Re: Calling a dissector: Type for data parameter

[Anders Broman <a.broman58 () gmail com>]

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 () heilmeier eu> 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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