Merge pull request 'docs(netpol): correct three comments that assert a boundary Cilium does not enforce (REN-108)' (#997) from atlas/ren-108-trust-boundary-comments into master

kubernetes/apps/navidrome/deployment.yaml

@@ -8,8 +8,27 @@ data:
   ND_LOGLEVEL: "info"
   ND_SCANNER_SCHEDULE: "0 * * * *"
   ND_ENABLEINSIGHTSCOLLECTOR: "false"
-  # Identity from the navidrome-gate outpost; the CNP admits only the outpost
-  # and Traefik, and Traefik strips this header on the ungated routes.
+  # Identity from the navidrome-gate outpost. Traefik strips this header on
+  # the ungated /rest and /share routes.
+  #
+  # ND_EXTAUTH_TRUSTEDSOURCES BELOW IS NOT A NARROWING. fd10:244::/48 plus
+  # 10.244.0.0/16 is the entire cluster pod CIDR, so navidrome's own
+  # reverse-proxy trust check accepts X-Authentik-Username from ANY pod.
+  # The CiliumNetworkPolicy is the only real boundary, and it is wider than
+  # "the outpost and Traefik" — default-deny-ingress in
+  # kubernetes/infrastructure/network-policies/navidrome-ns.yaml uses
+  # `endpointSelector: {}` and admits, on every port:
+  #   - the navidrome namespace     (navidrome-ns.yaml:9-11)
+  #   - traefik                     (navidrome-ns.yaml:13-16)
+  #   - the navidrome-gate outpost  (navidrome-ns.yaml:17-20)
+  #   - the lidarr-gate outpost     (navidrome-ns.yaml:21-24) - reaches navidrome too
+  #   - the monitoring namespace    (navidrome-ns.yaml:25-27)
+  #   - host / remote-node          (navidrome-ns.yaml:28-30)
+  # The value stays at the pod CIDR ON PURPOSE - see REN-28. The address
+  # navidrome sees is the outpost's POD IP, which is not stable across
+  # reschedules, so a narrower literal here fails open-ended and silently
+  # the next time that pod moves. Tightening the CNP is the control that
+  # would actually do work.
   ND_EXTAUTH_USERHEADER: "X-Authentik-Username"
   ND_EXTAUTH_TRUSTEDSOURCES: "fd10:244::/48,10.244.0.0/16"
 ---

kubernetes/apps/paperless/network-policy.yaml

@@ -1,9 +1,23 @@
 ---
-# Trust boundary: paperless-gate (the dedicated Authentik proxy outpost
-# in the authentik namespace). Header-based remote-user auth means
-# paperless trusts whatever fills X-Authentik-Username unconditionally,
-# so any pod that can talk directly to paperless's HTTP listener can
-# claim any username. Lock the ingress side to the gate outpost only.
+# Intended trust boundary: paperless-gate (the dedicated Authentik proxy
+# outpost in the authentik namespace). Header-based remote-user auth means
+# paperless trusts whatever fills X-Authentik-Username unconditionally, so
+# any pod that can talk directly to paperless's HTTP listener can claim any
+# username.
+#
+# WHAT IS ENFORCED IS WIDER THAN THIS RULE. default-deny-ingress in
+# kubernetes/infrastructure/network-policies/paperless-ns.yaml uses
+# `endpointSelector: {}`, so it selects this pod as well, and Cilium unions
+# the allow rules of every CNP selecting an endpoint (the same mechanism
+# described below). The effective ingress set is this outpost PLUS, on
+# every port:
+#   - the paperless namespace   (paperless-ns.yaml:9-11)
+#   - the database namespace    (paperless-ns.yaml:30-32)
+#   - the monitoring namespace  (paperless-ns.yaml:33-35)
+#   - host / remote-node        (paperless-ns.yaml:36-38)
+# So any pod in database or monitoring can reach this HTTP listener
+# directly and set X-Authentik-Username to any value. Do not read this
+# rule as the whole boundary. Narrowing is tracked in REN-28.
 #
 # This is a CiliumNetworkPolicy (not a standard NetworkPolicy) so it
 # composes additively with the cluster's baseline CNP

kubernetes/infrastructure/network-policies/paperless-ns.yaml

@@ -18,6 +18,15 @@ spec:
     # the trust boundary off the gate outpost — see
     # kubernetes/apps/paperless/network-policy.yaml for the
     # gate-specific ingress rule.
+    #
+    # Note: the database and monitoring allows below DO broaden the trust
+    # boundary in the way this note warns about, because endpointSelector
+    # is {} and therefore covers the paperless pod too. They are kept
+    # because both are load-bearing — CNPG reaches the postgres cluster
+    # from `database`, and the blackbox probe of
+    # http://paperless.paperless.svc.cluster.local:80/accounts/login/
+    # (monitoring-rules/probes-blackbox.yaml:250) runs from `monitoring`.
+    # Scoping them to specific pods and ports is tracked in REN-28.
     - fromEndpoints:
         - matchLabels:
             "k8s:io.kubernetes.pod.namespace": database