1 - Apply Pod Security Standards at the Cluster Level

Pod Security admission (PSA) is enabled by default in v1.23 and later, as it has graduated to beta. Pod Security is an admission controller that carries out checks against the Kubernetes Pod Security Standards when new pods are created. This tutorial shows you how to enforce the baseline Pod Security Standard at the cluster level which applies a standard configuration to all namespaces in a cluster.

To apply Pod Security Standards to specific namespaces, refer to Apply Pod Security Standards at the namespace level.

If you are running a version of Kubernetes other than v1.24, check the documentation for that version.

Before you begin

Install the following on your workstation:

Choose the right Pod Security Standard to apply

Pod Security Admission lets you apply built-in Pod Security Standards with the following modes: enforce, audit, and warn.

To gather information that helps you to choose the Pod Security Standards that are most appropriate for your configuration, do the following:

  1. Create a cluster with no Pod Security Standards applied:

    kind create cluster --name psa-wo-cluster-pss --image kindest/node:v1.24.0
    

    The output is similar to this:

    Creating cluster "psa-wo-cluster-pss" ...
    ✓ Ensuring node image (kindest/node:v1.24.0) 🖼
    ✓ Preparing nodes 📦  
    ✓ Writing configuration 📜
    ✓ Starting control-plane 🕹️
    ✓ Installing CNI 🔌
    ✓ Installing StorageClass 💾
    Set kubectl context to "kind-psa-wo-cluster-pss"
    You can now use your cluster with:
    
    kubectl cluster-info --context kind-psa-wo-cluster-pss
    
    Thanks for using kind! 😊
    
  2. Set the kubectl context to the new cluster:

    kubectl cluster-info --context kind-psa-wo-cluster-pss
    

    The output is similar to this:

     Kubernetes control plane is running at https://127.0.0.1:61350
    
    CoreDNS is running at https://127.0.0.1:61350/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy
    
    To further debug and diagnose cluster problems, use 'kubectl cluster-info dump'.
    
  3. Get a list of namespaces in the cluster:

    kubectl get ns
    

    The output is similar to this:

    NAME                 STATUS   AGE
    default              Active   9m30s
    kube-node-lease      Active   9m32s
    kube-public          Active   9m32s
    kube-system          Active   9m32s
    local-path-storage   Active   9m26s
    
  4. Use --dry-run=server to understand what happens when different Pod Security Standards are applied:

    1. Privileged
      kubectl label --dry-run=server --overwrite ns --all \
      pod-security.kubernetes.io/enforce=privileged
      

    The output is similar to this:

    namespace/default labeled
    namespace/kube-node-lease labeled
    namespace/kube-public labeled
    namespace/kube-system labeled
    namespace/local-path-storage labeled
    
    1. Baseline
      kubectl label --dry-run=server --overwrite ns --all \
      pod-security.kubernetes.io/enforce=baseline
      

    The output is similar to this:

    namespace/default labeled
    namespace/kube-node-lease labeled
    namespace/kube-public labeled
    Warning: existing pods in namespace "kube-system" violate the new PodSecurity enforce level "baseline:latest"
    Warning: etcd-psa-wo-cluster-pss-control-plane (and 3 other pods): host namespaces, hostPath volumes
    Warning: kindnet-vzj42: non-default capabilities, host namespaces, hostPath volumes
    Warning: kube-proxy-m6hwf: host namespaces, hostPath volumes, privileged
    namespace/kube-system labeled
    namespace/local-path-storage labeled
    
    1. Restricted
     kubectl label --dry-run=server --overwrite ns --all \
     pod-security.kubernetes.io/enforce=restricted
    

    The output is similar to this:

    namespace/default labeled
    namespace/kube-node-lease labeled
    namespace/kube-public labeled
    Warning: existing pods in namespace "kube-system" violate the new PodSecurity enforce level "restricted:latest"
    Warning: coredns-7bb9c7b568-hsptc (and 1 other pod): unrestricted capabilities, runAsNonRoot != true, seccompProfile
    Warning: etcd-psa-wo-cluster-pss-control-plane (and 3 other pods): host namespaces, hostPath volumes, allowPrivilegeEscalation != false, unrestricted capabilities, restricted volume types, runAsNonRoot != true
    Warning: kindnet-vzj42: non-default capabilities, host namespaces, hostPath volumes, allowPrivilegeEscalation != false, unrestricted capabilities, restricted volume types, runAsNonRoot != true, seccompProfile
    Warning: kube-proxy-m6hwf: host namespaces, hostPath volumes, privileged, allowPrivilegeEscalation != false, unrestricted capabilities, restricted volume types, runAsNonRoot != true, seccompProfile
    namespace/kube-system labeled
    Warning: existing pods in namespace "local-path-storage" violate the new PodSecurity enforce level "restricted:latest"
    Warning: local-path-provisioner-d6d9f7ffc-lw9lh: allowPrivilegeEscalation != false, unrestricted capabilities, runAsNonRoot != true, seccompProfile
    namespace/local-path-storage labeled
    

From the previous output, you'll notice that applying the privileged Pod Security Standard shows no warnings for any namespaces. However, baseline and restricted standards both have warnings, specifically in the kube-system namespace.

Set modes, versions and standards

In this section, you apply the following Pod Security Standards to the latest version:

  • baseline standard in enforce mode.
  • restricted standard in warn and audit mode.

The baseline Pod Security Standard provides a convenient middle ground that allows keeping the exemption list short and prevents known privilege escalations.

Additionally, to prevent pods from failing in kube-system, you'll exempt the namespace from having Pod Security Standards applied.

When you implement Pod Security Admission in your own environment, consider the following:

  1. Based on the risk posture applied to a cluster, a stricter Pod Security Standard like restricted might be a better choice.

  2. Exempting the kube-system namespace allows pods to run as privileged in this namespace. For real world use, the Kubernetes project strongly recommends that you apply strict RBAC policies that limit access to kube-system, following the principle of least privilege. To implement the preceding standards, do the following:

  3. Create a configuration file that can be consumed by the Pod Security Admission Controller to implement these Pod Security Standards:

    mkdir -p /tmp/pss
    cat <<EOF > /tmp/pss/cluster-level-pss.yaml 
    apiVersion: apiserver.config.k8s.io/v1
    kind: AdmissionConfiguration
    plugins:
    - name: PodSecurity
      configuration:
        apiVersion: pod-security.admission.config.k8s.io/v1beta1
        kind: PodSecurityConfiguration
        defaults:
          enforce: "baseline"
          enforce-version: "latest"
          audit: "restricted"
          audit-version: "latest"
          warn: "restricted"
          warn-version: "latest"
        exemptions:
          usernames: []
          runtimeClasses: []
          namespaces: [kube-system]
    EOF
    
  4. Configure the API server to consume this file during cluster creation:

    cat <<EOF > /tmp/pss/cluster-config.yaml 
    kind: Cluster
    apiVersion: kind.x-k8s.io/v1alpha4
    nodes:
    - role: control-plane
      kubeadmConfigPatches:
      - |
        kind: ClusterConfiguration
        apiServer:
            extraArgs:
              admission-control-config-file: /etc/config/cluster-level-pss.yaml
            extraVolumes:
              - name: accf
                hostPath: /etc/config
                mountPath: /etc/config
                readOnly: false
                pathType: "DirectoryOrCreate"
      extraMounts:
      - hostPath: /tmp/pss
        containerPath: /etc/config
        # optional: if set, the mount is read-only.
        # default false
        readOnly: false
        # optional: if set, the mount needs SELinux relabeling.
        # default false
        selinuxRelabel: false
        # optional: set propagation mode (None, HostToContainer or Bidirectional)
        # see https://kubernetes.io/docs/concepts/storage/volumes/#mount-propagation
        # default None
        propagation: None
    EOF
    
  5. Create a cluster that uses Pod Security Admission to apply these Pod Security Standards:

     kind create cluster --name psa-with-cluster-pss --image kindest/node:v1.24.0 --config /tmp/pss/cluster-config.yaml
    

    The output is similar to this:

     Creating cluster "psa-with-cluster-pss" ...
      ✓ Ensuring node image (kindest/node:v1.24.0) 🖼 
      ✓ Preparing nodes 📦  
      ✓ Writing configuration 📜 
      ✓ Starting control-plane 🕹️ 
      ✓ Installing CNI 🔌 
      ✓ Installing StorageClass 💾 
     Set kubectl context to "kind-psa-with-cluster-pss"
     You can now use your cluster with:
    
     kubectl cluster-info --context kind-psa-with-cluster-pss
    
     Have a question, bug, or feature request? Let us know! https://kind.sigs.k8s.io/#community 🙂
    
  6. Point kubectl to the cluster

     kubectl cluster-info --context kind-psa-with-cluster-pss
    

    The output is similar to this:

     Kubernetes control plane is running at https://127.0.0.1:63855
     CoreDNS is running at https://127.0.0.1:63855/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy
    
     To further debug and diagnose cluster problems, use 'kubectl cluster-info dump'.
    
  7. Create the following Pod specification for a minimal configuration in the default namespace:

    cat <<EOF > /tmp/pss/nginx-pod.yaml
    apiVersion: v1
    kind: Pod
    metadata:
      name: nginx
    spec:
      containers:
        - image: nginx
          name: nginx
          ports:
            - containerPort: 80
    EOF
    
  8. Create the Pod in the cluster:

     kubectl apply -f /tmp/pss/nginx-pod.yaml
    

    The output is similar to this:

     Warning: would violate PodSecurity "restricted:latest": allowPrivilegeEscalation != false (container "nginx" must set securityContext.allowPrivilegeEscalation=false), unrestricted capabilities (container "nginx" must set securityContext.capabilities.drop=["ALL"]), runAsNonRoot != true (pod or container "nginx" must set securityContext.runAsNonRoot=true), seccompProfile (pod or container "nginx" must set securityContext.seccompProfile.type to "RuntimeDefault" or "Localhost")
     pod/nginx created
    

Clean up

Run kind delete cluster --name psa-with-cluster-pss and kind delete cluster --name psa-wo-cluster-pss to delete the clusters you created.

What's next

2 - Apply Pod Security Standards at the Namespace Level

Pod Security admission (PSA) is enabled by default in v1.23 and later, as it graduated to beta. Pod Security Admission is an admission controller that applies Pod Security Standards when pods are created. In this tutorial, you will enforce the baseline Pod Security Standard, one namespace at a time.

You can also apply Pod Security Standards to multiple namespaces at once at the cluster level. For instructions, refer to Apply Pod Security Standards at the cluster level.

Before you begin

Install the following on your workstation:

Create cluster

  1. Create a KinD cluster as follows:

    kind create cluster --name psa-ns-level --image kindest/node:v1.23.0
    

    The output is similar to this:

    Creating cluster "psa-ns-level" ...
     ✓ Ensuring node image (kindest/node:v1.23.0) 🖼 
     ✓ Preparing nodes 📦  
     ✓ Writing configuration 📜 
     ✓ Starting control-plane 🕹️ 
     ✓ Installing CNI 🔌 
     ✓ Installing StorageClass 💾 
    Set kubectl context to "kind-psa-ns-level"
    You can now use your cluster with:
    
    kubectl cluster-info --context kind-psa-ns-level
    
    Not sure what to do next? 😅  Check out https://kind.sigs.k8s.io/docs/user/quick-start/
    
  2. Set the kubectl context to the new cluster:

    kubectl cluster-info --context kind-psa-ns-level
    

    The output is similar to this:

    Kubernetes control plane is running at https://127.0.0.1:50996
    CoreDNS is running at https://127.0.0.1:50996/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy
    
    To further debug and diagnose cluster problems, use 'kubectl cluster-info dump'.
    

Create a namespace

Create a new namespace called example:

kubectl create ns example

The output is similar to this:

namespace/example created

Apply Pod Security Standards

  1. Enable Pod Security Standards on this namespace using labels supported by built-in Pod Security Admission. In this step we will warn on baseline pod security standard as per the latest version (default value)

    kubectl label --overwrite ns example \
       pod-security.kubernetes.io/warn=baseline \
       pod-security.kubernetes.io/warn-version=latest
    
  2. Multiple pod security standards can be enabled on any namespace, using labels. Following command will enforce the baseline Pod Security Standard, but warn and audit for restricted Pod Security Standards as per the latest version (default value)

    kubectl label --overwrite ns example \
      pod-security.kubernetes.io/enforce=baseline \
      pod-security.kubernetes.io/enforce-version=latest \
      pod-security.kubernetes.io/warn=restricted \
      pod-security.kubernetes.io/warn-version=latest \
      pod-security.kubernetes.io/audit=restricted \
      pod-security.kubernetes.io/audit-version=latest
    

Verify the Pod Security Standards

  1. Create a minimal pod in example namespace:

    cat <<EOF > /tmp/pss/nginx-pod.yaml
    apiVersion: v1
    kind: Pod
    metadata:
      name: nginx
    spec:
      containers:
        - image: nginx
          name: nginx
          ports:
            - containerPort: 80
    EOF
    
  2. Apply the pod spec to the cluster in example namespace:

    kubectl apply -n example -f /tmp/pss/nginx-pod.yaml
    

    The output is similar to this:

    Warning: would violate PodSecurity "restricted:latest": allowPrivilegeEscalation != false (container "nginx" must set securityContext.allowPrivilegeEscalation=false), unrestricted capabilities (container "nginx" must set securityContext.capabilities.drop=["ALL"]), runAsNonRoot != true (pod or container "nginx" must set securityContext.runAsNonRoot=true), seccompProfile (pod or container "nginx" must set securityContext.seccompProfile.type to "RuntimeDefault" or "Localhost")
    pod/nginx created
    
  3. Apply the pod spec to the cluster in default namespace:

    kubectl apply -n default -f /tmp/pss/nginx-pod.yaml
    

    Output is similar to this:

    pod/nginx created
    

The Pod Security Standards were applied only to the example namespace. You could create the same Pod in the default namespace with no warnings.

Clean up

Run kind delete cluster -name psa-ns-level to delete the cluster created.

What's next

3 - Restrict a Container's Access to Resources with AppArmor

FEATURE STATE: Kubernetes v1.4 [beta]

AppArmor is a Linux kernel security module that supplements the standard Linux user and group based permissions to confine programs to a limited set of resources. AppArmor can be configured for any application to reduce its potential attack surface and provide greater in-depth defense. It is configured through profiles tuned to allow the access needed by a specific program or container, such as Linux capabilities, network access, file permissions, etc. Each profile can be run in either enforcing mode, which blocks access to disallowed resources, or complain mode, which only reports violations.

AppArmor can help you to run a more secure deployment by restricting what containers are allowed to do, and/or provide better auditing through system logs. However, it is important to keep in mind that AppArmor is not a silver bullet and can only do so much to protect against exploits in your application code. It is important to provide good, restrictive profiles, and harden your applications and cluster from other angles as well.

Objectives

  • See an example of how to load a profile on a node
  • Learn how to enforce the profile on a Pod
  • Learn how to check that the profile is loaded
  • See what happens when a profile is violated
  • See what happens when a profile cannot be loaded

Before you begin

Make sure:

  1. Kubernetes version is at least v1.4 -- Kubernetes support for AppArmor was added in v1.4. Kubernetes components older than v1.4 are not aware of the new AppArmor annotations, and will silently ignore any AppArmor settings that are provided. To ensure that your Pods are receiving the expected protections, it is important to verify the Kubelet version of your nodes:

    kubectl get nodes -o=jsonpath=$'{range .items[*]}{@.metadata.name}: {@.status.nodeInfo.kubeletVersion}\n{end}'
    
    gke-test-default-pool-239f5d02-gyn2: v1.4.0
    gke-test-default-pool-239f5d02-x1kf: v1.4.0
    gke-test-default-pool-239f5d02-xwux: v1.4.0
    
  2. AppArmor kernel module is enabled -- For the Linux kernel to enforce an AppArmor profile, the AppArmor kernel module must be installed and enabled. Several distributions enable the module by default, such as Ubuntu and SUSE, and many others provide optional support. To check whether the module is enabled, check the /sys/module/apparmor/parameters/enabled file:

    cat /sys/module/apparmor/parameters/enabled
    Y
    

    If the Kubelet contains AppArmor support (>= v1.4), it will refuse to run a Pod with AppArmor options if the kernel module is not enabled.

  1. Container runtime supports AppArmor -- Currently all common Kubernetes-supported container runtimes should support AppArmor, like Docker, CRI-O or containerd. Please refer to the corresponding runtime documentation and verify that the cluster fulfills the requirements to use AppArmor.

  2. Profile is loaded -- AppArmor is applied to a Pod by specifying an AppArmor profile that each container should be run with. If any of the specified profiles is not already loaded in the kernel, the Kubelet (>= v1.4) will reject the Pod. You can view which profiles are loaded on a node by checking the /sys/kernel/security/apparmor/profiles file. For example:

    ssh gke-test-default-pool-239f5d02-gyn2 "sudo cat /sys/kernel/security/apparmor/profiles | sort"
    
    apparmor-test-deny-write (enforce)
    apparmor-test-audit-write (enforce)
    docker-default (enforce)
    k8s-nginx (enforce)
    

    For more details on loading profiles on nodes, see Setting up nodes with profiles.

As long as the Kubelet version includes AppArmor support (>= v1.4), the Kubelet will reject a Pod with AppArmor options if any of the prerequisites are not met. You can also verify AppArmor support on nodes by checking the node ready condition message (though this is likely to be removed in a later release):

kubectl get nodes -o=jsonpath=$'{range .items[*]}{@.metadata.name}: {.status.conditions[?(@.reason=="KubeletReady")].message}\n{end}'
gke-test-default-pool-239f5d02-gyn2: kubelet is posting ready status. AppArmor enabled
gke-test-default-pool-239f5d02-x1kf: kubelet is posting ready status. AppArmor enabled
gke-test-default-pool-239f5d02-xwux: kubelet is posting ready status. AppArmor enabled

Securing a Pod

AppArmor profiles are specified per-container. To specify the AppArmor profile to run a Pod container with, add an annotation to the Pod's metadata:

container.apparmor.security.beta.kubernetes.io/<container_name>: <profile_ref>

Where <container_name> is the name of the container to apply the profile to, and <profile_ref> specifies the profile to apply. The profile_ref can be one of:

  • runtime/default to apply the runtime's default profile
  • localhost/<profile_name> to apply the profile loaded on the host with the name <profile_name>
  • unconfined to indicate that no profiles will be loaded

See the API Reference for the full details on the annotation and profile name formats.

Kubernetes AppArmor enforcement works by first checking that all the prerequisites have been met, and then forwarding the profile selection to the container runtime for enforcement. If the prerequisites have not been met, the Pod will be rejected, and will not run.

To verify that the profile was applied, you can look for the AppArmor security option listed in the container created event:

kubectl get events | grep Created
22s        22s         1         hello-apparmor     Pod       spec.containers{hello}   Normal    Created     {kubelet e2e-test-stclair-node-pool-31nt}   Created container with docker id 269a53b202d3; Security:[seccomp=unconfined apparmor=k8s-apparmor-example-deny-write]

You can also verify directly that the container's root process is running with the correct profile by checking its proc attr:

kubectl exec <pod_name> cat /proc/1/attr/current
k8s-apparmor-example-deny-write (enforce)

Example

This example assumes you have already set up a cluster with AppArmor support.

First, we need to load the profile we want to use onto our nodes. This profile denies all file writes:

#include <tunables/global>

profile k8s-apparmor-example-deny-write flags=(attach_disconnected) {
  #include <abstractions/base>

  file,

  # Deny all file writes.
  deny /** w,
}

Since we don't know where the Pod will be scheduled, we'll need to load the profile on all our nodes. For this example we'll use SSH to install the profiles, but other approaches are discussed in Setting up nodes with profiles.

NODES=(
    # The SSH-accessible domain names of your nodes
    gke-test-default-pool-239f5d02-gyn2.us-central1-a.my-k8s
    gke-test-default-pool-239f5d02-x1kf.us-central1-a.my-k8s
    gke-test-default-pool-239f5d02-xwux.us-central1-a.my-k8s)
for NODE in ${NODES[*]}; do ssh $NODE 'sudo apparmor_parser -q <<EOF
#include <tunables/global>

profile k8s-apparmor-example-deny-write flags=(attach_disconnected) {
  #include <abstractions/base>

  file,

  # Deny all file writes.
  deny /** w,
}
EOF'
done

Next, we'll run a simple "Hello AppArmor" pod with the deny-write profile:

apiVersion: v1
kind: Pod
metadata:
  name: hello-apparmor
  annotations:
    # Tell Kubernetes to apply the AppArmor profile "k8s-apparmor-example-deny-write".
    # Note that this is ignored if the Kubernetes node is not running version 1.4 or greater.
    container.apparmor.security.beta.kubernetes.io/hello: localhost/k8s-apparmor-example-deny-write
spec:
  containers:
  - name: hello
    image: busybox:1.28
    command: [ "sh", "-c", "echo 'Hello AppArmor!' && sleep 1h" ]
kubectl create -f ./hello-apparmor.yaml

If we look at the pod events, we can see that the Pod container was created with the AppArmor profile "k8s-apparmor-example-deny-write":

kubectl get events | grep hello-apparmor
14s        14s         1         hello-apparmor   Pod                                Normal    Scheduled   {default-scheduler }                           Successfully assigned hello-apparmor to gke-test-default-pool-239f5d02-gyn2
14s        14s         1         hello-apparmor   Pod       spec.containers{hello}   Normal    Pulling     {kubelet gke-test-default-pool-239f5d02-gyn2}   pulling image "busybox"
13s        13s         1         hello-apparmor   Pod       spec.containers{hello}   Normal    Pulled      {kubelet gke-test-default-pool-239f5d02-gyn2}   Successfully pulled image "busybox"
13s        13s         1         hello-apparmor   Pod       spec.containers{hello}   Normal    Created     {kubelet gke-test-default-pool-239f5d02-gyn2}   Created container with docker id 06b6cd1c0989; Security:[seccomp=unconfined apparmor=k8s-apparmor-example-deny-write]
13s        13s         1         hello-apparmor   Pod       spec.containers{hello}   Normal    Started     {kubelet gke-test-default-pool-239f5d02-gyn2}   Started container with docker id 06b6cd1c0989

We can verify that the container is actually running with that profile by checking its proc attr:

kubectl exec hello-apparmor -- cat /proc/1/attr/current
k8s-apparmor-example-deny-write (enforce)

Finally, we can see what happens if we try to violate the profile by writing to a file:

kubectl exec hello-apparmor -- touch /tmp/test
touch: /tmp/test: Permission denied
error: error executing remote command: command terminated with non-zero exit code: Error executing in Docker Container: 1

To wrap up, let's look at what happens if we try to specify a profile that hasn't been loaded:

kubectl create -f /dev/stdin <<EOF
apiVersion: v1
kind: Pod
metadata:
  name: hello-apparmor-2
  annotations:
    container.apparmor.security.beta.kubernetes.io/hello: localhost/k8s-apparmor-example-allow-write
spec:
  containers:
  - name: hello
    image: busybox:1.28
    command: [ "sh", "-c", "echo 'Hello AppArmor!' && sleep 1h" ]
EOF
pod/hello-apparmor-2 created
kubectl describe pod hello-apparmor-2
Name:          hello-apparmor-2
Namespace:     default
Node:          gke-test-default-pool-239f5d02-x1kf/
Start Time:    Tue, 30 Aug 2016 17:58:56 -0700
Labels:        <none>
Annotations:   container.apparmor.security.beta.kubernetes.io/hello=localhost/k8s-apparmor-example-allow-write
Status:        Pending
Reason:        AppArmor
Message:       Pod Cannot enforce AppArmor: profile "k8s-apparmor-example-allow-write" is not loaded
IP:
Controllers:   <none>
Containers:
  hello:
    Container ID:
    Image:     busybox
    Image ID:
    Port:
    Command:
      sh
      -c
      echo 'Hello AppArmor!' && sleep 1h
    State:              Waiting
      Reason:           Blocked
    Ready:              False
    Restart Count:      0
    Environment:        <none>
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-dnz7v (ro)
Conditions:
  Type          Status
  Initialized   True
  Ready         False
  PodScheduled  True
Volumes:
  default-token-dnz7v:
    Type:    Secret (a volume populated by a Secret)
    SecretName:    default-token-dnz7v
    Optional:   false
QoS Class:      BestEffort
Node-Selectors: <none>
Tolerations:    <none>
Events:
  FirstSeen    LastSeen    Count    From                        SubobjectPath    Type        Reason        Message
  ---------    --------    -----    ----                        -------------    --------    ------        -------
  23s          23s         1        {default-scheduler }                         Normal      Scheduled     Successfully assigned hello-apparmor-2 to e2e-test-stclair-node-pool-t1f5
  23s          23s         1        {kubelet e2e-test-stclair-node-pool-t1f5}             Warning        AppArmor    Cannot enforce AppArmor: profile "k8s-apparmor-example-allow-write" is not loaded

Note the pod status is Pending, with a helpful error message: Pod Cannot enforce AppArmor: profile "k8s-apparmor-example-allow-write" is not loaded. An event was also recorded with the same message.

Administration

Setting up nodes with profiles

Kubernetes does not currently provide any native mechanisms for loading AppArmor profiles onto nodes. There are lots of ways to set up the profiles though, such as:

  • Through a DaemonSet that runs a Pod on each node to ensure the correct profiles are loaded. An example implementation can be found here.
  • At node initialization time, using your node initialization scripts (e.g. Salt, Ansible, etc.) or image.
  • By copying the profiles to each node and loading them through SSH, as demonstrated in the Example.

The scheduler is not aware of which profiles are loaded onto which node, so the full set of profiles must be loaded onto every node. An alternative approach is to add a node label for each profile (or class of profiles) on the node, and use a node selector to ensure the Pod is run on a node with the required profile.

Restricting profiles with the PodSecurityPolicy

If the PodSecurityPolicy extension is enabled, cluster-wide AppArmor restrictions can be applied. To enable the PodSecurityPolicy, the following flag must be set on the apiserver:

--enable-admission-plugins=PodSecurityPolicy[,others...]

The AppArmor options can be specified as annotations on the PodSecurityPolicy:

apparmor.security.beta.kubernetes.io/defaultProfileName: <profile_ref>
apparmor.security.beta.kubernetes.io/allowedProfileNames: <profile_ref>[,others...]

The default profile name option specifies the profile to apply to containers by default when none is specified. The allowed profile names option specifies a list of profiles that Pod containers are allowed to be run with. If both options are provided, the default must be allowed. The profiles are specified in the same format as on containers. See the API Reference for the full specification.

Disabling AppArmor

If you do not want AppArmor to be available on your cluster, it can be disabled by a command-line flag:

--feature-gates=AppArmor=false

When disabled, any Pod that includes an AppArmor profile will fail validation with a "Forbidden" error.

Authoring Profiles

Getting AppArmor profiles specified correctly can be a tricky business. Fortunately there are some tools to help with that:

  • aa-genprof and aa-logprof generate profile rules by monitoring an application's activity and logs, and admitting the actions it takes. Further instructions are provided by the AppArmor documentation.
  • bane is an AppArmor profile generator for Docker that uses a simplified profile language.

To debug problems with AppArmor, you can check the system logs to see what, specifically, was denied. AppArmor logs verbose messages to dmesg, and errors can usually be found in the system logs or through journalctl. More information is provided in AppArmor failures.

API Reference

Pod Annotation

Specifying the profile a container will run with:

  • key: container.apparmor.security.beta.kubernetes.io/<container_name> Where <container_name> matches the name of a container in the Pod. A separate profile can be specified for each container in the Pod.
  • value: a profile reference, described below

Profile Reference

  • runtime/default: Refers to the default runtime profile.
  • localhost/<profile_name>: Refers to a profile loaded on the node (localhost) by name.
  • unconfined: This effectively disables AppArmor on the container.

Any other profile reference format is invalid.

PodSecurityPolicy Annotations

Specifying the default profile to apply to containers when none is provided:

  • key: apparmor.security.beta.kubernetes.io/defaultProfileName
  • value: a profile reference, described above

Specifying the list of profiles Pod containers is allowed to specify:

  • key: apparmor.security.beta.kubernetes.io/allowedProfileNames
  • value: a comma-separated list of profile references (described above)
    • Although an escaped comma is a legal character in a profile name, it cannot be explicitly allowed here.

What's next

Additional resources:

4 - Restrict a Container's Syscalls with seccomp

FEATURE STATE: Kubernetes v1.19 [stable]

Seccomp stands for secure computing mode and has been a feature of the Linux kernel since version 2.6.12. It can be used to sandbox the privileges of a process, restricting the calls it is able to make from userspace into the kernel. Kubernetes lets you automatically apply seccomp profiles loaded onto a node to your Pods and containers.

Identifying the privileges required for your workloads can be difficult. In this tutorial, you will go through how to load seccomp profiles into a local Kubernetes cluster, how to apply them to a Pod, and how you can begin to craft profiles that give only the necessary privileges to your container processes.

Objectives

  • Learn how to load seccomp profiles on a node
  • Learn how to apply a seccomp profile to a container
  • Observe auditing of syscalls made by a container process
  • Observe behavior when a missing profile is specified
  • Observe a violation of a seccomp profile
  • Learn how to create fine-grained seccomp profiles
  • Learn how to apply a container runtime default seccomp profile

Before you begin

In order to complete all steps in this tutorial, you must install kind and kubectl.

This tutorial shows some examples that are still alpha (since v1.22) and others that use only generally available seccomp functionality. You should make sure that your cluster is configured correctly for the version you are using.

The tutorial also uses the curl tool for downloading examples to your computer. You can adapt the steps to use a different tool if you prefer.

Download example seccomp profiles

The contents of these profiles will be explored later on, but for now go ahead and download them into a directory named profiles/ so that they can be loaded into the cluster.

{
    "defaultAction": "SCMP_ACT_LOG"
}

{
    "defaultAction": "SCMP_ACT_ERRNO"
}

{
    "defaultAction": "SCMP_ACT_ERRNO",
    "architectures": [
        "SCMP_ARCH_X86_64",
        "SCMP_ARCH_X86",
        "SCMP_ARCH_X32"
    ],
    "syscalls": [
        {
            "names": [
                "accept4",
                "epoll_wait",
                "pselect6",
                "futex",
                "madvise",
                "epoll_ctl",
                "getsockname",
                "setsockopt",
                "vfork",
                "mmap",
                "read",
                "write",
                "close",
                "arch_prctl",
                "sched_getaffinity",
                "munmap",
                "brk",
                "rt_sigaction",
                "rt_sigprocmask",
                "sigaltstack",
                "gettid",
                "clone",
                "bind",
                "socket",
                "openat",
                "readlinkat",
                "exit_group",
                "epoll_create1",
                "listen",
                "rt_sigreturn",
                "sched_yield",
                "clock_gettime",
                "connect",
                "dup2",
                "epoll_pwait",
                "execve",
                "exit",
                "fcntl",
                "getpid",
                "getuid",
                "ioctl",
                "mprotect",
                "nanosleep",
                "open",
                "poll",
                "recvfrom",
                "sendto",
                "set_tid_address",
                "setitimer",
                "writev"
            ],
            "action": "SCMP_ACT_ALLOW"
        }
    ]
}

Run these commands:

mkdir ./profiles
curl -L -o profiles/audit.json https://k8s.io/examples/pods/security/seccomp/profiles/audit.json
curl -L -o profiles/violation.json https://k8s.io/examples/pods/security/seccomp/profiles/violation.json
curl -L -o profiles/fine-grained.json https://k8s.io/examples/pods/security/seccomp/profiles/fine-grained.json
ls profiles

You should see three profiles listed at the end of the final step:

audit.json  fine-grained.json  violation.json

Create a local Kubernetes cluster with kind

For simplicity, kind can be used to create a single node cluster with the seccomp profiles loaded. Kind runs Kubernetes in Docker, so each node of the cluster is a container. This allows for files to be mounted in the filesystem of each container similar to loading files onto a node.

apiVersion: kind.x-k8s.io/v1alpha4
kind: Cluster
nodes:
- role: control-plane
  extraMounts:
  - hostPath: "./profiles"
    containerPath: "/var/lib/kubelet/seccomp/profiles"

Download that example kind configuration, and save it to a file named kind.yaml:

curl -L -O https://k8s.io/examples/pods/security/seccomp/kind.yaml

You can set a specific Kubernetes version by setting the node's container image. See Nodes within the kind documentation about configuration for more details on this. This tutorial assumes you are using Kubernetes v1.24.

As an alpha feature, you can configure Kubernetes to use the profile that the container runtime prefers by default, rather than falling back to Unconfined. If you want to try that, see enable the use of RuntimeDefault as the default seccomp profile for all workloads before you continue.

Once you have a kind configuration in place, create the kind cluster with that configuration:

kind create cluster --config=kind.yaml

After the new Kubernetes cluster is ready, identify the Docker container running as the single node cluster:

docker ps

You should see output indicating that a container is running with name kind-control-plane. The output is similar to:

CONTAINER ID        IMAGE                  COMMAND                  CREATED             STATUS              PORTS                       NAMES
6a96207fed4b        kindest/node:v1.18.2   "/usr/local/bin/entr…"   27 seconds ago      Up 24 seconds       127.0.0.1:42223->6443/tcp   kind-control-plane

If observing the filesystem of that container, you should see that the profiles/ directory has been successfully loaded into the default seccomp path of the kubelet. Use docker exec to run a command in the Pod:

# Change 6a96207fed4b to the container ID you saw from "docker ps"
docker exec -it 6a96207fed4b ls /var/lib/kubelet/seccomp/profiles
audit.json  fine-grained.json  violation.json

You have verified that these seccomp profiles are available to the kubelet running within kind.

Enable the use of RuntimeDefault as the default seccomp profile for all workloads

FEATURE STATE: Kubernetes v1.22 [alpha]

SeccompDefault is an optional kubelet feature gate as well as corresponding --seccomp-default command line flag. Both have to be enabled simultaneously to use the feature.

If enabled, the kubelet will use the RuntimeDefault seccomp profile by default, which is defined by the container runtime, instead of using the Unconfined (seccomp disabled) mode. The default profiles aim to provide a strong set of security defaults while preserving the functionality of the workload. It is possible that the default profiles differ between container runtimes and their release versions, for example when comparing those from CRI-O and containerd.

Some workloads may require a lower amount of syscall restrictions than others. This means that they can fail during runtime even with the RuntimeDefault profile. To mitigate such a failure, you can:

  • Run the workload explicitly as Unconfined.
  • Disable the SeccompDefault feature for the nodes. Also making sure that workloads get scheduled on nodes where the feature is disabled.
  • Create a custom seccomp profile for the workload.

If you were introducing this feature into production-like cluster, the Kubernetes project recommends that you enable this feature gate on a subset of your nodes and then test workload execution before rolling the change out cluster-wide.

More detailed information about a possible upgrade and downgrade strategy can be found in the related Kubernetes Enhancement Proposal (KEP).

Since the feature is in alpha state it is disabled per default. To enable it, pass the flags --feature-gates=SeccompDefault=true --seccomp-default to the kubelet CLI or enable it via the kubelet configuration file. To enable the feature gate in kind, ensure that kind provides the minimum required Kubernetes version and enables the SeccompDefault feature in the kind configuration:

kind: Cluster
apiVersion: kind.x-k8s.io/v1alpha4
featureGates:
  SeccompDefault: true
nodes:
  - role: control-plane
    image: kindest/node:v1.23.0@sha256:49824ab1727c04e56a21a5d8372a402fcd32ea51ac96a2706a12af38934f81ac
    kubeadmConfigPatches:
      - |
        kind: JoinConfiguration
        nodeRegistration:
          kubeletExtraArgs:
            seccomp-default: "true"        
  - role: worker
    image: kindest/node:v1.23.0@sha256:49824ab1727c04e56a21a5d8372a402fcd32ea51ac96a2706a12af38934f81ac
    kubeadmConfigPatches:
      - |
        kind: JoinConfiguration
        nodeRegistration:
          kubeletExtraArgs:
            feature-gates: SeccompDefault=true
            seccomp-default: "true"        

If the cluster is ready, then running a pod:

kubectl run --rm -it --restart=Never --image=alpine alpine -- sh

Should now have the default seccomp profile attached. This can be verified by using docker exec to run crictl inspect for the container on the kind worker:

docker exec -it kind-worker bash -c \
    'crictl inspect $(crictl ps --name=alpine -q) | jq .info.runtimeSpec.linux.seccomp'
{
  "defaultAction": "SCMP_ACT_ERRNO",
  "architectures": ["SCMP_ARCH_X86_64", "SCMP_ARCH_X86", "SCMP_ARCH_X32"],
  "syscalls": [
    {
      "names": ["..."]
    }
  ]
}

Create a Pod with a seccomp profile for syscall auditing

To start off, apply the audit.json profile, which will log all syscalls of the process, to a new Pod.

Here's a manifest for that Pod:

apiVersion: v1
kind: Pod
metadata:
  name: audit-pod
  labels:
    app: audit-pod
spec:
  securityContext:
    seccompProfile:
      type: Localhost
      localhostProfile: profiles/audit.json
  containers:
  - name: test-container
    image: hashicorp/http-echo:0.2.3
    args:
    - "-text=just made some syscalls!"
    securityContext:
      allowPrivilegeEscalation: false

Create the Pod in the cluster:

kubectl apply -f https://k8s.io/examples/pods/security/seccomp/ga/audit-pod.yaml

This profile does not restrict any syscalls, so the Pod should start successfully.

kubectl get pod/audit-pod
NAME        READY   STATUS    RESTARTS   AGE
audit-pod   1/1     Running   0          30s

In order to be able to interact with this endpoint exposed by this container, create a NodePort Services that allows access to the endpoint from inside the kind control plane container.

kubectl expose pod audit-pod --type NodePort --port 5678

Check what port the Service has been assigned on the node.

kubectl get service audit-pod

The output is similar to:

NAME        TYPE       CLUSTER-IP      EXTERNAL-IP   PORT(S)          AGE
audit-pod   NodePort   10.111.36.142   <none>        5678:32373/TCP   72s

Now you can use curl to access that endpoint from inside the kind control plane container, at the port exposed by this Service. Use docker exec to run the curl command within the container belonging to that control plane container:

# Change 6a96207fed4b to the control plane container ID you saw from "docker ps"
docker exec -it 6a96207fed4b curl localhost:32373
just made some syscalls!

You can see that the process is running, but what syscalls did it actually make? Because this Pod is running in a local cluster, you should be able to see those in /var/log/syslog. Open up a new terminal window and tail the output for calls from http-echo:

tail -f /var/log/syslog | grep 'http-echo'

You should already see some logs of syscalls made by http-echo, and if you curl the endpoint in the control plane container you will see more written.

For example:

Jul  6 15:37:40 my-machine kernel: [369128.669452] audit: type=1326 audit(1594067860.484:14536): auid=4294967295 uid=0 gid=0 ses=4294967295 pid=29064 comm="http-echo" exe="/http-echo" sig=0 arch=c000003e syscall=51 compat=0 ip=0x46fe1f code=0x7ffc0000
Jul  6 15:37:40 my-machine kernel: [369128.669453] audit: type=1326 audit(1594067860.484:14537): auid=4294967295 uid=0 gid=0 ses=4294967295 pid=29064 comm="http-echo" exe="/http-echo" sig=0 arch=c000003e syscall=54 compat=0 ip=0x46fdba code=0x7ffc0000
Jul  6 15:37:40 my-machine kernel: [369128.669455] audit: type=1326 audit(1594067860.484:14538): auid=4294967295 uid=0 gid=0 ses=4294967295 pid=29064 comm="http-echo" exe="/http-echo" sig=0 arch=c000003e syscall=202 compat=0 ip=0x455e53 code=0x7ffc0000
Jul  6 15:37:40 my-machine kernel: [369128.669456] audit: type=1326 audit(1594067860.484:14539): auid=4294967295 uid=0 gid=0 ses=4294967295 pid=29064 comm="http-echo" exe="/http-echo" sig=0 arch=c000003e syscall=288 compat=0 ip=0x46fdba code=0x7ffc0000
Jul  6 15:37:40 my-machine kernel: [369128.669517] audit: type=1326 audit(1594067860.484:14540): auid=4294967295 uid=0 gid=0 ses=4294967295 pid=29064 comm="http-echo" exe="/http-echo" sig=0 arch=c000003e syscall=0 compat=0 ip=0x46fd44 code=0x7ffc0000
Jul  6 15:37:40 my-machine kernel: [369128.669519] audit: type=1326 audit(1594067860.484:14541): auid=4294967295 uid=0 gid=0 ses=4294967295 pid=29064 comm="http-echo" exe="/http-echo" sig=0 arch=c000003e syscall=270 compat=0 ip=0x4559b1 code=0x7ffc0000
Jul  6 15:38:40 my-machine kernel: [369188.671648] audit: type=1326 audit(1594067920.488:14559): auid=4294967295 uid=0 gid=0 ses=4294967295 pid=29064 comm="http-echo" exe="/http-echo" sig=0 arch=c000003e syscall=270 compat=0 ip=0x4559b1 code=0x7ffc0000
Jul  6 15:38:40 my-machine kernel: [369188.671726] audit: type=1326 audit(1594067920.488:14560): auid=4294967295 uid=0 gid=0 ses=4294967295 pid=29064 comm="http-echo" exe="/http-echo" sig=0 arch=c000003e syscall=202 compat=0 ip=0x455e53 code=0x7ffc0000

You can begin to understand the syscalls required by the http-echo process by looking at the syscall= entry on each line. While these are unlikely to encompass all syscalls it uses, it can serve as a basis for a seccomp profile for this container.

Clean up that Pod and Service before moving to the next section:

kubectl delete service audit-pod --wait
kubectl delete pod audit-pod --wait --now

Create Pod with seccomp profile that causes violation

For demonstration, apply a profile to the Pod that does not allow for any syscalls.

The manifest for this demonstration is:

apiVersion: v1
kind: Pod
metadata:
  name: violation-pod
  labels:
    app: violation-pod
spec:
  securityContext:
    seccompProfile:
      type: Localhost
      localhostProfile: profiles/violation.json
  containers:
  - name: test-container
    image: hashicorp/http-echo:0.2.3
    args:
    - "-text=just made some syscalls!"
    securityContext:
      allowPrivilegeEscalation: false

Attempt to create the Pod in the cluster:

kubectl apply -f https://k8s.io/examples/pods/security/seccomp/ga/violation-pod.yaml

The Pod creates, but there is an issue. If you check the status of the Pod, you should see that it failed to start.

kubectl get pod/violation-pod
NAME            READY   STATUS             RESTARTS   AGE
violation-pod   0/1     CrashLoopBackOff   1          6s

As seen in the previous example, the http-echo process requires quite a few syscalls. Here seccomp has been instructed to error on any syscall by setting "defaultAction": "SCMP_ACT_ERRNO". This is extremely secure, but removes the ability to do anything meaningful. What you really want is to give workloads only the privileges they need.

Clean up that Pod before moving to the next section:

kubectl delete pod violation-pod --wait --now

Create Pod with seccomp profile that only allows necessary syscalls

If you take a look at the fine-grained.json profile, you will notice some of the syscalls seen in syslog of the first example where the profile set "defaultAction": "SCMP_ACT_LOG". Now the profile is setting "defaultAction": "SCMP_ACT_ERRNO", but explicitly allowing a set of syscalls in the "action": "SCMP_ACT_ALLOW" block. Ideally, the container will run successfully and you will see no messages sent to syslog.

The manifest for this example is:

apiVersion: v1
kind: Pod
metadata:
  name: fine-pod
  labels:
    app: fine-pod
spec:
  securityContext:
    seccompProfile:
      type: Localhost
      localhostProfile: profiles/fine-grained.json
  containers:
  - name: test-container
    image: hashicorp/http-echo:0.2.3
    args:
    - "-text=just made some syscalls!"
    securityContext:
      allowPrivilegeEscalation: false

Create the Pod in your cluster:

kubectl apply -f https://k8s.io/examples/pods/security/seccomp/ga/fine-pod.yaml
kubectl get pod fine-pod

The Pod should be showing as having started successfully:

NAME        READY   STATUS    RESTARTS   AGE
fine-pod   1/1     Running   0          30s

Open up a new terminal window and use tail to monitor for log entries that mention calls from http-echo:

# The log path on your computer might be different from "/var/log/syslog"
tail -f /var/log/syslog | grep 'http-echo'

Next, expose the Pod with a NodePort Service:

kubectl expose pod fine-pod --type NodePort --port 5678

Check what port the Service has been assigned on the node:

kubectl get service fine-pod

The output is similar to:

NAME        TYPE       CLUSTER-IP      EXTERNAL-IP   PORT(S)          AGE
fine-pod    NodePort   10.111.36.142   <none>        5678:32373/TCP   72s

Use curl to access that endpoint from inside the kind control plane container:

# Change 6a96207fed4b to the control plane container ID you saw from "docker ps"
docker exec -it 6a96207fed4b curl localhost:32373
just made some syscalls!

You should see no output in the syslog. This is because the profile allowed all necessary syscalls and specified that an error should occur if one outside of the list is invoked. This is an ideal situation from a security perspective, but required some effort in analyzing the program. It would be nice if there was a simple way to get closer to this security without requiring as much effort.

Clean up that Pod and Service before moving to the next section:

kubectl delete service fine-pod --wait
kubectl delete pod fine-pod --wait --now

Create Pod that uses the container runtime default seccomp profile

Most container runtimes provide a sane set of default syscalls that are allowed or not. You can adopt these defaults for your workload by setting the seccomp type in the security context of a pod or container to RuntimeDefault.

Here's a manifest for a Pod that requests the RuntimeDefault seccomp profile for all its containers:

apiVersion: v1
kind: Pod
metadata:
  name: default-pod
  labels:
    app: default-pod
spec:
  securityContext:
    seccompProfile:
      type: RuntimeDefault
  containers:
  - name: test-container
    image: hashicorp/http-echo:0.2.3
    args:
    - "-text=just made some more syscalls!"
    securityContext:
      allowPrivilegeEscalation: false

Create that Pod:

kubectl apply -f https://k8s.io/examples/pods/security/seccomp/ga/default-pod.yaml
kubectl get pod default-pod

The Pod should be showing as having started successfully:

NAME        READY   STATUS    RESTARTS   AGE
default-pod 1/1     Running   0          20s

Finally, now that you saw that work OK, clean up:

kubectl delete pod default-pod --wait --now

What's next

You can learn more about Linux seccomp: