exec auth: support TLS config caching

This change updates the transport.Config .Dial and .TLS.GetCert fields
to use a struct wrapper.  This indirection via a pointer allows the
functions to be compared and thus makes them valid to use as map keys.
This change is then leveraged by the existing global exec auth and TLS
config caches to return the same authenticator and TLS config even when
distinct but identical rest configs were used to create distinct
clientsets.

Signed-off-by: Monis Khan <mok@microsoft.com>

Kubernetes-commit: 01044903860c7e2463888c48db91270dc9c7281d

Author: enj

plugin/pkg/client/auth/exec/exec.go

@@ -199,14 +199,18 @@ func newAuthenticator(c *cache, isTerminalFunc func(int) bool, config *api.ExecC
 		now:             time.Now,
 		environ:         os.Environ,
 
-		defaultDialer: defaultDialer,
-		connTracker:   connTracker,
+		connTracker: connTracker,
 	}
 
 	for _, env := range config.Env {
 		a.env = append(a.env, env.Name+"="+env.Value)
 	}
 
+	// these functions are made comparable and stored in the cache so that repeated clientset
+	// construction with the same rest.Config results in a single TLS cache and Authenticator
+	a.getCert = &transport.GetCertHolder{GetCert: a.cert}
+	a.dial = &transport.DialHolder{Dial: defaultDialer.DialContext}
+
 	return c.put(key, a), nil
 }
 
@@ -261,8 +265,6 @@ type Authenticator struct {
 	now             func() time.Time
 	environ         func() []string
 
-	// defaultDialer is used for clients which don't specify a custom dialer
-	defaultDialer *connrotation.Dialer
 	// connTracker tracks all connections opened that we need to close when rotating a client certificate
 	connTracker *connrotation.ConnectionTracker
 
@@ -273,6 +275,12 @@ type Authenticator struct {
 	mu          sync.Mutex
 	cachedCreds *credentials
 	exp         time.Time
+
+	// getCert makes Authenticator.cert comparable to support TLS config caching
+	getCert *transport.GetCertHolder
+	// dial is used for clients which do not specify a custom dialer
+	// it is comparable to support TLS config caching
+	dial *transport.DialHolder
 }
 
 type credentials struct {
@@ -300,18 +308,20 @@ func (a *Authenticator) UpdateTransportConfig(c *transport.Config) error {
 	if c.HasCertCallback() {
 		return errors.New("can't add TLS certificate callback: transport.Config.TLS.GetCert already set")
 	}
-	c.TLS.GetCert = a.cert
+	c.TLS.GetCert = a.getCert.GetCert
+	c.TLS.GetCertHolder = a.getCert // comparable for TLS config caching
 
-	var d *connrotation.Dialer
 	if c.Dial != nil {
 		// if c has a custom dialer, we have to wrap it
-		d = connrotation.NewDialerWithTracker(c.Dial, a.connTracker)
+		// TLS config caching is not supported for this config
+		d := connrotation.NewDialerWithTracker(c.Dial, a.connTracker)
+		c.Dial = d.DialContext
+		c.DialHolder = nil
 	} else {
-		d = a.defaultDialer
+		c.Dial = a.dial.Dial
+		c.DialHolder = a.dial // comparable for TLS config caching
 	}
 
-	c.Dial = d.DialContext
-
 	return nil
 }
 

plugin/pkg/client/auth/exec/exec_cache_test.go

@@ -0,0 +1,106 @@
+/*
+Copyright 2022 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package exec_test // separate package to prevent circular import
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	utilnet "k8s.io/apimachinery/pkg/util/net"
+	clientset "k8s.io/client-go/kubernetes"
+	"k8s.io/client-go/rest"
+	clientcmdapi "k8s.io/client-go/tools/clientcmd/api"
+)
+
+// TestExecTLSCache asserts the semantics of the TLS cache when exec auth is used.
+//
+// In particular, when:
+//   - multiple identical rest configs exist as distinct objects, and
+//   - these rest configs use exec auth, and
+//   - these rest configs are used to create distinct clientsets, then
+//
+// the underlying TLS config is shared between those clientsets.
+func TestExecTLSCache(t *testing.T) {
+	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
+	t.Cleanup(cancel)
+
+	config1 := &rest.Config{
+		Host: "https://localhost",
+		ExecProvider: &clientcmdapi.ExecConfig{
+			Command:         "./testdata/test-plugin.sh",
+			APIVersion:      "client.authentication.k8s.io/v1",
+			InteractiveMode: clientcmdapi.IfAvailableExecInteractiveMode,
+		},
+	}
+	client1 := clientset.NewForConfigOrDie(config1)
+
+	config2 := &rest.Config{
+		Host: "https://localhost",
+		ExecProvider: &clientcmdapi.ExecConfig{
+			Command:         "./testdata/test-plugin.sh",
+			APIVersion:      "client.authentication.k8s.io/v1",
+			InteractiveMode: clientcmdapi.IfAvailableExecInteractiveMode,
+		},
+	}
+	client2 := clientset.NewForConfigOrDie(config2)
+
+	config3 := &rest.Config{
+		Host: "https://localhost",
+		ExecProvider: &clientcmdapi.ExecConfig{
+			Command:         "./testdata/test-plugin.sh",
+			Args:            []string{"make this exec auth different"},
+			APIVersion:      "client.authentication.k8s.io/v1",
+			InteractiveMode: clientcmdapi.IfAvailableExecInteractiveMode,
+		},
+	}
+	client3 := clientset.NewForConfigOrDie(config3)
+
+	_, _ = client1.CoreV1().Nodes().List(ctx, metav1.ListOptions{})
+	_, _ = client2.CoreV1().Namespaces().List(ctx, metav1.ListOptions{})
+	_, _ = client3.CoreV1().PersistentVolumes().List(ctx, metav1.ListOptions{})
+
+	rt1 := client1.RESTClient().(*rest.RESTClient).Client.Transport
+	rt2 := client2.RESTClient().(*rest.RESTClient).Client.Transport
+	rt3 := client3.RESTClient().(*rest.RESTClient).Client.Transport
+
+	tlsConfig1, err := utilnet.TLSClientConfig(rt1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	tlsConfig2, err := utilnet.TLSClientConfig(rt2)
+	if err != nil {
+		t.Fatal(err)
+	}
+	tlsConfig3, err := utilnet.TLSClientConfig(rt3)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if tlsConfig1 == nil || tlsConfig2 == nil || tlsConfig3 == nil {
+		t.Fatal("expected non-nil TLS configs")
+	}
+
+	if tlsConfig1 != tlsConfig2 {
+		t.Fatal("expected the same TLS config for matching exec config via rest config")
+	}
+
+	if tlsConfig1 == tlsConfig3 {
+		t.Fatal("expected different TLS config for non-matching exec config via rest config")
+	}
+}

transport/cache.go

@@ -17,6 +17,7 @@ limitations under the License.
 package transport
 
 import (
+	"context"
 	"fmt"
 	"net"
 	"net/http"
@@ -55,14 +56,18 @@ type tlsCacheKey struct {
 	serverName         string
 	nextProtos         string
 	disableCompression bool
+	// these functions are wrapped to allow them to be used as map keys
+	getCert *GetCertHolder
+	dial    *DialHolder
 }
 
 func (t tlsCacheKey) String() string {
 	keyText := "<none>"
 	if len(t.keyData) > 0 {
 		keyText = "<redacted>"
 	}
-	return fmt.Sprintf("insecure:%v, caData:%#v, certData:%#v, keyData:%s, serverName:%s, disableCompression:%t", t.insecure, t.caData, t.certData, keyText, t.serverName, t.disableCompression)
+	return fmt.Sprintf("insecure:%v, caData:%#v, certData:%#v, keyData:%s, serverName:%s, disableCompression:%t, getCert:%p, dial:%p",
+		t.insecure, t.caData, t.certData, keyText, t.serverName, t.disableCompression, t.getCert, t.dial)
 }
 
 func (c *tlsTransportCache) get(config *Config) (http.RoundTripper, error) {
@@ -92,8 +97,10 @@ func (c *tlsTransportCache) get(config *Config) (http.RoundTripper, error) {
 		return http.DefaultTransport, nil
 	}
 
-	dial := config.Dial
-	if dial == nil {
+	var dial func(ctx context.Context, network, address string) (net.Conn, error)
+	if config.Dial != nil {
+		dial = config.Dial
+	} else {
 		dial = (&net.Dialer{
 			Timeout:   30 * time.Second,
 			KeepAlive: 30 * time.Second,
@@ -138,17 +145,27 @@ func tlsConfigKey(c *Config) (tlsCacheKey, bool, error) {
 		return tlsCacheKey{}, false, err
 	}
 
-	if c.TLS.GetCert != nil || c.Dial != nil || c.Proxy != nil {
+	if c.Proxy != nil {
 		// cannot determine equality for functions
 		return tlsCacheKey{}, false, nil
 	}
+	if c.Dial != nil && c.DialHolder == nil {
+		// cannot determine equality for dial function that doesn't have non-nil DialHolder set as well
+		return tlsCacheKey{}, false, nil
+	}
+	if c.TLS.GetCert != nil && c.TLS.GetCertHolder == nil {
+		// cannot determine equality for getCert function that doesn't have non-nil GetCertHolder set as well
+		return tlsCacheKey{}, false, nil
+	}
 
 	k := tlsCacheKey{
 		insecure:           c.TLS.Insecure,
 		caData:             string(c.TLS.CAData),
 		serverName:         c.TLS.ServerName,
 		nextProtos:         strings.Join(c.TLS.NextProtos, ","),
 		disableCompression: c.DisableCompression,
+		getCert:            c.TLS.GetCertHolder,
+		dial:               c.DialHolder,
 	}
 
 	if c.TLS.ReloadTLSFiles {

transport/cache_test.go

@@ -21,6 +21,7 @@ import (
 	"crypto/tls"
 	"net"
 	"net/http"
+	"net/url"
 	"testing"
 )
 
@@ -58,16 +59,24 @@ func TestTLSConfigKey(t *testing.T) {
 				t.Errorf("Expected identical cache keys for %q and %q, got:\n\t%s\n\t%s", nameA, nameB, keyA, keyB)
 				continue
 			}
+			if keyA != (tlsCacheKey{}) {
+				t.Errorf("Expected empty cache keys for %q and %q, got:\n\t%s\n\t%s", nameA, nameB, keyA, keyB)
+				continue
+			}
 		}
 	}
 
 	// Make sure config fields that affect the tls config affect the cache key
 	dialer := net.Dialer{}
 	getCert := func() (*tls.Certificate, error) { return nil, nil }
+	getCertHolder := &GetCertHolder{GetCert: getCert}
 	uniqueConfigurations := map[string]*Config{
+		"proxy":    {Proxy: func(request *http.Request) (*url.URL, error) { return nil, nil }},
 		"no tls":   {},
 		"dialer":   {Dial: dialer.DialContext},
 		"dialer2":  {Dial: func(ctx context.Context, network, address string) (net.Conn, error) { return nil, nil }},
+		"dialer3":  {Dial: dialer.DialContext, DialHolder: &DialHolder{Dial: dialer.DialContext}},
+		"dialer4":  {Dial: func(ctx context.Context, network, address string) (net.Conn, error) { return nil, nil }, DialHolder: &DialHolder{Dial: func(ctx context.Context, network, address string) (net.Conn, error) { return nil, nil }}},
 		"insecure": {TLS: TLSConfig{Insecure: true}},
 		"cadata 1": {TLS: TLSConfig{CAData: []byte{1}}},
 		"cadata 2": {TLS: TLSConfig{CAData: []byte{2}}},
@@ -128,6 +137,13 @@ func TestTLSConfigKey(t *testing.T) {
 				GetCert: func() (*tls.Certificate, error) { return nil, nil },
 			},
 		},
+		"getCert3": {
+			TLS: TLSConfig{
+				KeyData:       []byte{1},
+				GetCert:       getCert,
+				GetCertHolder: getCertHolder,
+			},
+		},
 		"getCert1, key 2": {
 			TLS: TLSConfig{
 				KeyData: []byte{2},

transport/config.go

@@ -68,7 +68,11 @@ type Config struct {
 	WrapTransport WrapperFunc
 
 	// Dial specifies the dial function for creating unencrypted TCP connections.
+	// If specified, this transport will be non-cacheable unless DialHolder is also set.
 	Dial func(ctx context.Context, network, address string) (net.Conn, error)
+	// DialHolder can be populated to make transport configs cacheable.
+	// If specified, DialHolder.Dial must be equal to Dial.
+	DialHolder *DialHolder
 
 	// Proxy is the proxy func to be used for all requests made by this
 	// transport. If Proxy is nil, http.ProxyFromEnvironment is used. If Proxy
@@ -78,6 +82,11 @@ type Config struct {
 	Proxy func(*http.Request) (*url.URL, error)
 }
 
+// DialHolder is used to make the wrapped function comparable so that it can be used as a map key.
+type DialHolder struct {
+	Dial func(ctx context.Context, network, address string) (net.Conn, error)
+}
+
 // ImpersonationConfig has all the available impersonation options
 type ImpersonationConfig struct {
 	// UserName matches user.Info.GetName()
@@ -143,5 +152,15 @@ type TLSConfig struct {
 	// To use only http/1.1, set to ["http/1.1"].
 	NextProtos []string
 
-	GetCert func() (*tls.Certificate, error) // Callback that returns a TLS client certificate. CertData, CertFile, KeyData and KeyFile supercede this field.
+	// Callback that returns a TLS client certificate. CertData, CertFile, KeyData and KeyFile supercede this field.
+	// If specified, this transport is non-cacheable unless CertHolder is populated.
+	GetCert func() (*tls.Certificate, error)
+	// CertHolder can be populated to make transport configs that set GetCert cacheable.
+	// If set, CertHolder.GetCert must be equal to GetCert.
+	GetCertHolder *GetCertHolder
+}
+
+// GetCertHolder is used to make the wrapped function comparable so that it can be used as a map key.
+type GetCertHolder struct {
+	GetCert func() (*tls.Certificate, error)
 }

transport/transport.go

@@ -24,6 +24,7 @@ import (
 	"fmt"
 	"io/ioutil"
 	"net/http"
+	"reflect"
 	"sync"
 	"time"
 
@@ -39,6 +40,10 @@ func New(config *Config) (http.RoundTripper, error) {
 		return nil, fmt.Errorf("using a custom transport with TLS certificate options or the insecure flag is not allowed")
 	}
 
+	if !isValidHolders(config) {
+		return nil, fmt.Errorf("misconfigured holder for dialer or cert callback")
+	}
+
 	var (
 		rt  http.RoundTripper
 		err error
@@ -56,6 +61,26 @@ func New(config *Config) (http.RoundTripper, error) {
 	return HTTPWrappersForConfig(config, rt)
 }
 
+func isValidHolders(config *Config) bool {
+	if config.TLS.GetCertHolder != nil {
+		if config.TLS.GetCertHolder.GetCert == nil ||
+			config.TLS.GetCert == nil ||
+			reflect.ValueOf(config.TLS.GetCertHolder.GetCert).Pointer() != reflect.ValueOf(config.TLS.GetCert).Pointer() {
+			return false
+		}
+	}
+
+	if config.DialHolder != nil {
+		if config.DialHolder.Dial == nil ||
+			config.Dial == nil ||
+			reflect.ValueOf(config.DialHolder.Dial).Pointer() != reflect.ValueOf(config.Dial).Pointer() {
+			return false
+		}
+	}
+
+	return true
+}
+
 // TLSConfigFor returns a tls.Config that will provide the transport level security defined
 // by the provided Config. Will return nil if no transport level security is requested.
 func TLSConfigFor(c *Config) (*tls.Config, error) {