handler.go

package agent_inject

import (
	"encoding/json"
	"fmt"
	"io/ioutil"
	"net/http"
	"strings"

	"github.com/hashicorp/go-hclog"
	"github.com/hashicorp/vault-k8s/agent-inject/agent"
	"github.com/hashicorp/vault/sdk/helper/strutil"
	"github.com/mattbaird/jsonpatch"
	admissionv1 "k8s.io/api/admission/v1"
	"k8s.io/api/admission/v1beta1"
	corev1 "k8s.io/api/core/v1"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/runtime"
	"k8s.io/apimachinery/pkg/runtime/schema"
	"k8s.io/apimachinery/pkg/runtime/serializer"
	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
	"k8s.io/client-go/kubernetes"
)

var (
	admissionScheme = runtime.NewScheme()
	deserializer    = func() runtime.Decoder {
		codecs := serializer.NewCodecFactory(admissionScheme)
		return codecs.UniversalDeserializer()
	}

	kubeSystemNamespaces = []string{
		metav1.NamespaceSystem,
		metav1.NamespacePublic,
	}
)

func init() {
	utilruntime.Must(admissionv1.AddToScheme(admissionScheme))
	utilruntime.Must(v1beta1.AddToScheme(admissionScheme))
}

// Handler is the HTTP handler for admission webhooks.
type Handler struct {
	// RequireAnnotation means that the annotation must be given to inject.
	// If this is false, injection is default.
	RequireAnnotation          bool
	VaultAddress               string
	VaultAuthType              string
	VaultAuthPath              string
	ProxyAddress               string
	ImageVault                 string
	Clientset                  *kubernetes.Clientset
	Log                        hclog.Logger
	RevokeOnShutdown           bool
	UserID                     string
	GroupID                    string
	SameID                     bool
	SetSecurityContext         bool
	DefaultTemplate            string
	ResourceRequestCPU         string
	ResourceRequestMem         string
	ResourceLimitCPU           string
	ResourceLimitMem           string
	ExitOnRetryFailure         bool
	StaticSecretRenderInterval string
	AuthMinBackoff             string
	AuthMaxBackoff             string
}

// Handle is the http.HandlerFunc implementation that actually handles the
// webhook request for admission control. This should be registered or
// served via an HTTP server.
func (h *Handler) Handle(w http.ResponseWriter, r *http.Request) {
	h.Log.Info("Request received", "Method", r.Method, "URL", r.URL)

	if ct := r.Header.Get("Content-Type"); ct != "application/json" {
		msg := fmt.Sprintf("Invalid content-type: %q", ct)
		http.Error(w, msg, http.StatusBadRequest)
		h.Log.Warn("warning for request", "Warn", msg, "Code", http.StatusBadRequest)
		return
	}

	var body []byte
	if r.Body != nil {
		var err error
		if body, err = ioutil.ReadAll(r.Body); err != nil {
			msg := fmt.Sprintf("error reading request body: %s", err)
			http.Error(w, msg, http.StatusBadRequest)
			h.Log.Error("error on request", "Error", msg, "Code", http.StatusBadRequest)
			return
		}
	}
	if len(body) == 0 {
		msg := "Empty request body"
		http.Error(w, msg, http.StatusBadRequest)
		h.Log.Error("warning for request", "Warn", msg, "Code", http.StatusBadRequest)
		return
	}

	var admResp admissionv1.AdmissionReview

	// Both v1 and v1beta1 AdmissionReview types are exactly the same, so the v1beta1 type can
	// be decoded into the v1 type. However the runtime codec's decoder guesses which type to
	// decode into by type name if an Object's TypeMeta isn't set. By setting TypeMeta of an
	// unregistered type to the v1 GVK, the decoder will coerce a v1beta1 AdmissionReview to v1.
	// The actual AdmissionReview GVK will be used to write a typed response in case the
	// webhook config permits multiple versions, otherwise this response will fail.
	admReq := unversionedAdmissionReview{}
	admReq.SetGroupVersionKind(admissionv1.SchemeGroupVersion.WithKind("AdmissionReview"))
	_, actualAdmRevGVK, err := deserializer().Decode(body, nil, &admReq)
	if err != nil {
		msg := fmt.Sprintf("error decoding admission request: %s", err)
		http.Error(w, msg, http.StatusInternalServerError)
		h.Log.Error("error on request", "Error", msg, "Code", http.StatusInternalServerError)
		return
	} else {
		admResp.Response = h.Mutate(admReq.Request)
	}

	// Default to a v1 AdmissionReview, otherwise the API server may not recognize the request
	// if multiple AdmissionReview versions are permitted by the webhook config.
	if actualAdmRevGVK == nil || *actualAdmRevGVK == (schema.GroupVersionKind{}) {
		admResp.SetGroupVersionKind(admissionv1.SchemeGroupVersion.WithKind("AdmissionReview"))
	} else {
		admResp.SetGroupVersionKind(*actualAdmRevGVK)
	}

	resp, err := json.Marshal(&admResp)
	if err != nil {
		msg := fmt.Sprintf("error marshalling admission response: %s", err)
		http.Error(w, msg, http.StatusInternalServerError)
		h.Log.Error("error on request", "Error", msg, "Code", http.StatusInternalServerError)
		return
	}

	if _, err := w.Write(resp); err != nil {
		h.Log.Error("error writing response", "Error", err)
	}
}

// Mutate takes an admission request and performs mutation if necessary,
// returning the final API response.
func (h *Handler) Mutate(req *admissionv1.AdmissionRequest) *admissionv1.AdmissionResponse {
	// Decode the pod from the request
	var pod corev1.Pod
	if err := json.Unmarshal(req.Object.Raw, &pod); err != nil {
		h.Log.Error("could not unmarshal request to pod: %s", err)
		h.Log.Debug("%s", req.Object.Raw)
		return &admissionv1.AdmissionResponse{
			Result: &metav1.Status{
				Message: err.Error(),
			},
		}
	}

	// Build the basic response
	resp := &admissionv1.AdmissionResponse{
		Allowed: true,
		UID:     req.UID,
	}

	h.Log.Debug("checking if should inject agent..")
	inject, err := agent.ShouldInject(&pod)
	if err != nil && !strings.Contains(err.Error(), "no inject annotation found") {
		err := fmt.Errorf("error checking if should inject agent: %s", err)
		return admissionError(err)
	} else if !inject {
		return resp
	}

	h.Log.Debug("checking namespaces..")
	if strutil.StrListContains(kubeSystemNamespaces, req.Namespace) {
		err := fmt.Errorf("error with request namespace: cannot inject into system namespaces: %s", req.Namespace)
		return admissionError(err)
	}

	h.Log.Debug("setting default annotations..")
	var patches []*jsonpatch.JsonPatchOperation
	cfg := agent.AgentConfig{
		Image:                      h.ImageVault,
		Address:                    h.VaultAddress,
		AuthType:                   h.VaultAuthType,
		AuthPath:                   h.VaultAuthPath,
		ProxyAddress:               h.ProxyAddress,
		Namespace:                  req.Namespace,
		RevokeOnShutdown:           h.RevokeOnShutdown,
		UserID:                     h.UserID,
		GroupID:                    h.GroupID,
		SameID:                     h.SameID,
		SetSecurityContext:         h.SetSecurityContext,
		DefaultTemplate:            h.DefaultTemplate,
		ResourceRequestCPU:         h.ResourceRequestCPU,
		ResourceRequestMem:         h.ResourceRequestMem,
		ResourceLimitCPU:           h.ResourceLimitCPU,
		ResourceLimitMem:           h.ResourceLimitMem,
		ExitOnRetryFailure:         h.ExitOnRetryFailure,
		StaticSecretRenderInterval: h.StaticSecretRenderInterval,
		AuthMinBackoff:             h.AuthMinBackoff,
		AuthMaxBackoff:             h.AuthMaxBackoff,
	}
	err = agent.Init(&pod, cfg)
	if err != nil {
		err := fmt.Errorf("error adding default annotations: %s", err)
		return admissionError(err)
	}

	h.Log.Debug("creating new agent..")
	agentSidecar, err := agent.New(&pod, patches)
	if err != nil {
		err := fmt.Errorf("error creating new agent sidecar: %s", err)
		return admissionError(err)
	}

	h.Log.Debug("validating agent configuration..")
	err = agentSidecar.Validate()
	if err != nil {
		err := fmt.Errorf("error validating agent configuration: %s", err)
		return admissionError(err)
	}

	h.Log.Debug("creating patches for the pod..")
	patch, err := agentSidecar.Patch()
	if err != nil {
		err := fmt.Errorf("error creating patch for agent: %s", err)
		return admissionError(err)
	}

	resp.Patch = patch
	patchType := admissionv1.PatchTypeJSONPatch
	resp.PatchType = &patchType

	return resp
}

func admissionError(err error) *admissionv1.AdmissionResponse {
	return &admissionv1.AdmissionResponse{
		Result: &metav1.Status{
			Message: err.Error(),
		},
	}
}

// unversionedAdmissionReview is used to decode both v1 and v1beta1 AdmissionReview types.
type unversionedAdmissionReview struct {
	admissionv1.AdmissionReview
}

var _ runtime.Object = &unversionedAdmissionReview{}