Subject: [Tsvwg] SCTP- processing of bundled chunks

From: bhanu <[email-masked]>
Date: Tue, 31 Aug 2004 14:32:21 +0530

Hai All

While processing each chunk from a bundle, individual chunks are extracted
using the chunk_length parameter as the size of that chunk.
So the next chunk will be at the location = CHUNK_HEADER_SIZE +  
CHUNK_LENGTH.

Consider the processing of any variable length chunk (e.g : COOKIE ECHO 
or DATA).
If the chunk_length parameter of a chunk indicates a size which is more 
than the actual size
of the chunk, what should be the action by the reciever of such chunk..???
what about extracting and processing of the chunks which are bundled 
after this,
as the chunk_length indicates some wrong value it is not possible to 
know the end of this chunk.
(The RFC-2960 does not talk about handling of such scenario).

Can anybody guide us in this regard.

Regards
Bhanu.

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From: Michael Tuexen <[email-masked]>
Date: Tue, 31 Aug 2004 15:49:14 +0200

Hi Bhanu,

see my comments in-line.

Best regards
Michael

> So the next chunk will be at the location = CHUNK_HEADER_SIZE +  
No, the chunk size does include the chunk header, So you need to do
offset += ADD_PADDING(chunk_length)
where ADD_PADDING adds the padding (0 to 3 Bytes).
> Consider the processing of any variable length chunk (e.g : COOKIE 
> ECHO or DATA).
> If the chunk_length parameter of a chunk indicates a size which is 
> more than the actual size
Well, that chunk is violating the spec, right? So I would send back an
ABORT with error cause 'PROTOCOL VIOLATION'.
> know the end of this chunk.
Since you do not know the 'real' size you have to give up, I think. 
That is
why I'm suggesting the ABORT...

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From: bhanu <[email-masked]>
Date: Tue, 31 Aug 2004 19:48:24 +0530

Hai Michael

The feedback was helpfull

But again, is it really possible to find out wheather the size indicated 
by the
chunk_length parameter is correct or not..???

Is there exists an ABORT with error cause 'PROTOCOL VIOLATION' !!!!!

Thanks
Bhanu.

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From: Vladislav Yasevich <[email-masked]>
Date: Tue, 31 Aug 2004 10:43:00 -0400

Bhanu

> chunk_length parameter is correct or not..???

I think, as long as the end of the chunk is computed to be within the
payload, you have to assume that it's valid.  The only additional
assuarances I can think of require some sort of transport or network
security.

> Is there exists an ABORT with error cause 'PROTOCOL VIOLATION' !!!!!

It is definied in the SCTP Implementer's Guide 
(draft-ietf-tsvwg-sctpimpguide-nn).

-vlad

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Vladislav Yasevich		Linux and Open Source Lab
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