polaris/pkg/webhook/webhook.go

// Copyright 2019 FairwindsOps Inc
//
// 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 webhook

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"net/http"

	"github.com/fairwindsops/polaris/pkg/config"
	"github.com/fairwindsops/polaris/pkg/kube"
	validator "github.com/fairwindsops/polaris/pkg/validator"

	"github.com/sirupsen/logrus"
	admissionregistrationv1beta1 "k8s.io/api/admissionregistration/v1beta1"
	corev1 "k8s.io/api/core/v1"
	"k8s.io/apimachinery/pkg/runtime"
	"sigs.k8s.io/controller-runtime/pkg/client"
	"sigs.k8s.io/controller-runtime/pkg/manager"
	"sigs.k8s.io/controller-runtime/pkg/runtime/inject"
	"sigs.k8s.io/controller-runtime/pkg/webhook/admission"
	"sigs.k8s.io/controller-runtime/pkg/webhook/admission/builder"
	"sigs.k8s.io/controller-runtime/pkg/webhook/admission/types"
)

// Validator validates k8s resources.
type Validator struct {
	client  client.Client
	decoder types.Decoder
	Config  config.Configuration
}

var _ inject.Client = &Validator{}

// InjectClient injects the client.
func (v *Validator) InjectClient(c client.Client) error {
	v.client = c
	return nil
}

var _ inject.Decoder = &Validator{}

// InjectDecoder injects the decoder.
func (v *Validator) InjectDecoder(d types.Decoder) error {
	v.decoder = d
	return nil
}

var _ admission.Handler = &Validator{}

// NewWebhook creates a validating admission webhook for the apiType.
func NewWebhook(name string, mgr manager.Manager, validator Validator, apiType runtime.Object) (*admission.Webhook, error) {
	name = fmt.Sprintf("%s.k8s.io", name)
	path := fmt.Sprintf("/validating-%s", name)

	webhook, err := builder.NewWebhookBuilder().
		Name(name).
		Validating().
		Path(path).
		Operations(admissionregistrationv1beta1.Create, admissionregistrationv1beta1.Update).
		WithManager(mgr).
		ForType(apiType).
		Handlers(&validator).
		Build()
	if err != nil {
		return nil, err
	}
	return webhook, nil
}

func (v *Validator) handleInternal(ctx context.Context, req types.Request) (*validator.PodResult, error) {
	pod := corev1.Pod{}
	var originalObject interface{}
	if req.AdmissionRequest.Kind.Kind == "Pod" {
		err := v.decoder.Decode(req, &pod)
		if err != nil {
			return nil, err
		}
		if len(pod.ObjectMeta.OwnerReferences) > 0 {
			logrus.Infof("Allowing owned pod %s/%s to pass through webhook", pod.ObjectMeta.Namespace, pod.ObjectMeta.Name)
			return nil, nil
		}
		originalObject = pod
	} else {
		decoded := map[string]interface{}{}
		err := json.Unmarshal(req.AdmissionRequest.Object.Raw, &decoded)
		if err != nil {
			return nil, err
		}
		podMap := kube.GetPodSpec(decoded)
		if podMap == nil {
			return nil, errors.New("Object does not contain pods")
		}
		encoded, err := json.Marshal(podMap)
		if err != nil {
			return nil, err
		}
		err = json.Unmarshal(encoded, &pod.Spec)
		if err != nil {
			return nil, err
		}
		originalObject = decoded
	}
	controller, err := kube.NewGenericWorkloadFromPod(pod, originalObject)
	if err != nil {
		return nil, err
	}
	controller.Kind = req.AdmissionRequest.Kind.Kind
	controllerResult, err := validator.ValidateController(&v.Config, controller)
	if err != nil {
		return nil, err
	}
	return &controllerResult.PodResult, nil
}

// Handle for Validator to run validation checks.
func (v *Validator) Handle(ctx context.Context, req types.Request) types.Response {
	podResult, err := v.handleInternal(ctx, req)
	if err != nil {
		logrus.Errorf("Error validating request: %v", err)
		return admission.ErrorResponse(http.StatusBadRequest, err)
	}
	allowed := true
	reason := ""
	if podResult != nil {
		numDangers := podResult.GetSummary().Dangers
		if numDangers > 0 {
			allowed = false
			reason = getFailureReason(*podResult)
		}
		logrus.Infof("%d validation errors found when validating %s", numDangers, podResult.Name)
	}
	return admission.ValidationResponse(allowed, reason)
}

func getFailureReason(podResult validator.PodResult) string {
	reason := "\nPolaris prevented this deployment due to configuration problems:\n"

	for _, message := range podResult.Results {
		if !message.Success && message.Severity == config.SeverityDanger {
			reason += fmt.Sprintf("- Pod: %s\n", message.Message)
		}
	}

	for _, containerResult := range podResult.ContainerResults {
		for _, message := range containerResult.Results {
			if !message.Success && message.Severity == config.SeverityDanger {
				reason += fmt.Sprintf("- Container %s: %s\n", containerResult.Name, message.Message)
			}
		}
	}

	return reason
}