Drop All Capabilities in CEL expressions

 1apiVersion: kyverno.io/v1
 2kind: ClusterPolicy
 3metadata:
 4  name: drop-all-capabilities
 5  annotations:
 6    policies.kyverno.io/title: Drop All Capabilities in CEL expressions
 7    policies.kyverno.io/category: Best Practices in CEL 
 8    policies.kyverno.io/severity: medium
 9    kyverno.io/kubernetes-version: "1.26-1.27"
10    policies.kyverno.io/minversion: 1.11.0
11    policies.kyverno.io/subject: Pod
12    policies.kyverno.io/description: >-
13      Capabilities permit privileged actions without giving full root access. All
14      capabilities should be dropped from a Pod, with only those required added back.
15      This policy ensures that all containers explicitly specify the `drop: ["ALL"]`
16      ability. Note that this policy also illustrates how to cover drop entries in any
17      case although this may not strictly conform to the Pod Security Standards.
18spec:
19  validationFailureAction: Audit
20  background: true
21  rules:
22    - name: require-drop-all
23      match:
24        any:
25        - resources:
26            kinds:
27              - Pod
28            operations:
29            - CREATE
30            - UPDATE
31      validate:
32        cel:
33          variables:
34            - name: allContainers
35              expression: "object.spec.containers + object.spec.?initContainers.orValue([]) + object.spec.?ephemeralContainers.orValue([])"
36          expressions:
37            - expression: >-
38                variables.allContainers.all(container, 
39                container.?securityContext.?capabilities.?drop.orValue([]).exists(capability, capability.upperAscii() == 'ALL'))
40              message: "Containers must drop `ALL` capabilities."