kubernetes.go

/*
Copyright 2023 The Dapr 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 kubernetes

import (
	"context"
	"errors"
	"fmt"
	"strings"

	"github.com/lestrrat-go/jwx/v2/jwt"
	"github.com/spiffe/go-spiffe/v2/spiffeid"
	kauthapi "k8s.io/api/authentication/v1"
	corev1 "k8s.io/api/core/v1"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/runtime"
	"k8s.io/apimachinery/pkg/types"
	cl "k8s.io/client-go/kubernetes"
	clauthv1 "k8s.io/client-go/kubernetes/typed/authentication/v1"
	"k8s.io/client-go/rest"
	"sigs.k8s.io/controller-runtime/pkg/cache"
	"sigs.k8s.io/controller-runtime/pkg/client"

	configv1alpha1 "github.com/dapr/dapr/pkg/apis/configuration/v1alpha1"
	"github.com/dapr/dapr/pkg/injector/annotations"
	sentryv1pb "github.com/dapr/dapr/pkg/proto/sentry/v1"
	"github.com/dapr/dapr/pkg/security/consts"
	"github.com/dapr/dapr/pkg/sentry/server/validator"
	"github.com/dapr/dapr/pkg/sentry/server/validator/internal"
	"github.com/dapr/kit/logger"
)

const (
	// TODO: @joshvanl: Before 1.11, dapr would use this generic audience. After
	// 1.11, clients use the sentry SPIFFE ID as the audience. Remove legacy
	// audience in v1.12
	LegacyServiceAccountAudience = "dapr.io/sentry"
)

var (
	log = logger.NewLogger("dapr.sentry.identity.kubernetes")

	errMissingPodClaim = errors.New("kubernetes.io/pod/name claim is missing from Kubernetes token")
)

type Options struct {
	RestConfig     *rest.Config
	SentryID       spiffeid.ID
	ControlPlaneNS string
}

// kubernetes implements the validator.Interface. It validates the request by
// doing a Kubernetes token review.
type kubernetes struct {
	auth           clauthv1.AuthenticationV1Interface
	client         client.Reader
	ready          func(context.Context) bool
	sentryAudience string
	controlPlaneNS string
	controlPlaneTD spiffeid.TrustDomain
}

func New(ctx context.Context, opts Options) (validator.Validator, error) {
	kubeClient, err := cl.NewForConfig(opts.RestConfig)
	if err != nil {
		return nil, err
	}

	scheme := runtime.NewScheme()
	if err = configv1alpha1.AddToScheme(scheme); err != nil {
		return nil, err
	}
	if err = corev1.AddToScheme(scheme); err != nil {
		return nil, err
	}

	cache, err := cache.New(opts.RestConfig, cache.Options{Scheme: scheme})
	if err != nil {
		return nil, err
	}

	for _, obj := range []client.Object{
		&metav1.PartialObjectMetadata{TypeMeta: metav1.TypeMeta{Kind: "Pod", APIVersion: "v1"}},
		&configv1alpha1.Configuration{},
	} {
		if _, err := cache.GetInformer(ctx, obj); err != nil {
			return nil, err
		}
	}

	return &kubernetes{
		auth:           kubeClient.AuthenticationV1(),
		client:         cache,
		ready:          cache.WaitForCacheSync,
		sentryAudience: opts.SentryID.String(),
		controlPlaneNS: opts.ControlPlaneNS,
		controlPlaneTD: opts.SentryID.TrustDomain(),
	}, nil
}

func (k *kubernetes) Start(ctx context.Context) error {
	if err := k.client.(cache.Cache).Start(ctx); err != nil {
		return err
	}

	<-ctx.Done()
	return nil
}

func (k *kubernetes) Validate(ctx context.Context, req *sentryv1pb.SignCertificateRequest) (spiffeid.TrustDomain, bool, error) {
	if !k.ready(ctx) {
		return spiffeid.TrustDomain{}, false, errors.New("validator not ready")
	}

	prts, err := k.executeTokenReview(ctx, req.GetToken(), LegacyServiceAccountAudience, k.sentryAudience)
	if err != nil {
		return spiffeid.TrustDomain{}, false, err
	}

	if len(prts) != 4 || prts[0] != "system" {
		return spiffeid.TrustDomain{}, false, errors.New("provided token is not a properly structured service account token")
	}

	saNamespace := prts[2]

	// We have already validated to the token against Kubernetes API server, so
	// we do not need to supply a key.
	ptoken, err := jwt.ParseInsecure([]byte(req.GetToken()), jwt.WithTypedClaim("kubernetes.io", new(k8sClaims)))
	if err != nil {
		return spiffeid.TrustDomain{}, false, fmt.Errorf("failed to parse Kubernetes token: %s", err)
	}
	claimsT, ok := ptoken.Get("kubernetes.io")
	if !ok {
		return spiffeid.TrustDomain{}, false, errMissingPodClaim
	}
	claims, ok := claimsT.(*k8sClaims)
	if !ok || len(claims.Pod.Name) == 0 {
		return spiffeid.TrustDomain{}, false, errMissingPodClaim
	}

	var pod corev1.Pod
	err = k.client.Get(ctx, types.NamespacedName{Namespace: saNamespace, Name: claims.Pod.Name}, &pod)
	if err != nil {
		log.Errorf("Failed to get pod %s/%s for requested identity: %s", saNamespace, claims.Pod.Name, err)
		return spiffeid.TrustDomain{}, false, errors.New("failed to get pod of identity")
	}

	// TODO: @joshvanl: Remove is v1.13 when injector no longer needs to request
	// daprd identities.
	var injectorRequesting bool
	var overrideDuration bool
	if ctrlPlane, oka := pod.Annotations[consts.AnnotationKeyControlPlane]; oka && ctrlPlane == "injector" {
		injectorRequesting = pod.Namespace == k.controlPlaneNS
	}

	if saNamespace != req.GetNamespace() {
		if injectorRequesting {
			overrideDuration = true
		} else {
			return spiffeid.TrustDomain{}, false, fmt.Errorf("namespace mismatch; received namespace: %s", req.GetNamespace())
		}
	}

	if pod.Spec.ServiceAccountName != prts[3] {
		log.Errorf("Service account on pod %s/%s does not match token", req.GetNamespace(), claims.Pod.Name)
		return spiffeid.TrustDomain{}, false, errors.New("pod service account mismatch")
	}

	expID, isControlPlane, err := k.expectedID(&pod)
	if err != nil {
		log.Errorf("Failed to get expected ID for pod %s/%s: %s", req.GetNamespace(), claims.Pod.Name, err)
		return spiffeid.TrustDomain{}, false, err
	}

	// TODO: @joshvanl: Before v1.12, the injector instructed daprd to request
	// for the ID containing their namespace and service account (ns:sa). This
	// is wrong- dapr identities are based on daprd namespace + _app ID_.
	// Remove this allowance in v1.13.
	if pod.Namespace+":"+pod.Spec.ServiceAccountName == req.GetId() {
		req.Id = expID
	}

	// The TrustDomain field is ignored by the Kubernetes validator. We must
	// validate the request _after_ performing the token review so that in the
	// event the client is uing the "legacy" <ns>:<sa> ID, we can override it
	// with the expected app ID.
	if _, _, err = internal.Validate(ctx, req); err != nil {
		return spiffeid.TrustDomain{}, false, err
	}

	// TODO: @joshvanl: Remove is v1.13 when injector no longer needs to request
	// daprd identities.
	if expID != req.GetId() {
		if injectorRequesting {
			overrideDuration = true
		} else {
			return spiffeid.TrustDomain{}, false, fmt.Errorf("app-id mismatch. expected: %s, received: %s", expID, req.GetId())
		}
	}

	if isControlPlane {
		return k.controlPlaneTD, overrideDuration, nil
	}

	configName, ok := pod.GetAnnotations()[annotations.KeyConfig]
	if !ok {
		// Return early with default trust domain if no config annotation is found.
		return spiffeid.RequireTrustDomainFromString("public"), overrideDuration, nil
	}

	var config configv1alpha1.Configuration
	err = k.client.Get(ctx, types.NamespacedName{Namespace: req.GetNamespace(), Name: configName}, &config)
	if err != nil {
		log.Errorf("Failed to get configuration %q: %v", configName, err)
		return spiffeid.TrustDomain{}, false, errors.New("failed to get configuration")
	}

	if config.Spec.AccessControlSpec == nil || len(config.Spec.AccessControlSpec.TrustDomain) == 0 {
		return spiffeid.RequireTrustDomainFromString("public"), overrideDuration, nil
	}

	td, err := spiffeid.TrustDomainFromString(config.Spec.AccessControlSpec.TrustDomain)
	return td, overrideDuration, err
}

// expectedID returns the expected ID for the pod. If the pod is a control
// plane service (has the dapr.io/control-plane annotation), the ID will be the
// control plane service name prefixed with "dapr-". Otherwise, the ID will be
// `dapr.io/app-id` annotation or the pod name.
func (k *kubernetes) expectedID(pod *corev1.Pod) (string, bool, error) {
	ctrlPlane, ctrlOK := pod.Annotations[consts.AnnotationKeyControlPlane]
	appID, appOK := pod.Annotations[annotations.KeyAppID]

	if ctrlOK {
		if pod.Namespace != k.controlPlaneNS {
			return "", false, fmt.Errorf("control plane service in namespace '%s' is not allowed", pod.Namespace)
		}

		if !isControlPlaneService(ctrlPlane) {
			return "", false, fmt.Errorf("unknown control plane service '%s'", pod.Name)
		}

		if appOK {
			return "", false, fmt.Errorf("control plane service '%s' cannot have annotation '%s'", pod.Name, annotations.KeyAppID)
		}

		return "dapr-" + ctrlPlane, true, nil
	}

	if !appOK {
		return pod.Name, false, nil
	}

	return appID, false, nil
}

// Executes a tokenReview, returning an error if the token is invalid or if
// there's a failure.
// If successful, returns the username of the token, split by the Kubernetes
// ':' separator.
func (k *kubernetes) executeTokenReview(ctx context.Context, token string, audiences ...string) ([]string, error) {
	review, err := k.auth.TokenReviews().Create(ctx, &kauthapi.TokenReview{
		Spec: kauthapi.TokenReviewSpec{Token: token, Audiences: audiences},
	}, metav1.CreateOptions{})
	if err != nil {
		return nil, fmt.Errorf("token review failed: %w", err)
	}

	if len(review.Status.Error) > 0 {
		return nil, fmt.Errorf("invalid token: %s", review.Status.Error)
	}

	if !review.Status.Authenticated {
		return nil, errors.New("authentication failed")
	}

	return strings.Split(review.Status.User.Username, ":"), nil
}

// k8sClaims is a subset of the claims in a Kubernetes service account token
// containing the name of the Pod that the token was issued for.
type k8sClaims struct {
	Pod struct {
		Name string `json:"name"`
	} `json:"pod"`
}

// IsControlPlaneService returns true if the app ID corresponds to a Dapr control plane service.
// Note: callers must additionally validate the namespace to ensure it matches the one of the Dapr control plane.
func isControlPlaneService(id string) bool {
	switch id {
	case "operator",
		"placement",
		"injector",
		"sentry":
		return true
	default:
		return false
	}
}