[23.0 backport] daemon: set docker0 subpool as the IPAM pool

daemon/daemon_unix.go

@@ -1000,6 +1000,9 @@ func initBridgeDriver(controller libnetwork.NetworkController, config *config.Co
 		}
 
 		ipamV4Conf.SubPool = fCIDR.String()
+		if ipamV4Conf.PreferredPool == "" {
+			ipamV4Conf.PreferredPool = fCIDR.String()
+		}
 	}
 
 	if config.BridgeConfig.DefaultGatewayIPv4 != nil {

integration/daemon/daemon_test.go

@@ -21,6 +21,7 @@ import (
 	"github.com/docker/docker/testutil/daemon"
 	"gotest.tools/v3/assert"
 	is "gotest.tools/v3/assert/cmp"
+	"gotest.tools/v3/icmd"
 	"gotest.tools/v3/skip"
 )
 
@@ -416,3 +417,30 @@ func testLiveRestoreVolumeReferences(t *testing.T) {
 		runTest(t, "no")
 	})
 }
+
+func TestDaemonDefaultBridgeWithFixedCidrButNoBip(t *testing.T) {
+	skip.If(t, runtime.GOOS == "windows")
+
+	bridgeName := "ext-bridge1"
+	d := daemon.New(t, daemon.WithEnvVars("DOCKER_TEST_CREATE_DEFAULT_BRIDGE="+bridgeName))
+	defer func() {
+		d.Stop(t)
+		d.Cleanup(t)
+	}()
+
+	defer func() {
+		// No need to clean up when running this test in rootless mode, as the
+		// interface is deleted when the daemon is stopped and the netns
+		// reclaimed by the kernel.
+		if !testEnv.IsRootless() {
+			deleteInterface(t, bridgeName)
+		}
+	}()
+	d.StartWithBusybox(t, "--bridge", bridgeName, "--fixed-cidr", "192.168.130.0/24")
+}
+
+func deleteInterface(t *testing.T, ifName string) {
+	icmd.RunCommand("ip", "link", "delete", ifName).Assert(t, icmd.Success)
+	icmd.RunCommand("iptables", "-t", "nat", "--flush").Assert(t, icmd.Success)
+	icmd.RunCommand("iptables", "--flush").Assert(t, icmd.Success)
+}

libnetwork/drivers/bridge/setup_device.go

@@ -16,8 +16,14 @@ import (
 // SetupDevice create a new bridge interface/
 func setupDevice(config *networkConfiguration, i *bridgeInterface) error {
 	// We only attempt to create the bridge when the requested device name is
-	// the default one.
-	if config.BridgeName != DefaultBridgeName && config.DefaultBridge {
+	// the default one. The default bridge name can be overridden with the
+	// DOCKER_TEST_CREATE_DEFAULT_BRIDGE env var. It should be used only for
+	// test purpose.
+	var defaultBridgeName string
+	if defaultBridgeName = os.Getenv("DOCKER_TEST_CREATE_DEFAULT_BRIDGE"); defaultBridgeName == "" {
+		defaultBridgeName = DefaultBridgeName
+	}
+	if config.BridgeName != defaultBridgeName && config.DefaultBridge {
 		return NonDefaultBridgeExistError(config.BridgeName)
 	}