Ethereal-dev: Re: [Ethereal-dev] Re: rev 17527: /trunk/plugins/profinet/: packet-pn-dcp.c

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From: "Lars Roland" <Lars.Roland@xxxxxxx>
Date: Fri, 10 Mar 2006 18:09:04 +0100
Am 10.03.2006, 17:00 Uhr, schrieb Ulf Lamping <ulf.lamping@xxxxxx>:




Use this updated patch instead.



You make things worse than they are.
Don't manipulate data coming from a packet! If the block_length in the packet is invalid, use it anyway.
Stopping the dissection of a packet because there are not enough data is a bad idea. Showing Malformed Packet is the way to go here.
You are right. If a dissector requests more bytes than the packet contains, the packet has to be shown as malformed. But the question here is, how much data the dissector should request. We have a length field for the pdu, and a length field for each value. Should we stop dissection, if a value exceeds the boundaries of the pdu? What shall we do, if enough bytes are available beyond the pdu boundary? I agree that we should show it as a "Malformed Packet" in this situation anyway. But you won't catch wrong pdu lengths by just using the block_length. This way you would catch only wrong lengths for values. 

Regards,
Lars