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Refresh AppArmor documentation

pull/45471/head
Tim Allclair 2024-02-16 11:49:16 -08:00
parent 5341afa4eb
commit 49ace75b78
2 changed files with 42 additions and 155 deletions
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196
content/en/docs/tutorials/security/apparmor.md
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@ -11,7 +11,7 @@ weight: 30
{{< feature-state for_k8s_version="v1.4" state="beta" >}}
AppArmor is a Linux kernel security module that supplements the standard Linux user and group based
[AppArmor](https://apparmor.net/) 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,
@ -19,7 +19,7 @@ such as Linux capabilities, network access, file permissions, etc. Each profile
*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
On Kubernetes, 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
@ -41,23 +41,10 @@ applications and cluster from other angles as well.
## {{% heading "prerequisites" %}}
Make sure:
AppArmor is an optional kernel module and Kubernetes feature, so verify it is supported on your
nodes before proceeding:
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:
```shell
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
1. 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:
@ -67,24 +54,17 @@ Make sure:
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.
{{< note >}}
Ubuntu carries many AppArmor patches that have not been merged into the upstream Linux
kernel, including patches that add additional hooks and features. Kubernetes has only been
tested with the upstream version, and does not promise support for other features.
{{< /note >}}
The Kubelet will verify that AppArmor is enabled on the host before admitting a pod with AppArmor
explicitly configured.
3. Container runtime supports AppArmor -- Currently all common Kubernetes-supported container
runtimes should support AppArmor, like {{< glossary_tooltip term_id="docker">}},
{{< glossary_tooltip term_id="cri-o" >}} or {{< glossary_tooltip term_id="containerd" >}}.
Please refer to the corresponding runtime documentation and verify that the cluster fulfills
the requirements to use AppArmor.
runtimes should support AppArmor, including {{< glossary_tooltip term_id="containerd" >}} and
{{< glossary_tooltip term_id="cri-o" >}}. Please refer to the corresponding runtime
documentation and verify that the cluster fulfills the requirements to use AppArmor.
4. 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
kernel, the Kubelet 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:
```shell
@ -100,22 +80,6 @@ Make sure:
For more details on loading profiles on nodes, see
[Setting up nodes with profiles](#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):
```shell
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
```
<!-- lessoncontent -->
## Securing a Pod
@ -141,24 +105,15 @@ specifies the profile to apply. The `profile_ref` can be one of:
See the [API Reference](#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:
```shell
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:
To verify that the profile was applied, you can check that the container's root process is
running with the correct profile by examining its proc attr:
```shell
kubectl exec <pod_name> -- cat /proc/1/attr/current
```
The output should look something like this:
```
k8s-apparmor-example-deny-write (enforce)
```
@ -169,7 +124,7 @@ k8s-apparmor-example-deny-write (enforce)
First, we need to load the profile we want to use onto our nodes. This profile denies all file writes:
```shell
```
#include <tunables/global>
profile k8s-apparmor-example-deny-write flags=(attach_disconnected) {
@ -187,11 +142,9 @@ nodes. For this example we'll use SSH to install the profiles, but other approac
discussed in [Setting up nodes with profiles](#setting-up-nodes-with-profiles).
```shell
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)
# This example assumes that node names match host names, and are reachable via SSH.
NODES=($(kubectl get nodes -o name))
for NODE in ${NODES[*]}; do ssh $NODE 'sudo apparmor_parser -q <<EOF
#include <tunables/global>
@ -212,21 +165,7 @@ Next, we'll run a simple "Hello AppArmor" pod with the deny-write profile:
{{% code_sample file="pods/security/hello-apparmor.yaml" %}}
```shell
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":
```shell
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
kubectl create -f hello-apparmor.yaml
```
We can verify that the container is actually running with that profile by checking its proc attr:
@ -252,8 +191,6 @@ To wrap up, let's look at what happens if we try to specify a profile that hasn'
```shell
kubectl create -f /dev/stdin <<EOF
```
```yaml
apiVersion: v1
kind: Pod
metadata:
@ -266,78 +203,47 @@ spec:
image: busybox:1.28
command: [ "sh", "-c", "echo 'Hello AppArmor!' && sleep 1h" ]
EOF
```
```
pod/hello-apparmor-2 created
```
Although the pod was created successfully, further examination will show that it is stuck in pending:
```shell
kubectl describe pod hello-apparmor-2
```
```
Name: hello-apparmor-2
Namespace: default
Node: gke-test-default-pool-239f5d02-x1kf/
Node: gke-test-default-pool-239f5d02-x1kf/10.128.0.27
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
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Scheduled 10s default-scheduler Successfully assigned default/hello-apparmor to gke-test-default-pool-239f5d02-x1kf
Normal Pulled 8s kubelet Successfully pulled image "busybox:1.28" in 370.157088ms (370.172701ms including waiting)
Normal Pulling 7s (x2 over 9s) kubelet Pulling image "busybox:1.28"
Warning Failed 7s (x2 over 8s) kubelet Error: failed to get container spec opts: failed to generate apparmor spec opts: apparmor profile not found k8s-apparmor-example-allow-write
Normal Pulled 7s kubelet Successfully pulled image "busybox:1.28" in 90.980331ms (91.005869ms including waiting)
```
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.
An event provides the error message with the reason. Note that the specific wording is runtime-dependent:
```
Warning Failed 7s (x2 over 8s) kubelet Error: failed to get container spec opts: failed to generate apparmor spec opts: apparmor profile not found
```
## 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](/docs/concepts/workloads/controllers/daemonset/) that runs a Pod on each node to
ensure the correct profiles are loaded. An example implementation can be found
[here](https://git.k8s.io/kubernetes/test/images/apparmor-loader).
* 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](#example).
Kubernetes does not currently provide any built-in mechanisms for loading AppArmor profiles onto
nodes. Profiles can be loaded through custom infrastructure or tools like the
[Kubernetes Security Profiles Operator](https://github.com/kubernetes-sigs/security-profiles-operator).
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
@ -345,23 +251,6 @@ class of profiles) on the node, and use a
[node selector](/docs/concepts/scheduling-eviction/assign-pod-node/) to ensure the Pod is run on a
node with the required profile.
### 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.
{{<note>}}
Even if the Kubernetes feature is disabled, runtimes may still enforce the default profile. The
option to disable the AppArmor feature will be removed when AppArmor graduates to general
availability (GA).
{{</note>}}
## Authoring Profiles
Getting AppArmor profiles specified correctly can be a tricky business. Fortunately there are some
@ -393,8 +282,7 @@ Specifying the profile a container will run with:
### Profile Reference
- `runtime/default`: Refers to the default runtime profile.
- Equivalent to not specifying a profile, except it still
requires AppArmor to be enabled.
- Equivalent to not specifying a profile, except it still requires AppArmor to be enabled.
- In practice, many container runtimes use the same OCI default profile, defined here:
https://github.com/containers/common/blob/main/pkg/apparmor/apparmor_linux_template.go
- `localhost/<profile_name>`: Refers to a profile loaded on the node (localhost) by name.

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content/en/examples/pods/security/hello-apparmor.yaml
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@ -4,7 +4,6 @@ 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: