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tailscale/cmd/containerboot/kube.go

279 lines
8.0 KiB
Go

// Copyright (c) 2022 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build linux
package main
import (
"bytes"
"context"
"crypto/tls"
"crypto/x509"
"encoding/base64"
"encoding/json"
"fmt"
"io"
"log"
"net/http"
"os"
"path/filepath"
"strings"
"time"
"tailscale.com/tailcfg"
"tailscale.com/util/multierr"
)
// checkSecretPermissions checks the secret access permissions of the current
// pod. It returns an error if the basic permissions tailscale needs are
// missing, and reports whether the patch permission is additionally present.
//
// Errors encountered during the access checking process are logged, but ignored
// so that the pod tries to fail alive if the permissions exist and there's just
// something wrong with SelfSubjectAccessReviews. There shouldn't be, pods
// should always be able to use SSARs to assess their own permissions, but since
// we didn't use to check permissions this way we'll be cautious in case some
// old version of k8s deviates from the current behavior.
func checkSecretPermissions(ctx context.Context, secretName string) (canPatch bool, err error) {
var errs []error
for _, verb := range []string{"get", "update"} {
ok, err := checkPermission(ctx, verb, secretName)
if err != nil {
log.Printf("error checking %s permission on secret %s: %v", verb, secretName, err)
} else if !ok {
errs = append(errs, fmt.Errorf("missing %s permission on secret %q", verb, secretName))
}
}
if len(errs) > 0 {
return false, multierr.New(errs...)
}
ok, err := checkPermission(ctx, "patch", secretName)
if err != nil {
log.Printf("error checking patch permission on secret %s: %v", secretName, err)
return false, nil
}
return ok, nil
}
// checkPermission reports whether the current pod has permission to use the
// given verb (e.g. get, update, patch) on secretName.
func checkPermission(ctx context.Context, verb, secretName string) (bool, error) {
sar := map[string]any{
"apiVersion": "authorization.k8s.io/v1",
"kind": "SelfSubjectAccessReview",
"spec": map[string]any{
"resourceAttributes": map[string]any{
"namespace": kubeNamespace,
"verb": verb,
"resource": "secrets",
"name": secretName,
},
},
}
bs, err := json.Marshal(sar)
if err != nil {
return false, err
}
req, err := http.NewRequest("POST", "/apis/authorization.k8s.io/v1/selfsubjectaccessreviews", bytes.NewReader(bs))
if err != nil {
return false, err
}
resp, err := doKubeRequest(ctx, req)
if err != nil {
return false, err
}
defer resp.Body.Close()
bs, err = io.ReadAll(resp.Body)
if err != nil {
return false, err
}
var res struct {
Status struct {
Allowed bool `json:"allowed"`
} `json:"status"`
}
if err := json.Unmarshal(bs, &res); err != nil {
return false, err
}
return res.Status.Allowed, nil
}
// findKeyInKubeSecret inspects the kube secret secretName for a data
// field called "authkey", and returns its value if present.
func findKeyInKubeSecret(ctx context.Context, secretName string) (string, error) {
req, err := http.NewRequest("GET", fmt.Sprintf("/api/v1/namespaces/%s/secrets/%s", kubeNamespace, secretName), nil)
if err != nil {
return "", err
}
resp, err := doKubeRequest(ctx, req)
if err != nil {
if resp != nil && resp.StatusCode == http.StatusNotFound {
// Kube secret doesn't exist yet, can't have an authkey.
return "", nil
}
return "", err
}
defer resp.Body.Close()
bs, err := io.ReadAll(resp.Body)
if err != nil {
return "", err
}
// We use a map[string]any here rather than import corev1.Secret,
// because we only do very limited things to the secret, and
// importing corev1 adds 12MiB to the compiled binary.
var s map[string]any
if err := json.Unmarshal(bs, &s); err != nil {
return "", err
}
if d, ok := s["data"].(map[string]any); ok {
if v, ok := d["authkey"].(string); ok {
bs, err := base64.StdEncoding.DecodeString(v)
if err != nil {
return "", err
}
return string(bs), nil
}
}
return "", nil
}
// storeDeviceInfo writes deviceID into the "device_id" data field of the kube
// secret secretName.
func storeDeviceInfo(ctx context.Context, secretName string, deviceID tailcfg.StableNodeID, fqdn string) error {
// First check if the secret exists at all. Even if running on
// kubernetes, we do not necessarily store state in a k8s secret.
req, err := http.NewRequest("GET", fmt.Sprintf("/api/v1/namespaces/%s/secrets/%s", kubeNamespace, secretName), nil)
if err != nil {
return err
}
resp, err := doKubeRequest(ctx, req)
if err != nil {
if resp != nil && resp.StatusCode >= 400 && resp.StatusCode <= 499 {
// Assume the secret doesn't exist, or we don't have
// permission to access it.
return nil
}
return err
}
m := map[string]map[string]string{
"stringData": {
"device_id": string(deviceID),
"device_fqdn": fqdn,
},
}
var b bytes.Buffer
if err := json.NewEncoder(&b).Encode(m); err != nil {
return err
}
req, err = http.NewRequest("PATCH", fmt.Sprintf("/api/v1/namespaces/%s/secrets/%s?fieldManager=tailscale-container", kubeNamespace, secretName), &b)
if err != nil {
return err
}
req.Header.Set("Content-Type", "application/strategic-merge-patch+json")
if _, err := doKubeRequest(ctx, req); err != nil {
return err
}
return nil
}
// deleteAuthKey deletes the 'authkey' field of the given kube
// secret. No-op if there is no authkey in the secret.
func deleteAuthKey(ctx context.Context, secretName string) error {
// m is a JSON Patch data structure, see https://jsonpatch.com/ or RFC 6902.
m := []struct {
Op string `json:"op"`
Path string `json:"path"`
}{
{
Op: "remove",
Path: "/data/authkey",
},
}
var b bytes.Buffer
if err := json.NewEncoder(&b).Encode(m); err != nil {
return err
}
req, err := http.NewRequest("PATCH", fmt.Sprintf("/api/v1/namespaces/%s/secrets/%s?fieldManager=tailscale-container", kubeNamespace, secretName), &b)
if err != nil {
return err
}
req.Header.Set("Content-Type", "application/json-patch+json")
if resp, err := doKubeRequest(ctx, req); err != nil {
if resp != nil && resp.StatusCode == http.StatusUnprocessableEntity {
// This is kubernetes-ese for "the field you asked to
// delete already doesn't exist", aka no-op.
return nil
}
return err
}
return nil
}
var (
kubeHost string
kubeNamespace string
kubeToken string
kubeHTTP *http.Transport
)
func initKube(root string) {
// If running in Kubernetes, set things up so that doKubeRequest
// can talk successfully to the kube apiserver.
if os.Getenv("KUBERNETES_SERVICE_HOST") == "" {
return
}
kubeHost = os.Getenv("KUBERNETES_SERVICE_HOST") + ":" + os.Getenv("KUBERNETES_SERVICE_PORT_HTTPS")
bs, err := os.ReadFile(filepath.Join(root, "var/run/secrets/kubernetes.io/serviceaccount/namespace"))
if err != nil {
log.Fatalf("Error reading kube namespace: %v", err)
}
kubeNamespace = strings.TrimSpace(string(bs))
bs, err = os.ReadFile(filepath.Join(root, "var/run/secrets/kubernetes.io/serviceaccount/token"))
if err != nil {
log.Fatalf("Error reading kube token: %v", err)
}
kubeToken = strings.TrimSpace(string(bs))
bs, err = os.ReadFile(filepath.Join(root, "var/run/secrets/kubernetes.io/serviceaccount/ca.crt"))
if err != nil {
log.Fatalf("Error reading kube CA cert: %v", err)
}
cp := x509.NewCertPool()
cp.AppendCertsFromPEM(bs)
kubeHTTP = &http.Transport{
TLSClientConfig: &tls.Config{
RootCAs: cp,
},
IdleConnTimeout: time.Second,
}
}
// doKubeRequest sends r to the kube apiserver.
func doKubeRequest(ctx context.Context, r *http.Request) (*http.Response, error) {
if kubeHTTP == nil {
panic("not in kubernetes")
}
r.URL.Scheme = "https"
r.URL.Host = kubeHost
r.Header.Set("Authorization", "Bearer "+kubeToken)
r.Header.Set("Accept", "application/json")
resp, err := kubeHTTP.RoundTrip(r)
if err != nil {
return nil, err
}
if resp.StatusCode != http.StatusOK && resp.StatusCode != http.StatusCreated {
return resp, fmt.Errorf("got non-200/201 status code %d", resp.StatusCode)
}
return resp, nil
}