Re: [secdir] secdir review of draft-ietf-tcpm-tcpmss-04

["Klaas Wierenga (kwiereng)" <[e-mail]>]

Hi David,


On 30 mei 2012, at 19:29, "David Borman" <[e-mail]> wrote:

> Klass,
> 
> Thanks for the review.
> 
> On May 30, 2012, at 10:05 AM, Klaas Wierenga wrote:
> 
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>> Hi,
>> 
>> I have reviewed this document as part of the security directorate's
>> ongoing effort to review all IETF documents being processed by the
>> IESG.  These comments were written primarily for the benefit of the
>> security area directors.  Document editors and WG chairs should treat
>> these comments just like any other last call comments.
>> 
>> General comments:
>> ==================
>> 
>> This is a short, clear and to the point draft. I have only a few
>> general comments
>> 
>> 1 (introduction)
>> - ----------------
>> 
>> - - Please expand MSS on first use
> 
> Agreed.
> 
>> 
>> - - "(see appendix A)" and "but there still seems to be some confusion"
>> 
>> This sounds pretty vague to me. I thought Appendix A would be a
>> verbatim copy of the text from 1122, but it is much more, and I
>> appreciated the discussion. I propose to make that explicit:
>> 
>> "RFC1122 clarified the MSS option, but confusion remains as discussed
>> in Appendix A"
> 
> I've changed it to:
>   RFC 1122 [RFC1122] clarified the MSS
>   option, which is discussed in Appendix A, but there still seems to be
>   some confusion.


Ah, I thought you had listed all confusion in appendix A. Since that does not seem to be the case, can you say anything about the nature of the remaining confusion?

>> 
>> Security Considerations:
>> ========================
>> I don't really think what you have written down here qualifies as
>> security considerations. It sort of hints to a denial-of-service, but
>> I don't see any evil, just an operational problem.
> 
> Another review said more or less the same thing..

Great minds..... ;-)

> 
>> What I wonder about
>> (but I am not knowledgable to judge) is whether wrong MSS size
>> settings could be exploited for for example buffer overflow attacks.
> 
> There shouldn't be any problem.  The MSS is just an upper bound
> for the size of packets that can be reassembled by the receiving
> hosts; in theory most IPv4 hosts should be using 65535 because they
> don't have a fixed limit, and then just let Path MTU discovery sort
> it out.  In practice, though, the MSS is used as an upper bound for what
> size of packet can be received without the need for fragmentation,
> avoiding PMTU from probing for larger sizes that will never succeed.
> 
> I don't have a strong opinion about the current content of the
> Security Considerations section.  My leaning is to just leave it
> as is, but I'd be fine with moving the content up to section 5.4
> as an "Additional Consideration", and then have section 6, "Security
> Considerations" just have a comment that there are no security
> considerations, if folks generally feel that would be better.

I don't feel comfortable with a security consideration that isn't, so I would lean towards your alternative proposal.

Thanks for the fast response!

Klaas

> 
>        -David Borman
> 
>> 
>> 
>> Cheers,
>> 
>> Klaas
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