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

Hitoshi Asaeda <asaeda@ieee.org> Wed, 28 February 2018 08:57 UTC

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From: Hitoshi Asaeda <asaeda@ieee.org>
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Date: Tue, 27 Feb 2018 22:57:38 -1000
Cc: Eric Rescorla <ekr@rtfm.com>, draft-ietf-mboned-mtrace-v2@ietf.org, mboned@ietf.org, mboned-chairs@ietf.org, Toerless Eckert <tte@cs.fau.de>
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References: <151628969901.2325.7724014542086691903.idtracker@ietfa.amsl.com> <20180119193149.GA26689@faui40p.informatik.uni-erlangen.de> <CABcZeBNDqq_5XPad76WrsrN_JS2J1iAAC068=y0Nq12SKJOQ=Q@mail.gmail.com> <20180125223335.GA16477@faui40p.informatik.uni-erlangen.de> <CABcZeBPbCJfP=VVC6irEUtbiFuQgmMCQMEUBern=kAG-KP1SQQ@mail.gmail.com> <20180126013118.GD16477@faui40p.informatik.uni-erlangen.de> <CABcZeBN5dWkn7dGZ00tw2AkGPPAdfS+C_8mrVMuB9efc4o1a9Q@mail.gmail.com> <CAHw9_iJtqpKVDgVscQ0UwZVAHbVhTJhjPsgWLkfzCk=gQoBs7g@mail.gmail.com>
To: Warren Kumari <warren@kumari.net>
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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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Hi again,

> 2018/02/27 8:56, Warren Kumari <warren@kumari.net> wrote:
> 
> [ - IESG for clutter ]
> 
> On Fri, Jan 26, 2018 at 4:58 PM, Eric Rescorla <ekr@rtfm.com> wrote:
>> Hi Toerless,
>> 
>> I appreciate the solution thinking, but I don't want to overrotate on these
>> specific threats (though of course we must address them). My concern is that
>> if there are threats this obvious then we need a more complete threat
>> analysis. I.e., what are the avenues for attack with this protocol and then
>> what mechanisms prevent those things. The purpose of the security
>> considerations section is to make sure that that happens. Has someone done
>> that somewhere and it just didn't make it into the document?
> 
> 
> Toerless / authors,
> 
> It has been around a month since this reply -- I'm hoping that the
> there has been more discussion and that I just fell off the thread and
> / or that my search foo has failed me.
> 
> EKR makes good points (and holds a DISCUSS) - we need to figure out
> how to address them. Was there more discussions on the thread
> analysis? Clue bat appreciated.

We may have to do some sort of security threat analysis and document the results,
along with possible remedies to address the existing threats.
We’ll seek comments in the ML after the authors agree on the idea.

Best regards,

Hitoshi


> 
>> 
>> -Ekr
>> 
>> 
>> On Thu, Jan 25, 2018 at 5:31 PM, Toerless Eckert <tte@cs.fau.de> wrote:
>>> 
>>> 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
>> 
>> 
> 
> 
> 
> -- 
> I don't think the execution is relevant when it was obviously a bad
> idea in the first place.
> This is like putting rabid weasels in your pants, and later expressing
> regret at having chosen those particular rabid weasels and that pair
> of pants.
>   ---maf
> 
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