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, ipconfigme@gmail.com
- -- 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
参考
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