adding cel for allow-privilege-escalation (#503)

* Example of a VAP constraint template: allow-privilege-escalation

Signed-off-by: Max Smythe <[email protected]>

* Update library/pod-security-policy/allow-privilege-escalation/template.yaml

Co-authored-by: Rita Zhang <[email protected]>
Signed-off-by: Max Smythe <[email protected]>

* Fix regex parsing

Signed-off-by: Max Smythe <[email protected]>

* Use image path rather than container contents for exemptions

Signed-off-by: Max Smythe <[email protected]>

* More explicity replicate glob-matching rego logic

Signed-off-by: Max Smythe <[email protected]>

* Switch to build system, use anyObject

Signed-off-by: Max Smythe <[email protected]>

* Bump minor version

Signed-off-by: Max Smythe <[email protected]>

---------

Signed-off-by: Max Smythe <[email protected]>
Signed-off-by: Max Smythe <[email protected]>
Co-authored-by: Rita Zhang <[email protected]>
Co-authored-by: Jaydipkumar Arvindbhai Gabani <[email protected]>

artifacthub/library/pod-security-policy/allow-privilege-escalation/1.1.0/artifacthub-pkg.yml

@@ -0,0 +1,22 @@
+version: 1.1.0
+name: k8spspallowprivilegeescalationcontainer
+displayName: Allow Privilege Escalation in Container
+createdAt: "2024-05-29T23:41:40Z"
+description: Controls restricting escalation to root privileges. Corresponds to the `allowPrivilegeEscalation` field in a PodSecurityPolicy. For more information, see https://kubernetes.io/docs/concepts/policy/pod-security-policy/#privilege-escalation
+digest: b88d5016b878fe37a461123069589385e3d082311bcaa93f9c73cedb0201cbbd
+license: Apache-2.0
+homeURL: https://open-policy-agent.github.io/gatekeeper-library/website/allow-privilege-escalation
+keywords:
+    - gatekeeper
+    - open-policy-agent
+    - policies
+readme: |-
+    # Allow Privilege Escalation in Container
+    Controls restricting escalation to root privileges. Corresponds to the `allowPrivilegeEscalation` field in a PodSecurityPolicy. For more information, see https://kubernetes.io/docs/concepts/policy/pod-security-policy/#privilege-escalation
+install: |-
+    ### Usage
+    ```shell
+    kubectl apply -f https://raw.githubusercontent.com/open-policy-agent/gatekeeper-library/master/artifacthub/library/pod-security-policy/allow-privilege-escalation/1.1.0/template.yaml
+    ```
+provider:
+    name: Gatekeeper Library

artifacthub/library/pod-security-policy/allow-privilege-escalation/1.1.0/kustomization.yaml

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

artifacthub/library/pod-security-policy/allow-privilege-escalation/1.1.0/samples/psp-allow-privilege-escalation-container/constraint.yaml

@@ -0,0 +1,11 @@
+apiVersion: constraints.gatekeeper.sh/v1beta1
+kind: K8sPSPAllowPrivilegeEscalationContainer
+metadata:
+  name: psp-allow-privilege-escalation-container
+spec:
+  match:
+    kinds:
+      - apiGroups: [""]
+        kinds: ["Pod"]
+  parameters:
+    exemptImages: ["nonexistant/*"]

artifacthub/library/pod-security-policy/allow-privilege-escalation/1.1.0/samples/psp-allow-privilege-escalation-container/disallowed_ephemeral.yaml

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

artifacthub/library/pod-security-policy/allow-privilege-escalation/1.1.0/samples/psp-allow-privilege-escalation-container/example_allowed.yaml

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

artifacthub/library/pod-security-policy/allow-privilege-escalation/1.1.0/samples/psp-allow-privilege-escalation-container/example_disallowed.yaml

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

artifacthub/library/pod-security-policy/allow-privilege-escalation/1.1.0/samples/psp-allow-privilege-escalation-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-privilege-escalation-disallowed
+      labels:
+        app: nginx-privilege-escalation
+    spec:
+      containers:
+      - name: nginx
+        image: nginx
+        securityContext:
+          allowPrivilegeEscalation: true

artifacthub/library/pod-security-policy/allow-privilege-escalation/1.1.0/suite.yaml

@@ -0,0 +1,25 @@
+kind: Suite
+apiVersion: test.gatekeeper.sh/v1alpha1
+metadata:
+  name: allow-privilege-escalation
+tests:
+  - name: allow-privilege-escalation
+    template: template.yaml
+    constraint: samples/psp-allow-privilege-escalation-container/constraint.yaml
+    cases:
+      - name: example-allowed
+        object: samples/psp-allow-privilege-escalation-container/example_allowed.yaml
+        assertions:
+          - violations: no
+      - name: example-disallowed
+        object: samples/psp-allow-privilege-escalation-container/example_disallowed.yaml
+        assertions:
+          - violations: yes
+      - name: disallowed-ephemeral
+        object: samples/psp-allow-privilege-escalation-container/disallowed_ephemeral.yaml
+        assertions:
+          - violations: yes
+      - name: update
+        object: samples/psp-allow-privilege-escalation-container/update.yaml
+        assertions:
+          - violations: no

artifacthub/library/pod-security-policy/allow-privilege-escalation/1.1.0/template.yaml

@@ -0,0 +1,138 @@
+apiVersion: templates.gatekeeper.sh/v1
+kind: ConstraintTemplate
+metadata:
+  name: k8spspallowprivilegeescalationcontainer
+  annotations:
+    metadata.gatekeeper.sh/title: "Allow Privilege Escalation in Container"
+    metadata.gatekeeper.sh/version: 1.1.0
+    description: >-
+      Controls restricting escalation to root privileges. Corresponds to the
+      `allowPrivilegeEscalation` field in a PodSecurityPolicy. For more
+      information, see
+      https://kubernetes.io/docs/concepts/policy/pod-security-policy/#privilege-escalation
+spec:
+  crd:
+    spec:
+      names:
+        kind: K8sPSPAllowPrivilegeEscalationContainer
+      validation:
+        openAPIV3Schema:
+          type: object
+          description: >-
+            Controls restricting escalation to root privileges. Corresponds to the
+            `allowPrivilegeEscalation` field in a PodSecurityPolicy. For more
+            information, see
+            https://kubernetes.io/docs/concepts/policy/pod-security-policy/#privilege-escalation
+          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.allowPrivilegeEscalation) ||
+                  container.securityContext.allowPrivilegeEscalation != false
+                )
+              )
+          validations:
+          - expression: '(has(request.operation) && request.operation == "UPDATE") || size(variables.badContainers) == 0'
+            messageExpression: '"Privilege escalation container is not allowed: " + variables.badContainers.map(c, c.image).join(", ")'
+      - engine: Rego
+        source:
+          rego: |
+            package k8spspallowprivilegeescalationcontainer
+
+            import data.lib.exclude_update.is_update
+            import data.lib.exempt_container.is_exempt
+
+            violation[{"msg": msg, "details": {}}] {
+                # spec.containers.securityContext.allowPrivilegeEscalation field is immutable.
+                not is_update(input.review)
+
+                c := input_containers[_]
+                not is_exempt(c)
+                input_allow_privilege_escalation(c)
+                msg := sprintf("Privilege escalation container is not allowed: %v", [c.name])
+            }
+
+            input_allow_privilege_escalation(c) {
+                not has_field(c, "securityContext")
+            }
+            input_allow_privilege_escalation(c) {
+                not c.securityContext.allowPrivilegeEscalation == false
+            }
+            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[_]
+            }
+            # has_field returns whether an object has a field
+            has_field(object, field) = true {
+                object[field]
+            }
+          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/allow-privilege-escalation/samples/psp-allow-privilege-escalation-container/constraint.yaml

@@ -7,3 +7,5 @@ spec:
     kinds:
       - apiGroups: [""]
         kinds: ["Pod"]
+  parameters:
+    exemptImages: ["nonexistant/*"]