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tailscale/kube/client.go

317 lines
8.8 KiB
Go

// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
// Package kube provides a client to interact with Kubernetes.
// This package is Tailscale-internal and not meant for external consumption.
// Further, the API should not be considered stable.
package kube
import (
"bytes"
"context"
"crypto/tls"
"crypto/x509"
"encoding/json"
"fmt"
"io"
"log"
"net/http"
"net/url"
"os"
"path/filepath"
"sync"
"time"
"tailscale.com/util/multierr"
)
const (
saPath = "/var/run/secrets/kubernetes.io/serviceaccount"
defaultURL = "https://kubernetes.default.svc"
)
// rootPathForTests is set by tests to override the root path to the
// service account directory.
var rootPathForTests string
// SetRootPathForTesting sets the path to the service account directory.
func SetRootPathForTesting(p string) {
rootPathForTests = p
}
func readFile(n string) ([]byte, error) {
if rootPathForTests != "" {
return os.ReadFile(filepath.Join(rootPathForTests, saPath, n))
}
return os.ReadFile(filepath.Join(saPath, n))
}
// Client handles connections to Kubernetes.
// It expects to be run inside a cluster.
type Client struct {
mu sync.Mutex
url string
ns string
client *http.Client
token string
tokenExpiry time.Time
}
// New returns a new client
func New() (*Client, error) {
ns, err := readFile("namespace")
if err != nil {
return nil, err
}
caCert, err := readFile("ca.crt")
if err != nil {
return nil, err
}
cp := x509.NewCertPool()
if ok := cp.AppendCertsFromPEM(caCert); !ok {
return nil, fmt.Errorf("kube: error in creating root cert pool")
}
return &Client{
url: defaultURL,
ns: string(ns),
client: &http.Client{
Transport: &http.Transport{
TLSClientConfig: &tls.Config{
RootCAs: cp,
},
},
},
}, nil
}
// SetURL sets the URL to use for the Kubernetes API.
// This is used only for testing.
func (c *Client) SetURL(url string) {
c.url = url
}
func (c *Client) expireToken() {
c.mu.Lock()
defer c.mu.Unlock()
c.tokenExpiry = time.Now()
}
func (c *Client) getOrRenewToken() (string, error) {
c.mu.Lock()
defer c.mu.Unlock()
tk, te := c.token, c.tokenExpiry
if time.Now().Before(te) {
return tk, nil
}
tkb, err := readFile("token")
if err != nil {
return "", err
}
c.token = string(tkb)
c.tokenExpiry = time.Now().Add(30 * time.Minute)
return c.token, nil
}
func (c *Client) secretURL(name string) string {
if name == "" {
return fmt.Sprintf("%s/api/v1/namespaces/%s/secrets", c.url, c.ns)
}
return fmt.Sprintf("%s/api/v1/namespaces/%s/secrets/%s", c.url, c.ns, name)
}
func getError(resp *http.Response) error {
if resp.StatusCode == 200 || resp.StatusCode == 201 {
// These are the only success codes returned by the Kubernetes API.
// https://github.com/kubernetes/community/blob/master/contributors/devel/sig-architecture/api-conventions.md#http-status-codes
return nil
}
st := &Status{}
if err := json.NewDecoder(resp.Body).Decode(st); err != nil {
return err
}
return st
}
func setHeader(key, value string) func(*http.Request) {
return func(req *http.Request) {
req.Header.Set(key, value)
}
}
// doRequest performs an HTTP request to the Kubernetes API.
// If in is not nil, it is expected to be a JSON-encodable object and will be
// sent as the request body.
// If out is not nil, it is expected to be a pointer to an object that can be
// decoded from JSON.
// If the request fails with a 401, the token is expired and a new one is
// requested.
func (c *Client) doRequest(ctx context.Context, method, url string, in, out any, opts ...func(*http.Request)) error {
req, err := c.newRequest(ctx, method, url, in)
if err != nil {
return err
}
for _, opt := range opts {
opt(req)
}
resp, err := c.client.Do(req)
if err != nil {
return err
}
defer resp.Body.Close()
if err := getError(resp); err != nil {
if st, ok := err.(*Status); ok && st.Code == 401 {
c.expireToken()
}
return err
}
if out != nil {
return json.NewDecoder(resp.Body).Decode(out)
}
return nil
}
func (c *Client) newRequest(ctx context.Context, method, url string, in any) (*http.Request, error) {
tk, err := c.getOrRenewToken()
if err != nil {
return nil, err
}
var body io.Reader
if in != nil {
switch in := in.(type) {
case []byte:
body = bytes.NewReader(in)
default:
var b bytes.Buffer
if err := json.NewEncoder(&b).Encode(in); err != nil {
return nil, err
}
body = &b
}
}
req, err := http.NewRequestWithContext(ctx, method, url, body)
if err != nil {
return nil, err
}
if body != nil {
req.Header.Add("Content-Type", "application/json")
}
req.Header.Add("Accept", "application/json")
req.Header.Add("Authorization", "Bearer "+tk)
return req, nil
}
// GetSecret fetches the secret from the Kubernetes API.
func (c *Client) GetSecret(ctx context.Context, name string) (*Secret, error) {
s := &Secret{Data: make(map[string][]byte)}
if err := c.doRequest(ctx, "GET", c.secretURL(name), nil, s); err != nil {
return nil, err
}
return s, nil
}
// CreateSecret creates a secret in the Kubernetes API.
func (c *Client) CreateSecret(ctx context.Context, s *Secret) error {
s.Namespace = c.ns
return c.doRequest(ctx, "POST", c.secretURL(""), s, nil)
}
// UpdateSecret updates a secret in the Kubernetes API.
func (c *Client) UpdateSecret(ctx context.Context, s *Secret) error {
return c.doRequest(ctx, "PUT", c.secretURL(s.Name), s, nil)
}
// JSONPatch is a JSON patch operation.
// It currently (2023-03-02) only supports the "remove" operation.
//
// https://tools.ietf.org/html/rfc6902
type JSONPatch struct {
Op string `json:"op"`
Path string `json:"path"`
}
// JSONPatchSecret updates a secret in the Kubernetes API using a JSON patch.
// It currently (2023-03-02) only supports the "remove" operation.
func (c *Client) JSONPatchSecret(ctx context.Context, name string, patch []JSONPatch) error {
for _, p := range patch {
if p.Op != "remove" {
panic(fmt.Errorf("unsupported JSON patch operation: %q", p.Op))
}
}
return c.doRequest(ctx, "PATCH", c.secretURL(name), patch, nil, setHeader("Content-Type", "application/json-patch+json"))
}
// StrategicMergePatchSecret updates a secret in the Kubernetes API using a
// strategic merge patch.
// If a fieldManager is provided, it will be used to track the patch.
func (c *Client) StrategicMergePatchSecret(ctx context.Context, name string, s *Secret, fieldManager string) error {
surl := c.secretURL(name)
if fieldManager != "" {
uv := url.Values{
"fieldManager": {fieldManager},
}
surl += "?" + uv.Encode()
}
s.Namespace = c.ns
s.Name = name
return c.doRequest(ctx, "PATCH", surl, s, nil, setHeader("Content-Type", "application/strategic-merge-patch+json"))
}
// 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 (c *Client) CheckSecretPermissions(ctx context.Context, secretName string) (canPatch bool, err error) {
var errs []error
for _, verb := range []string{"get", "update"} {
ok, err := c.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 := c.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 (c *Client) 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": c.ns,
"verb": verb,
"resource": "secrets",
"name": secretName,
},
},
}
var res struct {
Status struct {
Allowed bool `json:"allowed"`
} `json:"status"`
}
url := c.url + "/apis/authorization.k8s.io/v1/selfsubjectaccessreviews"
if err := c.doRequest(ctx, "POST", url, sar, &res); err != nil {
return false, err
}
return res.Status.Allowed, nil
}