Add seccomp GA version skew for pods

This adds a new conversion function to the pod strategy to handle the
seccomp version skew strategy:

https://github.com/kubernetes/enhancements/blob/master/keps/sig-node/20190717-seccomp-ga.mdversion-skew-strategy

Signed-off-by: Sascha Grunert <sgrunert@suse.com>

pkg/registry/core/pod/strategy.go

@@ -26,6 +26,7 @@ import (
 	"strings"
 	"time"
 
+	"k8s.io/api/core/v1"
 	"k8s.io/apimachinery/pkg/api/errors"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/fields"
@@ -74,6 +75,8 @@ func (podStrategy) PrepareForCreate(ctx context.Context, obj runtime.Object) {
 	}
 
 	podutil.DropDisabledPodFields(pod, nil)
+
+	applySeccompVersionSkew(pod)
 }
 
 // PrepareForUpdate clears fields that are not allowed to be set by end users on update.
@@ -569,3 +572,129 @@ func validateContainer(container string, pod *api.Pod) (string, error) {
 
 	return container, nil
 }
+
+// applySeccompVersionSkew implements the version skew behavior described in:
+// https://github.com/kubernetes/enhancements/blob/master/keps/sig-node/20190717-seccomp-ga.md#version-skew-strategy
+func applySeccompVersionSkew(pod *api.Pod) {
+	// get possible annotation and field
+	annotation, hasAnnotation := pod.Annotations[v1.SeccompPodAnnotationKey]
+	field, hasField := (*api.SeccompProfile)(nil), false
+
+	if pod.Spec.SecurityContext != nil && pod.Spec.SecurityContext.SeccompProfile != nil {
+		field = pod.Spec.SecurityContext.SeccompProfile
+		hasField = true
+	}
+
+	// sync field and annotation
+	if hasField && !hasAnnotation {
+		newAnnotation := seccompAnnotationForField(field)
+
+		if newAnnotation != "" {
+			if pod.Annotations == nil {
+				pod.Annotations = map[string]string{}
+			}
+			pod.Annotations[v1.SeccompPodAnnotationKey] = newAnnotation
+		}
+	} else if hasAnnotation && !hasField {
+		newField := seccompFieldForAnnotation(annotation)
+
+		if newField != nil {
+			if pod.Spec.SecurityContext == nil {
+				pod.Spec.SecurityContext = &api.PodSecurityContext{}
+			}
+			pod.Spec.SecurityContext.SeccompProfile = newField
+		}
+	}
+
+	// Handle the containers of the pod
+	podutil.VisitContainers(&pod.Spec, podutil.AllFeatureEnabledContainers(),
+		func(ctr *api.Container, _ podutil.ContainerType) bool {
+			// get possible annotation and field
+			key := api.SeccompContainerAnnotationKeyPrefix + ctr.Name
+			annotation, hasAnnotation := pod.Annotations[key]
+
+			field, hasField := (*api.SeccompProfile)(nil), false
+			if ctr.SecurityContext != nil && ctr.SecurityContext.SeccompProfile != nil {
+				field = ctr.SecurityContext.SeccompProfile
+				hasField = true
+			}
+
+			// sync field and annotation
+			if hasField && !hasAnnotation {
+				newAnnotation := seccompAnnotationForField(field)
+
+				if newAnnotation != "" {
+					if pod.Annotations == nil {
+						pod.Annotations = map[string]string{}
+					}
+					pod.Annotations[key] = newAnnotation
+				}
+			} else if hasAnnotation && !hasField {
+				newField := seccompFieldForAnnotation(annotation)
+
+				if newField != nil {
+					if ctr.SecurityContext == nil {
+						ctr.SecurityContext = &api.SecurityContext{}
+					}
+					ctr.SecurityContext.SeccompProfile = newField
+				}
+			}
+
+			return true
+		})
+}
+
+// seccompFieldForAnnotation takes a pod seccomp profile field and returns the
+// converted annotation value
+func seccompAnnotationForField(field *api.SeccompProfile) string {
+	// If only seccomp fields are specified, add the corresponding annotations.
+	// This ensures that the fields are enforced even if the node version
+	// trails the API version
+	switch field.Type {
+	case api.SeccompProfileTypeUnconfined:
+		return v1.SeccompProfileNameUnconfined
+
+	case api.SeccompProfileTypeRuntimeDefault:
+		return v1.SeccompProfileRuntimeDefault
+
+	case api.SeccompProfileTypeLocalhost:
+		if field.LocalhostProfile != nil {
+			return v1.SeccompLocalhostProfileNamePrefix + *field.LocalhostProfile
+		}
+	}
+
+	// we can only reach this code path if the LocalhostProfile is nil but the
+	// provided field type is SeccompProfileTypeLocalhost or if an unrecognized
+	// type is specified
+	return ""
+}
+
+// seccompFieldForAnnotation takes a pod annotation and returns the converted
+// seccomp profile field.
+func seccompFieldForAnnotation(annotation string) *api.SeccompProfile {
+	// If only seccomp annotations are specified, copy the values into the
+	// corresponding fields. This ensures that existing applications continue
+	// to enforce seccomp, and prevents the kubelet from needing to resolve
+	// annotations & fields.
+	if annotation == v1.SeccompProfileNameUnconfined {
+		return &api.SeccompProfile{Type: api.SeccompProfileTypeUnconfined}
+	}
+
+	if annotation == api.SeccompProfileRuntimeDefault || annotation == api.DeprecatedSeccompProfileDockerDefault {
+		return &api.SeccompProfile{Type: api.SeccompProfileTypeRuntimeDefault}
+	}
+
+	if strings.HasPrefix(annotation, v1.SeccompLocalhostProfileNamePrefix) {
+		localhostProfile := strings.TrimPrefix(annotation, v1.SeccompLocalhostProfileNamePrefix)
+		if localhostProfile != "" {
+			return &api.SeccompProfile{
+				Type:             api.SeccompProfileTypeLocalhost,
+				LocalhostProfile: &localhostProfile,
+			}
+		}
+	}
+
+	// we can only reach this code path if the localhostProfile name has a zero
+	// length or if the annotation has an unrecognized value
+	return nil
+}