adds policy to dynamic auditing KEP

keps/sig-auth/0014-dynamic-audit-configuration.md

@@ -17,8 +17,8 @@ approvers:
   - "@yliaog"
 editor: TBD
 creation-date: 2018-05-18
-last-updated: 2018-07-13
-status: provisional
+last-updated: 2018-07-31
+status: implementable
 ---
 
 # Dynamic Audit Control
@@ -49,18 +49,23 @@ status: provisional
 
 ## Summary
 
-We want to allow the advanced auditing features to be dynamically configured. Following in the same vein as [Dynamic Admission Control](https://kubernetes.io/docs/admin/extensible-admission-controllers/) we would like to provide a means of configuring the auditing features post cluster provisioning.
+We want to allow the advanced auditing features to be dynamically configured. Following in the same vein as 
+[Dynamic Admission Control](https://kubernetes.io/docs/admin/extensible-admission-controllers/) we would like to provide 
+a means of configuring the auditing features post cluster provisioning.
 
 ## Motivation
 
-The advanced auditing features are a powerful tool, yet difficult to configure. The configuration requires deep insight into the deployment mechanism of choice and often takes many iterations to configure properly requiring a restart of the apiserver each time. Moreover, the ability to install addon tools that configure and enhance audting is hindered by the overhead in configuration. Such tools frequently run on the cluster requiring future knowledge of how to reach them when the cluster is live. These tools could enhance the security and conformance of the cluster and its applications.
+The advanced auditing features are a powerful tool, yet difficult to configure. The configuration requires deep insight 
+into the deployment mechanism of choice and often takes many iterations to configure properly requiring a restart of 
+the apiserver each time. Moreover, the ability to install addon tools that configure and enhance auditing is hindered 
+by the overhead in configuration. Such tools frequently run on the cluster requiring future knowledge of how to reach 
+them when the cluster is live. These tools could enhance the security and conformance of the cluster and its applications.
 
 ### Goals
 - Provide an api and set of objects to configure the advanced auditing kube-apiserver configuration dynamically
 
 ### Non-Goals
 - Provide a generic interface to configure all kube-apiserver flags
-- composable audit policies per-endpoint
 - configuring non-webhook backends
 - configuring audit output (format or per-field filtering)
 - authorization of audit output
@@ -80,7 +85,11 @@ type ClusterAuditConfiguration struct {
 
     v1.ObjectMeta
 
-    // Backends to send events
+    // Policy is the current audit v1beta1 Policy object
+    // if undefined it will default to the runtime flag provided policy if available
+    Policy *Policy
+
+    // Backend to send events
     Backend *Backend
 }
 
@@ -133,6 +142,11 @@ apiVersion: audit.k8s.io/v1beta1
 kind: ClusterAuditConfiguration
 metadata:
   name: <name>
+policy:
+  rules:
+  - level: <level>
+  omitStages:
+  - stage: <stage>
 backend:
   webhook:
   - initialBackoff: <10s>
@@ -144,23 +158,34 @@ backend:
       service: <optional service name>
       caBundle: <ca bundle>
 ```
+A configuration flag will be added that enables dynamic auditing `--audit-dynamic-configuration`, which will default to false.
 
 ### User Stories
 
 #### Story 1
-As a cluster admin, I will easily be able to enable the interal auditing features of an existing cluster, and tweak the configurations as necessary. I want to prevent privilege escalation from being able to tamper with a root audit configuration.
+As a cluster admin, I will easily be able to enable the internal auditing features of an existing cluster, and tweak the configurations as necessary. I want to prevent privilege escalation from being able to tamper with a root audit configuration.
 
 #### Story 2
 As a Kubernetes extension developer, I will be able to provide drop in extensions that utilize audit data.
 
 #### Story 3
 As a cluster admin, I will be able configure multiple audit-policies and webhook endpoints to provide independent auditing facilities.
 
+#### Story 4
+As a kubernetes developer, I will be able to quickly turn up the audit level on a certain area to debug my application.
+
 ### Implementation Details/Notes/Constraints
 
-Any actions to the audit configuration objects will be hard coded to log at the `level=RequestResponse` to the previous backend and the new backend. If the apiserver is HA, the configuration will be rolled out in increments.
+#### Feature Gating
+Introduction of dynamic policy requires changes to the current audit pipeline. Care must be taken that these changes are properly gated and do not affect the stability or performance of the current features as they progress to GA. A new decorated handler will be provisioned similar to the [existing handlers](https://github.com/kubernetes/apiserver/blob/master/pkg/endpoints/filters/audit.go#L41) called `withDynamicAudit`. Another conditional clause will be added where the handlers are [provisioned](https://github.com/kubernetes/apiserver/blob/master/pkg/server/config.go#L536) allowing for the proper feature gating.
+
+#### Policy Enforcement
+This addition will move policy enforcement from the main handler to the backends. From the `withDynamicAudit` handler, the full event will be generated and then passed to the backends. Each backend will copy the event and then be required to drop any pieces that do not conform to its policy. A new sink interface will be required for these changes called `EnforcedSink`, this will largely follow suite with the existing sink but take a fully formed event and the authorizer attributes as its parameters. It will then utilize the `LevelAndStages` method in the policy [checker](https://github.com/kubernetes/apiserver/blob/master/pkg/audit/policy/checker.go) to enforce its policy on the event, and drop any unneeded sections. The new dynamic backend will implement the `EnforcedSink` interface, and update its state based on a shared informer. For the existing backends to comply, a method will be added that implements the `EnforcedSink` interface.
 
-Inherently apiserver aggregates and HA apiserver setups will work off the same dynamic configuration object. If separate objects are needed they should be configured as static objects on the node and set through the runtime flags. Aggregated servers will implement the same audit handling mechanisms. A conformance test should be provided as assurance. This needs further discussion with the participating sigs.
+Implementing the [attribute interface](/Users/patrick/go/src/k8s.io/kubernetes/vendor/k8s.io/apiserver/pkg/authorization/authorizer/interfaces.go) based on the Event struct was also explored. This would allow us to keep the existing `Sink` interfaces, however it would require parsing the request URI twice in the pipeline due to how that field is represented in the Event. This was determined to not be worth the cost.
+
+#### Aggregated Servers
+Inherently apiserver aggregates and HA apiserver setups will work off the same dynamic configuration object. If separate objects are needed they should be configured as static objects on the node and set through the runtime flags. Aggregated servers will implement the same audit handling mechanisms. A conformance test should be provided as assurance. Metadata level logging will happen by default at the main api server as it proxies the traffic. The aggregated server will then watch the same configuration objects and only log on resource types that it handles. This will duplicate the events sent to the receiving servers should they not expect to key off `{ Audit-ID x Stage }`.
 
 ### Risks and Mitigations
 
@@ -173,6 +198,11 @@ This does open up the attack surface of the audit mechanisms. Having them strict
 
 As a mitigation strategy policy configured through a static file on the api server will not be accessible through the api. This file ensures that an escalation attack cannot tamper with a root configuration, but works independently of any dynamically configured objects.
 
+#### Leaked Resources
+A user with permissions to create audit policies effectively has read access to the entire cluster (including all secrets data).
+
+A mitigation strategy will be to document the exposure space granted with this resource. Advice will be provided to only allow access to cluster admin level roles.
+
 #### Webhook Authentication
 With Dynamic Admission control today any authentication mechanism must be provided through a static kubeconfig file on the node. This hinders a lot of the advances in this proposal. All webhooks would require authentication as an unauthenticated endpoint would allow a bad actor to push phony events. Lack of dynamic credential provisioning is problematic to the drop-in extension use case, and difficult to configure.
 
@@ -182,6 +212,10 @@ It may also be reasonable to provide a dynamic auth configuration from secrets,
 
 This needs further discussion.
 
+#### Performance
+
+These changes will likely have an O(n) performance impact on the api server per policy.  A `DeepCopy` of the event will be required for each backend. Also, the request/response object would now be serialized on every [request](https://github.com/kubernetes/kubernetes/blob/cef2d325ee1be894e883d63013f75cfac5cb1246/staging/src/k8s.io/apiserver/pkg/audit/request.go#L150-L152). Benchmark testing will be required to understand the scope of the impact and what optimizations may be required. This impact is gated by opt-in feature flags, which allows it to move to alpha but these concerns must be tested and reconciled before it progresses to beta.
+
 ## Graduation Criteria
 
 Success will be determined by stability of the provided mechanisms and ease of understanding for the end user.
@@ -193,9 +227,20 @@ Success will be determined by stability of the provided mechanisms and ease of u
 
 - 05/18/2018: initial design
 - 06/13/2018: updated design
+- 07/31/2018: dynamic policy addition
 
 ## Alternatives
 
 ### Generalized Dynamic Configuration
 
 We could strive for all kube-apiserver flags to be able to be dynamically provisioned in a common way. This is likely a large task and out of the scope of the intentions of this feature.
+
+### Policy Override
+
+There has been discussion over whether the policy configured by api server flags should limit the policies configured dynamically. This would allow a cluster admin to narrowly define what is allowed to be logged by the dynamic configurations. While this has upsides it was ruled out for the following reasons: 
+
+* It would limit user story #4 in the ability to quickly turn up logging when needed 
+* It could prove difficult to understand as the policies themselves are fairly complex 
+* The use of CRDs would be difficult to bound
+
+The dynamic policy feature is gated by runtime flags. This still provides the cluster provisioner a means to limit audit logging to the single runtime object if needed.