fqdn proxy: fix data race detection on TCP fqdn proxy

pkg/fqdn/dnsproxy/noop_sessionudpfactory.go

@@ -0,0 +1,28 @@
+// SPDX-License-Identifier: Apache-2.0
+// Copyright Authors of Cilium
+
+package dnsproxy
+
+import (
+	"net"
+
+	"github.com/cilium/dns"
+)
+
+type noopSessionUDPFactory struct{}
+
+var _ dns.SessionUDPFactory = &noopSessionUDPFactory{}
+
+func (*noopSessionUDPFactory) InitPool(msgSize int) {}
+
+func (*noopSessionUDPFactory) ReadRequest(conn *net.UDPConn) ([]byte, dns.SessionUDP, error) {
+	return nil, nil, nil
+}
+
+func (*noopSessionUDPFactory) ReadRequestConn(conn net.PacketConn) ([]byte, net.Addr, error) {
+	return nil, nil, nil
+}
+
+func (*noopSessionUDPFactory) SetSocketOptions(conn *net.UDPConn) error {
+	return nil
+}

pkg/fqdn/dnsproxy/proxy.go

@@ -1118,6 +1118,9 @@ func bindToAddr(address string, port uint16, handler dns.Handler, ipv4, ipv6 boo
 		}
 		dnsServers = append(dnsServers, &dns.Server{
 			Listener: tcpListener, Handler: handler,
+			// Explicitly set a noop factory to prevent data race detection when InitPool is called
+			// multiple times on the default factory even for TCP (IPv4 & IPv6).
+			SessionUDPFactory: &noopSessionUDPFactory{},
 			// Net & Addr are only set for logging purposes and aren't used if using ActivateAndServe.
 			Net: ipFamily.TCPAddress, Addr: tcpListener.Addr().String(),
 		})