Wireshark · Ethereal-dev: Re: [Ethereal-dev] need help with tvb exceptions

[Peter Johansson <Peter.Johansson@xxxxxxxxxxxx>]

Andy Howell wrote:

> My dissector gets part way through a packet and then shows [ Malformed 
> Packet: mypacket ]
>
> I tried doing a printf of the tvb_get_remaining() just after the last 
> item that was added. It reports I have 48 bytes left. The next thing I 
> do is tvb_get_ntohs, but since it never reaches the following 
> statement, I assume its generating an exception.
>
> It most likely a problem in my code, but I don't know what to check 
> next. Is there any way to get more information about boundry errors etc?
>
> Thanks,
>
>     Andy

Somewhere in your code you are probably doing something similar to 
proto_tree_add_item(tree,  hf_something, tvb, some_offset, some_length, 
FALSE);
My guess is that some_offset + some_length exceeds the value returned by 
tvb_length(tvb).
Set a breakpoint in packet-frame.c near or at line 244 (search for 
"Malformed packet") and run again, check the stack to verify where in 
your code it causes "an exception" and why.

/ Peter