notation as string (like 1.2.3.4) to raw_string(4 bytes long)
function iptobin(str)
	local ret = ""
        for c in string.gmatch(str, "[0-9]+") do
                ret = ret .. string.char(c+0) -- automatic conversion to int
        end
	return ret
end
-- from raw_ip (four bytes string) to dot-notation (like 1.2.3.4)
function toip(raw_ip_addr)
	if not raw_ip_addr then
		return "?.?.?.?"
	end
	return string.format("%i.%i.%i.%i", string.byte(raw_ip_addr,1,4))
end
-- get unsigned byte
function Packet:u8(index)
        return u8(self.buf, index)
end
function Packet:u16(index)
        return u16(self.buf, index)
end
function Packet:u32(index)
        return u32(self.buf, index)
end
function Packet:raw(index, length)
        return string.char(string.byte(self.buf, index+1, index+1+length-1))
end

function Packet:set_u8(index, num)
        self.buf = set_u8(self.buf, index, num)
        return self.buf
end
function Packet:set_u16(index, num)
        self.buf = set_u16(self.buf, index, num)
        return self.buf
end
function Packet:set_u32(index, num)
        self.buf = set_u32(self.buf, index, num)
        return self.buf
end

-- PARSE IP PACKET HEADER
function Packet:ip_parse(force_continue)
	self.ip_offset		= 0
	if    string.len(self.buf) < 20 then 	-- too short
		return false
	end
	self.ip_v		= bit.rshift(bit.band(self:u8(self.ip_offset + 0), 0xF0), 4)
	self.ip_hl		=            bit.band(self:u8(self.ip_offset + 0), 0x0F)		-- header_length or data_offset
	if    self.ip_v ~= 4 then 	-- not ip
		return false
	end
	self.ip = true
	self.ip_tos		= self:u8(self.ip_offset + 1)
	self.ip_len		= self:u16(self.ip_offset + 2)
	self.ip_id		= self:u16(self.ip_offset + 4)
	self.ip_off		= self:u16(self.ip_offset + 6)
	self.ip_rf		= bit.band(self.ip_off, 0x8000)~=0		-- true/false
	self.ip_df		= bit.band(self.ip_off, 0x4000)~=0
	self.ip_mf		= bit.band(self.ip_off, 0x2000)~=0
	self.ip_off		= bit.band(self.ip_off, 0x1FFF)		-- fragment offset
	self.ip_ttl		= self:u8(self.ip_offset + 8)
	self.ip_p		= self:u8(self.ip_offset + 9)
	self.ip_sum		= self:u16(self.ip_offset + 10)
	self.ip_bin_src		= self:raw(self.ip_offset + 12,4)	-- raw 4-bytes string
	self.ip_bin_dst		= self:raw(self.ip_offset + 16,4)
	self.ip_src		= toip(self.ip_bin_src)		-- formatted string
	self.ip_dst		= toip(self.ip_bin_dst)
	self.ip_opt_offset	= self.ip_offset + 20
	self.ip_options		= self:parse_options(self.ip_opt_offset, ((self.ip_hl*4)-20))
	self.ip_data_offset	= self.ip_offset + self.ip_hl*4
	return true
end
-- set header length field
function Packet:ip_set_hl(len)
	self:set_u8(self.ip_offset + 0, bit.bor(bit.lshift(self.ip_v, 4), bit.band(len, 0x0F)))
	self.ip_v		= bit.rshift(bit.band(self:u8(self.ip_offset + 0), 0xF0), 4)
	self.ip_hl		=            bit.band(self:u8(self.ip_offset + 0), 0x0F)		-- header_length or data_offset
end
-- set packet length field
function Packet:ip_set_len(len)
	self:set_u16(self.ip_offset + 2, len)
end
-- set ttl
function Packet:ip_set_ttl(ttl)
	self:set_u8(self.ip_offset + 8, ttl)
end
-- set checksum
function Packet:ip_set_checksum(checksum)
	self:set_u16(self.ip_offset + 10, checksum)
end
-- count checksum for packet and save it
function Packet:ip_count_checksum()
	self:ip_set_checksum(0)
	local csum = in_cksum( self.buf:sub(0, self.ip_offset + self.ip_hl*4)  )
	self:ip_set_checksum(csum)
end
-- set source ip
function Packet:ip_set_bin_src(binip)
	nrip = u32(binip, 0)
	self:set_u32(self.ip_offset + 12, nrip)
	self.ip_bin_src		= self:raw(self.ip_offset + 12,4)	-- raw 4-bytes string
end
-- set destination ip
function Packet:ip_set_bin_dst(binip)
	nrip = u32(binip, 0)
	self:set_u32(self.ip_offset + 16, nrip)
	self.ip_bin_dst		= self:raw(self.ip_offset + 16,4)
end
-- set ip options field (and move the data, count new length etc)
function Packet:ip_set_options(ipoptions)
	-- packet = <ip header> + ipoptions + <payload>
	local buf = self.buf:sub(0+1,self.ip_offset + 20) .. ipoptions .. self.buf:sub(self.ip_data_offset+1)
	self.buf = buf
	-- set ip_len
	self:ip_set_len(self.buf:len())
	-- set ip_hl
	self:ip_set_hl(5 + ipoptions:len()/4)
	-- set data offset correctly
	self.ip_options		= self:parse_options(self.ip_opt_offset, ((self.ip_hl*4)-20))
	self.ip_data_offset	= self.ip_offset + self.ip_hl*4
	if self.tcp then
		self.tcp_offset		= self.ip_data_offset
	elseif self.icmp then
		self.icmp_offset	= self.ip_data_offset
	end
end

-- return short information about ip header
function Packet:ip_tostring()
	return string.format(
		"IP %s -> %s",
		self.ip_src,
		self.ip_dst)
end

-- parse ip/tcp options to dict structure
function Packet:parse_options(offset, length)
	local options = {}
	local op = 1
	local opt_ptr = 0
	while opt_ptr < length do
		local t, l, d
		options[op] = {}

		t = self:u8(offset + opt_ptr)
		options[op].type = t
		if t==0 or t==1 then
			l = 1
			d = nil