Fix race condition between service account availability and webhook invocation

Author: Jan Roehrich

pkg/cache/cache.go

@@ -42,7 +42,8 @@ type CacheResponse struct {
 
 type ServiceAccountCache interface {
 	Start(stop chan struct{})
-	Get(name, namespace string) (role, aud string, useRegionalSTS bool, tokenExpiration int64)
+	Get(name, namespace string) (role, aud string, useRegionalSTS bool, tokenExpiration int64, found bool)
+	GetOrNotify(name, namespace string, handler chan any) (role, aud string, useRegionalSTS bool, tokenExpiration int64, found bool)
 	GetCommonConfigurations(name, namespace string) (useRegionalSTS bool, tokenExpiration int64)
 	// ToJSON returns cache contents as JSON string
 	ToJSON() string
@@ -60,6 +61,7 @@ type serviceAccountCache struct {
 	composeRoleArn         ComposeRoleArn
 	defaultTokenExpiration int64
 	webhookUsage           prometheus.Gauge
+	notificationHandlers   map[string]chan any // type of channel doesn't matter. It's just for being notified
 }
 
 type ComposeRoleArn struct {
@@ -87,41 +89,51 @@ func init() {
 // Get will return the cached configuration of the given ServiceAccount.
 // It will first look at the set of ServiceAccounts configured using annotations. If none are found, it will look for any
 // ServiceAccount configured through the pod-identity-webhook ConfigMap.
-func (c *serviceAccountCache) Get(name, namespace string) (role, aud string, useRegionalSTS bool, tokenExpiration int64) {
+func (c *serviceAccountCache) Get(name, namespace string) (role, aud string, useRegionalSTS bool, tokenExpiration int64, found bool) {
+	return c.GetOrNotify(name, namespace, nil)
+}
+
+// GetOrNotify will return the cached configuration of the given ServiceAccount.
+// It will first look at the set of ServiceAccounts configured using annotations. If none is found, it will register
+// handler to be notified as soon as a ServiceAccount with given key is populated to the cache. Afterwards it will check
+// for a ServiceAccount configured through the pod-identity-webhook ConfigMap.
+func (c *serviceAccountCache) GetOrNotify(name, namespace string, handler chan any) (role, aud string, useRegionalSTS bool, tokenExpiration int64, found bool) {
 	klog.V(5).Infof("Fetching sa %s/%s from cache", namespace, name)
 	{
-		resp := c.getSA(name, namespace)
+		resp := c.getSAorNotify(name, namespace, handler)
 		if resp != nil && resp.RoleARN != "" {
-			return resp.RoleARN, resp.Audience, resp.UseRegionalSTS, resp.TokenExpiration
+			return resp.RoleARN, resp.Audience, resp.UseRegionalSTS, resp.TokenExpiration, true
 		}
 	}
 	{
 		resp := c.getCM(name, namespace)
 		if resp != nil {
-			return resp.RoleARN, resp.Audience, resp.UseRegionalSTS, resp.TokenExpiration
+			return resp.RoleARN, resp.Audience, resp.UseRegionalSTS, resp.TokenExpiration, true
 		}
 	}
 	klog.V(5).Infof("Service account %s/%s not found in cache", namespace, name)
-	return "", "", false, pkg.DefaultTokenExpiration
+	return "", "", false, pkg.DefaultTokenExpiration, false
 }
 
 // GetCommonConfigurations returns the common configurations that also applies to the new mutation method(i.e Container Credentials).
 // The config file for the container credentials does not contain "TokenExpiration" or "UseRegionalSTS". For backward compatibility,
 // Use these fields if they are set in the sa annotations or config map.
 func (c *serviceAccountCache) GetCommonConfigurations(name, namespace string) (useRegionalSTS bool, tokenExpiration int64) {
-	if resp := c.getSA(name, namespace); resp != nil {
+	if resp := c.getSAorNotify(name, namespace, nil); resp != nil {
 		return resp.UseRegionalSTS, resp.TokenExpiration
 	} else if resp := c.getCM(name, namespace); resp != nil {
 		return resp.UseRegionalSTS, resp.TokenExpiration
 	}
 	return false, pkg.DefaultTokenExpiration
 }
 
-func (c *serviceAccountCache) getSA(name, namespace string) *CacheResponse {
+func (c *serviceAccountCache) getSAorNotify(name, namespace string, handler chan any) *CacheResponse {
 	c.mu.RLock()
 	defer c.mu.RUnlock()
 	resp, ok := c.saCache[namespace+"/"+name]
-	if !ok {
+	if !ok && handler != nil {
+		klog.V(5).Infof("Service Account %s/%s not found in cache, adding notification handler", namespace, name)
+		c.notificationHandlers[namespace+"/"+name] = handler
 		return nil
 	}
 	return resp
@@ -212,8 +224,16 @@ func (c *serviceAccountCache) addSA(sa *v1.ServiceAccount) {
 func (c *serviceAccountCache) setSA(name, namespace string, resp *CacheResponse) {
 	c.mu.Lock()
 	defer c.mu.Unlock()
-	klog.V(5).Infof("Adding SA %s/%s to SA cache: %+v", namespace, name, resp)
+
+	key := namespace + "/" + name
+	klog.V(5).Infof("Adding SA %q to SA cache: %+v", key, resp)
 	c.saCache[namespace+"/"+name] = resp
+
+	if handler, found := c.notificationHandlers[key]; found {
+		klog.V(5).Infof("Notifying handler for %q", key)
+		handler <- 1
+		delete(c.notificationHandlers, key)
+	}
 }
 
 func (c *serviceAccountCache) setCM(name, namespace string, resp *CacheResponse) {
@@ -242,6 +262,7 @@ func New(defaultAudience, prefix string, defaultRegionalSTS bool, defaultTokenEx
 		defaultTokenExpiration: defaultTokenExpiration,
 		hasSynced:              hasSynced,
 		webhookUsage:           webhookUsage,
+		notificationHandlers:   map[string]chan any{},
 	}
 
 	saInformer.Informer().AddEventHandler(

pkg/cache/cache_test.go

@@ -36,16 +36,18 @@ func TestSaCache(t *testing.T) {
 		webhookUsage:     prometheus.NewGauge(prometheus.GaugeOpts{}),
 	}
 
-	role, aud, useRegionalSTS, tokenExpiration := cache.Get("default", "default")
+	role, aud, useRegionalSTS, tokenExpiration, found := cache.Get("default", "default")
 
+	assert.False(t, found, "Expected no cache entry to be found")
 	if role != "" || aud != "" {
 		t.Errorf("Expected role and aud to be empty, got %s, %s, %t, %d", role, aud, useRegionalSTS, tokenExpiration)
 	}
 
 	cache.addSA(testSA)
 
-	role, aud, useRegionalSTS, tokenExpiration = cache.Get("default", "default")
+	role, aud, useRegionalSTS, tokenExpiration, found = cache.Get("default", "default")
 
+	assert.True(t, found, "Expected cache entry to be found")
 	assert.Equal(t, roleArn, role, "Expected role to be %s, got %s", roleArn, role)
 	assert.Equal(t, "sts.amazonaws.com", aud, "Expected aud to be sts.amzonaws.com, got %s", aud)
 	assert.True(t, useRegionalSTS, "Expected regional STS to be true, got false")
@@ -157,7 +159,8 @@ func TestNonRegionalSTS(t *testing.T) {
 				t.Fatalf("cache never called addSA: %v", err)
 			}
 
-			gotRoleArn, gotAudience, useRegionalSTS, gotTokenExpiration := cache.Get("default", "default")
+			gotRoleArn, gotAudience, useRegionalSTS, gotTokenExpiration, found := cache.Get("default", "default")
+			assert.True(t, found, "Expected cache entry to be found")
 			if gotRoleArn != roleArn {
 				t.Errorf("got roleArn %v, expected %v", gotRoleArn, roleArn)
 			}
@@ -202,7 +205,7 @@ func TestPopulateCacheFromCM(t *testing.T) {
 			t.Errorf("failed to build cache: %v", err)
 		}
 
-		role, _, _, _ := c.Get("mysa2", "myns2")
+		role, _, _, _, _ := c.Get("mysa2", "myns2")
 		if role == "" {
 			t.Errorf("cloud not find entry that should have been added")
 		}
@@ -214,7 +217,7 @@ func TestPopulateCacheFromCM(t *testing.T) {
 			t.Errorf("failed to build cache: %v", err)
 		}
 
-		role, _, _, _ := c.Get("mysa2", "myns2")
+		role, _, _, _, _ := c.Get("mysa2", "myns2")
 		if role == "" {
 			t.Errorf("cloud not find entry that should have been added")
 		}
@@ -226,7 +229,7 @@ func TestPopulateCacheFromCM(t *testing.T) {
 			t.Errorf("failed to build cache: %v", err)
 		}
 
-		role, _, _, _ := c.Get("mysa2", "myns2")
+		role, _, _, _, _ := c.Get("mysa2", "myns2")
 		if role != "" {
 			t.Errorf("found entry that should have been removed")
 		}
@@ -256,7 +259,7 @@ func TestSAAnnotationRemoval(t *testing.T) {
 	c.addSA(oldSA)
 
 	{
-		gotRoleArn, _, _, _ := c.Get("default", "default")
+		gotRoleArn, _, _, _, _ := c.Get("default", "default")
 		if gotRoleArn != roleArn {
 			t.Errorf("got roleArn %q, expected %q", gotRoleArn, roleArn)
 		}
@@ -268,7 +271,7 @@ func TestSAAnnotationRemoval(t *testing.T) {
 	c.addSA(newSA)
 
 	{
-		gotRoleArn, _, _, _ := c.Get("default", "default")
+		gotRoleArn, _, _, _, _ := c.Get("default", "default")
 		if gotRoleArn != "" {
 			t.Errorf("got roleArn %v, expected %q", gotRoleArn, "")
 		}
@@ -323,7 +326,7 @@ func TestCachePrecedence(t *testing.T) {
 			t.Errorf("failed to build cache: %v", err)
 		}
 
-		role, _, _, exp := c.Get("mysa2", "myns2")
+		role, _, _, exp, _ := c.Get("mysa2", "myns2")
 		if role == "" {
 			t.Errorf("could not find entry that should have been added")
 		}
@@ -340,7 +343,7 @@ func TestCachePrecedence(t *testing.T) {
 		}
 
 		// Removing sa2 from CM, but SA still exists
-		role, _, _, exp := c.Get("mysa2", "myns2")
+		role, _, _, exp, _ := c.Get("mysa2", "myns2")
 		if role == "" {
 			t.Errorf("could not find entry that should still exist")
 		}
@@ -356,7 +359,7 @@ func TestCachePrecedence(t *testing.T) {
 		c.addSA(sa2)
 
 		// Neither cache should return any hits now
-		role, _, _, _ := c.Get("myns2", "mysa2")
+		role, _, _, _, _ := c.Get("myns2", "mysa2")
 		if role != "" {
 			t.Errorf("found entry that should not exist")
 		}
@@ -370,7 +373,7 @@ func TestCachePrecedence(t *testing.T) {
 			t.Errorf("failed to build cache: %v", err)
 		}
 
-		role, _, _, exp := c.Get("mysa2", "myns2")
+		role, _, _, exp, _ := c.Get("mysa2", "myns2")
 		if role == "" {
 			t.Errorf("cloud not find entry that should have been added")
 		}
@@ -422,7 +425,7 @@ func TestRoleArnComposition(t *testing.T) {
 
 	var roleArn string
 	err := wait.ExponentialBackoff(wait.Backoff{Duration: 10 * time.Millisecond, Factor: 1.0, Steps: 3}, func() (bool, error) {
-		roleArn, _, _, _ = cache.Get("default", "default")
+		roleArn, _, _, _, _ = cache.Get("default", "default")
 		return roleArn != "", nil
 	})
 	if err != nil {

pkg/cache/fake.go

@@ -44,14 +44,25 @@ var _ ServiceAccountCache = &FakeServiceAccountCache{}
 func (f *FakeServiceAccountCache) Start(chan struct{}) {}
 
 // Get gets a service account from the cache
-func (f *FakeServiceAccountCache) Get(name, namespace string) (role, aud string, useRegionalSTS bool, tokenExpiration int64) {
+func (f *FakeServiceAccountCache) Get(name, namespace string) (role, aud string, useRegionalSTS bool, tokenExpiration int64, found bool) {
 	f.mu.RLock()
 	defer f.mu.RUnlock()
 	resp, ok := f.cache[namespace+"/"+name]
 	if !ok {
-		return "", "", false, pkg.DefaultTokenExpiration
+		return "", "", false, pkg.DefaultTokenExpiration, false
 	}
-	return resp.RoleARN, resp.Audience, resp.UseRegionalSTS, resp.TokenExpiration
+	return resp.RoleARN, resp.Audience, resp.UseRegionalSTS, resp.TokenExpiration, true
+}
+
+// GetOrNotify gets a service account from the cache
+func (f *FakeServiceAccountCache) GetOrNotify(name, namespace string, handler chan any) (role, aud string, useRegionalSTS bool, tokenExpiration int64, found bool) {
+	f.mu.RLock()
+	defer f.mu.RUnlock()
+	resp, ok := f.cache[namespace+"/"+name]
+	if !ok {
+		return "", "", false, pkg.DefaultTokenExpiration, false
+	}
+	return resp.RoleARN, resp.Audience, resp.UseRegionalSTS, resp.TokenExpiration, true
 }
 
 func (f *FakeServiceAccountCache) GetCommonConfigurations(name, namespace string) (useRegionalSTS bool, tokenExpiration int64) {

pkg/handler/handler.go

@@ -24,6 +24,7 @@ import (
 	"path/filepath"
 	"strconv"
 	"strings"
+	"time"
 
 	"github.com/aws/amazon-eks-pod-identity-webhook/pkg/containercredentials"
 
@@ -425,7 +426,23 @@ func (m *Modifier) buildPodPatchConfig(pod *corev1.Pod) *podPatchConfig {
 	}
 
 	// Use the STS WebIdentity method if set
-	roleArn, audience, regionalSTS, tokenExpiration := m.Cache.Get(pod.Spec.ServiceAccountName, pod.Namespace)
+	handler := make(chan any, 1)
+	roleArn, audience, regionalSTS, tokenExpiration, found := m.Cache.GetOrNotify(pod.Spec.ServiceAccountName, pod.Namespace, handler)
+	if !found {
+		klog.Warningf("Service account %s/%s not found in the cache. Waiting up to 5s to be notified", pod.Namespace, pod.Spec.ServiceAccountName)
+		select {
+		case <-handler:
+			roleArn, audience, regionalSTS, tokenExpiration, found = m.Cache.Get(pod.Spec.ServiceAccountName, pod.Namespace)
+			if !found {
+				klog.Warningf("Service account %s/%s not found in the cache after being notified. Not mutating.", pod.Namespace, pod.Spec.ServiceAccountName)
+				return nil
+			}
+		case <-time.After(5 * time.Second):
+			klog.Warningf("Service account %s/%s not found in the cache after 5s. Not mutating.", pod.Namespace, pod.Spec.ServiceAccountName)
+			return nil
+		}
+	}
+	klog.V(5).Infof("Value of roleArn after after cache retrieval for service account %s/%s: %s", pod.Namespace, pod.Spec.ServiceAccountName, roleArn)
 	if roleArn != "" {
 		tokenExpiration, containersToSkip := m.parsePodAnnotations(pod, tokenExpiration)