Re: [lisp] Tsvart last call review of draft-ietf-lisp-pubsub-10

["Alberto Rodriguez-Natal (natal)" <[e-mail]>]

Dino, Joel,

The PubSub spec has traditionally required keeping incremental nonce state for the publish operation. This was the consensus of the WG after several discussions a few years back (you might remember this).

In the most recent iterations of the draft, the incremental nonce has also been applied to the subscribe operation (same nonce, no extra state). We have also polished the text to describe what to do when the nonce needs to be reset, etc.

Alberto

From: Joel Halpern <[e-mail]>
Date: Wednesday, February 15, 2023 at 11:17 PM
To: Dino Farinacci <[e-mail]>, Joel Halpern <[e-mail]>
Cc: [e-mail] <[e-mail]>, Magnus Westerlund <[e-mail]>, Alberto Rodriguez-Natal (natal) <[e-mail]>, [e-mail] <[e-mail]>, [e-mail] <[e-mail]>, [e-mail] <[e-mail]>, [e-mail] <[e-mail]>
Subject: Re: [lisp] Tsvart last call review of draft-ietf-lisp-pubsub-10

Well, the security folks usually want a stateless solution to this sort of problem.  The nonce increment requries keeping state per pending correspondent.

Yours,

Joel
On 2/15/2023 4:46 PM, Dino Farinacci wrote:
Tell me what you all think.  Can the map-server just store the nonce and then the next Map-Request have the map-server require nance+1?

Stops reply attacks at only the cost of storing an additional 64 bits.  Do you think that solves the problem?

Dino


On Feb 15, 2023, at 10:49 AM, Joel Halpern <[e-mail]><mailto:[e-mail]> wrote:


Given that a lot of the use cases have a lot of legitimate users, I think magnus concern is reasonable, but I am willing to settle for less.

If I am reading things right, the xTR<->Map_Resolver exchanges for pub-sub SHOULD use LISP-SEC.

And the Map-Resolver<->Map Server exchanges should magically know that the Map Resolvers are doing so?

The SHOULD needs some explanation as to when it is okay not to, or else it ought to be upgraded to a MUST.

The Map Server requirement seems like it would benefit from some explanation as to how this knowledge would exist.

Yours,

Joel

PS: If LISP Sec can be used along the lines Dino indicated, taht would be a nice way to combine some of the protections and better address the issues.
On 2/15/2023 1:36 PM, [e-mail]<mailto:[e-mail]> wrote:
Hi Joel,

The proposal is not to restrict the usage of PubSub to “limited domains” as per RFC8799. Please refer to https://github.com/boucadair/draft-ietf-lisp-pubsub/pull/16/files to see the text we are planning to include as applicability scope.

I think this is a reasonable suggestion especially that we want to leverage 9301/9303.

Thank you.

Cheers,
Med

De : Joel Halpern <[e-mail]><mailto:[e-mail]>
Envoyé : mercredi 15 février 2023 17:32
À : BOUCADAIR Mohamed INNOV/NET <[e-mail]><mailto:[e-mail]>; Magnus Westerlund <[e-mail]><mailto:[e-mail]>; Alberto Rodriguez-Natal (natal) <[e-mail]><mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>
Cc : [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>
Objet : Re: [lisp] Tsvart last call review of draft-ietf-lisp-pubsub-10


Hmmm.

Maybe I misunderstood, but a lot of the uses I have seen for the pub-sub mechanism do not seem to be limited enough to qualify for being a limited domain.

On the other hand, the general idea of the DDOS prevention mechanism (modeled loosely on the prevention of TCP State attacks) seems valuable and easy to add.  If a Map Server serving a broad community gets a pub-sub subscription request, and it is under any significant load, it can

1) craft a security token hashing the request, the current time, and a private key (and whatever else security says is needed

2) Sending the token and time back to the requestor in an error

3) When the requestor sends back the request, it includes the timestamp and token.  The server only processes the request if the information validates.

This validates that the response actually went to the requestor, and was a real request.  Yes, it slightly slows down the pub-sub registration under load.

I don't know if I caught all of Magnus' issue, but this would seem a good thing to do.

Yours,

Joel
On 2/15/2023 3:24 AM, [e-mail]<mailto:[e-mail]> wrote:
Hi Magnus,

Thank you for the follow-up.

First, your observation on the verification procedure at the Map-Server is fair. We have documented the issue in draft-boucadair-lisp-pubsub-flow-examples-03.html#name-failed-notification-with-ret<https://www.ietf.org/archive/id/draft-boucadair-lisp-pubsub-flow-examples-03.html#name-failed-notification-with-ret> and discussed the alternative to strengthen the verification based on the timestamp but we had also the constraint to navigate in the LISP environment where LISP-SEC messages are not timestamped. We think that the procedure in the draft is a good compromise of what we can achieve given that constraint. FWIW, the full reasoning is available at: timestamp to prevent replay attacks · Issue #1 · boucadair/draft-ietf-lisp-pubsub (github.com)<https://github.com/boucadair/draft-ietf-lisp-pubsub/issues/1>.

Second, I support your proposal to add an applicability statement to the document. The content will be basically moving (and adjusting the language) the following text in Section 7 to that section:

OLD:
   It is also RECOMMENDED that the Map-Resolver
   verifies that the xTR is allowed to use PubSub and to use the xTR-ID
   and ITR-RLOCs included in the Map-Request.  Map-Servers SHOULD be
   configured to only accept subscription requests from Map-Resolvers
   that verify Map-Requests as previously described.

I let Alberto further comment as appropriate.

Cheers,
Med

De : Magnus Westerlund <[e-mail]><mailto:[e-mail]>
Envoyé : mercredi 15 février 2023 08:33
À : Alberto Rodriguez-Natal (natal) <[e-mail]><mailto:[e-mail]>; BOUCADAIR Mohamed INNOV/NET <[e-mail]><mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>
Cc : [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>
Objet : Re: Tsvart last call review of draft-ietf-lisp-pubsub-10

Hi,

Thanks for the many improvements and I think this is likely safe enough for limited deployments when the Map-Server are not open to any xTR to send requests. I don’t think this is safe enough for general Internet usage for two reasons. First, the verification procedure forces the MAP-Server to hold state rather than the requestor and the messages only. Secondly, a lot of the security procedures are only RECOMMEND/SHOULD. For an open Internet I think a more tightly defined security mechanisms and protection profile should be specified.

Thus, my recommendation would be to add an applicability statement to the document making clear that this is intended for the deployments with more limited access to Map-Servers than what an open internet deployment provides.

Cheers

Magnus Westerlund

From: Alberto Rodriguez-Natal (natal) <[e-mail]<mailto:[e-mail]>>
Date: Monday, 13 February 2023 at 20:26
To: [e-mail]<mailto:[e-mail]> <[e-mail]<mailto:[e-mail]>>, Magnus Westerlund <[e-mail]<mailto:[e-mail]>>, [e-mail]<mailto:[e-mail]> <[e-mail]<mailto:[e-mail]>>
Cc: [e-mail]<mailto:[e-mail]> <[e-mail]<mailto:[e-mail]>>, [e-mail]<mailto:[e-mail]> <[e-mail]<mailto:[e-mail]>>, [e-mail]<mailto:[e-mail]> <[e-mail]<mailto:[e-mail]>>
Subject: Re: Tsvart last call review of draft-ietf-lisp-pubsub-10
Hi Magnus,

Just FYI, we have just published a new revision that further polishes some details.

https://datatracker.ietf.org/doc/html/draft-ietf-lisp-pubsub-12
https://author-tools.ietf.org/iddiff?url2=draft-ietf-lisp-pubsub-12

Thanks!
Alberto

From: [e-mail]<mailto:[e-mail]> <[e-mail]<mailto:[e-mail]>>
Date: Friday, February 10, 2023 at 3:55 PM
To: Magnus Westerlund <[e-mail]<mailto:[e-mail]>>, Alberto Rodriguez-Natal (natal) <[e-mail]<mailto:[e-mail]>>, [e-mail]<mailto:[e-mail]> <[e-mail]<mailto:[e-mail]>>
Cc: [e-mail]<mailto:[e-mail]> <[e-mail]<mailto:[e-mail]>>, [e-mail]<mailto:[e-mail]> <[e-mail]<mailto:[e-mail]>>, [e-mail]<mailto:[e-mail]> <[e-mail]<mailto:[e-mail]>>
Subject: RE: Tsvart last call review of draft-ietf-lisp-pubsub-10
Hi Magnus,

FWIW, an updated version that implements the changes that were discussed in this thread is now online:

https://author-tools.ietf.org/iddiff?url2=draft-ietf-lisp-pubsub-11

Cheers,
Med

De : BOUCADAIR Mohamed INNOV/NET
Envoyé : mardi 7 février 2023 13:15
À : 'Magnus Westerlund' <[e-mail]<mailto:[e-mail]>>; Alberto Rodriguez-Natal (natal) <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>
Cc : [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>
Objet : RE: Tsvart last call review of draft-ietf-lisp-pubsub-10

Hi Magnus,

Thanks for the follow-up.

Please see inline.

Cheers,
Med

De : Magnus Westerlund <[e-mail]<mailto:[e-mail]>>
Envoyé : vendredi 3 février 2023 10:49
À : BOUCADAIR Mohamed INNOV/NET <[e-mail]<mailto:[e-mail]>>; Alberto Rodriguez-Natal (natal) <[e-mail]<mailto:[e-mail]>>; [e-mail]<mailto:[e-mail]>
Cc : [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>
Objet : Re: Tsvart last call review of draft-ietf-lisp-pubsub-10

Hi Med,

Thanks, so that at least you can have a clear notification of the removal unless the packet loss rate is to high. What, is less ideal is the number of total messages that is going to be sent here towards the source address that sent a Map-Register?
[Med] I guess you meant Map-Request. Yes, there is a balance between the chattiness vs. reverse-routeablity checks and also the constraints imposed by the base spec for retransmission Map-Notifies. Having an explicit indication is superior as it allows an xTR to reinstall the state, otherwise it will be out of sync.

It would be good to have understanding of the amplification factor here that an attacker gets out it.
[Med] Such attacks assume that a Map-Request passes the authentication checks. This is typically the case of replayed Map-Requests. As you can see in https://datatracker.ietf.org/doc/draft-boucadair-lisp-pubsub-flow-examples/, a check based on the nonce would be sufficient to detect replayed messages: the nonce has to be greater than the local one. The message will be then silently ignored. We will be adding more details about nonce checks to the draft.

Also beyond rate limiting, is there a possibility here to reject the MAP-requests from a source address, without causing a denial of service attack possibility? My shallow review seem to indicate that there exist such a risk. What I am considering is that there is a legit xTR (B) with IP (IP-B). If the attacker sends a MAP-Request with nonce-A, with IP source address IP-B.
[Med] If the nonce checks are in place, this request will be silently discarded.

The Map-Notify will go to B. B can’t map this to a request it made as no Nonce matches what it sends and discards the message. Thus, the map server getting a mix of legit and spoofed requests may decide to band IP-B from asking things, thus enabling a denial of service on B.

The above worries me a bit as some mitigation may have really unwanted effects here.

Cheers

Magnus

From: [e-mail]<mailto:[e-mail]> <[e-mail]<mailto:[e-mail]>>
Date: Monday, 30 January 2023 at 13:45
To: Alberto Rodriguez-Natal (natal) <[e-mail]<mailto:[e-mail]>>, Magnus Westerlund <[e-mail]<mailto:[e-mail]>>, [e-mail]<mailto:[e-mail]> <[e-mail]<mailto:[e-mail]>>
Cc: [e-mail]<mailto:[e-mail]> <[e-mail]<mailto:[e-mail]>>, [e-mail]<mailto:[e-mail]> <[e-mail]<mailto:[e-mail]>>, [e-mail]<mailto:[e-mail]> <[e-mail]<mailto:[e-mail]>>
Subject: RE: Tsvart last call review of draft-ietf-lisp-pubsub-10
Re-,

Please see inline.

Cheers,
Med

> -----Message d'origine-----
> De : Alberto Rodriguez-Natal (natal) <[e-mail]<mailto:[e-mail]>>
> Envoyé : lundi 30 janvier 2023 12:27
> À : Magnus Westerlund <[e-mail]<mailto:[e-mail]>>; tsv-
> [e-mail]<mailto:[e-mail]>
> Cc : [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>;
> [e-mail]<mailto:[e-mail]>
> Objet : Re: Tsvart last call review of draft-ietf-lisp-pubsub-10
>
> Hi Magnus,
>
> Thanks again, please see inline.
>
> Alberto
>
> From: Magnus Westerlund <[e-mail]<mailto:[e-mail]>>
> Date: Monday, January 30, 2023 at 9:46 AM
> To: Alberto Rodriguez-Natal (natal) <[e-mail]<mailto:[e-mail]>>, tsv-
> [e-mail]<mailto:[e-mail]> <[e-mail]<mailto:[e-mail]>>
> Cc: [e-mail]<mailto:[e-mail]> <draft-ietf-lisp-
> [e-mail]<mailto:[e-mail]>>, [e-mail]<mailto:[e-mail]> <[e-mail]<mailto:[e-mail]>>,
> [e-mail]<mailto:[e-mail]> <[e-mail]<mailto:[e-mail]>>
> Subject: Re: Tsvart last call review of draft-ietf-lisp-pubsub-10
> Hi Alberto,
>
> I think the below maybe works, but I like to point out that the
> Map-Server per the below is likely a larger DDoS traffic reflector
> than if you require a one-to-one exchange where each subscription
> request only results in a single response message. Using Map-
> Notify and requiring Ack will result in that at least 3 Map-
> Notifies are being sent.
>
> [AR] Right, but this is required if we want to align with RFC9301,
> afaik.

[Med] ACK. RFC9301 says the following:

   A
   Map-Notify is retransmitted until a Map-Notify-Ack is received by the
   Map-Server with the same nonce used in the Map-Notify message.

>
> I am also worried about the state uncertainty here. Because if the
> client sends Map-Notify-Ack on a Map-Notify it will think the
> subscription has succeeded, but if that ACK is lost and the
> MapServer has used up all retransmission it will silently remove
> the requested subscription. Is that not an issue?
>
> [AR] I've been thinking about this as well. Maybe some middle
> ground, assuming that xTRs can be authenticated to some extend as
> being discussed in the other email, could be as follows. Rather
> than wait for the Map-Notify-Ack to mark the subscription state as
> completed, we still mark the subscription as complete as soon as
> the Map-Notify is sent. We still wait for the Map-Notify-Ack to be
> received, and if we exhaust all the retransmissions without
> receiving it, we don't remove the subscription, we keep it as
> unacknowledged. However, we only allow the xTR to have a single
> unacknowledged subscription, subsequent subscription requests from
> the same xTR will be denied (i.e. Map-Reply returned) until the
> xTR is able to properly subscribe and acknowledge the previous
> one. Maybe this could work?
>

[Med] Rather than keeping the state, the Map-Server can remove the unacknowledged subscription with a Map-Notify with AFI = 0. We may also consider defining a new ACT value so the xTR have a hint about why the subscription was removed.






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