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Re: [netmod] [core] CBOR YANG encoding of union & bits [draft-ietf-core-yang-cbor-12]

Michael Richardson <mcr+ietf@sandelman.ca> Wed, 06 May 2020 17:21 UTC

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From: Michael Richardson <mcr+ietf@sandelman.ca>
To: Carsten Bormann <cabo@tzi.org>, "netmod@ietf.org" <netmod@ietf.org>, "core@ietf.org" <core@ietf.org>
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Date: Wed, 06 May 2020 13:21:24 -0400
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Subject: Re: [netmod] [core] CBOR YANG encoding of union & bits [draft-ietf-core-yang-cbor-12]
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Carsten Bormann <cabo@tzi.org> wrote:
    >> Or, if it is supported by the language then is it reasonable that
    >> implementation SHOULD support it?  In which case I think that we might
    >> need a second encoding of bits that supports this pathological case.
    >> Perhaps an array of 'set' bit positions, or alternatively the union
    >> string encoding of bits could be used.

    > This could reduce the attack vector by malicious YANG specification,
    > but I think an arbitrary limit (such as the 256 mentioned above) should
    > work, too.  (Except that arbitrary limits always come back to bite you,
    > but that’s what we have software maintenance contracts for.)

I think that the YANG knows what the maximum value is.
So I think that anyone generating code from specific YANG definitions could
size their array based upon that value.
If it's a generic decoder for YANG encoded content, then it might need
a hint from the application, or it could have a compile-time arbitrary limit.

--
Michael Richardson <mcr+IETF@sandelman.ca>, Sandelman Software Works
 -= IPv6 IoT consulting =-

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