storage.go

/*
Copyright 2016 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 policybased implements a standard storage for ClusterRoleBinding that prevents privilege escalation.
package policybased

import (
	"context"

	rbacv1 "k8s.io/api/rbac/v1"
	"k8s.io/apimachinery/pkg/api/errors"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/runtime"
	"k8s.io/apiserver/pkg/authorization/authorizer"
	"k8s.io/apiserver/pkg/registry/rest"
	kapihelper "k8s.io/kubernetes/pkg/apis/core/helper"
	"k8s.io/kubernetes/pkg/apis/rbac"
	rbacv1helpers "k8s.io/kubernetes/pkg/apis/rbac/v1"
	rbacregistry "k8s.io/kubernetes/pkg/registry/rbac"
	rbacregistryvalidation "k8s.io/kubernetes/pkg/registry/rbac/validation"
)

var groupResource = rbac.Resource("clusterrolebindings")

type Storage struct {
	rest.StandardStorage

	authorizer authorizer.Authorizer

	ruleResolver rbacregistryvalidation.AuthorizationRuleResolver
}

func NewStorage(s rest.StandardStorage, authorizer authorizer.Authorizer, ruleResolver rbacregistryvalidation.AuthorizationRuleResolver) *Storage {
	return &Storage{s, authorizer, ruleResolver}
}

func (r *Storage) NamespaceScoped() bool {
	return false
}

func (r *Storage) StorageVersion() runtime.GroupVersioner {
	svp, ok := r.StandardStorage.(rest.StorageVersionProvider)
	if !ok {
		return nil
	}
	return svp.StorageVersion()
}

var _ rest.StorageVersionProvider = &Storage{}

func (s *Storage) Create(ctx context.Context, obj runtime.Object, createValidation rest.ValidateObjectFunc, options *metav1.CreateOptions) (runtime.Object, error) {
	if rbacregistry.EscalationAllowed(ctx) {
		return s.StandardStorage.Create(ctx, obj, createValidation, options)
	}

	clusterRoleBinding := obj.(*rbac.ClusterRoleBinding)
	if rbacregistry.BindingAuthorized(ctx, clusterRoleBinding.RoleRef, metav1.NamespaceNone, s.authorizer) {
		return s.StandardStorage.Create(ctx, obj, createValidation, options)
	}

	v1RoleRef := rbacv1.RoleRef{}
	err := rbacv1helpers.Convert_rbac_RoleRef_To_v1_RoleRef(&clusterRoleBinding.RoleRef, &v1RoleRef, nil)
	if err != nil {
		return nil, err
	}
	rules, err := s.ruleResolver.GetRoleReferenceRules(v1RoleRef, metav1.NamespaceNone)
	if err != nil {
		return nil, err
	}
	if err := rbacregistryvalidation.ConfirmNoEscalation(ctx, s.ruleResolver, rules); err != nil {
		return nil, errors.NewForbidden(groupResource, clusterRoleBinding.Name, err)
	}
	return s.StandardStorage.Create(ctx, obj, createValidation, options)
}

func (s *Storage) Update(ctx context.Context, name string, obj rest.UpdatedObjectInfo, createValidation rest.ValidateObjectFunc, updateValidation rest.ValidateObjectUpdateFunc, forceAllowCreate bool, options *metav1.UpdateOptions) (runtime.Object, bool, error) {
	if rbacregistry.EscalationAllowed(ctx) {
		return s.StandardStorage.Update(ctx, name, obj, createValidation, updateValidation, forceAllowCreate, options)
	}

	nonEscalatingInfo := rest.WrapUpdatedObjectInfo(obj, func(ctx context.Context, obj runtime.Object, oldObj runtime.Object) (runtime.Object, error) {
		clusterRoleBinding := obj.(*rbac.ClusterRoleBinding)

		// if we're only mutating fields needed for the GC to eventually delete this obj, return
		if rbacregistry.IsOnlyMutatingGCFields(obj, oldObj, kapihelper.Semantic) {
			return obj, nil
		}

		// if we're explicitly authorized to bind this clusterrole, return
		if rbacregistry.BindingAuthorized(ctx, clusterRoleBinding.RoleRef, metav1.NamespaceNone, s.authorizer) {
			return obj, nil
		}

		// Otherwise, see if we already have all the permissions contained in the referenced clusterrole
		v1RoleRef := rbacv1.RoleRef{}
		err := rbacv1helpers.Convert_rbac_RoleRef_To_v1_RoleRef(&clusterRoleBinding.RoleRef, &v1RoleRef, nil)
		if err != nil {
			return nil, err
		}
		rules, err := s.ruleResolver.GetRoleReferenceRules(v1RoleRef, metav1.NamespaceNone)
		if err != nil {
			return nil, err
		}
		if err := rbacregistryvalidation.ConfirmNoEscalation(ctx, s.ruleResolver, rules); err != nil {
			return nil, errors.NewForbidden(groupResource, clusterRoleBinding.Name, err)
		}
		return obj, nil
	})

	return s.StandardStorage.Update(ctx, name, nonEscalatingInfo, createValidation, updateValidation, forceAllowCreate, options)
}