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tailscale/cmd/k8s-operator/proxy.go

275 lines
8.7 KiB
Go

// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
//go:build !plan9
package main
import (
"context"
"crypto/tls"
"fmt"
"log"
"net/http"
"net/http/httputil"
"net/url"
"os"
"strings"
"go.uber.org/zap"
"k8s.io/client-go/rest"
"k8s.io/client-go/transport"
"tailscale.com/client/tailscale"
"tailscale.com/client/tailscale/apitype"
"tailscale.com/tailcfg"
"tailscale.com/tsnet"
"tailscale.com/types/logger"
"tailscale.com/util/clientmetric"
"tailscale.com/util/set"
)
type whoIsKey struct{}
// whoIsFromRequest returns the WhoIsResponse previously stashed by a call to
// addWhoIsToRequest.
func whoIsFromRequest(r *http.Request) *apitype.WhoIsResponse {
return r.Context().Value(whoIsKey{}).(*apitype.WhoIsResponse)
}
// addWhoIsToRequest stashes who in r's context, retrievable by a call to
// whoIsFromRequest.
func addWhoIsToRequest(r *http.Request, who *apitype.WhoIsResponse) *http.Request {
return r.WithContext(context.WithValue(r.Context(), whoIsKey{}, who))
}
var counterNumRequestsProxied = clientmetric.NewCounter("k8s_auth_proxy_requests_proxied")
type apiServerProxyMode int
const (
apiserverProxyModeDisabled apiServerProxyMode = iota
apiserverProxyModeEnabled
apiserverProxyModeNoAuth
)
func parseAPIProxyMode() apiServerProxyMode {
haveAuthProxyEnv := os.Getenv("AUTH_PROXY") != ""
haveAPIProxyEnv := os.Getenv("APISERVER_PROXY") != ""
switch {
case haveAPIProxyEnv && haveAuthProxyEnv:
log.Fatal("AUTH_PROXY and APISERVER_PROXY are mutually exclusive")
case haveAuthProxyEnv:
var authProxyEnv = defaultBool("AUTH_PROXY", false) // deprecated
if authProxyEnv {
return apiserverProxyModeEnabled
}
return apiserverProxyModeDisabled
case haveAPIProxyEnv:
var apiProxyEnv = defaultEnv("APISERVER_PROXY", "") // true, false or "noauth"
switch apiProxyEnv {
case "true":
return apiserverProxyModeEnabled
case "false", "":
return apiserverProxyModeDisabled
case "noauth":
return apiserverProxyModeNoAuth
default:
panic(fmt.Sprintf("unknown APISERVER_PROXY value %q", apiProxyEnv))
}
}
return apiserverProxyModeDisabled
}
// maybeLaunchAPIServerProxy launches the auth proxy, which is a small HTTP server
// that authenticates requests using the Tailscale LocalAPI and then proxies
// them to the kube-apiserver.
func maybeLaunchAPIServerProxy(zlog *zap.SugaredLogger, restConfig *rest.Config, s *tsnet.Server, mode apiServerProxyMode) {
if mode == apiserverProxyModeDisabled {
return
}
startlog := zlog.Named("launchAPIProxy")
if mode == apiserverProxyModeNoAuth {
restConfig = rest.AnonymousClientConfig(restConfig)
}
cfg, err := restConfig.TransportConfig()
if err != nil {
startlog.Fatalf("could not get rest.TransportConfig(): %v", err)
}
// Kubernetes uses SPDY for exec and port-forward, however SPDY is
// incompatible with HTTP/2; so disable HTTP/2 in the proxy.
tr := http.DefaultTransport.(*http.Transport).Clone()
tr.TLSClientConfig, err = transport.TLSConfigFor(cfg)
if err != nil {
startlog.Fatalf("could not get transport.TLSConfigFor(): %v", err)
}
tr.TLSNextProto = make(map[string]func(authority string, c *tls.Conn) http.RoundTripper)
rt, err := transport.HTTPWrappersForConfig(cfg, tr)
if err != nil {
startlog.Fatalf("could not get rest.TransportConfig(): %v", err)
}
go runAPIServerProxy(s, rt, zlog.Named("apiserver-proxy").Infof, mode)
}
// apiserverProxy is an http.Handler that authenticates requests using the Tailscale
// LocalAPI and then proxies them to the Kubernetes API.
type apiserverProxy struct {
logf logger.Logf
lc *tailscale.LocalClient
rp *httputil.ReverseProxy
}
func (h *apiserverProxy) ServeHTTP(w http.ResponseWriter, r *http.Request) {
who, err := h.lc.WhoIs(r.Context(), r.RemoteAddr)
if err != nil {
h.logf("failed to authenticate caller: %v", err)
http.Error(w, "failed to authenticate caller", http.StatusInternalServerError)
return
}
counterNumRequestsProxied.Add(1)
h.rp.ServeHTTP(w, addWhoIsToRequest(r, who))
}
// runAPIServerProxy runs an HTTP server that authenticates requests using the
// Tailscale LocalAPI and then proxies them to the Kubernetes API.
// It listens on :443 and uses the Tailscale HTTPS certificate.
// s will be started if it is not already running.
// rt is used to proxy requests to the Kubernetes API.
//
// mode controls how the proxy behaves:
// - apiserverProxyModeDisabled: the proxy is not started.
// - apiserverProxyModeEnabled: the proxy is started and requests are impersonated using the
// caller's identity from the Tailscale LocalAPI.
// - apiserverProxyModeNoAuth: the proxy is started and requests are not impersonated and
// are passed through to the Kubernetes API.
//
// It never returns.
func runAPIServerProxy(s *tsnet.Server, rt http.RoundTripper, logf logger.Logf, mode apiServerProxyMode) {
if mode == apiserverProxyModeDisabled {
return
}
ln, err := s.Listen("tcp", ":443")
if err != nil {
log.Fatalf("could not listen on :443: %v", err)
}
u, err := url.Parse(fmt.Sprintf("https://%s:%s", os.Getenv("KUBERNETES_SERVICE_HOST"), os.Getenv("KUBERNETES_SERVICE_PORT_HTTPS")))
if err != nil {
log.Fatalf("runAPIServerProxy: failed to parse URL %v", err)
}
lc, err := s.LocalClient()
if err != nil {
log.Fatalf("could not get local client: %v", err)
}
ap := &apiserverProxy{
logf: logf,
lc: lc,
rp: &httputil.ReverseProxy{
Rewrite: func(r *httputil.ProxyRequest) {
// Replace the URL with the Kubernetes APIServer.
r.Out.URL.Scheme = u.Scheme
r.Out.URL.Host = u.Host
if mode == apiserverProxyModeNoAuth {
// If we are not providing authentication, then we are just
// proxying to the Kubernetes API, so we don't need to do
// anything else.
return
}
// We want to proxy to the Kubernetes API, but we want to use
// the caller's identity to do so. We do this by impersonating
// the caller using the Kubernetes User Impersonation feature:
// https://kubernetes.io/docs/reference/access-authn-authz/authentication/#user-impersonation
// Out of paranoia, remove all authentication headers that might
// have been set by the client.
r.Out.Header.Del("Authorization")
r.Out.Header.Del("Impersonate-Group")
r.Out.Header.Del("Impersonate-User")
r.Out.Header.Del("Impersonate-Uid")
for k := range r.Out.Header {
if strings.HasPrefix(k, "Impersonate-Extra-") {
r.Out.Header.Del(k)
}
}
// Now add the impersonation headers that we want.
if err := addImpersonationHeaders(r.Out); err != nil {
panic("failed to add impersonation headers: " + err.Error())
}
},
Transport: rt,
},
}
hs := &http.Server{
// Kubernetes uses SPDY for exec and port-forward, however SPDY is
// incompatible with HTTP/2; so disable HTTP/2 in the proxy.
TLSConfig: &tls.Config{
GetCertificate: lc.GetCertificate,
NextProtos: []string{"http/1.1"},
},
TLSNextProto: make(map[string]func(*http.Server, *tls.Conn, http.Handler)),
Handler: ap,
}
if err := hs.ServeTLS(ln, "", ""); err != nil {
log.Fatalf("runAPIServerProxy: failed to serve %v", err)
}
}
const capabilityName = "https://tailscale.com/cap/kubernetes"
type capRule struct {
// Impersonate is a list of rules that specify how to impersonate the caller
// when proxying to the Kubernetes API.
Impersonate *impersonateRule `json:"impersonate,omitempty"`
}
// TODO(maisem): move this to some well-known location so that it can be shared
// with control.
type impersonateRule struct {
Groups []string `json:"groups,omitempty"`
}
// addImpersonationHeaders adds the appropriate headers to r to impersonate the
// caller when proxying to the Kubernetes API. It uses the WhoIsResponse stashed
// in the context by the apiserverProxy.
func addImpersonationHeaders(r *http.Request) error {
who := whoIsFromRequest(r)
rules, err := tailcfg.UnmarshalCapJSON[capRule](who.CapMap, capabilityName)
if err != nil {
return fmt.Errorf("failed to unmarshal capability: %v", err)
}
var groupsAdded set.Slice[string]
for _, rule := range rules {
if rule.Impersonate == nil {
continue
}
for _, group := range rule.Impersonate.Groups {
if groupsAdded.Contains(group) {
continue
}
r.Header.Add("Impersonate-Group", group)
groupsAdded.Add(group)
}
}
if !who.Node.IsTagged() {
r.Header.Set("Impersonate-User", who.UserProfile.LoginName)
return nil
}
// "Impersonate-Group" requires "Impersonate-User" to be set, so we set it
// to the node FQDN for tagged nodes.
r.Header.Set("Impersonate-User", strings.TrimSuffix(who.Node.Name, "."))
// For legacy behavior (before caps), set the groups to the nodes tags.
if groupsAdded.Slice().Len() == 0 {
for _, tag := range who.Node.Tags {
r.Header.Add("Impersonate-Group", tag)
}
}
return nil
}