Merge pull request quic-go#1937 from lucas-clemente/fix-hrr-race

fix race condition in crypto setup when sending a HelloRetryRequest

internal/handshake/crypto_setup.go

@@ -220,7 +220,7 @@ func newCryptoSetup(
 		messageChan:            make(chan []byte, 100),
 		receivedReadKey:        make(chan struct{}),
 		receivedWriteKey:       make(chan struct{}),
-		writeRecord:            make(chan struct{}),
+		writeRecord:            make(chan struct{}, 1),
 		closeChan:              make(chan struct{}),
 	}
 	qtlsConf := tlsConfigToQtlsConfig(tlsConf, cs, extHandler)
@@ -510,13 +510,6 @@ func (h *cryptoSetup) SetWriteKey(suite *qtls.CipherSuite, trafficSecret []byte)
 
 // WriteRecord is called when TLS writes data
 func (h *cryptoSetup) WriteRecord(p []byte) (int, error) {
-	defer func() {
-		select {
-		case h.writeRecord <- struct{}{}:
-		default:
-		}
-	}()
-
 	h.mutex.Lock()
 	defer h.mutex.Unlock()
 
@@ -527,6 +520,11 @@ func (h *cryptoSetup) WriteRecord(p []byte) (int, error) {
 		if !h.clientHelloWritten && h.perspective == protocol.PerspectiveClient {
 			h.clientHelloWritten = true
 			close(h.clientHelloWrittenChan)
+		} else {
+			// We need additional signaling to properly detect HelloRetryRequests.
+			// For servers: when the ServerHello is written.
+			// For clients: when a reply is sent in response to a ServerHello.
+			h.writeRecord <- struct{}{}
 		}
 		return n, err
 	case protocol.EncryptionHandshake: