Wireshark · Wireshark-dev: Re: [Wireshark-dev] Calling a dissector: Type for data parameter

[Uli Heilmeier <zeugs@xxxxxxxxxxxx>]

Makes sense for me. I will change the MQTT dissector to call call_dissector_with_data() only for sparkplug payload.

Am 29.05.2021 um 09:12 schrieb Anders Broman <a.broman58@xxxxxxxxx>:

Hi,

Shouldn't the caller be calling with the right data type or NULL? So a bug in the MQTT disector?

Regards

Anders

Den lör 29 maj 2021 09:07Uli Heilmeier <zeugs@xxxxxxxxxxxx> skrev:

With MR 2706 [1] the MQTT dissector calls now subdissectors with call_dissector_with_data() [2]. Previously this was call_dissector().

With this change the JSON dissector crashes WS with a memory access segfault (while using MQTT decode topic as option).
This is because for JSON we expect http_message_info_t for data pointer [3]. MQTT hands over a pointer to a char array (topic_str) for data.

How do we handle data type for the data parameter pointer? Would it make sense to compare at least the size of data with the size of http_message_info_t?

I don’t know any way to check the data type of a pointer address location.

Cheers
Uli

[1]: https://gitlab.com/wireshark/wireshark/-/merge_requests/2706/
[2]: https://gitlab.com/wireshark/wireshark/-/merge_requests/2706//diffs#07171e000b3caaabee32ab5dc04a5d28efbaaae3_755_755
[3]: https://gitlab.com/wireshark/wireshark/-/blob/master/epan/dissectors/packet-json.c#L221
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