helm-charts/cyberchef/templates/cyberchef.networkpolicy.yaml

{{- /*
NetworkPolicy for cyberchef (Gitea #5).

CyberChef is a static web app: nginx serves files, the recipes run in the
visitor's browser, and the pod holds no state and talks to nothing. That makes
this the simplest policy in the repository and a good one to read first.

What it is worth here is almost entirely the two CEILINGS rather than any
source restriction: only 8080 is reachable, and outbound traffic is capped at
DNS. The pod has no reason to open a single outbound connection - it serves
static files - so the egress cap is as tight as the object allows. Were this
image ever to gain a second listener, or were the container ever compromised,
neither could be reached or could reach out.

The ingress direction is NOT restricted by source in the default, and that is
not an oversight: 8080 is the port all three probes address. See the probe note
on the rule below.

WHAT THIS OBJECT IS: a ceiling on reachability, not an authentication layer.
Only the ports declared below are reachable at all - whatever else the process
binds, now or after the next app update, is blocked without anyone having to
notice it exists.

WHAT IT IS NOT:
  - EGRESS IS COARSE. A NetworkPolicy matches CIDRs and selectors and NEVER
    hostnames, so "only to the database host" cannot be expressed at all. This
    cluster's CNI is Canal (Flannel plus Calico for policy) and has no FQDN
    rule; Calico's GlobalNetworkSet could express one but would bind this chart
    to Calico, the same argument that kept implementation-specific objects out
    of the Gateway-API sweep (#114). Each egress rule therefore permits its
    PORT to any destination.
  - NOT A BOUNDARY WHERE THE CNI DOES NOT ENFORCE ONE. An unenforced policy is
    accepted by the API server and filters nothing, so everything reads as
    configured while nothing is filtered.
  - THE REASONING IS IN TEMPLATE COMMENTS, not in "#" comments: those are part
    of the rendered object, travel into the cluster and appear in every release
    diff. ci/run-networkpolicy-test.sh fails on a rendered "#".

THE PORT NUMBERS BELOW ARE POD PORTS, NEVER NODEPORTS. A NetworkPolicy is
evaluated at the pod's network interface, after kube-proxy has already
translated a NodePort to the targetPort, so a NodePort number here would match
nothing while looking strict - and, being the only rule for that port, would
block every inbound connection instead. ci/run-networkpolicy-test.sh asserts
every port here against the containerPorts of the pod spec this policy
selects.
*/ -}}
{{- if .Values.networkPolicy.enabled }}
{{- $np := .Values.networkPolicy }}
{{- $ns := .Release.Namespace }}
{{- $probeSources := $np.probeSources | default list }}
{{- $allowedNs := $np.allowedNamespaces | default list }}
{{- $ic := $np.ingressController | default dict }}
{{- $routed := or .Values.ingress.enabled .Values.httpRoute.enabled }}
{{- /* networkPolicy.ingress - the policy's INBOUND side, and not the same thing
       as networkPolicy.ingressController (the SOURCE SELECTOR for the ingress
       controller's pods, a SIBLING of it and no part of it) nor as the
       top-level .Values.ingress (the Ingress object). All three match a search
       for "ingress"; one round of this work already mistook the second for an
       inbound escape hatch on the strength of the substring. */}}
{{- $npIngress := $np.ingress | default dict }}
{{- $ambientMesh := $npIngress.ambientMesh }}
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: {{ .Release.Name }}-{{ .Chart.Name }}-networkpolicy
  labels:
    app: {{ .Release.Name }}-{{ .Chart.Name }}-networkpolicy
spec:
  {{- /*
  Selects the Deployment's pods. ci/run-networkpolicy-test.sh fails if
  this matches no pod spec of the same render - which is the mistake that
  would otherwise leave a policy in the namespace filtering nothing, and
  its usual cause is a label renamed in the workload template.
  */}}
  podSelector:
    matchLabels:
      app: {{ .Release.Name }}-{{ .Chart.Name }}-deployment
  policyTypes:
    - Ingress
    {{- /*
    Egress is listed because there IS something to restrict, and here the
    restriction is close to total: a static file server needs name resolution and
    nothing else, so DNS is the only rule. That is as tight as this object can be
    made without breaking the pod.
    */}}
    - Egress
  ingress:
    {{- /*
    8080 - the only port this pod declares, the one the Service targets, and the
    one all three probes address. It is therefore the probe path, and the shape
    below is the whole reason networkPolicy.probeSources exists.
    */}}
    - ports:
        - protocol: TCP
          port: 8080
        {{- if $ambientMesh }}
        {{- /* FIRST HALF OF networkPolicy.ingress.ambientMesh (Gitea #143). 15008/TCP
               is ztunnel's HBONE tunnel, the port every inbound connection arrives on
               once the namespace carries istio.io/dataplane-mode - ambient "does not
               and will never bypass Kubernetes NetworkPolicy enforcement", so without
               it a pod in the mesh is simply unreachable.

               It is the one port here that is NOT a containerPort of the selected pod
               spec: ztunnel terminates it, not the application. ci/run-networkpolicy-
               test.sh therefore holds a NAMED exception for exactly this number, gated
               on exactly this value - and assertion 7 of that script proves, on a
               second render, that 15008 stays the ONLY such port and that it is absent
               while the value is false.

               NOT MEASURED: that 15008 alone suffices comes from Istio's
               documentation. Measured on this cluster is only which listeners ztunnel
               opens. Provable at the first namespace to join the mesh; none has. */}}
        - protocol: TCP
          port: 15008
        {{- end }}
      {{- if $probeSources }}
      {{- /*
      RESTRICTED, because the operator supplied probeSources. The kubelet's probes
      come from the IP of the WORKER NODE running the pod, so that address has to be
      in the list or the pod never becomes Ready - and a pod that is never Ready
      reads as a broken application rather than as a policy.

      The ingress controller is added to the same rule, or the Ingress (and the
      HTTPRoute - the same Traefik serves both here) goes dark the moment this list
      is filled.
      */}}
      from:
        - namespaceSelector:
            matchLabels:
              {{- /*
              Set by Kubernetes itself on every namespace (>= 1.21), so this needs no
              labelling work on a namespace this chart does not own.
              */}}
              kubernetes.io/metadata.name: {{ $ns }}
        {{- if and $routed $ic.namespace }}
        {{- /*
        ONE from-entry with TWO selectors, which is an AND: pods carrying these labels
        IN that namespace. Written as two list entries it would be an OR, and would
        open the port to every pod in kube-system.
        */}}
        - namespaceSelector:
            matchLabels:
              kubernetes.io/metadata.name: {{ $ic.namespace | quote }}
          {{- with $ic.podLabels }}
          podSelector:
            matchLabels:
              {{- toYaml . | nindent 14 }}
          {{- end }}
        {{- end }}
        {{- range $allowedNs }}
        - namespaceSelector:
            matchLabels:
              kubernetes.io/metadata.name: {{ . | quote }}
        {{- end }}
        {{- range $probeSources }}
        - ipBlock:
            cidr: {{ . | quote }}
        {{- end }}
        {{- if $ambientMesh }}
        {{- /* SECOND HALF OF networkPolicy.ingress.ambientMesh, and the reason it is
               one value and not two. Inside the mesh the kubelet's probes are
               redirected and no longer arrive from the worker node's address: they
               arrive from 169.254.7.127.

               An operator who only opens 15008 by hand writes a policy that passes
               review - and the moment probeSources is non-empty every probe is
               dropped, the pod never becomes Ready, and the symptom reads as a broken
               application rather than as a policy. That is assertion 4 of
               ci/run-networkpolicy-test.sh one value further along. A switch whose
               halves can only be had together cannot be set halfway.

               Only in this branch, because this is the only branch with a "from" list:
               with no sources restricted the rule is open and needs no peer. The IPv6
               counterpart is deliberately absent - this cluster is SingleStack IPv4,
               and an ipBlock of the wrong family is accepted and matches nothing.

               UNPROVEN IN OPERATION: probeSources is empty in every chart here, so no
               release reaches this branch. CI proves its render, through the overlays
               in ci/networkpolicy. */}}
        - ipBlock:
            cidr: 169.254.7.127/32
        {{- end }}
      {{- else }}
      {{- /*
      NO "from" SELECTOR, WHICH MEANS OPEN - deliberately, and only inside the
      cluster, because this port carries no NodePort. The alternative was to guess
      the worker node CIDRs, and a wrong guess blocks every kubelet probe: the pod
      stays un-Ready, the rollout times out, and the cause looks like the
      application. An empty "from: []" would be worse than either - it allows
      everything too, but while reading as a restriction. Narrow it with
      networkPolicy.probeSources.
      */}}
      {{- end }}
  egress:
    {{- /*
    DNS, unconditionally. There is no value to switch this off, and that is
    deliberate: a knob whose only other setting breaks every name lookup in
    the pod is a trap and not a feature.
    */}}
    - ports:
        - protocol: UDP
          port: 53
        - protocol: TCP
          port: 53
    {{- with $np.egress }}
    {{- with .extraPorts }}
    {{- /*
    Ports only, to any destination - see the header. This is the operator's
    escape hatch from the egress cap, and the only alternative to switching
    the whole policy off.
    */}}
    - ports:
        {{- range . }}
        - protocol: TCP
          port: {{ int . }}
        {{- end }}
    {{- end }}
    {{- end }}
{{- end }}