claims.go

/*
Copyright 2018 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 serviceaccount

import (
	"errors"
	"fmt"
	"time"

	"github.com/golang/glog"
	apiserverserviceaccount "k8s.io/apiserver/pkg/authentication/serviceaccount"
	"k8s.io/kubernetes/pkg/apis/core"

	"gopkg.in/square/go-jose.v2/jwt"
)

// time.Now stubbed out to allow testing
var now = time.Now

type privateClaims struct {
	Kubernetes kubernetes `json:"kubernetes.io,omitempty"`
}

type kubernetes struct {
	Namespace string `json:"namespace,omitempty"`
	Svcacct   ref    `json:"serviceaccount,omitempty"`
	Pod       *ref   `json:"pod,omitempty"`
	Secret    *ref   `json:"secret,omitempty"`
}

type ref struct {
	Name string `json:"name,omitempty"`
	UID  string `json:"uid,omitempty"`
}

func Claims(sa core.ServiceAccount, pod *core.Pod, secret *core.Secret, expirationSeconds int64, audience []string) (*jwt.Claims, interface{}) {
	now := now()
	sc := &jwt.Claims{
		Subject:   apiserverserviceaccount.MakeUsername(sa.Namespace, sa.Name),
		Audience:  jwt.Audience(audience),
		IssuedAt:  jwt.NewNumericDate(now),
		NotBefore: jwt.NewNumericDate(now),
		Expiry:    jwt.NewNumericDate(now.Add(time.Duration(expirationSeconds) * time.Second)),
	}
	pc := &privateClaims{
		Kubernetes: kubernetes{
			Namespace: sa.Namespace,
			Svcacct: ref{
				Name: sa.Name,
				UID:  string(sa.UID),
			},
		},
	}
	switch {
	case pod != nil:
		pc.Kubernetes.Pod = &ref{
			Name: pod.Name,
			UID:  string(pod.UID),
		}
	case secret != nil:
		pc.Kubernetes.Secret = &ref{
			Name: secret.Name,
			UID:  string(secret.UID),
		}
	}
	return sc, pc
}

func NewValidator(audiences []string, getter ServiceAccountTokenGetter) Validator {
	return &validator{
		auds:   audiences,
		getter: getter,
	}
}

type validator struct {
	auds   []string
	getter ServiceAccountTokenGetter
}

var _ = Validator(&validator{})

func (v *validator) Validate(_ string, public *jwt.Claims, privateObj interface{}) (string, string, string, error) {
	private, ok := privateObj.(*privateClaims)
	if !ok {
		glog.Errorf("jwt validator expected private claim of type *privateClaims but got: %T", privateObj)
		return "", "", "", errors.New("Token could not be validated.")
	}
	err := public.Validate(jwt.Expected{
		Time: now(),
	})
	switch {
	case err == nil:
	case err == jwt.ErrExpired:
		return "", "", "", errors.New("Token has expired.")
	default:
		glog.Errorf("unexpected validation error: %T", err)
		return "", "", "", errors.New("Token could not be validated.")
	}

	var audValid bool

	for _, aud := range v.auds {
		audValid = public.Audience.Contains(aud)
		if audValid {
			break
		}
	}

	if !audValid {
		return "", "", "", errors.New("Token is invalid for this audience.")
	}

	namespace := private.Kubernetes.Namespace
	saref := private.Kubernetes.Svcacct
	podref := private.Kubernetes.Pod
	secref := private.Kubernetes.Secret
	// Make sure service account still exists (name and UID)
	serviceAccount, err := v.getter.GetServiceAccount(namespace, saref.Name)
	if err != nil {
		glog.V(4).Infof("Could not retrieve service account %s/%s: %v", namespace, saref.Name, err)
		return "", "", "", err
	}
	if serviceAccount.DeletionTimestamp != nil {
		glog.V(4).Infof("Service account has been deleted %s/%s", namespace, saref.Name)
		return "", "", "", fmt.Errorf("ServiceAccount %s/%s has been deleted", namespace, saref.Name)
	}
	if string(serviceAccount.UID) != saref.UID {
		glog.V(4).Infof("Service account UID no longer matches %s/%s: %q != %q", namespace, saref.Name, string(serviceAccount.UID), saref.UID)
		return "", "", "", fmt.Errorf("ServiceAccount UID (%s) does not match claim (%s)", serviceAccount.UID, saref.UID)
	}

	if secref != nil {
		// Make sure token hasn't been invalidated by deletion of the secret
		secret, err := v.getter.GetSecret(namespace, secref.Name)
		if err != nil {
			glog.V(4).Infof("Could not retrieve bound secret %s/%s for service account %s/%s: %v", namespace, secref.Name, namespace, saref.Name, err)
			return "", "", "", errors.New("Token has been invalidated")
		}
		if secret.DeletionTimestamp != nil {
			glog.V(4).Infof("Bound secret is deleted and awaiting removal: %s/%s for service account %s/%s", namespace, secref.Name, namespace, saref.Name)
			return "", "", "", errors.New("Token has been invalidated")
		}
		if secref.UID != string(secret.UID) {
			glog.V(4).Infof("Secret UID no longer matches %s/%s: %q != %q", namespace, secref.Name, string(secret.UID), secref.UID)
			return "", "", "", fmt.Errorf("Secret UID (%s) does not match claim (%s)", secret.UID, secref.UID)
		}
	}

	if podref != nil {
		// Make sure token hasn't been invalidated by deletion of the pod
		pod, err := v.getter.GetPod(namespace, podref.Name)
		if err != nil {
			glog.V(4).Infof("Could not retrieve bound secret %s/%s for service account %s/%s: %v", namespace, podref.Name, namespace, saref.Name, err)
			return "", "", "", errors.New("Token has been invalidated")
		}
		if pod.DeletionTimestamp != nil {
			glog.V(4).Infof("Bound pod is deleted and awaiting removal: %s/%s for service account %s/%s", namespace, podref.Name, namespace, saref.Name)
			return "", "", "", errors.New("Token has been invalidated")
		}
		if podref.UID != string(pod.UID) {
			glog.V(4).Infof("Pod UID no longer matches %s/%s: %q != %q", namespace, podref.Name, string(pod.UID), podref.UID)
			return "", "", "", fmt.Errorf("Pod UID (%s) does not match claim (%s)", pod.UID, podref.UID)
		}
	}

	return private.Kubernetes.Namespace, private.Kubernetes.Svcacct.Name, private.Kubernetes.Svcacct.UID, nil
}

func (v *validator) NewPrivateClaims() interface{} {
	return &privateClaims{}
}