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admission.go
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admission.go
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// Copyright (c) 2021 SAP SE or an SAP affiliate company. All rights reserved. This file is licensed under the Apache Software License, v. 2 except as noted otherwise in the LICENSE file
//
// 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 kubeconfigsecret
import (
"context"
"fmt"
"net/http"
"github.com/go-logr/logr"
admissionv1 "k8s.io/api/admission/v1"
corev1 "k8s.io/api/core/v1"
metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
"k8s.io/client-go/tools/clientcmd"
"sigs.k8s.io/controller-runtime/pkg/webhook/admission"
"github.com/gardener/gardener/pkg/admissioncontroller/metrics"
acadmission "github.com/gardener/gardener/pkg/admissioncontroller/webhooks/admission"
"github.com/gardener/gardener/pkg/client/kubernetes"
"github.com/gardener/gardener/pkg/logger"
"github.com/gardener/gardener/pkg/utils"
)
const (
// HandlerName is the name of this admission webhook handler.
HandlerName = "kubeconfig_validator"
// WebhookPath is the HTTP handler path for this admission webhook handler.
WebhookPath = "/webhooks/validate-kubeconfig-secrets"
// statusReasonInvalidKubeconfig is a StatusReason that will be sent as part of the webhook's response if the secret
// contains an invalid kubeconfig.
statusReasonInvalidKubeconfig = metav1.StatusReason("InvalidKubeconfig")
// metricReasonRejectedKubeconfig is a metric reason value for a reason when a kubeconfig was rejected.
metricReasonRejectedKubeconfig = "Rejected Kubeconfig"
)
var secretGVK = metav1.GroupVersionKind{Group: "", Kind: "Secret", Version: "v1"}
// New creates a new webhook handler validating CREATE and UPDATE requests on secrets. It checks, if the secrets
// contains a kubeconfig and denies kubeconfigs with invalid fields (e.g. tokenFile or exec).
func New(logger logr.Logger) *handler {
return &handler{logger: logger}
}
type handler struct {
logger logr.Logger
decoder *admission.Decoder
}
var _ admission.Handler = &handler{}
func (h *handler) InjectDecoder(d *admission.Decoder) error {
h.decoder = d
return nil
}
func (h *handler) Handle(_ context.Context, request admission.Request) admission.Response {
// If the request does not indicate the correct operations (CREATE, UPDATE) we allow the review without further doing.
if request.Operation != admissionv1.Create && request.Operation != admissionv1.Update {
return acadmission.Allowed("operation is neither CREATE nor UPDATE")
}
if request.Kind != secretGVK {
return acadmission.Allowed("resource is not corev1.Secret")
}
if request.SubResource != "" {
return acadmission.Allowed("subresources on secrets are not handled")
}
requestID, err := utils.GenerateRandomString(8)
if err != nil {
return admission.Errored(http.StatusInternalServerError, err)
}
requestLogger := h.logger.WithValues(logger.IDFieldName, requestID)
secret := &corev1.Secret{}
if err := h.decoder.Decode(request, secret); err != nil {
return admission.Errored(http.StatusInternalServerError, err)
}
response := admitKubeconfigSecret(secret)
if !response.Allowed && response.Result != nil {
response.Result.Reason = statusReasonInvalidKubeconfig
requestLogger.Info("rejected secret", "reason", response.Result.Reason,
"message", response.Result.Message, "operation", request.Operation,
"namespace", request.Namespace, "name", request.Name, "username", request.UserInfo.Username)
metrics.RejectedResources.WithLabelValues(
string(request.Operation),
request.Kind.Kind,
request.Namespace,
metricReasonRejectedKubeconfig,
).Inc()
}
return response
}
func admitKubeconfigSecret(secret *corev1.Secret) admission.Response {
kubeconfig, ok := secret.Data[kubernetes.KubeConfig]
if !ok {
return acadmission.Allowed("secret does not contain kubeconfig")
}
clientConfig, err := clientcmd.NewClientConfigFromBytes(kubeconfig)
if err != nil {
return admission.Errored(http.StatusUnprocessableEntity, err)
}
// Validate that the given kubeconfig doesn't have fields in its auth-info that are
// not acceptable.
rawConfig, err := clientConfig.RawConfig()
if err != nil {
return admission.Errored(http.StatusUnprocessableEntity, err)
}
if err := kubernetes.ValidateConfig(rawConfig); err != nil {
return admission.Errored(http.StatusUnprocessableEntity, fmt.Errorf("secret contains invalid kubeconfig: %w", err))
}
return acadmission.Allowed("kubeconfig is valid")
}