webrtc: fix memory leak with udpmux.muxedConnection context (#3243)

This context wasn't being cancelled on all code paths. In particular,
contexts for connections that didn't complete negotiation were not being
cancelled.

The change arranges for either `udpmux.muxedConnection.Close` or 
`RemoveConnByUfrag` to call the other.

Fixes: #3223

p2p/transport/webrtc/udpmux/mux.go

@@ -271,12 +271,13 @@ func (mux *UDPMux) RemoveConnByUfrag(ufrag string) {
 
 	for _, isIPv6 := range [...]bool{true, false} {
 		key := ufragConnKey{ufrag: ufrag, isIPv6: isIPv6}
-		if _, ok := mux.ufragMap[key]; ok {
+		if conn, ok := mux.ufragMap[key]; ok {
 			delete(mux.ufragMap, key)
 			for _, addr := range mux.ufragAddrMap[key] {
 				delete(mux.addrMap, addr.String())
 			}
 			delete(mux.ufragAddrMap, key)
+			conn.close()
 		}
 	}
 }
@@ -293,7 +294,7 @@ func (mux *UDPMux) getOrCreateConn(ufrag string, isIPv6 bool, _ *UDPMux, addr ne
 		return false, conn
 	}
 
-	conn := newMuxedConnection(mux, func() { mux.RemoveConnByUfrag(ufrag) })
+	conn := newMuxedConnection(mux, ufrag)
 	mux.ufragMap[key] = conn
 	mux.addrMap[addr.String()] = conn
 	mux.ufragAddrMap[key] = append(mux.ufragAddrMap[key], addr)

p2p/transport/webrtc/udpmux/mux_test.go

@@ -8,6 +8,7 @@ import (
 	"time"
 
 	"github.com/pion/stun"
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
@@ -246,3 +247,28 @@ func TestMuxedConnection(t *testing.T) {
 	}
 	require.Empty(t, addrUfragMap)
 }
+
+func TestRemovingUfragClosesConn(t *testing.T) {
+	c := newPacketConn(t)
+	m := NewUDPMux(c)
+	m.Start()
+	defer m.Close()
+	remoteAddr := &net.UDPAddr{IP: net.ParseIP("127.0.0.1"), Port: 1234}
+	conn, err := m.GetConn("a", remoteAddr)
+	require.NoError(t, err)
+	defer conn.Close()
+
+	connClosed := make(chan bool)
+	go func() {
+		_, _, err := conn.ReadFrom(make([]byte, 100))
+		assert.ErrorIs(t, err, context.Canceled)
+		close(connClosed)
+	}()
+	require.NoError(t, err)
+	m.RemoveConnByUfrag("a")
+	select {
+	case <-connClosed:
+	case <-time.After(1 * time.Second):
+		t.Fatalf("expected the connection to be closed")
+	}
+}

p2p/transport/webrtc/udpmux/muxed_connection.go

@@ -23,31 +23,29 @@ const queueLen = 128
 // from which this connection (indexed by ufrag) received
 // data.
 type muxedConnection struct {
-	ctx     context.Context
-	cancel  context.CancelFunc
-	onClose func()
-	queue   chan packet
-	mux     *UDPMux
+	ctx    context.Context
+	cancel context.CancelFunc
+	queue  chan packet
+	mux    *UDPMux
+	ufrag  string
 }
 
 var _ net.PacketConn = &muxedConnection{}
 
-func newMuxedConnection(mux *UDPMux, onClose func()) *muxedConnection {
+func newMuxedConnection(mux *UDPMux, ufrag string) *muxedConnection {
 	ctx, cancel := context.WithCancel(mux.ctx)
 	return &muxedConnection{
-		ctx:     ctx,
-		cancel:  cancel,
-		queue:   make(chan packet, queueLen),
-		onClose: onClose,
-		mux:     mux,
+		ctx:    ctx,
+		cancel: cancel,
+		queue:  make(chan packet, queueLen),
+		mux:    mux,
+		ufrag:  ufrag,
 	}
 }
 
 func (c *muxedConnection) Push(buf []byte, addr net.Addr) error {
-	select {
-	case <-c.ctx.Done():
+	if c.ctx.Err() != nil {
 		return errors.New("closed")
-	default:
 	}
 	select {
 	case c.queue <- packet{buf: buf, addr: addr}:
@@ -76,12 +74,21 @@ func (c *muxedConnection) WriteTo(p []byte, addr net.Addr) (n int, err error) {
 }
 
 func (c *muxedConnection) Close() error {
-	select {
-	case <-c.ctx.Done():
+	if c.ctx.Err() != nil {
 		return nil
-	default:
 	}
-	c.onClose()
+	// mux calls close to actually close the connection
+	//
+	// Removing the connection from the mux or closing the connection
+	// must trigger the other.
+	// Doing this here ensures we don't need to call both RemoveConnByUfrag
+	// and close on all code paths.
+	c.mux.RemoveConnByUfrag(c.ufrag)
+	return nil
+}
+
+// closes the connection. Must only be called by the mux.
+func (c *muxedConnection) close() {
 	c.cancel()
 	// drain the packet queue
 	for {
@@ -89,7 +96,7 @@ func (c *muxedConnection) Close() error {
 		case p := <-c.queue:
 			pool.Put(p.buf)
 		default:
-			return nil
+			return
 		}
 	}
 }