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tailscale/cmd/k8s-operator/proxy.go

401 lines
13 KiB
Go

// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
//go:build !plan9
package main
import (
"crypto/tls"
"fmt"
"log"
"net/http"
"net/http/httputil"
"net/netip"
"net/url"
"os"
"strings"
"github.com/pkg/errors"
"go.uber.org/zap"
"k8s.io/client-go/rest"
"k8s.io/client-go/transport"
"tailscale.com/client/tailscale"
"tailscale.com/client/tailscale/apitype"
tskube "tailscale.com/kube"
"tailscale.com/ssh/tailssh"
"tailscale.com/tailcfg"
"tailscale.com/tsnet"
"tailscale.com/util/clientmetric"
"tailscale.com/util/ctxkey"
"tailscale.com/util/set"
)
var whoIsKey = ctxkey.New("", (*apitype.WhoIsResponse)(nil))
var (
// counterNumRequestsproxies counts the number of API server requests proxied via this proxy.
counterNumRequestsProxied = clientmetric.NewCounter("k8s_auth_proxy_requests_proxied")
// counterSessionRecordingsAttempted counts the number of session recording attempts.
counterSessionRecordingsAttempted = clientmetric.NewCounter("k8s_auth_proxy__session_recordings_attempted")
// counterSessionRecordingsUploaded counts the number of successfully uploaded session recordings.
counterSessionRecordingsUploaded = clientmetric.NewCounter("k8s_auth_proxy_session_recordings_uploaded")
)
type apiServerProxyMode int
func (a apiServerProxyMode) String() string {
switch a {
case apiserverProxyModeDisabled:
return "disabled"
case apiserverProxyModeEnabled:
return "auth"
case apiserverProxyModeNoAuth:
return "noauth"
default:
return "unknown"
}
}
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"), mode, restConfig.Host)
}
// 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(ts *tsnet.Server, rt http.RoundTripper, log *zap.SugaredLogger, mode apiServerProxyMode, host string) {
if mode == apiserverProxyModeDisabled {
return
}
ln, err := ts.Listen("tcp", ":443")
if err != nil {
log.Fatalf("could not listen on :443: %v", err)
}
u, err := url.Parse(host)
if err != nil {
log.Fatalf("runAPIServerProxy: failed to parse URL %v", err)
}
lc, err := ts.LocalClient()
if err != nil {
log.Fatalf("could not get local client: %v", err)
}
ap := &apiserverProxy{
log: log,
lc: lc,
mode: mode,
upstreamURL: u,
ts: ts,
}
ap.rp = &httputil.ReverseProxy{
Rewrite: func(pr *httputil.ProxyRequest) {
ap.addImpersonationHeadersAsRequired(pr.Out)
},
Transport: rt,
}
mux := http.NewServeMux()
mux.HandleFunc("/", ap.serveDefault)
mux.HandleFunc("/api/v1/namespaces/{namespace}/pods/{pod}/exec", ap.serveExec)
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: mux,
}
log.Infof("API server proxy in %q mode is listening on %s", mode, ln.Addr())
if err := hs.ServeTLS(ln, "", ""); err != nil {
log.Fatalf("runAPIServerProxy: failed to serve %v", err)
}
}
// apiserverProxy is an [net/http.Handler] that authenticates requests using the Tailscale
// LocalAPI and then proxies them to the Kubernetes API.
type apiserverProxy struct {
log *zap.SugaredLogger
lc *tailscale.LocalClient
rp *httputil.ReverseProxy
mode apiServerProxyMode
ts *tsnet.Server
upstreamURL *url.URL
}
// serveDefault is the default handler for Kubernetes API server requests.
func (ap *apiserverProxy) serveDefault(w http.ResponseWriter, r *http.Request) {
who, err := ap.whoIs(r)
if err != nil {
ap.authError(w, err)
return
}
counterNumRequestsProxied.Add(1)
ap.rp.ServeHTTP(w, r.WithContext(whoIsKey.WithValue(r.Context(), who)))
}
// serveExec serves 'kubectl exec' requests, optionally configuring the kubectl
// exec sessions to be recorded.
func (ap *apiserverProxy) serveExec(w http.ResponseWriter, r *http.Request) {
who, err := ap.whoIs(r)
if err != nil {
ap.authError(w, err)
return
}
counterNumRequestsProxied.Add(1)
failOpen, addrs, err := determineRecorderConfig(who)
if err != nil {
ap.log.Errorf("error trying to determine whether the 'kubectl exec' session needs to be recorded: %v", err)
return
}
if failOpen && len(addrs) == 0 { // will not record
ap.rp.ServeHTTP(w, r.WithContext(whoIsKey.WithValue(r.Context(), who)))
return
}
counterSessionRecordingsAttempted.Add(1) // at this point we know that users intended for this session to be recorded
if !failOpen && len(addrs) == 0 {
msg := "forbidden: 'kubectl exec' session must be recorded, but no recorders are available."
ap.log.Error(msg)
http.Error(w, msg, http.StatusForbidden)
return
}
if r.Method != "POST" || r.Header.Get("Upgrade") != "SPDY/3.1" {
msg := "'kubectl exec' session recording is configured, but the request is not over SPDY. Session recording is currently only supported for SPDY based clients"
if failOpen {
msg = msg + "; failure mode is 'fail open'; continuing session without recording."
ap.log.Warn(msg)
ap.rp.ServeHTTP(w, r.WithContext(whoIsKey.WithValue(r.Context(), who)))
return
}
ap.log.Error(msg)
msg += "; failure mode is 'fail closed'; closing connection."
http.Error(w, msg, http.StatusForbidden)
return
}
spdyH := &spdyHijacker{
ts: ap.ts,
req: r,
who: who,
ResponseWriter: w,
log: ap.log,
pod: r.PathValue("pod"),
ns: r.PathValue("namespace"),
addrs: addrs,
failOpen: failOpen,
connectToRecorder: tailssh.ConnectToRecorder,
}
ap.rp.ServeHTTP(spdyH, r.WithContext(whoIsKey.WithValue(r.Context(), who)))
}
func (h *apiserverProxy) addImpersonationHeadersAsRequired(r *http.Request) {
r.URL.Scheme = h.upstreamURL.Scheme
r.URL.Host = h.upstreamURL.Host
if h.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.Header.Del("Authorization")
r.Header.Del("Impersonate-Group")
r.Header.Del("Impersonate-User")
r.Header.Del("Impersonate-Uid")
for k := range r.Header {
if strings.HasPrefix(k, "Impersonate-Extra-") {
r.Header.Del(k)
}
}
// Now add the impersonation headers that we want.
if err := addImpersonationHeaders(r, h.log); err != nil {
log.Printf("failed to add impersonation headers: " + err.Error())
}
}
func (ap *apiserverProxy) whoIs(r *http.Request) (*apitype.WhoIsResponse, error) {
return ap.lc.WhoIs(r.Context(), r.RemoteAddr)
}
func (ap *apiserverProxy) authError(w http.ResponseWriter, err error) {
ap.log.Errorf("failed to authenticate caller: %v", err)
http.Error(w, "failed to authenticate caller", http.StatusInternalServerError)
}
const (
// oldCapabilityName is a legacy form of
// tailfcg.PeerCapabilityKubernetes capability. The only capability rule
// that is respected for this form is group impersonation - for
// backwards compatibility reasons.
// TODO (irbekrm): determine if anyone uses this and remove if possible.
oldCapabilityName = "https://" + tailcfg.PeerCapabilityKubernetes
)
// 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, log *zap.SugaredLogger) error {
log = log.With("remote", r.RemoteAddr)
who := whoIsKey.Value(r.Context())
rules, err := tailcfg.UnmarshalCapJSON[tskube.KubernetesCapRule](who.CapMap, tailcfg.PeerCapabilityKubernetes)
if len(rules) == 0 && err == nil {
// Try the old capability name for backwards compatibility.
rules, err = tailcfg.UnmarshalCapJSON[tskube.KubernetesCapRule](who.CapMap, oldCapabilityName)
}
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)
log.Debugf("adding group impersonation header for user group %s", group)
}
}
if !who.Node.IsTagged() {
r.Header.Set("Impersonate-User", who.UserProfile.LoginName)
log.Debugf("adding user impersonation header for user %s", who.UserProfile.LoginName)
return nil
}
// "Impersonate-Group" requires "Impersonate-User" to be set, so we set it
// to the node FQDN for tagged nodes.
nodeName := strings.TrimSuffix(who.Node.Name, ".")
r.Header.Set("Impersonate-User", nodeName)
log.Debugf("adding user impersonation header for node name %s", nodeName)
// 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)
log.Debugf("adding group impersonation header for node tag %s", tag)
}
}
return nil
}
// determineRecorderConfig determines recorder config from requester's peer
// capabilities. Determines whether a 'kubectl exec' session from this requester
// needs to be recorded and what recorders the recording should be sent to.
func determineRecorderConfig(who *apitype.WhoIsResponse) (failOpen bool, recorderAddresses []netip.AddrPort, _ error) {
if who == nil {
return false, nil, errors.New("[unexpected] cannot determine caller")
}
failOpen = true
rules, err := tailcfg.UnmarshalCapJSON[tskube.KubernetesCapRule](who.CapMap, tailcfg.PeerCapabilityKubernetes)
if err != nil {
return failOpen, nil, fmt.Errorf("failed to unmarshal Kubernetes capability: %w", err)
}
if len(rules) == 0 {
return failOpen, nil, nil
}
for _, rule := range rules {
if len(rule.RecorderAddrs) != 0 {
// TODO (irbekrm): here or later determine if the
// recorders behind those addrs are online - else we
// spend 30s trying to reach a recorder whose tailscale
// status is offline.
recorderAddresses = append(recorderAddresses, rule.RecorderAddrs...)
}
if rule.EnforceRecorder {
failOpen = false
}
}
return failOpen, recorderAddresses, nil
}