Failed to use lua's built-in string function in ResourceInterpreterCustomization lua script

[XiShanYongYe-Chang]

What happened:

For the following ResourceInterpreterCustomization resource:

apiVersion: config.karmada.io/v1alpha1
kind: ResourceInterpreterCustomization
metadata:
  name: declarative-configuration-example
spec:
  target:
    apiVersion: v1
    kind: Service
  customizations:
    statusReflection:
      luaScript: >
        function ReflectStatus (observedObj)
          print(string.len("abc"))
          return observedObj.status
        end

I want to interpret the Service Status resource with the interpretStatus operation:

apiVersion: v1
kind: Service
metadata:
  creationTimestamp: "2023-03-06T12:24:10Z"
  labels:
    component: apiserver
    provider: kubernetes
  name: kubernetes
  namespace: default
  resourceVersion: "190"
  uid: 79febb3b-af42-4e83-aa4f-9095112771fb
spec:
  clusterIP: 10.96.0.1
  clusterIPs:
  - 10.96.0.1
  internalTrafficPolicy: Cluster
  ipFamilies:
  - IPv4
  ipFamilyPolicy: SingleStack
  ports:
  - name: https
    port: 443
    protocol: TCP
    targetPort: 5443
  sessionAffinity: None
  type: ClusterIP
status:
  loadBalancer:
    ingress:
    - ip: 172.1.1.1
    - ip: 192.1.3.2

When I run with the following command:

karmadactl interpret -f reflectstatus.yaml --operation interpretStatus --observed-file service-status.yaml

I got the bellow error:

Execute InterpretStatus error: <string>:2: attempt to index a non-table object(nil) with key 'len'
stack traceback:
        <string>:2: in main chunk
        [G]: ?

Then I tried other string functions, and it returned similar errors.

What you expected to happen:

The string function can be used normally.

How to reproduce it (as minimally and precisely as possible):

Anything else we need to know?:

This issue is related to lua VM initialization: pkg/resourceinterpreter/configurableinterpreter/luavm/lua.go:43

Environment:

• Karmada version: karmada v1.4 and later
• kubectl-karmada or karmadactl version (the result of kubectl-karmada version or karmadactl version): karmada v1.4 and later
• Others:

[chaunceyjiang]

Have you tested the #str method?

[XiShanYongYe-Chang]

Have you tested the #str method?

Can you give me a demo usage?

[chaunceyjiang]

/assign

[XiShanYongYe-Chang]

Found the same problem that argo-cd had before: argoproj/argo-cd#6039

The solution is to introduce the useOpenLibs parameter, allow administrator enable lua standard library for health checks:

argoproj/argo-cd#6087

For us, opening a parameter for user settings may not be the best option.

The reason of disable lua standard library is:

karmada/pkg/util/lifted/lua_oslib_safe.go

Lines 7 to 10 in 83c7862

	// oslib_safe contains a subset of the lua OS library. For security reasons, we do not expose
	// the entirety of lua OS library to custom actions, such as ones which can exit, read files, etc.
	// Only the safe functions like os.time(), os.date() are exposed. Implementation was copied from
	// github.com/yuin/gopher-lua.

The lua standard libraries we want to use are string, math, so we can set up these two standard libraries additionally.