ensure the /etc/os-release is mounted read only

roles/kubernetes/node/templates/kubelet-container.j2

@@ -25,7 +25,7 @@
   -v /var/lib/cni:/var/lib/cni:shared \
   -v /var/run:/var/run:rw \
   -v {{kube_config_dir}}:{{kube_config_dir}}:ro \
-  -v /etc/os-release:/etc/os-release \
+  -v /etc/os-release:/etc/os-release:ro \
   {{ hyperkube_image_repo }}:{{ hyperkube_image_tag}} \
   ./hyperkube kubelet \
   "$@"

roles/kubernetes/node/templates/kubelet.rkt.service.j2

@@ -20,7 +20,7 @@ ExecStartPre=-/bin/mkdir -p /var/lib/kubelet
 EnvironmentFile={{kube_config_dir}}/kubelet.env
 # stage1-fly mounts /proc /sys /dev so no need to duplicate the mounts
 ExecStart=/usr/bin/rkt run \
-        --volume os-release,kind=host,source=/etc/os-release \
+        --volume os-release,kind=host,source=/etc/os-release,readOnly=true \
         --volume dns,kind=host,source=/etc/resolv.conf \
         --volume etc-kubernetes,kind=host,source={{ kube_config_dir }},readOnly=false \
         --volume etc-ssl-certs,kind=host,source=/etc/ssl/certs,readOnly=true \