ceph-csi/vendor/k8s.io/pod-security-admission/policy/check_procMount.go

/*
Copyright 2021 The Kubernetes Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package policy

import (
	"fmt"

	corev1 "k8s.io/api/core/v1"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/util/sets"
	"k8s.io/pod-security-admission/api"
)

/*

The default /proc masks are set up to reduce attack surface, and should be required.

**Restricted Fields:**
spec.containers[*].securityContext.procMount
spec.initContainers[*].securityContext.procMount

**Allowed Values:** undefined/null, "Default"

However, if the pod is in a user namespace (`hostUsers: false`), and the
UserNamespacesPodSecurityStandards feature is enabled, all values are allowed.

*/

func init() {
	addCheck(CheckProcMount)
}

// CheckProcMount returns a baseline level check that restricts
// setting the value of securityContext.procMount to DefaultProcMount
// in 1.0+
func CheckProcMount() Check {
	return Check{
		ID:    "procMount",
		Level: api.LevelBaseline,
		Versions: []VersionedCheck{
			{
				MinimumVersion: api.MajorMinorVersion(1, 0),
				CheckPod:       procMount_1_0,
			},
		},
	}
}

func procMount_1_0(podMetadata *metav1.ObjectMeta, podSpec *corev1.PodSpec) CheckResult {
	// TODO: When we remove the UserNamespacesPodSecurityStandards feature gate (and GA this relaxation),
	// create a new policy version.
	// Note: pod validation will check for well formed procMount type, so avoid double validation and allow everything
	// here.
	if relaxPolicyForUserNamespacePod(podSpec) {
		return CheckResult{Allowed: true}
	}

	var badContainers []string
	forbiddenProcMountTypes := sets.NewString()
	visitContainers(podSpec, func(container *corev1.Container) {
		// allow if the security context is nil.
		if container.SecurityContext == nil {
			return
		}
		// allow if proc mount is not set.
		if container.SecurityContext.ProcMount == nil {
			return
		}
		// check if the value of the proc mount type is valid.
		if *container.SecurityContext.ProcMount != corev1.DefaultProcMount {
			badContainers = append(badContainers, container.Name)
			forbiddenProcMountTypes.Insert(string(*container.SecurityContext.ProcMount))
		}
	})
	if len(badContainers) > 0 {
		return CheckResult{
			Allowed:         false,
			ForbiddenReason: "procMount",
			ForbiddenDetail: fmt.Sprintf(
				"%s %s must not set securityContext.procMount to %s",
				pluralize("container", "containers", len(badContainers)),
				joinQuote(badContainers),
				joinQuote(forbiddenProcMountTypes.List()),
			),
		}
	}
	return CheckResult{Allowed: true}
}