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AppArmor documentation

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Tim St. Clair 2016-08-30 18:42:53 -07:00
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path: /docs/admin/salt/
- title: Monitoring Node Health
path: /docs/admin/node-problem/
- title: AppArmor
path: /docs/admin/apparmor/

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#include <tunables/global>
profile k8s-apparmor-example-deny-write flags=(attach_disconnected) {
#include <abstractions/base>
file,
# Deny all file writes.
deny /** w,
}

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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
command: [ "sh", "-c", "echo 'Hello AppArmor!' && sleep 1h" ]

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---
assignees:
- stclair
---
AppArmor is a Linux kernel enhancement that can reduce the potential attack surface of an
application and provide greater defense in depth for Applications. Beta support for AppArmor was
added in Kubernetes v1.4.
* TOC
{:toc}
## What is AppArmor
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 defense in depth. It is
configured through profiles tuned to whitelist 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 providing 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.
AppArmor support in Kubernetes is currently in beta.
## Prerequisites
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.
*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.*
3. **Container runtime is Docker**. Currently the only Kubernetes-supported container runtime that
also supports AppArmor is Docker. As more runtimes add AppArmor support, the options will be
expanded. You can verify that your nodes are running docker with:
$ kubectl get nodes -o=jsonpath=$'{range .items[*]}{@.metadata.name}: {@.status.nodeInfo.containerRuntimeVersion}\n{end}'
gke-test-default-pool-239f5d02-gyn2: docker://1.11.2
gke-test-default-pool-239f5d02-x1kf: docker://1.11.2
gke-test-default-pool-239f5d02-xwux: docker://1.11.2
If the Kubelet contains AppArmor support (>= v1.4), it will refuse to run a Pod with AppArmor
options if the runtime is not Docker.
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
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](#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
*Note: AppArmor is currently in beta, so options are specified as annotations. Once support graduates to
general availability, the annotations will be replaced with first-class fields (more details in
[Upgrade path to GA](#upgrade-path-to-general-availability)).*
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>`
See the [API Reference](#api-reference) for the full details on the annotation and profile name formats.
The 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 expect to see 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-minion-group-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
In this example you'll see:
- One way to load a profile on a node
- How to enforce the profile on a Pod
- How to check that the profile is loaded
- What happens when a profile is violated
- What happens when a profile cannot be loaded
*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. The profile we'll use simply
denies all file writes:
{% include code.html language="text" file="deny-write.profile" ghlink="/docs/admin/apparmor/deny-write.profile" %}
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 just use SSH to install the profiles, but other approaches are
discussed in [Setting up nodes with profiles](#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:
{% include code.html language="yaml" file="hello-apparmor-pod.yaml" ghlink="/docs/admin/apparmor/hello-apparmor-pod.yaml" %}
$ kubectl create -f /dev/stdin <<EOF
apiVersion: v1
kind: Pod
metadata:
name: hello-apparmor
annotations:
container.apparmor.security.beta.kubernetes.io/hello: localhost/k8s-apparmor-example-deny-write
spec:
containers:
- name: hello
image: busybox
command: [ "sh", "-c", "echo 'Hello AppArmor!' && sleep 1h" ]
EOF
pod "hello-apparmor" created
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
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>
Status: Failed
Reason: AppArmor
Message: Pod Cannot enforce AppArmor: profile "k8s-apparmor-example-allow-write" is not loaded
IP:
Controllers: <none>
Containers:
hello:
Image: busybox
Port:
Command:
sh
-c
echo 'Hello AppArmor!' && sleep 1h
Requests:
cpu: 100m
Environment Variables: <none>
Volumes:
default-token-dnz7v:
Type: Secret (a volume populated by a Secret)
SecretName: default-token-dnz7v
QoS Tier: Burstable
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-minion-group-t1f5
23s 23s 1 {kubelet e2e-test-stclair-minion-group-t1f5} Warning AppArmor Cannot enforce AppArmor: profile "k8s-apparmor-example-allow-write" is not loaded
Note the pod status is Failed, 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 setup the profiles though, such as:
- Through a [DaemonSet](../daemons/) that runs a Pod on each node to
ensure the correct profiles are loaded. An example implementation can be found
[here](https://github.com/kubernetes/contrib/tree/master/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).
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](../../user-guide/node-selection/) 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, two flags must be set on the `apiserver`:
--admission-control=PodSecurityPolicy[,others...]
--runtime-config=extensions/v1beta1/podsecuritypolicy[,others...]
With the extension enabled, 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](#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. Note that by default docker always enables the "docker-default" profile on non-privileged
pods (if the AppArmor kernel module is enabled), and will continue to do so even if the feature-gate
is disabled. The option to disable AppArmor will be removed when AppArmor graduates to general
availability (GA).
### Upgrading to Kubernetes v1.4 with AppArmor
No action is required with respect to AppArmor to upgrade your cluster to v1.4. However, if any
existing pods had an AppArmor annotation, they will not go through validation (or PodSecurityPolicy
admission). If permissive profiles are loaded on the nodes, a malicious user could pre-apply a
permissive profile to escalate the pod privileges above the docker-default. If this is a concern, it
is recommended to scrub the cluster of any pods containing an annotation with
`apparmor.security.beta.kubernetes.io`.
### Upgrade path to General Availability
When AppArmor is ready to be graduated to general availability (GA), the options currently specified
through annotations will be converted to fields. Supporting all the upgrade and downgrade paths
through the transition is very nuanced, and will be explained in detail when the transition
occurs. We will commit to supporting both fields and annotations for at least 2 releases, and will
explicitly reject the annotations for at least 2 releases after that.
## 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](http://wiki.apparmor.net/index.php/Profiling_with_tools).
- [bane](https://github.com/jfrazelle/bane) is an AppArmor profile generator for Docker that uses a
simplified profile language.
It is recommended to run your application through Docker on a development workstation to generate
the profiles, but there is nothing preventing running the tools on the Kubernetes node where your
Pod is running.
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](http://wiki.apparmor.net/index.php/AppArmor_Failures).
Additional resources:
- http://wiki.apparmor.net/index.php/QuickProfileLanguage
- http://wiki.apparmor.net/index.php/ProfileLanguage
## 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.
- Equivalent to not specifying a profile (without a PodSecurityPolicy default), except it still
requires AppArmor to be enabled.
- For Docker, this resolves to the
[`docker-default`](https://docs.docker.com/engine/security/apparmor/) profile for non-privileged
containers, and unconfined (no profile) for privileged containers.
- `localhost/<profile_name>`: Refers to a profile loaded on the node (localhost) by name.
- The possible profile names are detailed in the
[core policy reference](http://wiki.apparmor.net/index.php/AppArmor_Core_Policy_Reference#Profile_names_and_attachment_specifications)
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 are 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