daemon: firewall pods

This introduces a new tc rule that blocks traffic from outside the
cluster targeting pod IPs directly. It requires an adjustment of the BPF
filter priority to above 32, which is expected to be set by the
Constellation Helm installer.

install/kubernetes/cilium/templates/cilium-agent/daemonset.yaml

@@ -740,6 +740,37 @@ spec:
           - name: cni-path
             mountPath: /host/opt/cni/bin
       {{- end }} # .Values.cni.install
+      - name: firewall-pods
+        image: {{ include "cilium.image" .Values.image | quote }}
+        imagePullPolicy: IfNotPresent
+        command:
+        - /bin/bash
+        - -exc
+        - |
+          pref=32
+          interface=$(ip route | awk '/^default/ { print $5 }')
+          tc qdisc add dev "${interface}" clsact || true
+          tc filter del dev "${interface}" ingress pref "${pref}" 2>/dev/null || true
+          handle=0
+          for cidr in ${POD_CIDRS}; do
+            handle=$((handle + 1))
+            tc filter replace dev "${interface}" ingress pref "${pref}" handle "${handle}" protocol ip flower dst_ip "${cidr}" action drop
+          done
+        env:
+        - name: POD_CIDRS
+          valueFrom:
+            configMapKeyRef:
+              key: encryption-strict-mode-pod-cidrs
+              name: cilium-config
+              optional: true
+        resources:
+          requests:
+            cpu: 100m
+            memory: 20Mi
+        securityContext:
+          capabilities:
+            add:
+            - NET_ADMIN
       restartPolicy: Always
       priorityClassName: {{ include "cilium.priorityClass" (list $ .Values.priorityClassName "system-node-critical") }}
       serviceAccount: {{ .Values.serviceAccounts.cilium.name | quote }}