Re: [MBONED] Eric Rescorla's Discuss on draft-ietf-mboned-mtrace-v2-22: (with DISCUSS and COMMENT)

Toerless Eckert <tte@cs.fau.de> Fri, 26 January 2018 01:31 UTC

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Date: Fri, 26 Jan 2018 02:31:18 +0100
From: Toerless Eckert <tte@cs.fau.de>
To: Eric Rescorla <ekr@rtfm.com>
Cc: The IESG <iesg@ietf.org>, draft-ietf-mboned-mtrace-v2@ietf.org, mboned@ietf.org, mboned-chairs@ietf.org
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Subject: Re: [MBONED] Eric Rescorla's Discuss on draft-ietf-mboned-mtrace-v2-22: (with DISCUSS and COMMENT)
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On Thu, Jan 25, 2018 at 03:08:58PM -0800, Eric Rescorla wrote:
> > My point B.1) explicitly disables lying about the requesting address, so
> > it is explicitly meant to prohibit amplification attacks.
> >
> 
> I don't see how that's true. The attack I am concerned about is that you
> forge a *Request*, not a *Query*. And because the request indicates the original
> requester.

Ah, sorry. I thought to remember that the text from you said query.
I just replied for query messages so far.

> (give or take the subnet local limitations and/or additional L2 security
> >  required to prohibit intra-l2-lying that i mentioned in my original mail).
> 
> Sorry, I'm not seeing this. The point is that you pretend to be a router
> that is forwarding a Request and fill in a bogus Client Address field. Waht
> stops that.

In practical deployments IMHO we can only reasonable get similar solutions to
what customer are also willing to deploy with PIM. For 99% deployments that
is configured classificatio of interfaces as trusted/inside-clamshell or
untrusted/user-facing, and on the untrusted interfaces you don't accept
requests, just queries. And apply the suggested B.1 policy (Mtracev2 Client
Address must be connected on receiving interface).

It might still be useful to have mtrace prepared for customers protecting it
with IPsec - without requiring special features in mtrace or IPsec for it.

IMHO for that, we need to have one UDP port for mtrace NNI messages
(requests), and another for UNI messages (query, response).
That would allow customers to take a vanilla IPsec implementation and protect
the mtrace NNI messages and therefore eleiminate interface clamshell
classification.  In multicast signaling we got this for free: PIM is NNI,
IGMP/MLD UNI. Easy to distinguish for IPsec.

> > My points B.1, B.2, B.3) provide solid access control mechanisms for
> > mtrace using mechanisms that are the most widely adopted form of security
> > in ISPs
> > and that this option of security in mtrace should not be dismissed just
> > because
> > it took us so long to bring the protocol in front of IESG review even if
> > we agree
> > that we should have better options beyond that.
> 
> The question is whether those options are in fact adequate. For the reasons
> above I don't believe that.
>
> -Ekr

Cheers
    Toerless

> 
> 
> >
> > The other point was that better security options are something we should
> > not
> > invent as one-off protocol hack sinto mtrace (even if some mtrace none
> > request/reply
> > messages might be fun to define) but instead we should adopt solutions
> > that are more
> > likely in-line with existing network OAM security strategies. TLS
> > connections,
> > netconf/yang etc. pp. As i described in my email.
> >
> > Cheers
> >     toerless
> >
> > > -Ekr
> > >
> > >
> > >
> > > The most likely next step to overcome the trusted path issue between
> > > > query initiator to query responder is to make an mtrace yang model
> > where
> > > > you can actually initiate an mtrace via netconf/yang, aka: replace
> > > > the query with netconf. Like you would today just ssh into the
> > > > LHR and run a local mtrace client there.
> > > >
> > > > Alas, i see no easy way to get back to support A) in a lightweight
> > > > fashion ;-(
> > > >
> > > > Cheers
> > > >     Toerless
> > > >
> > > > On Thu, Jan 18, 2018 at 07:34:59AM -0800, Eric Rescorla wrote:
> > > > > Eric Rescorla has entered the following ballot position for
> > > > > draft-ietf-mboned-mtrace-v2-22: Discuss
> > > > >
> > > > > When responding, please keep the subject line intact and reply to all
> > > > > email addresses included in the To and CC lines. (Feel free to cut
> > this
> > > > > introductory paragraph, however.)
> > > > >
> > > > >
> > > > > Please refer to https://www.ietf.org/iesg/stat
> > > > ement/discuss-criteria.html
> > > > > for more information about IESG DISCUSS and COMMENT positions.
> > > > >
> > > > >
> > > > > The document, along with other ballot positions, can be found here:
> > > > > https://datatracker.ietf.org/doc/draft-ietf-mboned-mtrace-v2/
> > > > >
> > > > >
> > > > >
> > > > > ------------------------------------------------------------
> > ----------
> > > > > DISCUSS:
> > > > > ------------------------------------------------------------
> > ----------
> > > > >
> > > > > The security considerations of this document are inadequate. My
> > review
> > > > > turns up at least the following potential issues which do
> > > > > not seem to be addressed or even discussed:
> > > > >
> > > > > - Amplification: this protocol does not appear to verify that the
> > > > >   sender of the query actually owns the IP it claims. Because
> > > > >   responses are much larger than queries, this allows for an
> > > > amplification
> > > > >   attack, especially if the client is able to send a query that
> > elicits
> > > > >   multiple replies. One defense here would be to fill the rest of the
> > > > packet
> > > > >   with zeroes, thus somewhat reducing the amplification factor.
> > Access
> > > > >   control would also help.
> > > > >
> > > > > - Forgery of responses: because the query id is so short, an attacker
> > > > >   can generally produce a message which has a nontrivial chance of
> > > > >   corresponding to an extant query. This could be addressed by having
> > > > >   a query ID that was large and random.
> > > > >
> > > > > - Anyone on-path can forge responses.
> > > > >
> > > > > In addition, Section 9.4 seems inadequate. Isn't it generally the
> > case
> > > > that
> > > > > who is sending to who is sensitive? This seems like a fairly serious
> > > > privacy
> > > > > obstacle to using this protocol at all.
> > > > >
> > > > > It seems like many of the issues I raise above would be fixed or at
> > > > > least mitigated by having some sort of access control mechanism.  I
> > > > > understand why it might be the case that it's not practical to have
> > > > > full communication security between the links (though it would of
> > > > > course be desirable), but it's not clear to me why arbitrary people
> > > > > should be allowed to instantiate queries.
> > > > >
> > > > >
> > > > > ------------------------------------------------------------
> > ----------
> > > > > COMMENT:
> > > > > ------------------------------------------------------------
> > ----------
> > > > >
> > > > > S 1.
> > > > >    When an Mtrace2 client initiates a multicast trace, it sends an
> > > > >    Mtrace2 Query packet to the LHR or RP for a multicast group and,
> > > > >
> > > > > This seems a bit confusing as there are multiple LHRs for the group.
> > > > > Can you rephrase?
> > > > >
> > > > >
> > > > > S 2.1.
> > > > >    ALL-[protocol]-ROUTERS group
> > > > >       It is a link-local multicast address for multicast routers to
> > > > >
> > > > > This is grammatically funny. Perhaps remove "It is"
> > > > >
> > > > >
> > > > > S 3.
> > > > >    additional information associated with the message.  If an
> > > > >    implementation receives an unknown TLV type for the first TLV in a
> > > > >    message (i.e., the header TLV), it SHOULD ignore and silently
> > discard
> > > > >    the entire packet.  If an implementation receives an unknown TLV
> > type
> > > > >    for a subsequent TLV within a message, it SHOULD ignore and
> > silently
> > > > >    discard the entire packet.
> > > > >
> > > > > ISTM that these cases are handled identically so is there a reason
> > > > > not just to remove the first sentence and change the second one to
> > > > > "for any TLV"/
> > > > >
> > > > >
> > > > >
> > > > > S 3.2.1
> > > > >    An Mtrace2 Query is usually originated by an Mtrace2 client which
> > > > >    sends an Mtrace2 Query message to the LHR.  When tracing towards
> > the
> > > > >    source or the RP, the intermediate routers MUST NOT modify the
> > Query
> > > > >    message except the Type field.
> > > > >
> > > > > I'm not sure I follow this. Don't routers either (a) not touch this
> > at
> > > > all
> > > > > or (b) if they are the LHR, change Type from Query -> Request and
> > then
> > > > > add a response block? This text seems to not really capture either
> > case.
> > > > >
> > > > >
> > > > > S 3.2.4.
> > > > >       Note that Mtrace2 does not require all the routers on the path
> > to
> > > > >       have synchronized clocks in order to measure one-way latency.
> > > > >
> > > > > It's not clear to me how one does this. Can you expand?
> > > > >
> > > > >
> > > > > S 3.2.6.
> > > > >
> > > > >           0x01    # of the returned Standard Response Blocks
> > > > >
> > > > > Nit: Do you want to say 0x0001
> > > > >
> > > > > Also, an example of the case covered by this section would help, I
> > think.
> > > > >
> > > > >
> > > > >
> > > > > S 4.4.
> > > > > It might be clearer to move this up a bit in the text as it sort of
> > > > > summarizes some cases you already covered before. It would be easier
> > > > > if it provided an overview instead.
> > > > >
> > > > >
> > > > > S 5.9.
> > > > >
> > > > >    In this case, the Mtrace2
> > > > >    client may receive multiple Mtrace2 Replies from different routers
> > > > >    along the path.  When this happens, the client MUST treat them as
> > a
> > > > >    single Mtrace2 Reply message.
> > > > >
> > > > > Can you please describe how the client reassembles multiple messages
> > > > > into one. I think I may know how to do this, but the document should
> > > > > tell me.
> > > > >
> > > > > S 8.
> > > > >    The following new registries are to be created and maintained
> > under
> > > > >    the "RFC Required" registry policy as specified in [4].
> > > > >
> > > > > Why did you choose RFC Required rather than Specification Required?
> > > > > This just seems to unduly put load on the ISE.
> > > > >
> > > > >
> > > > > _______________________________________________
> > > > > MBONED mailing list
> > > > > MBONED@ietf.org
> > > > > https://www.ietf.org/mailman/listinfo/mboned
> > > >
> > > > --
> > > > ---
> > > > tte@cs.fau.de