fix(k8spspprivilegedcontainer): exemptImages CEL bug (#591)

I recently found (#584) that some K8sNativeValidation implementations of
certain templates that iterate over and exempt containers by image had a
bug preventing the exemption logic from working.

I've fixed that bug here by mapping from container struct to
container.image string. I've also added a suite test to verify this.
That case fails without the change to the CEL logic.

Signed-off-by: juliankatz <[email protected]>
Co-authored-by: Sertaç Özercan <[email protected]>

artifacthub/library/pod-security-policy/privileged-containers/1.1.1/artifacthub-pkg.yml

@@ -0,0 +1,22 @@
+version: 1.1.1
+name: k8spspprivilegedcontainer
+displayName: Privileged Container
+createdAt: "2024-08-30T22:14:08Z"
+description: Controls the ability of any container to enable privileged mode. Corresponds to the `privileged` field in a PodSecurityPolicy. For more information, see https://kubernetes.io/docs/concepts/policy/pod-security-policy/#privileged
+digest: 5d9b2b840bb1f530d3e66cb44d4ab170e7d4b7895d722a51999134a032b61c6f
+license: Apache-2.0
+homeURL: https://open-policy-agent.github.io/gatekeeper-library/website/privileged-containers
+keywords:
+    - gatekeeper
+    - open-policy-agent
+    - policies
+readme: |-
+    # Privileged Container
+    Controls the ability of any container to enable privileged mode. Corresponds to the `privileged` field in a PodSecurityPolicy. For more information, see https://kubernetes.io/docs/concepts/policy/pod-security-policy/#privileged
+install: |-
+    ### Usage
+    ```shell
+    kubectl apply -f https://raw.githubusercontent.com/open-policy-agent/gatekeeper-library/master/artifacthub/library/pod-security-policy/privileged-containers/1.1.1/template.yaml
+    ```
+provider:
+    name: Gatekeeper Library

artifacthub/library/pod-security-policy/privileged-containers/1.1.1/kustomization.yaml

@@ -0,0 +1,2 @@
+resources:
+  - template.yaml

artifacthub/library/pod-security-policy/privileged-containers/1.1.1/samples/psp-privileged-container/constraint.yaml

@@ -0,0 +1,13 @@
+apiVersion: constraints.gatekeeper.sh/v1beta1
+kind: K8sPSPPrivilegedContainer
+metadata:
+  name: psp-privileged-container
+spec:
+  match:
+    kinds:
+      - apiGroups: [""]
+        kinds: ["Pod"]
+    excludedNamespaces: ["kube-system"]
+  parameters:
+    exemptImages:
+    - "safeimages.com/*"

artifacthub/library/pod-security-policy/privileged-containers/1.1.1/samples/psp-privileged-container/disallowed_ephemeral.yaml

@@ -0,0 +1,12 @@
+apiVersion: v1
+kind: Pod
+metadata:
+  name: nginx-privileged-disallowed
+  labels:
+    app: nginx-privileged
+spec:
+  ephemeralContainers:
+  - name: nginx
+    image: nginx
+    securityContext:
+      privileged: true

artifacthub/library/pod-security-policy/privileged-containers/1.1.1/samples/psp-privileged-container/example_allowed.yaml

@@ -0,0 +1,12 @@
+apiVersion: v1
+kind: Pod
+metadata:
+  name: nginx-privileged-allowed
+  labels:
+    app: nginx-privileged
+spec:
+  containers:
+  - name: nginx
+    image: nginx
+    securityContext:
+      privileged: false

artifacthub/library/pod-security-policy/privileged-containers/1.1.1/samples/psp-privileged-container/example_allowed_exempt.yaml

@@ -0,0 +1,12 @@
+apiVersion: v1
+kind: Pod
+metadata:
+  name: nginx-privileged-allowed-exempt
+  labels:
+    app: nginx-privileged
+spec:
+  containers:
+  - name: nginx
+    image: safeimages.com/nginx
+    securityContext:
+      privileged: true

artifacthub/library/pod-security-policy/privileged-containers/1.1.1/samples/psp-privileged-container/example_disallowed.yaml

@@ -0,0 +1,12 @@
+apiVersion: v1
+kind: Pod
+metadata:
+  name: nginx-privileged-disallowed
+  labels:
+    app: nginx-privileged
+spec:
+  containers:
+  - name: nginx
+    image: nginx
+    securityContext:
+      privileged: true

artifacthub/library/pod-security-policy/privileged-containers/1.1.1/samples/psp-privileged-container/update.yaml

@@ -0,0 +1,17 @@
+kind: AdmissionReview
+apiVersion: admission.k8s.io/v1beta1
+request:
+  operation: "UPDATE"
+  object:
+    apiVersion: v1
+    kind: Pod
+    metadata:
+      name: nginx-privileged-disallowed
+      labels:
+        app: nginx-privileged
+    spec:
+      containers:
+      - name: nginx
+        image: nginx
+        securityContext:
+          privileged: true

artifacthub/library/pod-security-policy/privileged-containers/1.1.1/suite.yaml

@@ -0,0 +1,29 @@
+kind: Suite
+apiVersion: test.gatekeeper.sh/v1alpha1
+metadata:
+  name: privileged-containers
+tests:
+- name: privileged-containers-disallowed
+  template: template.yaml
+  constraint: samples/psp-privileged-container/constraint.yaml
+  cases:
+  - name: example-disallowed
+    object: samples/psp-privileged-container/example_disallowed.yaml
+    assertions:
+    - violations: yes
+  - name: example-allowed
+    object: samples/psp-privileged-container/example_allowed.yaml
+    assertions:
+    - violations: no
+  - name: disallowed-ephemeral
+    object: samples/psp-privileged-container/disallowed_ephemeral.yaml
+    assertions:
+    - violations: yes
+  - name: update
+    object: samples/psp-privileged-container/update.yaml
+    assertions:
+    - violations: no
+  - name: exempted-image
+    object: samples/psp-privileged-container/example_allowed_exempt.yaml
+    assertions:
+    - violations: no

artifacthub/library/pod-security-policy/privileged-containers/1.1.1/template.yaml

@@ -0,0 +1,129 @@
+apiVersion: templates.gatekeeper.sh/v1
+kind: ConstraintTemplate
+metadata:
+  name: k8spspprivilegedcontainer
+  annotations:
+    metadata.gatekeeper.sh/title: "Privileged Container"
+    metadata.gatekeeper.sh/version: 1.1.1
+    description: >-
+      Controls the ability of any container to enable privileged mode.
+      Corresponds to the `privileged` field in a PodSecurityPolicy. For more
+      information, see
+      https://kubernetes.io/docs/concepts/policy/pod-security-policy/#privileged
+spec:
+  crd:
+    spec:
+      names:
+        kind: K8sPSPPrivilegedContainer
+      validation:
+        openAPIV3Schema:
+          type: object
+          description: >-
+            Controls the ability of any container to enable privileged mode.
+            Corresponds to the `privileged` field in a PodSecurityPolicy. For more
+            information, see
+            https://kubernetes.io/docs/concepts/policy/pod-security-policy/#privileged
+          properties:
+            exemptImages:
+              description: >-
+                Any container that uses an image that matches an entry in this list will be excluded
+                from enforcement. Prefix-matching can be signified with `*`. For example: `my-image-*`.
+
+                It is recommended that users use the fully-qualified Docker image name (e.g. start with a domain name)
+                in order to avoid unexpectedly exempting images from an untrusted repository.
+              type: array
+              items:
+                type: string
+  targets:
+    - target: admission.k8s.gatekeeper.sh
+      code:
+      - engine: K8sNativeValidation
+        source:
+          variables:
+          - name: containers
+            expression: 'has(variables.anyObject.spec.containers) ? variables.anyObject.spec.containers : []'
+          - name: initContainers
+            expression: 'has(variables.anyObject.spec.initContainers) ? variables.anyObject.spec.initContainers : []'
+          - name: ephemeralContainers
+            expression: 'has(variables.anyObject.spec.ephemeralContainers) ? variables.anyObject.spec.ephemeralContainers : []'
+          - name: exemptImagePrefixes
+            expression: |
+              !has(variables.params.exemptImages) ? [] :
+                variables.params.exemptImages.filter(image, image.endsWith("*")).map(image, string(image).replace("*", ""))
+          - name: exemptImageExplicit
+            expression: |
+              !has(variables.params.exemptImages) ? [] : 
+                variables.params.exemptImages.filter(image, !image.endsWith("*"))
+          - name: exemptImages
+            expression: |
+              (variables.containers + variables.initContainers + variables.ephemeralContainers).filter(container,
+                container.image in variables.exemptImageExplicit ||
+                variables.exemptImagePrefixes.exists(exemption, string(container.image).startsWith(exemption))
+              ).map(container, container.image)
+          - name: badContainers
+            expression: |
+              (variables.containers + variables.initContainers + variables.ephemeralContainers).filter(container,
+                !(container.image in variables.exemptImages) &&
+                (has(container.securityContext) && has(container.securityContext.privileged) && container.securityContext.privileged == true)
+              ).map(container, "Privileged container is not allowed: " + container.name +", securityContext: " + container.securityContext)
+          - name: isUpdate
+            expression: has(request.operation) && request.operation == "UPDATE"
+          validations:
+          - expression: variables.isUpdate || size(variables.badContainers) == 0
+            messageExpression: 'variables.badContainers.join("\n")' 
+      - engine: Rego
+        source:
+          rego: |
+            package k8spspprivileged
+
+            import data.lib.exclude_update.is_update
+            import data.lib.exempt_container.is_exempt
+
+            violation[{"msg": msg, "details": {}}] {
+                # spec.containers.privileged field is immutable.
+                not is_update(input.review)
+
+                c := input_containers[_]
+                not is_exempt(c)
+                c.securityContext.privileged
+                msg := sprintf("Privileged container is not allowed: %v, securityContext: %v", [c.name, c.securityContext])
+            }
+
+            input_containers[c] {
+                c := input.review.object.spec.containers[_]
+            }
+
+            input_containers[c] {
+                c := input.review.object.spec.initContainers[_]
+            }
+
+            input_containers[c] {
+                c := input.review.object.spec.ephemeralContainers[_]
+            }
+          libs:
+            - |
+              package lib.exclude_update
+
+              is_update(review) {
+                  review.operation == "UPDATE"
+              }
+            - |
+              package lib.exempt_container
+
+              is_exempt(container) {
+                  exempt_images := object.get(object.get(input, "parameters", {}), "exemptImages", [])
+                  img := container.image
+                  exemption := exempt_images[_]
+                  _matches_exemption(img, exemption)
+              }
+
+              _matches_exemption(img, exemption) {
+                  not endswith(exemption, "*")
+                  exemption == img
+              }
+
+              _matches_exemption(img, exemption) {
+                  endswith(exemption, "*")
+                  prefix := trim_suffix(exemption, "*")
+                  startswith(img, prefix)
+              }

library/pod-security-policy/privileged-containers/samples/psp-privileged-container/constraint.yaml

@@ -8,3 +8,6 @@ spec:
       - apiGroups: [""]
         kinds: ["Pod"]
     excludedNamespaces: ["kube-system"]
+  parameters:
+    exemptImages:
+    - "safeimages.com/*"

library/pod-security-policy/privileged-containers/samples/psp-privileged-container/example_allowed_exempt.yaml

@@ -0,0 +1,12 @@
+apiVersion: v1
+kind: Pod
+metadata:
+  name: nginx-privileged-allowed-exempt
+  labels:
+    app: nginx-privileged
+spec:
+  containers:
+  - name: nginx
+    image: safeimages.com/nginx
+    securityContext:
+      privileged: true

library/pod-security-policy/privileged-containers/suite.yaml

@@ -23,3 +23,7 @@ tests:
     object: samples/psp-privileged-container/update.yaml
     assertions:
     - violations: no
+  - name: exempted-image
+    object: samples/psp-privileged-container/example_allowed_exempt.yaml
+    assertions:
+    - violations: no

library/pod-security-policy/privileged-containers/template.yaml

@@ -4,7 +4,7 @@ metadata:
   name: k8spspprivilegedcontainer
   annotations:
     metadata.gatekeeper.sh/title: "Privileged Container"
-    metadata.gatekeeper.sh/version: 1.1.0
+    metadata.gatekeeper.sh/version: 1.1.1
     description: >-
       Controls the ability of any container to enable privileged mode.
       Corresponds to the `privileged` field in a PodSecurityPolicy. For more
@@ -58,15 +58,18 @@ spec:
             expression: |
               (variables.containers + variables.initContainers + variables.ephemeralContainers).filter(container,
                 container.image in variables.exemptImageExplicit ||
-                variables.exemptImagePrefixes.exists(exemption, string(container.image).startsWith(exemption)))
+                variables.exemptImagePrefixes.exists(exemption, string(container.image).startsWith(exemption))
+              ).map(container, container.image)
           - name: badContainers
             expression: |
               (variables.containers + variables.initContainers + variables.ephemeralContainers).filter(container,
                 !(container.image in variables.exemptImages) &&
                 (has(container.securityContext) && has(container.securityContext.privileged) && container.securityContext.privileged == true)
               ).map(container, "Privileged container is not allowed: " + container.name +", securityContext: " + container.securityContext)
+          - name: isUpdate
+            expression: has(request.operation) && request.operation == "UPDATE"
           validations:
-          - expression: '(has(request.operation) && request.operation == "UPDATE") || size(variables.badContainers) == 0'
+          - expression: variables.isUpdate || size(variables.badContainers) == 0
             messageExpression: 'variables.badContainers.join("\n")' 
       - engine: Rego
         source:

src/pod-security-policy/privileged-containers/constraint.tmpl

@@ -4,7 +4,7 @@ metadata:
   name: k8spspprivilegedcontainer
   annotations:
     metadata.gatekeeper.sh/title: "Privileged Container"
-    metadata.gatekeeper.sh/version: 1.1.0
+    metadata.gatekeeper.sh/version: 1.1.1
     description: >-
       Controls the ability of any container to enable privileged mode.
       Corresponds to the `privileged` field in a PodSecurityPolicy. For more

src/pod-security-policy/privileged-containers/src.cel

@@ -17,13 +17,16 @@ variables:
   expression: |
     (variables.containers + variables.initContainers + variables.ephemeralContainers).filter(container,
       container.image in variables.exemptImageExplicit ||
-      variables.exemptImagePrefixes.exists(exemption, string(container.image).startsWith(exemption)))
+      variables.exemptImagePrefixes.exists(exemption, string(container.image).startsWith(exemption))
+    ).map(container, container.image)
 - name: badContainers
   expression: |
     (variables.containers + variables.initContainers + variables.ephemeralContainers).filter(container,
       !(container.image in variables.exemptImages) &&
       (has(container.securityContext) && has(container.securityContext.privileged) && container.securityContext.privileged == true)
     ).map(container, "Privileged container is not allowed: " + container.name +", securityContext: " + container.securityContext)
+- name: isUpdate
+  expression: has(request.operation) && request.operation == "UPDATE"
 validations:
-- expression: '(has(request.operation) && request.operation == "UPDATE") || size(variables.badContainers) == 0'
-  messageExpression: 'variables.badContainers.join("\n")' 
+- expression: variables.isUpdate || size(variables.badContainers) == 0
+  messageExpression: 'variables.badContainers.join("\n")'