Repository: pion/turn (go)

Issue:
Memory leak because server.go nonces increasing
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### Your environment.
  - Version: latest
  - Browser: any (server problem)

### What did you do?
<!--
If possible, provide an example for reproducing the error.
A complete runnable program is good.
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In our production environment, TURN server runs a long time.


### What did you expect?
Not expect memory leak.

### What happened?
RSS memory of TURN server is increasing.

Troubleshoot:
I use Golang pprof to profile the server and find that `nonces` map of the global server is large. The code about nonce creation and deletion is in `authenticateRequest`. After a normal TURN request, the nonce remains in the map.

How to solve? I propose three methods:
1、WebRTC turn_server.cc ( https://source.chromium.org/chromium/chromium/src/+/main:third_party/webrtc/p2p/base/turn_server.cc;drc=8e78783dc1f7007bad46d657c9f332614e240fd8;l=385?q=turn_server.cc ) decodes nonce to get timestamp. So no need to save nonce and timestamp in a map.

2、coturn seems to save nonce to a session. You known, TCP (client to TURN) has connection, so we can save nonce to something like connection (in pion/turn `readListener` ). If the connection is broken, nonce also doesn't exist. I think UDP (client to TURN)  is quite troublesome, we must create a structure to represent the UDP session.

3、Using a timer to delete expired nonce in the nonces map. However nonce expiration time is one hour, the map may remain large.

I prefer the first method.

Pull request description:
Use signed timestamp for nonce
#### Description
implements nonce generation using the method from chromium (https://source.chromium.org/chromium/chromium/src/+/main:third_party/webrtc/p2p/base/turn_server.cc;l=385;drc=8e78783dc1f7007bad46d657c9f332614e240fd8?q=turn_server.cc). create a random hmac and use it to hash the timestamp of the authentication request. validate by checking the hash and time elapsed since the nonce was generated.

#### Reference issue
Fixes #361 


Patch:
diff --git a/internal/server/errors.go b/internal/server/errors.go
index 3a8911c..ea6da83 100644
--- a/internal/server/errors.go
+++ b/internal/server/errors.go
@@ -7,8 +7,8 @@ import "errors"
 
 var (
 	errFailedToGenerateNonce                  = errors.New("failed to generate nonce")
+	errInvalidNonce                           = errors.New("invalid nonce")
 	errFailedToSendError                      = errors.New("failed to send error message")
-	errDuplicatedNonce                        = errors.New("duplicated Nonce generated, discarding request")
 	errNoSuchUser                             = errors.New("no such user exists")
 	errUnexpectedClass                        = errors.New("unexpected class")
 	errUnexpectedMethod                       = errors.New("unexpected method")
diff --git a/internal/server/nonce.go b/internal/server/nonce.go
new file mode 100644
index 0000000..b3f3131
--- /dev/null
+++ b/internal/server/nonce.go
@@ -0,0 +1,71 @@
+// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
+// SPDX-License-Identifier: MIT
+
+package server
+
+import (
+	"crypto/hmac"
+	"crypto/rand"
+	"crypto/sha256"
+	"encoding/binary"
+	"encoding/hex"
+	"fmt"
+	"time"
+)
+
+const (
+	nonceLifetime  = time.Hour // See: https://tools.ietf.org/html/rfc5766#section-4
+	nonceLength    = 40
+	nonceKeyLength = 64
+)
+
+// NewNonceHash creates a NonceHash
+func NewNonceHash() (*NonceHash, error) {
+	key := make([]byte, nonceKeyLength)
+	if _, err := rand.Read(key); err != nil {
+		return nil, err
+	}
+
+	return &NonceHash{key}, nil
+}
+
+// NonceHash is used to create and verify nonces
+type NonceHash struct {
+	key []byte
+}
+
+// Generate a nonce
+func (n *NonceHash) Generate() (string, error) {
+	nonce := make([]byte, 8, nonceLength)
+	binary.BigEndian.PutUint64(nonce, uint64(time.Now().UnixMilli()))
+
+	hash := hmac.New(sha256.New, n.key)
+	if _, err := hash.Write(nonce[:8]); err != nil {
+		return "", fmt.Errorf("%w: %v", errFailedToGenerateNonce, err) //nolint:errorlint
+	}
+	nonce = hash.Sum(nonce)
+
+	return hex.EncodeToString(nonce), nil
+}
+
+// Validate checks that nonce is signed and is not expired
+func (n *NonceHash) Validate(nonce string) error {
+	b, err := hex.DecodeString(nonce)
+	if err != nil || len(b) != nonceLength {
+		return fmt.Errorf("%w: %v", errInvalidNonce, err) //nolint:errorlint
+	}
+
+	if ts := time.UnixMilli(int64(binary.BigEndian.Uint64(b))); time.Since(ts) > nonceLifetime {
+		return errInvalidNonce
+	}
+
+	hash := hmac.New(sha256.New, n.key)
+	if _, err = hash.Write(b[:8]); err != nil {
+		return fmt.Errorf("%w: %v", errInvalidNonce, err) //nolint:errorlint
+	}
+	if !hmac.Equal(b[8:], hash.Sum(nil)) {
+		return errInvalidNonce
+	}
+
+	return nil
+}
diff --git a/internal/server/server.go b/internal/server/server.go
index 9dadf13..ae2dcec 100644
--- a/internal/server/server.go
+++ b/internal/server/server.go
@@ -7,7 +7,6 @@ package server
 import (
 	"fmt"
 	"net"
-	"sync"
 	"time"
 
 	"github.com/pion/logging"
@@ -25,7 +24,7 @@ type Request struct {
 
 	// Server State
 	AllocationManager *allocation.Manager
-	Nonces            *sync.Map
+	NonceHash         *NonceHash
 
 	// User Configuration
 	AuthHandler        func(username string, realm string, srcAddr net.Addr) (key []byte, ok bool)
diff --git a/internal/server/util.go b/internal/server/util.go
index d11f529..d34d7b1 100644
--- a/internal/server/util.go
+++ b/internal/server/util.go
@@ -4,14 +4,9 @@
 package server
 
 import (
-	"crypto/md5" //nolint:gosec,gci
-	"crypto/rand"
 	"errors"
 	"fmt"
-	"io"
-	"math/big"
 	"net"
-	"strconv"
 	"time"
 
 	"github.com/pion/stun/v2"
@@ -20,29 +15,8 @@ import (
 
 const (
 	maximumAllocationLifetime = time.Hour // See: https://tools.ietf.org/html/rfc5766#section-6.2 defines 3600 seconds recommendation
-	nonceLifetime             = time.Hour // See: https://tools.ietf.org/html/rfc5766#section-4
 )
 
-func buildNonce() (string, error) {
-	/* #nosec */
-	h := md5.New()
-	if _, err := io.WriteString(h, strconv.FormatInt(time.Now().Unix(), 10)); err != nil {
-		return "", fmt.Errorf("%w: %v", errFailedToGenerateNonce, err) //nolint:errorlint
-	}
-
-	maxInt63 := big.NewInt(1<<63 - 1)
-	maxInt63.Add(maxInt63, big.NewInt(1))
-	randInt63, err := rand.Int(rand.Reader, maxInt63)
-	if err != nil {
-		return "", fmt.Errorf("%w: %v", errFailedToGenerateNonce, err) //nolint:errorlint
-	}
-
-	if _, err := io.WriteString(h, randInt63.String()); err != nil { //nolint:gosec
-		return "", fmt.Errorf("%w: %v", errFailedToGenerateNonce, err) //nolint:errorlint
-	}
-	return fmt.Sprintf("%x", h.Sum(nil)), nil
-}
-
 func buildAndSend(conn net.PacketConn, dst net.Addr, attrs ...stun.Setter) error {
 	msg, err := stun.Build(attrs...)
 	if err != nil {
@@ -70,16 +44,11 @@ func buildMsg(transactionID [stun.TransactionIDSize]byte, msgType stun.MessageTy
 
 func authenticateRequest(r Request, m *stun.Message, callingMethod stun.Method) (stun.MessageIntegrity, bool, error) {
 	respondWithNonce := func(responseCode stun.ErrorCode) (stun.MessageIntegrity, bool, error) {
-		nonce, err := buildNonce()
+		nonce, err := r.NonceHash.Generate()
 		if err != nil {
 			return nil, false, err
 		}
 
-		// Nonce has already been taken
-		if _, keyCollision := r.Nonces.LoadOrStore(nonce, time.Now()); keyCollision {
-			return nil, false, errDuplicatedNonce
-		}
-
 		return nil, false, buildAndSend(r.Conn, r.SrcAddr, buildMsg(m.TransactionID,
 			stun.NewType(callingMethod, stun.ClassErrorResponse),
 			&stun.ErrorCodeAttribute{Code: responseCode},
@@ -101,15 +70,8 @@ func authenticateRequest(r Request, m *stun.Message, callingMethod stun.Method)
 		return nil, false, buildAndSendErr(r.Conn, r.SrcAddr, err, badRequestMsg...)
 	}
 
-	// Assert Nonce exists and is not expired
-	nonceCreationTime, nonceFound := r.Nonces.Load(string(*nonceAttr))
-	if !nonceFound {
-		r.Nonces.Delete(nonceAttr)
-		return respondWithNonce(stun.CodeStaleNonce)
-	}
-
-	if timeValue, ok := nonceCreationTime.(time.Time); !ok || time.Since(timeValue) >= nonceLifetime {
-		r.Nonces.Delete(nonceAttr)
+	// Assert Nonce is signed and is not expired
+	if err := r.NonceHash.Validate(nonceAttr.String()); err != nil {
 		return respondWithNonce(stun.CodeStaleNonce)
 	}
 
diff --git a/server.go b/server.go
index 7da6ba7..db1c185 100644
--- a/server.go
+++ b/server.go
@@ -8,7 +8,6 @@ import (
 	"errors"
 	"fmt"
 	"net"
-	"sync"
 	"time"
 
 	"github.com/pion/logging"
@@ -27,7 +26,7 @@ type Server struct {
 	authHandler        AuthHandler
 	realm              string
 	channelBindTimeout time.Duration
-	nonces             *sync.Map
+	nonceHash          *server.NonceHash
 
 	packetConnConfigs  []PacketConnConfig
 	listenerConfigs    []ListenerConfig
@@ -53,6 +52,11 @@ func NewServer(config ServerConfig) (*Server, error) {
 		mtu = config.InboundMTU
 	}
 
+	nonceHash, err := server.NewNonceHash()
+	if err != nil {
+		return nil, err
+	}
+
 	s := &Server{
 		log:                loggerFactory.NewLogger("turn"),
 		authHandler:        config.AuthHandler,
@@ -60,7 +64,7 @@ func NewServer(config ServerConfig) (*Server, error) {
 		channelBindTimeout: config.ChannelBindTimeout,
 		packetConnConfigs:  config.PacketConnConfigs,
 		listenerConfigs:    config.ListenerConfigs,
-		nonces:             &sync.Map{},
+		nonceHash:          nonceHash,
 		inboundMTU:         mtu,
 	}
 
@@ -205,7 +209,7 @@ func (s *Server) readLoop(p net.PacketConn, allocationManager *allocation.Manage
 			Realm:              s.realm,
 			AllocationManager:  allocationManager,
 			ChannelBindTimeout: s.channelBindTimeout,
-			Nonces:             s.nonces,
+			NonceHash:          s.nonceHash,
 		}); err != nil {
 			s.log.Errorf("Failed to handle datagram: %v", err)
 		}


Test patch:
diff --git a/client_test.go b/client_test.go
index 0830af3..2e7e934 100644
--- a/client_test.go
+++ b/client_test.go
@@ -177,11 +177,6 @@ func TestClientNonceExpiration(t *testing.T) {
 	allocation, err := client.Allocate()
 	assert.NoError(t, err)
 
-	server.nonces.Range(func(key, value interface{}) bool {
-		server.nonces.Delete(key)
-		return true
-	})
-
 	_, err = allocation.WriteTo([]byte{0x00}, &net.UDPAddr{IP: net.ParseIP("127.0.0.1"), Port: 8080})
 	assert.NoError(t, err)
 
diff --git a/internal/server/nonce_test.go b/internal/server/nonce_test.go
new file mode 100644
index 0000000..1b92de3
--- /dev/null
+++ b/internal/server/nonce_test.go
@@ -0,0 +1,20 @@
+// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
+// SPDX-License-Identifier: MIT
+
+package server
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestNonceHash(t *testing.T) {
+	t.Run("generated hashes validate", func(t *testing.T) {
+		h, err := NewNonceHash()
+		assert.NoError(t, err)
+		nonce, err := h.Generate()
+		assert.NoError(t, err)
+		assert.NoError(t, h.Validate(nonce))
+	})
+}
diff --git a/internal/server/turn_test.go b/internal/server/turn_test.go
index 3e41940..b188fac 100644
--- a/internal/server/turn_test.go
+++ b/internal/server/turn_test.go
@@ -8,7 +8,6 @@ package server
 
 import (
 	"net"
-	"sync"
 	"testing"
 	"time"
 
@@ -80,18 +79,21 @@ func TestAllocationLifeTime(t *testing.T) {
 		})
 		assert.NoError(t, err)
 
-		staticKey := []byte("ABC")
+		nonceHash, err := NewNonceHash()
+		assert.NoError(t, err)
+		staticKey, err := nonceHash.Generate()
+		assert.NoError(t, err)
+
 		r := Request{
 			AllocationManager: allocationManager,
-			Nonces:            &sync.Map{},
+			NonceHash:         nonceHash,
 			Conn:              l,
 			SrcAddr:           &net.UDPAddr{IP: net.ParseIP("127.0.0.1"), Port: 5000},
 			Log:               logger,
 			AuthHandler: func(username string, realm string, srcAddr net.Addr) (key []byte, ok bool) {
-				return staticKey, true
+				return []byte(staticKey), true
 			},
 		}
-		r.Nonces.Store(string(staticKey), time.Now())
 
 		fiveTuple := &allocation.FiveTuple{SrcAddr: r.SrcAddr, DstAddr: r.Conn.LocalAddr(), Protocol: allocation.UDP}