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Re: [tsvwg] OCS option in draft-ietf-tsvwg-udp-options-07

"C. M. Heard" <heard@pobox.com> Wed, 13 March 2019 03:27 UTC

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From: "C. M. Heard" <heard@pobox.com>
Date: Tue, 12 Mar 2019 20:26:39 -0700
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To: Joe Touch <touch@strayalpha.com>
Cc: Raffaele Zullo <raffaele@erg.abdn.ac.uk>, Gorry Fairhurst <gorry@erg.abdn.ac.uk>, tsvwg <tsvwg@ietf.org>
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Subject: Re: [tsvwg] OCS option in draft-ietf-tsvwg-udp-options-07
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On Tue, Mar 12, 2019 at 4:16 PM Joe Touch <touch@strayalpha.com> wrote:
> > On 2019-03-12 16:01, Raffaele Zullo wrote:
> > OK, but what happens if UDP Length (that was 8) is increased to
> > 8 < UDP Length <= IPPayloadLength?
> > Will part of the Options area be delivered to user as a regular UDP
> > Payload?
>
> If the reassembly checksum isn't zero, this would be caught (with high
> probability) during reassembly.

If LITE+FRAG is being used, then the initial LITE option will be corrupted,
as at least one octet will be skipped. With exceedingly high probability,
the LITE option will not be processed. The remaining options won't be
found, and what is there is unlikely to be parsed. Result: the
(UDP Length - 8) octets that appear to be conventional UDP user data
will be delivered, and the trailing octets will be discarded since they
will not appear to be valid UDP options.

Reassembly won't even be invoked.

So, CS=0 does have its risks even for the length field.

Mike Heard

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