使用lua给wireshark编写uTP的Dissector

lonelycastle做uTP的实验，使用wireshark捕包，但是最初没有找到wireshark下的uTP的dissector，每次都需要比对文档，这样做实验理解报文含义，效率非常低。作为程序猿就想写一个uTP的dissector来实现这些工作。说干就干，查了一下发现wireshark可以使用lua来实现dissector，这样就简单过了，不用编写C的dissector了。本身是lua盲，又不了解wireshark的dissector开发，中间遇到了很多问题，还好逻辑比较简单，折腾了一个晚上就搞定了;-)

BTW: 后来发现wireshark中已经有了bt-utp这个dissector，但是没有判断PIECE分包。

1. 如何定义小于1个字节的field

>> 查了一下User Guide，发现可以在创建ProtoField的时候，使用mask参数就可以了。

2. 如何取小于1个字节field的值

>> 这个需要位操作进行处理，具体见参考文献1。主要是bit.band, bit.bor, bit.bxor, bit.rshift, bit.lshift等。注意右移位是bit.rshift，而不是bit.brshift。

3. 如何调用其他Dissector

>> Dissector.get()获得系统中已经有的dissector；DissectorTable.get()获得系统中已经有的dissector table，再调用get_dissector()获得最终的dissector。

>> 获得dissector后，就可以直接调用call，call的参数跟dissector function的参数一致。

xx_protocol.dissector = function(buffer,pinfo,tree)
--定义这个协议的解析函数，最后会将这个函数注册到wireshark用来解析数据的表中。这个函数的三个参数很重要，是wireshark引擎在调用该函数是会传入，
--buffer就是我们要分析的数据，
--pinfo记录了前面分析过协议留下的信息，
--tree是用来在详细框中添加我们信息的结构。

4. 如何设置报文信息

>>直接修改pkt.cols.info，其中pkt是dissector function传入的参数，具体见参考文献4.

5. 如何处理一个应用报文跨多个uTP报文

>>在BitTorrent中，PIECE报文比较大，会跨多个uTP报文，这个时候需要判断出第一个PIECE报文，进行解析，后面的PIECE报文不需要解析，如果解析就会导致出错。这里是使用一个检查函数，判断每种type下，协议中数据长度是否满足限制来实现的。

具体如何运行这里就不多说了，直接在init.lua中最后增加dofile就可以，注意要首先把lua_disable关上，debian用户需要保证root也可以在wireshark中运行lua。调试的时候可以看wireshark的报错信息。

示例代码如下，BitTorrent的解析调用了wireshark内部已有的bittorrent.tcp dissector：

do
-- Desc: uTP Protocol lua version
-- Author: WangYao, [email protected]
-- Date: 2011/10/19
-- protol name
local p_utp = Proto("utp", "Micro Transport Protocol");
-- protocol fields
local f_version = ProtoField.uint8("utp.version", "Version", base.DEC,
{[1]="V1"}, 0x0F)
local f_type = ProtoField.uint8("utp.type", "Type", base.DEC,
{[0]="ST_DATA", [1]="ST_FIN", [2]="ST_STATE", [3]="ST_RESET", [4]="ST_SYN"}, 0xF0)
local f_next_extension_type = ProtoField.uint8("utp.next_extension_type", "Next Extension Type", base.DEC,
{[0]="No Extension", [1]="Selective acks", [2]="Extension bits"})
local f_extension_len = ProtoField.uint8("utp.extension_len", "Extension Length", base.DEC)
local f_extension_bitmask = ProtoField.bytes("utp.extension_bitmask", "Extension Bitmask", base.NONE)
local f_connection_id = ProtoField.uint16("utp.connection_id", "Connection_ID", base.DEC)
local f_timestamp_microseconds = ProtoField.uint32("utp.timestamp_microseconds", "timestamp_microseconds", base.DEC)
local f_timestamp_difference_microseconds = ProtoField.uint32("utp.timestamp_difference_microseconds", "timestamp_difference_microseconds", base.DEC)
local f_wnd_size = ProtoField.uint32("utp.wnd_size", "wnd_size", base.DEC)
local f_seq_nr = ProtoField.uint16("utp.seq_nr", "seq_nr", base.DEC)
local f_ack_nr = ProtoField.uint16("utp.ack_nr", "ack_nr", base.DEC)
p_utp.fields = {f_version, f_type, f_next_extension_type, f_extension_len, f_extension_bitmask, f_connection_id, f_timestamp_microseconds, f_timestamp_difference_microseconds, f_wnd_size, f_seq_nr, f_ack_nr}
-- other dissector
local data_dis = Dissector.get("data")
local bittorrent_dissector = Dissector.get("bittorrent.tcp")
-- utp dissector, return OFFSET
local function utp_dissector(buf,pkt,root)
local buf_len = buf:len()
local offset = 0
-- check pack len
if buf_len < 20 then return 0 end
-- get fields
local v_version = buf(offset, 1)
local v_type = buf(offset, 1)
offset = offset + 1
local v_next_extension_type = buf(offset, 1)
offset = offset + 1
local v_connection_id = buf(offset, 2)
offset = offset + 2
local v_timestamp_microseconds = buf(offset, 4)
offset = offset + 4
local v_timestamp_difference_microseconds = buf(offset, 4)
offset = offset + 4
local v_wnd_size = buf(offset, 4)
offset = offset + 4
local v_seq_nr = buf(offset, 2)
offset = offset + 2
local v_ack_nr = buf(offset, 2)
offset = offset + 2
-- check uTP
local i_version = bit.band(v_version:uint(), 0x0F)
-- local i_type = bit.band(bit.rshift(v_type:uint(), 4), 0x0F)
local i_type = bit.rshift(bit.band(v_type:uint(), 0xF0), 4)
if( (i_version~=1) or (i_type~=0 and i_type~=1 and i_type~=2 and i_type~=3 and i_type~=4))
then return 0 end
local subtree = root:add(p_utp, buf(),"Micro Transport Protocol")
-- just add header
subtree:add(buf(0,0),"uTP Header: ")
subtree:add(f_version, v_version)
subtree:add(f_type, v_type)
subtree:add(f_next_extension_type, v_next_extension_type)
subtree:add(f_connection_id, v_connection_id)
subtree:add(f_timestamp_microseconds, v_timestamp_microseconds)
subtree:add(f_timestamp_difference_microseconds, v_timestamp_difference_microseconds)
subtree:add(f_wnd_size, v_wnd_size)
subtree:add(f_seq_nr, v_seq_nr)
subtree:add(f_ack_nr, v_ack_nr)
-- add pkt info
pkt.cols.protocol = "uTP"
if(i_type==0) then
pkt.cols.info = "uTP ST_DATA"
elseif(i_type==1) then
pkt.cols.info = "uTP ST_FIN"
elseif(i_type==2) then
pkt.cols.info = "uTP ST_STATE"
elseif(i_type==3) then
pkt.cols.info = "uTP ST_RESET"
elseif(i_type==4) then
pkt.cols.info = "uTP ST_SYN"
else
pkt.cols.info = "uTP UNKNOW"
end
while(v_next_extension_type:uint()~=0) do
-- add extension tree
local extendtree = subtree:add(p_utp, buf(offset, buf_len-offset):tvb(),"Extension")
if(v_next_extension_type:uint()==0) then
extendtree:append_text(": NO Extension")
elseif(v_next_extension_type:uint()==1) then
extendtree:append_text(": Selective acks")
elseif(v_next_extension_type:uint()==2) then
extendtree:append_text(": Extension bits")
end
v_next_extension_type = buf(offset, 1)
offset = offset + 1
extendtree:add(f_next_extension_type, v_next_extension_type)
local v_extension_len = buf(offset, 1)
offset = offset + 1
extendtree:add(f_extension_len, v_extension_len)
local i_extension_len = v_extension_len:int()
local v_extension_bitmask = buf(offset, i_extension_len)
offset = offset + i_extension_len
extendtree:add(f_extension_bitmask, v_extension_bitmask)
end
return offset
end
-- check packet is bittorrent? header legal
local function check_bittorrent(buf)
local len = buf:len()
local pack_len = buf(0,4)
local pack_type
if(len<4) then
return false
elseif(buf(0,1):uint()==19 and len==68) then --handshake
return true
elseif(len==4) then --keepalive
if(pack_len:uint()==0) then return true
else return false
end
else
pack_type = buf(4,1)
--choke, unchoke, interested, not interested, have all, have none
if(pack_type:uint()==0 or pack_type:uint()==1 or pack_type:uint()==2 or pack_type:uint()==3 or pack_type:uint()==0x0E or pack_type:uint()==0x0F) then
if(pack_len:uint()==1) then return true
else return false
end
--request, cancel, reject
elseif(pack_type:uint()==6 or pack_type:uint()==8 or pack_type:uint()==0x10) then
if(pack_len:uint()==13) then return true
else return false
end
--port
elseif(pack_type:uint()==9) then
if(pack_len:uint()==3) then return true
else return false
end
--have, suggest, allowed fast
elseif(pack_type:uint()==4 or pack_type:uint()==0x0D or pack_type:uint()==0x11) then
if(pack_len:uint()==5) then return true
else return false
end
--bitfield, extend
elseif(pack_type:uint()==5 or pack_type:uint()==0x14) then
if(pack_len:uint()<1024) then return true
else return false
end
--piece, max than 16K
elseif(pack_type:uint()==7) then
if(pack_len:uint()>=16384) then return true
else return false
end
else
return false
end
end
return false
end
-- protocol dissector, include bittorrent
function p_utp.dissector(buf,pkt,root)
local len = buf:len()
local offset = utp_dissector(buf, pkt, root)
if len>offset and offset>0 then
-- call bittorrent dissector
-- pass split PIECE pack
if check_bittorrent(buf(offset, len-offset)) then
bittorrent_dissector:call(buf(offset, len-offset):tvb(), pkt, root)
else
data_dis:call(buf(offset,len-offset):tvb(), pkt, root)
end
elseif offset==0 then
-- call data dissector
data_dis:call(buf,pkt,root)
end
end
-- add to DissectorTable
local udp_table = DissectorTable.get("udp.port")
-- udp_table:add(4135, p_utp)
udp_table:add(10000, p_utp)
end