Add validating admission webhook to verify opaque configs

This is a straight copy of this PR
kubernetes-sigs/dra-example-driver#75, with
minimal changes to make it work in this repo.

Signed-off-by: Kevin Klues <kklues@nvidia.com>

Author: klueska

README.md

@@ -46,6 +46,22 @@ As of today, the recommended installation method is via Helm.
 Detailed instructions can (for now) be found [here](https://github.com/NVIDIA/k8s-dra-driver-gpu/discussions/249).
 In the future, this driver will be included in the [NVIDIA GPU Operator](https://github.com/NVIDIA/gpu-operator) and does not need to be installed separately anymore.
 
+### Validating Admission Webhook
+
+The validating admission webhook is disabled by default. To enable it, install cert-manager and its CRDs, then set the `webhook.enabled=true` value when the nvidia-dra-driver-gpu chart is installed.
+
+```bash
+helm install \
+  --repo https://charts.jetstack.io \
+  --version v1.16.3 \
+  --create-namespace \
+  --namespace cert-manager \
+  --wait \
+  --set crds.enabled=true \
+  cert-manager \
+  cert-manager
+```
+
 ## A (kind) demo
 
 Below, we demonstrate a basic use case: sharing a single GPU across two containers running in the same Kubernetes pod.

cmd/webhook/main.go

@@ -0,0 +1,308 @@
+/*
+Copyright 2025 The Kubernetes Authors.
+Copyright 2025 NVIDIA Corporation.
+
+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 main
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"strings"
+
+	"github.com/urfave/cli/v2"
+
+	admissionv1 "k8s.io/api/admission/v1"
+	resourceapi "k8s.io/api/resource/v1beta1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apimachinery/pkg/runtime/serializer"
+	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
+	"k8s.io/klog/v2"
+
+	configapi "github.com/NVIDIA/k8s-dra-driver-gpu/api/nvidia.com/resource/v1beta1"
+	"github.com/NVIDIA/k8s-dra-driver-gpu/pkg/flags"
+)
+
+const (
+	DriverName = "gpu.nvidia.com"
+)
+
+var (
+	resourceClaimResource = metav1.GroupVersionResource{
+		Group:    resourceapi.SchemeGroupVersion.Group,
+		Version:  resourceapi.SchemeGroupVersion.Version,
+		Resource: "resourceclaims",
+	}
+	resourceClaimTemplateResource = metav1.GroupVersionResource{
+		Group:    resourceapi.SchemeGroupVersion.Group,
+		Version:  resourceapi.SchemeGroupVersion.Version,
+		Resource: "resourceclaimtemplates",
+	}
+)
+
+type Flags struct {
+	loggingConfig *flags.LoggingConfig
+
+	certFile string
+	keyFile  string
+	port     int
+}
+
+var scheme = runtime.NewScheme()
+var codecs = serializer.NewCodecFactory(scheme)
+
+func init() {
+	utilruntime.Must(admissionv1.AddToScheme(scheme))
+}
+
+func main() {
+	if err := newApp().Run(os.Args); err != nil {
+		fmt.Fprintf(os.Stderr, "Error: %v\n", err)
+		os.Exit(1)
+	}
+}
+
+func newApp() *cli.App {
+	flags := &Flags{
+		loggingConfig: flags.NewLoggingConfig(),
+	}
+	cliFlags := []cli.Flag{
+		&cli.StringFlag{
+			Name:        "tls-cert-file",
+			Usage:       "File containing the default x509 Certificate for HTTPS. (CA cert, if any, concatenated after server cert).",
+			Destination: &flags.certFile,
+			Required:    true,
+		},
+		&cli.StringFlag{
+			Name:        "tls-private-key-file",
+			Usage:       "File containing the default x509 private key matching --tls-cert-file.",
+			Destination: &flags.keyFile,
+			Required:    true,
+		},
+		&cli.IntFlag{
+			Name:        "port",
+			Usage:       "Secure port that the webhook listens on",
+			Value:       443,
+			Destination: &flags.port,
+		},
+	}
+	cliFlags = append(cliFlags, flags.loggingConfig.Flags()...)
+
+	app := &cli.App{
+		Name:            "webhook",
+		Usage:           "webhook implements a validating admission webhook complementing a DRA driver plugin.",
+		ArgsUsage:       " ",
+		HideHelpCommand: true,
+		Flags:           cliFlags,
+		Before: func(c *cli.Context) error {
+			if c.Args().Len() > 0 {
+				return fmt.Errorf("arguments not supported: %v", c.Args().Slice())
+			}
+			return flags.loggingConfig.Apply()
+		},
+		Action: func(c *cli.Context) error {
+			server := &http.Server{
+				Handler: newMux(),
+				Addr:    fmt.Sprintf(":%d", flags.port),
+			}
+			klog.Info("starting webhook server on", server.Addr)
+			return server.ListenAndServeTLS(flags.certFile, flags.keyFile)
+		},
+	}
+
+	return app
+}
+
+func newMux() *http.ServeMux {
+	mux := http.NewServeMux()
+	mux.HandleFunc("/validate-resource-claim-parameters", serveResourceClaim)
+	mux.HandleFunc("/readyz", func(w http.ResponseWriter, req *http.Request) {
+		_, err := w.Write([]byte("ok"))
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+			return
+		}
+	})
+	return mux
+}
+
+func serveResourceClaim(w http.ResponseWriter, r *http.Request) {
+	serve(w, r, admitResourceClaimParameters)
+}
+
+// serve handles the http portion of a request prior to handing to an admit
+// function.
+func serve(w http.ResponseWriter, r *http.Request, admit func(admissionv1.AdmissionReview) *admissionv1.AdmissionResponse) {
+	var body []byte
+	if r.Body != nil {
+		data, err := io.ReadAll(r.Body)
+		if err != nil {
+			klog.Error(err)
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+			return
+		}
+		body = data
+	}
+
+	// verify the content type is accurate
+	contentType := r.Header.Get("Content-Type")
+	if contentType != "application/json" {
+		msg := fmt.Sprintf("contentType=%s, expected application/json", contentType)
+		klog.Error(msg)
+		http.Error(w, msg, http.StatusUnsupportedMediaType)
+		return
+	}
+
+	klog.V(2).Infof("handling request: %s", body)
+
+	requestedAdmissionReview, err := readAdmissionReview(body)
+	if err != nil {
+		msg := fmt.Sprintf("failed to read AdmissionReview from request body: %v", err)
+		klog.Error(msg)
+		http.Error(w, msg, http.StatusBadRequest)
+		return
+	}
+	responseAdmissionReview := &admissionv1.AdmissionReview{}
+	responseAdmissionReview.SetGroupVersionKind(requestedAdmissionReview.GroupVersionKind())
+	responseAdmissionReview.Response = admit(*requestedAdmissionReview)
+	responseAdmissionReview.Response.UID = requestedAdmissionReview.Request.UID
+
+	klog.V(2).Infof("sending response: %v", responseAdmissionReview)
+	respBytes, err := json.Marshal(responseAdmissionReview)
+	if err != nil {
+		klog.Error(err)
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	w.Header().Set("Content-Type", "application/json")
+	if _, err := w.Write(respBytes); err != nil {
+		klog.Error(err)
+	}
+}
+
+func readAdmissionReview(data []byte) (*admissionv1.AdmissionReview, error) {
+	deserializer := codecs.UniversalDeserializer()
+	obj, gvk, err := deserializer.Decode(data, nil, nil)
+	if err != nil {
+		return nil, fmt.Errorf("request could not be decoded: %w", err)
+	}
+
+	if *gvk != admissionv1.SchemeGroupVersion.WithKind("AdmissionReview") {
+		return nil, fmt.Errorf("unsupported group version kind: %v", gvk)
+	}
+
+	requestedAdmissionReview, ok := obj.(*admissionv1.AdmissionReview)
+	if !ok {
+		return nil, fmt.Errorf("expected v1.AdmissionReview but got: %T", obj)
+	}
+
+	return requestedAdmissionReview, nil
+}
+
+// admitResourceClaimParameters accepts both ResourceClaims and ResourceClaimTemplates and validates their
+// opaque device configuration parameters for this driver.
+func admitResourceClaimParameters(ar admissionv1.AdmissionReview) *admissionv1.AdmissionResponse {
+	klog.V(2).Info("admitting resource claim parameters")
+
+	var deviceConfigs []resourceapi.DeviceClaimConfiguration
+	var specPath string
+
+	raw := ar.Request.Object.Raw
+	deserializer := codecs.UniversalDeserializer()
+
+	switch ar.Request.Resource {
+	case resourceClaimResource:
+		claim := resourceapi.ResourceClaim{}
+		if _, _, err := deserializer.Decode(raw, nil, &claim); err != nil {
+			klog.Error(err)
+			return &admissionv1.AdmissionResponse{
+				Result: &metav1.Status{
+					Message: err.Error(),
+					Reason:  metav1.StatusReasonBadRequest,
+				},
+			}
+		}
+		deviceConfigs = claim.Spec.Devices.Config
+		specPath = "spec"
+	case resourceClaimTemplateResource:
+		claimTemplate := resourceapi.ResourceClaimTemplate{}
+		if _, _, err := deserializer.Decode(raw, nil, &claimTemplate); err != nil {
+			klog.Error(err)
+			return &admissionv1.AdmissionResponse{
+				Result: &metav1.Status{
+					Message: err.Error(),
+					Reason:  metav1.StatusReasonBadRequest,
+				},
+			}
+		}
+		deviceConfigs = claimTemplate.Spec.Spec.Devices.Config
+		specPath = "spec.spec"
+	default:
+		msg := fmt.Sprintf("expected resource to be %s or %s, got %s", resourceClaimResource, resourceClaimTemplateResource, ar.Request.Resource)
+		klog.Error(msg)
+		return &admissionv1.AdmissionResponse{
+			Result: &metav1.Status{
+				Message: msg,
+				Reason:  metav1.StatusReasonBadRequest,
+			},
+		}
+	}
+
+	var errs []error
+	for configIndex, config := range deviceConfigs {
+		if config.Opaque == nil || config.Opaque.Driver != DriverName {
+			continue
+		}
+
+		fieldPath := fmt.Sprintf("%s.devices.config[%d].opaque.parameters", specPath, configIndex)
+		decodedConfig, err := runtime.Decode(configapi.Decoder, config.Opaque.Parameters.Raw)
+		if err != nil {
+			errs = append(errs, fmt.Errorf("error decoding object at %s: %w", fieldPath, err))
+			continue
+		}
+		gpuConfig, ok := decodedConfig.(*configapi.GpuConfig)
+		if !ok {
+			errs = append(errs, fmt.Errorf("expected v1beta1.GpuConfig at %s but got: %T", fieldPath, decodedConfig))
+			continue
+		}
+		err = gpuConfig.Validate()
+		if err != nil {
+			errs = append(errs, fmt.Errorf("object at %s is invalid: %w", fieldPath, err))
+		}
+	}
+
+	if len(errs) > 0 {
+		var errMsgs []string
+		for _, err := range errs {
+			errMsgs = append(errMsgs, err.Error())
+		}
+		msg := fmt.Sprintf("%d configs failed to validate: %s", len(errs), strings.Join(errMsgs, "; "))
+		klog.Error(msg)
+		return &admissionv1.AdmissionResponse{
+			Result: &metav1.Status{
+				Message: msg,
+				Reason:  metav1.StatusReason(metav1.StatusReasonInvalid),
+			},
+		}
+	}
+
+	return &admissionv1.AdmissionResponse{
+		Allowed: true,
+	}
+}