Re: [I2nsf] Yangdoctors last call review of draft-ietf-i2nsf-consumer-facing-interface-dm-07

Jan Lindblad <janl@tail-f.com> Thu, 19 March 2020 17:25 UTC

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From: Jan Lindblad <janl@tail-f.com>
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Cc: YANG Doctors <yang-doctors@ietf.org>, "i2nsf@ietf.org" <i2nsf@ietf.org>, last-call@ietf.org, draft-ietf-i2nsf-consumer-facing-interface-dm.all@ietf.org, skku-iotlab-members <skku-iotlab-members@googlegroups.com>
To: "Mr. Jaehoon Paul Jeong" <jaehoon.paul@gmail.com>
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Subject: Re: [I2nsf] Yangdoctors last call review of draft-ietf-i2nsf-consumer-facing-interface-dm-07
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Paul,

Thank you for all your work with the module, and for the reminder for me to verify all the changes. 

I am afraid I think the module is still not ready for last call, even if it is better shape than ever thanks to your efforts. I went through the module from top to bottom, so this is sorted in order of appearance.

Line 107-204: The following identities are declared in the module, but never referenced. They should either have a common base with something, or be referenced somewhere. If not, why are they defined here? They currently serve no purpose in this YANG module.
  identity ddos {
  identity enforce-type {
  identity admin {
  identity time {

Line 377: Defining a custom date-and-time type seems odd. You should probably use one that has already been defined
  typedef date-and-time {

Line 513: The leaf represents the name of a user, but the format is undefined. What should be the format for the string value? How would a user know what to configure here? Email addresses? If implementation dependent, say so.
    leaf name {
      type string;
      description
        "This represents the name of a user.";

Line 518: If no IP address information is specified for the user-group, what happens then? Is the user access accepted, rejected, or something else?
    uses ip-address-info;

Line 658: Key leaf declared mandatory. All keys are mandatory, so mandatory is not needed on this leaf.
    leaf policy-name {
      type string;
      mandatory true;

Line 664: Users mentioned in the owners-ref should have full CRUD privileges to the policy. But what about everyone else? Should they have R(ead) privileges? Can anyone create new policies? If not, who can? If someone creates a policy, but does not mention his own name among owners (e.g. misspells or does not get the format right), he will not be able to modify or remove the policy. If no owner is mentioned, then noone can.
    uses owners-ref;

Line 673: Key leaf declared mandatory. All keys are mandatory, so mandatory is not needed on this leaf.
        leaf rule-name {
          type string;
          mandatory true;

Line 682: Users mentioned in the owners-ref should have full CRUD privileges to the rule. But what about everyone else? Should they have R(ead) privileges? Can anyone create new rules, or only those that have full CRUD privileges for the policy? If someone creates a rule, but does not mention his own name among owners (e.g. misspells or does not get the format right), he will not be able to modify or remove the rule. 
    uses owners-ref;

Line 697: Choice enforce-type has a description that I can't understand. What does this mean?
          choice enforce-type {
            description
              "There are two different enforcement types;
              admin, and time.
              It cannot be allowed to configure
              admin=='time' or enforce-time=='admin'.";

Line 703: In case of enforce-type admin (whatever that means), a string value needs to be configured. What are the valid values for this leaf?
            case enforce-admin {
              leaf admin {
                type string;
                description
                  "This represents the enforcement type
                  based on admin's decision.";

Line 711: In case of enforce-type time, three times can be configured. What is the relation between enforce-time, and the other two (begin-time, end-time)? 
            case time {
              container time-information {
                description
                  "The begin-time and end-time information
                  when the security rule should be applied.";
                leaf enforce-time {
                  type date-and-time;
                  description
                    "The enforcement type is time-enforced.";
                }
                leaf begin-time {
                  type date-and-time;
                  description
                    "This is start time for time zone";
                }
                leaf end-time {
                  type date-and-time;
                  description
                    "This is end time for time zone";
                }

Furthermore, the locally defined date-and-time type used includes both a date and time, which seems to be at odds with the example configurations in the draft. Example 9.2:
  <rules>
    <rule>
      <rule-name>block_access_to_sns_during_office_hours</rule-name>
      <event>
        <time-information>
          <begin-time>2020-03-11T09:00:00.00Z</begin-time>
          <end-time>2020-03-11T18:00:00.00Z</end-time>

In the example, the rule-name "block_access_to_sns_during_office_hours " suggests that the begin-time and end-time should be times of day between which the policy should be enforced. E.g. every day between 9.00 and 18.00. If that is a valid use case, using a time type with a date doesn't make much sense. In the context of the policy that repeats "daily", how should the start date-and-time value "2020-03-11T09:00:00.00Z " be interpreted? What if it was "monthly"?

Line 736: In the frequency leaf, the enumeration value only-once is for rules that don't repeat. But how long do they apply? A single packet? A single time the rule is triggered? How does a user know if the rule is still in effect, i.e. if the "once" has happened or not?
              enum only-once {

Line 835: Maybe it's just my limited understanding of how threat-feeds work, but I wonder i this construct with source and destinations for threat feeds is meaningful?
          container threat-feed-condition {
            description
              "The condition based on the threat-feed information.";
            leaf-list source {
              type leafref {
                path "/i2nsf-cfi-policy/threat-preventions/threat-feed-list/name";
              }
            description
              "Describes the threat-feed condition source.";
            }
            leaf dest-target {
              type leafref {
                path "/i2nsf-cfi-policy/threat-preventions/threat-feed-list/name";
              }
            description
              "Describes the threat-feed condition destination.";

Line 920: Location groups can be configured, but there seems to be no references to them. How are they supposed to be used?
      list location-group{
        key "name";
        uses location-group;

Line 931: Regarding point 16.1 in your revision letter, you say "We think list type of threat-feed-list can be configured more than one feed of the same type". I'm afraid that is not the case with the current YANG model. If you do wish to allow more than one threat-feed-list for the same threat-feed-type, you need to add an additional key to your threat-feed-list.
      list threat-feed-list {
        key "name";
        description
          "There can be a single or multiple number of
          threat-feeds.";
        uses threat-feed-info;

...
  grouping threat-feed-info {
    description
      "This is the grouping for the threat-feed-list";
    leaf name {
      type identityref {
        base threat-feed-type;


Generally, the indentation in the module is much improved. Some lines are still a bit off, however, so I would recommend using a tool that indents consistently.

Generally, I also wonder whether there has been any discussion with implementors around the admin security model proposed here. As noted before, it's a bit different from everything else I have seen. Is it well thought through? Do implementors feel this is doable and user friendly? Currently there are no examples involving owner. Perhaps an example that sheds some light over how different users create, modify and see the various rules would shed some light over this.

Best Regards,
/jan





> On 18 Mar 2020, at 18:41, Mr. Jaehoon Paul Jeong <jaehoon.paul@gmail.com> wrote:
> 
> Hi Jan,
> Could you update the state of YANGDOCTORS Last Call Review on
> I2NSF Consumer-Facing Interface YANG Data Model  if the updates are fine to you?
> 
> https://datatracker.ietf.org/doc/draft-ietf-i2nsf-consumer-facing-interface-dm/ <https://datatracker.ietf.org/doc/draft-ietf-i2nsf-consumer-facing-interface-dm/>
> 
> I think your comments are all addressed in this version.
> 
> Thanks.
> 
> Best Regards,
> Paul
> 
> On Thu, Mar 12, 2020 at 1:15 AM Mr. Jaehoon Paul Jeong <jaehoon.paul@gmail.com <mailto:jaehoon.paul@gmail.com>> wrote:
> Hi Jan,
> We authors have addressed your comments with the revision:
> https://tools.ietf.org/html/draft-ietf-i2nsf-consumer-facing-interface-dm-08 <https://tools.ietf.org/html/draft-ietf-i2nsf-consumer-facing-interface-dm-08>
> 
> I attach a revision letter to explain how to respond to your comments.
> 
> If you have further comments, please let me know.
> 
> Thanks.
> 
> Best Regards,
> Paul
> 
> On Tue, Nov 12, 2019 at 1:53 AM Jan Lindblad via Datatracker <noreply@ietf.org <mailto:noreply@ietf.org>> wrote:
> Reviewer: Jan Lindblad
> Review result: Almost Ready
> 
> This is my YD review of draft-ietf-i2nsf-consumer-facing-interface-dm-07. I
> have previously reviewed the -05 revision (~end June). I find the new revision
> much improved, but still with much to discuss. I will call this "almost ready".
> 
> Generally speaking, I think the YANG module lacks the precision and
> descriptions needed to foster interoperability. The examples at the end are
> very enlightening however, and compensate for much of that, but their informal
> nature can never replace proper YANG. The module usage needs to be mostly clear
> from the module itself.
> 
> The management access control model proposed here is, even with its latest
> adaptation towards NACM, is still quite different from NACM author's original
> ideas. I will therefore bring this use case up in the NETMOD WG for discussion.
> 
> 1. Network access control principles
> 
> Network access control is about which users are able to use the network being
> managed, for example connect to facebook. The purpose of the NSF module is to
> control this access. This version of the YANG module is now based on a list of
> policies.
> 
> Each policy has a list of rules. Each rule has an event -- condition -- action
> triplet. This resembles traditional firewall management, which is a good thing,
> because that concept is stable and much tried. This allows operators to create
> lists of rules in this style:
> 
> if pkt.x == 1: drop                     // Rule 1
> elif pkt.y > 2: alert                   // Rule 2
> elif pkt.z == 10: pass          // Rule 3
> else: drop                              // Rule 4
> 
> This pattern relies heavily on the ability to control the order of the rules.
> The current model relies on the alphabetical sorting of names rules for the
> ordering. The YANG trick I would recommend to give operators the ability to
> insert and move rules as they wish is to add ordered-by user on the list:
> 
>     list rule {
>       ordered-by user;  // <== Add this line
>       leaf rule-name {
> 
> Nothing is said about what the system should do in case policies conflict. What
> if one policy says pass, the other drop for the same packet? Please clarify.
> What should happen to packets that do not match any of the policies?
> 
> This module also assumes that all users in the operator's organization are
> listed in one or more NACM groups (e.g. "employees"). That wasn't really the
> NACM authors' original intent. Even if this could be made to work maybe, there
> is no strong reason to repurpose the NACM group concept for user network access
> purposes. It could easily be modeled differently. So in the cases where there
> are leafrefs to NACM groups when dealing with network access rather than
> management access, don't use NACM groups.
> 
>                 leaf src-target {
>                   type leafref {
>                     path /nacm:nacm/nacm:groups/nacm:group/nacm:user-name;  //
>                     <== Point to some other list of network users
> 
> 2. Management access control principles
> 
> Management access control is about which users are able to configure/run
> actions/the policies and rules. IMO, the most controversial aspect of this
> module has always been its new and creative management access control model. In
> this revision, the management principles have been remodeled greatly to fit in
> with NACM. I find this redesign very promising, but the result is still not
> quite ready for publication.
> 
> The point where integration with NACM concepts is important is when it comes to
> allow some users to CRUD the NSF policies and rules themselves. There is now a
> leaf-list "owners" on each policy and rule which point to a list of NACM
> groups. My understanding is that the idea is that the NSF module should be seen
> as a service model that translate high level ownership information to specific
> NACM rules. It would be good to mention these ideas somewhere in the NSF
> document.
> 
>   leaf-list owners {
>     type leafref {
>       path /nacm:nacm/nacm:groups/nacm:group/nacm:name;
> 
> I expect the intent is that any user listed in a NACM group mentioned in the
> owners list would get full CRUD privileges for the contents of the rule the
> owners leaf sits on. That is never spelled out anywhere, however.
> 
> It is a little less clear how leaf-list owners on policy objects should be
> handled. Should owners listed on a policy object get full CRUD powers over the
> entire policy, including all the rules inside? Or would they need to be listed
> on the rules as well? Not clear. Is the intent that users not listed on the
> policy object are unable to create new rules, but to be able to update rules
> they are listed as owners of, if any?
> 
> Who is allowed to create new policy objects? Should users that are not owners
> get read access to all the policies and rules?
> 
> Finally, there is an "owner" leaf on each rule with an identityref allowing
> operators to configure a role name like dept-head or sec-admin. It is marked
> mandatory, but never included in any of the examples at the end of the
> document. This makes me think this may be a remnant from bygone times and
> should be removed from the YANG. If not, an explanation of how to use this
> leaf, and how it interacts with "owners" needs to be added, and the examples
> updated.
> 
> 3. leafrefs crosspointing between policy instances
> 
> There are six leafrefs that point to various objects inside a policy, e.g. a
> rule condition pointing to a device group name. None of them restrict what can
> be pointed to so that only names within the current policy are valid. It is
> therefore possible to configure the name of a device group defined in a
> different policy. I suspect this is not the intention. In order to restrict the
> leafrefs to the same policy, the following predicate can be added:
> 
>                 leaf-list src-target {
>                   type leafref {
>                   path
>                   "/i2nsf-cfi-policy[policy-name=current()/../../../../../policy-name]/endpoint-group/device-group/name";
>                    // <== Add predicate
> 
> 4. Mandatory to implement all events, conditions, actions
> 
> Each rule is defined with a choice of different events (admin, time),
> conditions (firewall, ddos, custom, threat-feed) and actions (pass, drop,
> alert, mirror, ...). Is the intent that all of these options should be
> mandatory to implement? The current model requires this. Also, would it make
> sense to allow additional mechanisms here? If so, it may be good to explain to
> readers how the set of choices and identities can be extended by
> implementations.
> 
> 5. Optional and mandatory elements
> 
> In this revision of the module, 8 leafs have been marked mandatory. A few of
> them are list keys, which are conventionally not marked mandatory, since list
> keys are always mandatory. A few others are skipped in the XML examples at the
> end of the NSF document, which makes me believe they might not really be
> mandatory after all.
> 
> Three leafs have a default, but most leafs are left optional without any
> default. In many cases I think I understand what it means to not set a leaf,
> but with the ones listed here, I don't think it clear at all. Either add a
> default to make it clear, make them mandatory if they should be, or explain in
> the leaf description what happens if not set.
> 
> 493: leaf-list name
> 513: leaf-list protocol
> 531: leaf geo-ip-ipv4
> 541: leaf continent
> 562: leaf feed-server-ipv4
> 585: leaf payload-description
> 590: leaf-list content
> 600: leaf-list owners
> 870: leaf method
> 
> 6. Indentation
> 
> The YANG indentation is mostly wrong. Run the YANG text through pyang or some
> other tool that can indent the content correctly before you put it into a
> document.
> 
> 7. YANG element naming
> 
> The YANG convention is to not have lists on the top level in the YANG module,
> but to surround lists with a container. The surrounding container often has a
> name in the plural and the list in singluar, like this
> 
> container interfaces {
>     list interface {
> 
> To better fit into the world of IETF YANG modules, I'd recommend turning the
> top level list i2nsf-cfi-policy into this instead:
> 
> container i2nsf-cfi-policies {
>     list policy {
> 
> Further down, I would change container rule to rules:
> 
> container rules {
>     list rule {
> 
> Finally, it is customary to not repeat the names of parent object in the names
> of elements. For example, in the following:
> 
> list threat-feed-list
>     leaf feed-name
>     leaf feed-server-ipv4
>     leaf feed-server-ipv6
>     leaf feed-description
> 
> all the leafs should normally not repeat "feed-". Just leaf name, leaf
> server-ipv4, leaf server-ipv6, leaf description. There are many more examples
> of this throughout the module.
> 
> The condition choice has many containers with a single leaf inside (e.g.
> ddos-source). Their purpose is rather unclear to me. Remove?
> 
>               container ddos-source {
>                 description
>                 "This represents the source.";
>                 leaf-list src-target {
> 
> Also, I find the name "src-target" rather confusing. How about "source"?
> 
> 8. No date leaf
> 
> The draft text near fig 2 talks about a date leaf. There is no date object in
> this revision of te YANG.
> 
> "Date:  Date when this object was created or last modified"
> 
> 9. leaf owner
> 
> Near fig.3 leaf Owner is mentioned. Is this leaf still current?
> 
> "Owner: This field contains the onwer of the rule.  For example,
>              the person who created it, and eligible for modifying it."
> 
> 10. leaf packet-per-second
> 
> This is now modeled as uint16. Is this future proof? Many packet flows on the
> internet exceed 64k pps.
> 
> 11. container custon-source
> 
> Misspelled. Should be custom-source
> 
> 12. identity ddos
> 
> Is ddos a malware file-type? This is not exactly in line with my intuition.
> 
> 13. identity protocol-type
> 
> There are other modules that already define protocol-types. Would it be worth
> reusing one of them?
> 
> 14. identity palo-alto
> 
> Is it a good IETF practice to list vendor names in modules? Can we consider
> this a protocol name? Is there perhaps an RFC/specification name for it that we
> could reference instead?
> 
> 15. grouping ipsec-based-method
> 
> This grouping contains a list which allows listing none of, either of or both
> of ipsecike and ikeless. Are all valid configurations?
> 
> 16. leaf feed-name
> 
> This leaf is the key in a list, which makes it possible to have at most one
> feed of each type. If it would make sense to configure more than one feed of
> the same type, the YANG needs to be updated here.
> 
> 17. leaf-list content
> 
> This leaflist is of type string. What is the format of this string? Does the
> name refer to something?
> 
> 18. Event types
> 
> container event has a choice between enforce-admin and time alternatives. Each
> of those choices have a leaf that allows the operator to configure an
> identityref to an enforce-type value. What does that mean? What would it mean
> if an operator configured admin == 'time' (or enforce-time == 'admin')?
> 
> 19. leaf begin-time, end-time
> 
> >From the examples, it can be seen that these are meant to be a time of day
> values. Currently they are modeled as yang:date-and-time, which means they are
> a concrete time a specific day, e.g. 2019-11-11T16:07. This needs to be changed
> in order to be what the modeler intended. Perhaps like this:
> 
> typedef time-of-day {
>     type string {
>         pattern '(2[0-3]|[01]?[0-9]):[0-5][0-9]';
>     }
> }
> 
> 20. leaf frequency
> 
> This leaf is now modeled properly from a YANG perspective. But what does it
> mean? If this leaf is set to 'once-only', what exactly will happen only once?
> Please write a description that explains this.
> 
> 21. Example in Fig.17
> 
> The example contains XML that refers to "endpoint-group/user-group". There is
> no such element in the YANG.
> 
> <endpoint-group xmlns="urn:ietf:params:xml:ns:yang:ietf-i2nsf-cfi-policy">
>   <user-group>
> 
> Furthermore, there is nothing called range-ip-address, start-ip-address,
> end-ip-address. They are called range-ipv4-address, start-ipv4-address,
> end-ipv4-address.
> 
>     <range-ip-address>
>       <start-ip-address>221.159.112.1</start-ip-address>
>       <end-ip-address>221.159.112.90</end-ip-address>
>     </range-ip-address>
> 
> Finally, there must not be any xmlns attribute on an closing XML tag. So
> 
> </endpoint-group xmlns="urn:ietf:params:xml:ns:yang:ietf-i2nsf-cfi-policy">
> 
> should be
> 
> </endpoint-group>
> 
> This happens in several of the examples.
> 
> 22. Example in Fig.18
> 
> There is no element called policy any more. It's now i2nsf-cfi-policy.
> 
>    <policy xmlns="urn:ietf:params:xml:ns:yang:ietf-i2nsf-cfi-policy">
>      <policy-name>security_policy_for_blocking_sns</policy-name>
> 
> The rules are modeled in a container and list, both by the name rule. So there
> needs to be two <rule> tags.
> 
>      <rule>
>        <rule-name>block_access_to_sns_during_office_hours</rule-name>
> 
> The security-event element is marked mandatory in the YANG, but missing in the
> example. The times given below may be what is intended, but do not match the
> date format for the type used (which include a date, etc).
> 
>        <event>
>          <time-information>
>            <begin-time>09:00</begin-time>
>            <end-time>18:00</end-time>
>          </time-information>
>        </event>
> 
> Since the example is not mentioning leaf frequency, it will have the value
> 'once-only'. Maybe explain what that means in the context of the example?
> 
> The condition/firewall-condition says the src-target is mandatory and
> dest-target optional, exactly like below.
> condition/custom-destination/dest-target is mandatory and src-target is
> optional, exactly like below. Is this pure luck, or is there a logical
> explanation why exactly those should be mandatory, and the example use
> precisely those?
> 
>        <condition>
>          <firewall-condition>
>            <source-target>
>              <src-target>employees</src-target>
>            </source-target>
>          </firewall-condition>
>          <custom-condition>
>            <destination-target>
>              <dest-target>sns-websites</dest-target>
>            </destination-target>
>          </custom-condition>
> 
> The current YANG model does not allow setting both a firewall-condition and
> custom-condition. If that should be allowed, the model needs to change. Should
> it be possible to have multiple firewall- or other conditions? That is not
> currently possible.
> 
> This example leaves out the mandatory leaf owner. Is that a sign that it should
> not be mandatory, or perhaps not exist at all?
> 
> 23. Example in Fig.19
> 
> This example lists a firewall-condition with no src-target, which is mandatory.
> 
>       <firewall-condition>
>         <destination-target>
>           <dest-target>employees</dest-target>
>         </destination-target>
>       </firewall-condition>
> 
> Under condition, there is a container rate-limit with a leaf packet-per-second.
> Is this a trigger value for the condition, or is it an actual limit that the
> system is expected to enforce? If it's a trigger, it may be good to find a
> clearer name. If it's enforced, it's placement under condition is deceiving.
> 
> If a rule's action is set to 'rate-limit', to which rate will it be limited?
> 
> 24. Security Considerations
> 
> Section 10 in the NSF document under review is the Security Considerations. I
> think it would make sense to mention something about the management access
> control mechanism here, and its relation to NACM.
> 
> (End of list)
> 
> 
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> 
> 
> -- 
> ===========================
> Mr. Jaehoon (Paul) Jeong, Ph.D.
> Associate Professor
> Department of Software
> Sungkyunkwan University
> Office: +82-31-299-4957
> Email: jaehoon.paul@gmail.com <mailto:jaehoon.paul@gmail.com>, pauljeong@skku.edu <mailto:pauljeong@skku.edu>
> Personal Homepage: http://iotlab.skku.edu/people-jaehoon-jeong.php <http://cpslab.skku.edu/people-jaehoon-jeong.php>
> 
> 
> -- 
> ===========================
> Mr. Jaehoon (Paul) Jeong, Ph.D.
> Associate Professor
> Department of Software
> Sungkyunkwan University
> Office: +82-31-299-4957
> Email: jaehoon.paul@gmail.com <mailto:jaehoon.paul@gmail.com>, pauljeong@skku.edu <mailto:pauljeong@skku.edu>
> Personal Homepage: http://iotlab.skku.edu/people-jaehoon-jeong.php <http://cpslab.skku.edu/people-jaehoon-jeong.php>