Merge pull request #64473 from nberlee/master

Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Drop capabilities of CoreDNS container and run in read-only

**What this PR does / why we need it**: Make the CoreDNS container more secure by dropping (root) capabilities. Improve the integrity of the of the container by running the whole container in read-only.

**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes #

**Special notes for your reviewer**:
Same [changes](aba0245609) as in the CoreDNS deployment repository.
**Release note**:

```release-note
Kubeadm: Make CoreDNS run in read-only mode and drop all unneeded privileges 
```

cluster/addons/dns/coredns/coredns.yaml.base

@@ -118,6 +118,7 @@ spec:
         volumeMounts:
         - name: config-volume
           mountPath: /etc/coredns
+          readOnly: true
         ports:
         - containerPort: 53
           name: dns
@@ -137,6 +138,14 @@ spec:
           timeoutSeconds: 5
           successThreshold: 1
           failureThreshold: 5
+        securityContext:
+          allowPrivilegeEscalation: false
+          capabilities:
+            add:
+            - NET_BIND_SERVICE
+            drop:
+            - all
+          readOnlyRootFilesystem: true
       dnsPolicy: Default
       volumes:
         - name: config-volume

cluster/addons/dns/coredns/coredns.yaml.in

@@ -118,6 +118,7 @@ spec:
         volumeMounts:
         - name: config-volume
           mountPath: /etc/coredns
+          readOnly: true
         ports:
         - containerPort: 53
           name: dns
@@ -137,6 +138,14 @@ spec:
           timeoutSeconds: 5
           successThreshold: 1
           failureThreshold: 5
+        securityContext:
+          allowPrivilegeEscalation: false
+          capabilities:
+            add:
+            - NET_BIND_SERVICE
+            drop:
+            - all
+          readOnlyRootFilesystem: true
       dnsPolicy: Default
       volumes:
         - name: config-volume

cluster/addons/dns/coredns/coredns.yaml.sed

@@ -118,6 +118,7 @@ spec:
         volumeMounts:
         - name: config-volume
           mountPath: /etc/coredns
+          readOnly: true
         ports:
         - containerPort: 53
           name: dns
@@ -137,6 +138,14 @@ spec:
           timeoutSeconds: 5
           successThreshold: 1
           failureThreshold: 5
+        securityContext:
+          allowPrivilegeEscalation: false
+          capabilities:
+            add:
+            - NET_BIND_SERVICE
+            drop:
+            - all
+          readOnlyRootFilesystem: true
       dnsPolicy: Default
       volumes:
         - name: config-volume

cmd/kubeadm/app/phases/addons/dns/manifests.go

@@ -259,6 +259,7 @@ spec:
         volumeMounts:
         - name: config-volume
           mountPath: /etc/coredns
+          readOnly: true
         ports:
         - containerPort: 53
           name: dns
@@ -278,6 +279,14 @@ spec:
           timeoutSeconds: 5
           successThreshold: 1
           failureThreshold: 5
+        securityContext:
+          allowPrivilegeEscalation: false
+          capabilities:
+            add:
+            - NET_BIND_SERVICE
+            drop:
+            - all
+          readOnlyRootFilesystem: true
       dnsPolicy: Default
       volumes:
         - name: config-volume