[KMSv2] store hash of encrypted DEK as key in cache

Signed-off-by: Anish Ramasekar <anish.ramasekar@gmail.com>

staging/src/k8s.io/apiserver/pkg/storage/value/encrypt/envelope/kmsv2/cache.go

@@ -18,8 +18,11 @@ limitations under the License.
 package kmsv2
 
 import (
-	"encoding/base64"
+	"crypto/sha256"
+	"hash"
+	"sync"
 	"time"
+	"unsafe"
 
 	utilcache "k8s.io/apimachinery/pkg/util/cache"
 	"k8s.io/apiserver/pkg/storage/value"
@@ -29,18 +32,26 @@ import (
 type simpleCache struct {
 	cache *utilcache.Expiring
 	ttl   time.Duration
+	// hashPool is a per cache pool of hash.Hash (to avoid allocations from building the Hash)
+	// SHA-256 is used to prevent collisions
+	hashPool *sync.Pool
 }
 
 func newSimpleCache(clock clock.Clock, ttl time.Duration) *simpleCache {
 	return &simpleCache{
 		cache: utilcache.NewExpiringWithClock(clock),
 		ttl:   ttl,
+		hashPool: &sync.Pool{
+			New: func() interface{} {
+				return sha256.New()
+			},
+		},
 	}
 }
 
 // given a key, return the transformer, or nil if it does not exist in the cache
 func (c *simpleCache) get(key []byte) value.Transformer {
-	record, ok := c.cache.Get(base64.StdEncoding.EncodeToString(key))
+	record, ok := c.cache.Get(c.keyFunc(key))
 	if !ok {
 		return nil
 	}
@@ -55,5 +66,25 @@ func (c *simpleCache) set(key []byte, transformer value.Transformer) {
 	if transformer == nil {
 		panic("transformer must not be nil")
 	}
-	c.cache.Set(base64.StdEncoding.EncodeToString(key), transformer, c.ttl)
+	c.cache.Set(c.keyFunc(key), transformer, c.ttl)
+}
+
+// keyFunc generates a string key by hashing the inputs.
+// This lowers the memory requirement of the cache.
+func (c *simpleCache) keyFunc(s []byte) string {
+	h := c.hashPool.Get().(hash.Hash)
+	h.Reset()
+
+	if _, err := h.Write(s); err != nil {
+		panic(err) // Write() on hash never fails
+	}
+	key := toString(h.Sum(nil)) // skip base64 encoding to save an allocation
+	c.hashPool.Put(h)
+
+	return key
+}
+
+// toString performs unholy acts to avoid allocations
+func toString(b []byte) string {
+	return *(*string)(unsafe.Pointer(&b))
 }

staging/src/k8s.io/apiserver/pkg/storage/value/encrypt/envelope/kmsv2/cache_test.go

@@ -18,6 +18,9 @@ limitations under the License.
 package kmsv2
 
 import (
+	"crypto/sha256"
+	"fmt"
+	"sync"
 	"testing"
 	"time"
 
@@ -57,3 +60,75 @@ func TestSimpleCacheSetError(t *testing.T) {
 		})
 	}
 }
+
+func TestKeyFunc(t *testing.T) {
+	fakeClock := testingclock.NewFakeClock(time.Now())
+	cache := newSimpleCache(fakeClock, time.Second)
+
+	t.Run("AllocsPerRun test", func(t *testing.T) {
+		key, err := generateKey(encryptedDEKMaxSize) // simulate worst case EDEK
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		f := func() {
+			out := cache.keyFunc(key)
+			if len(out) != sha256.Size {
+				t.Errorf("Expected %d bytes, got %d", sha256.Size, len(out))
+			}
+		}
+
+		// prime the key func
+		var wg sync.WaitGroup
+		for i := 0; i < 100; i++ {
+			wg.Add(1)
+			go func() {
+				f()
+				wg.Done()
+			}()
+		}
+		wg.Wait()
+
+		allocs := testing.AllocsPerRun(100, f)
+		if allocs > 1 {
+			t.Errorf("Expected 1 allocations, got %v", allocs)
+		}
+	})
+}
+
+func TestSimpleCache(t *testing.T) {
+	fakeClock := testingclock.NewFakeClock(time.Now())
+	cache := newSimpleCache(fakeClock, 5*time.Second)
+	envelopeTransformer := &envelopeTransformer{}
+
+	wg := sync.WaitGroup{}
+	for i := 0; i < 10; i++ {
+		k := fmt.Sprintf("key-%d", i)
+		wg.Add(1)
+		go func(key string) {
+			defer wg.Done()
+			cache.set([]byte(key), envelopeTransformer)
+		}(k)
+	}
+	wg.Wait()
+
+	if cache.cache.Len() != 10 {
+		t.Fatalf("Expected 10 items in the cache, got %v", cache.cache.Len())
+	}
+
+	for i := 0; i < 10; i++ {
+		k := fmt.Sprintf("key-%d", i)
+		if cache.get([]byte(k)) != envelopeTransformer {
+			t.Fatalf("Expected to get the transformer for key %v", k)
+		}
+	}
+
+	// Wait for the cache to expire
+	fakeClock.Step(6 * time.Second)
+	for i := 0; i < 10; i++ {
+		k := fmt.Sprintf("key-%d", i)
+		if cache.get([]byte(k)) != nil {
+			t.Fatalf("Expected to get nil for key %v", k)
+		}
+	}
+}