Wireshark · Wireshark-dev: Re: [Wireshark-dev] Unable to detect custom protocol dissector

[sandip gangakhedkar <sandipfloyd@xxxxxxxxx>]

Hi Chris,

I confirm that I see the same issue with your Lua script. However, I am able to dissect the GeoNetworking header normally in another pcap trace that does not contain my proprietary header that encapsulates my GeoNetworking PDU. So I think the Native Wireshark gnw Dissector is working just fine. 

However, when I add the custom Dissector for my proprietary header and then chain the gnw Dissector to it, I am able to see my proprietary headers, but fail to see the GeoNetworking header dissected. 

@Anders: I did not notice anything particular in the way the gnw Dissector is registered:

expert_module_t* expert_geonw;
	module_t *geonw_module;
	proto_geonw = proto_register_protocol("GeoNetworking", "GNW", "gnw");
	geonw_handle = register_dissector("gnw", dissect_geonw, proto_geonw);
	proto_register_field_array(proto_geonw, hf_geonw, array_length(hf_geonw));
	proto_register_subtree_array(ett, array_length(ett));
	expert_geonw = expert_register_protocol(proto_geonw);
	expert_register_field_array(expert_geonw, ei, array_length(ei));

Am I missing something here?

Thanks again for your help.

On Thu, Feb 13, 2020 at 10:50 PM Maynard, Chris via Wireshark-dev <wireshark-dev@xxxxxxxxxxxxx> wrote:

I’m not sure what you’re trying to do, but there’s already a Wireshark built-in dissector for GeoNetworking[1].

 

If you’re trying to replace it for some reason, then you may either need to disable that one or remove it completely.  And if you’re trying to implement in Lua, then you’ll need to register it as a heuristic dissector using register_heuristic[2].  However, it seems that there might be a bug with respect to this function[3], as the following simple Lua script seems to indicate:

 

local p_gnw = Proto("gnwHdr", "GeoNetworkingHdr")

 

function p_gnw.dissector(tvbuf, pinfo, tree)

 

    local ethertype = tvbuf(12, 2):uint()

    if ethertype == 35143 then

        pinfo.cols.protocol:set("GNW")

        return true

    else

        return false

    end

end

 

p_gnw.register_heuristic("eth", p_gnw.dissector)

 

 

When Wireshark is started with this gnw.lua script loaded, the following error message is encountered:

 

Lua: Error during loading:

path\to\gnw.lua:14:bad

argument #1 to ‘register_heuristic’ (userdata expected, got string)

stack traceback:

         [C]: in function ‘register_heuristic’

         path\to\gnw.lua:14:

in main chunk

 

- Chris

[1]: https://code.wireshark.org/review/gitweb?p=wireshark.git;a=blob;f=epan/dissectors/packet-geonw.c;h=21290a3b179c8974483a2f762cbe512fbec67103;hb=HEAD

[2]: https://www.wireshark.org/docs/wsdg_html_chunked/lua_module_Proto.html (Section 11.6.5.3)

[3]: https://osqa-ask.wireshark.org/questions/54158/register-heuristic-function-for-multiple-heuristic-list-names-in-lua

 

 

From: Wireshark-dev <wireshark-dev-bounces@xxxxxxxxxxxxx> On Behalf Of sandip gangakhedkar
Sent: Wednesday, February 12, 2020 4:46 PM
To: wireshark-dev@xxxxxxxxxxxxx
Subject: [Wireshark-dev] Unable to detect custom protocol dissector

 

Hi,

 

I am using a Custom protocol dissector (Lua script) for the GeoNetworking header. I have build wireshark 3.2.1 from source on Ubuntu 18.04 and placed the Lua script in the Global plugins directory. However, the script fails when to find the Geonetworking protocol when I invoke it in the script:

 

  Dissector.get("gnw"):call(newTvb, pkt, root)

 

So I tried another approach:

 

  gnw_dissector = DissectorTable.get("ethertype"):get_dissector(35143)

 

The protocol gnw (GeoNetworking) corresponds to an EtherType of 35143 in my Wireshark protocols configuration. However, this also fails to find the "gnw" protocol.

 

How can I get wireshark to detect the GeoNetworking protocol from my custom Lua script?

 

Thanks in advance.

 

 

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