# Seccomp and Kubernetes LLMS index: [llms.txt](/llms.txt) --- 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. ## Seccomp fields
FEATURE STATE: Kubernetes v1.19 [stable]
There are four ways to specify a seccomp profile for a pod: - for the whole Pod using [`spec.securityContext.seccompProfile`](/docs/reference/kubernetes-api/workload-resources/pod-v1/#security-context) - for a single container using [`spec.containers[*].securityContext.seccompProfile`](/docs/reference/kubernetes-api/workload-resources/pod-v1/#security-context-1) - for an (restartable / sidecar) init container using [`spec.initContainers[*].securityContext.seccompProfile`](/docs/reference/kubernetes-api/workload-resources/pod-v1/#security-context-1) - for an [ephemeral container](/docs/concepts/workloads/pods/ephemeral-containers) using [`spec.ephemeralContainers[*].securityContext.seccompProfile`](/docs/reference/kubernetes-api/workload-resources/pod-v1/#security-context-2)
pods/security/seccomp/fields.yaml 
apiVersion: v1
kind: Pod
metadata:
  name: pod
spec:
  securityContext:
    seccompProfile:
      type: Unconfined
  # NOTE: ephemeralContainers cannot be specified when creating a Pod.
  # It can be specified only when updating a Pod.
  ephemeralContainers:
  - name: ephemeral-container
    image: debian
    securityContext:
      seccompProfile:
        type: RuntimeDefault
  initContainers:
  - name: init-container
    image: debian
    securityContext:
      seccompProfile:
        type: RuntimeDefault
  containers:
  - name: container
    image: docker.io/library/debian:stable
    securityContext:
      seccompProfile:
        type: Localhost
        localhostProfile: my-profile.json
The Pod in the example above runs as `Unconfined`, while the `ephemeral-container` and `init-container` specifically defines `RuntimeDefault`. If the ephemeral or init container would not have set the `securityContext.seccompProfile` field explicitly, then the value would be inherited from the Pod. The same applies to the container, which runs a `Localhost` profile `my-profile.json`. Generally speaking, fields from (ephemeral) containers have a higher priority than the Pod level value, while containers which do not set the seccomp field inherit the profile from the Pod.

Note:

It is not possible to apply a seccomp profile to a Pod or container running with privileged: true set in the container's securityContext. Privileged containers always run as Unconfined.
The following values are possible for the `seccompProfile.type`: `Unconfined` : The workload runs without any seccomp restrictions. `RuntimeDefault` : A default seccomp profile defined by the container runtime is applied. 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. `Localhost` : The `localhostProfile` will be applied, which has to be available on the node disk (on Linux it's `/var/lib/kubelet/seccomp`). The availability of the seccomp profile is verified by the container runtime on container creation. If the profile does not exist, then the container creation will fail with a `CreateContainerError`. ### `Localhost` profiles Seccomp profiles are JSON files following the scheme defined by the [OCI runtime specification](https://github.com/opencontainers/runtime-spec/blob/f329913/config-linux.md#seccomp). A profile basically defines actions based on matched syscalls, but also allows to pass specific values as arguments to syscalls. For example: ```json { "defaultAction": "SCMP_ACT_ERRNO", "defaultErrnoRet": 38, "syscalls": [ { "names": [ "adjtimex", "alarm", "bind", "waitid", "waitpid", "write", "writev" ], "action": "SCMP_ACT_ALLOW" } ] } ``` The `defaultAction` in the profile above is defined as `SCMP_ACT_ERRNO` and will return as fallback to the actions defined in `syscalls`. The error is defined as code `38` via the `defaultErrnoRet` field. The following actions are generally possible: `SCMP_ACT_ERRNO` : Return the specified error code. `SCMP_ACT_ALLOW` : Allow the syscall to be executed. `SCMP_ACT_KILL_PROCESS` : Kill the process. `SCMP_ACT_KILL_THREAD` and `SCMP_ACT_KILL` : Kill only the thread. `SCMP_ACT_TRAP` : Throw a `SIGSYS` signal. `SCMP_ACT_NOTIFY` and `SECCOMP_RET_USER_NOTIF`. : Notify the user space. `SCMP_ACT_TRACE` : Notify a tracing process with the specified value. `SCMP_ACT_LOG` : Allow the syscall to be executed after the action has been logged to syslog or auditd. Some actions like `SCMP_ACT_NOTIFY` or `SECCOMP_RET_USER_NOTIF` may be not supported depending on the container runtime, OCI runtime or Linux kernel version being used. There may be also further limitations, for example that `SCMP_ACT_NOTIFY` cannot be used as `defaultAction` or for certain syscalls like `write`. All those limitations are defined by either the OCI runtime ([runc](https://github.com/opencontainers/runc), [crun](https://github.com/containers/crun)) or [libseccomp](https://github.com/seccomp/libseccomp). The `syscalls` JSON array contains a list of objects referencing syscalls by their respective `names`. For example, the action `SCMP_ACT_ALLOW` can be used to create a whitelist of allowed syscalls as outlined in the example above. It would also be possible to define another list using the action `SCMP_ACT_ERRNO` but a different return (`errnoRet`) value. It is also possible to specify the arguments (`args`) passed to certain syscalls. More information about those advanced use cases can be found in the [OCI runtime spec](https://github.com/opencontainers/runtime-spec/blob/f329913/config-linux.md#seccomp) and the [Seccomp Linux kernel documentation](https://www.kernel.org/doc/Documentation/prctl/seccomp_filter.txt). ## Further reading - [Restrict a Container's Syscalls with seccomp](/docs/tutorials/security/seccomp/) - [Pod Security Standards](/docs/concepts/security/pod-security-standards/)