Synchronize legacy UDP crypto setup

gumble/gumble/crypt.go

@@ -233,6 +233,8 @@ type cryptState struct {
 }
 
 func (cs *cryptState) setup(key, iv []byte) error {
+	cs.mu.Lock()
+	defer cs.mu.Unlock()
 	if len(key) != 16 {
 		return errors.New("gumble: crypt key must be 16 bytes")
 	}
@@ -269,6 +271,8 @@ func (cs *cryptState) nonceForPacket(counter uint32) [12]byte {
 }
 
 func (cs *cryptState) encrypt(counter uint32, plaintext []byte) ([]byte, error) {
+	cs.mu.Lock()
+	defer cs.mu.Unlock()
 	if !cs.initialized {
 		return plaintext, nil
 	}
@@ -277,6 +281,8 @@ func (cs *cryptState) encrypt(counter uint32, plaintext []byte) ([]byte, error)
 }
 
 func (cs *cryptState) decrypt(counter uint32, ciphertext []byte) ([]byte, error) {
+	cs.mu.Lock()
+	defer cs.mu.Unlock()
 	if !cs.initialized {
 		return ciphertext, nil
 	}

gumble/gumble/crypt_test.go

@@ -7,9 +7,34 @@ import (
 	"encoding/hex"
 	"fmt"
 	"strings"
+	"sync"
 	"testing"
 )
 
+func TestCryptStateSetupAndEncryptAreConcurrentSafe(t *testing.T) {
+	key := make([]byte, 16)
+	iv := make([]byte, 16)
+	var cs cryptState
+	if err := cs.setup(key, iv); err != nil {
+		t.Fatal(err)
+	}
+	var wg sync.WaitGroup
+	for i := 0; i < 20; i++ {
+		wg.Add(1)
+		go func(counter uint32) {
+			defer wg.Done()
+			if counter%2 == 0 {
+				if err := cs.setup(key, iv); err != nil {
+					t.Error(err)
+				}
+			} else if _, err := cs.encrypt(counter, []byte("audio")); err != nil {
+				t.Error(err)
+			}
+		}(uint32(i))
+	}
+	wg.Wait()
+}
+
 // TestOCBRoundTrip verifies encrypt-then-decrypt returns the original.
 func TestOCBRoundTrip(t *testing.T) {
 	key := make([]byte, 16)