integration-cli: delete existing docker0 bridge to prevent it interfering

A number of tests in the TestDockerDaemonSuite create a custom bridge as part
of the test. In some cases, an existing `docker0` bridge could interfere with
those tests. For example, the `TestDaemonICCLinkExpose` and `TestDaemonICCPing`
verify that no "icc" communication is possible, and for this create a new
bridge with a custom IP-range.

However, depending on which tests ran before the test, a default `docker0` bridge
may exist (e.g., if the`TestDefaultGatewayIPv4Implicit`) with the same IP-range,
in which iptables rules may have been set up that allow communication, and thus
make the "icc" tests fail.

This patch removes the `docker0` interface at the start of tests that create
their own bridge to prevent it from interfering.

Note that alternatively, we could update those tests to use an IP-range that's
less likely to overlap, but this may be more brittle (but could still be done
in addition to this change as a follow-up).

To verify these changes;

    make DOCKER_GRAPHDRIVER=vfs TEST_SKIP_INTEGRATION=1 TESTFLAGS='-test.run TestDockerDaemonSuite/TestDaemon(DefaultGatewayIPv4|ICC)' test-integration-cli

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

integration-cli/docker_cli_daemon_test.go

@@ -597,6 +597,10 @@ func (s *DockerDaemonSuite) TestDaemonBridgeExternal(c *testing.T) {
 	assert.ErrorContains(c, err, "", `--bridge option with an invalid bridge should cause the daemon to fail`)
 	defer d.Restart(c)
 
+	// make sure the default docker0 bridge doesn't interfere with the test,
+	// which may happen if it was created with the same IP range.
+	deleteInterface(c, "docker0")
+
 	bridgeName := "external-bridge"
 	bridgeIP := "192.169.1.1/24"
 	_, bridgeIPNet, _ := net.ParseCIDR(bridgeIP)
@@ -712,6 +716,10 @@ func (s *DockerDaemonSuite) TestDaemonRestartWithBridgeIPChange(c *testing.T) {
 func (s *DockerDaemonSuite) TestDaemonBridgeFixedCidr(c *testing.T) {
 	d := s.d
 
+	// make sure the default docker0 bridge doesn't interfere with the test,
+	// which may happen if it was created with the same IP range.
+	deleteInterface(c, "docker0")
+
 	bridgeName := "external-bridge"
 	bridgeIP := "192.169.1.1/24"
 
@@ -734,6 +742,10 @@ func (s *DockerDaemonSuite) TestDaemonBridgeFixedCidr(c *testing.T) {
 func (s *DockerDaemonSuite) TestDaemonBridgeFixedCidr2(c *testing.T) {
 	d := s.d
 
+	// make sure the default docker0 bridge doesn't interfere with the test,
+	// which may happen if it was created with the same IP range.
+	deleteInterface(c, "docker0")
+
 	bridgeName := "external-bridge"
 	bridgeIP := "10.2.2.1/16"
 
@@ -759,6 +771,10 @@ func (s *DockerDaemonSuite) TestDaemonBridgeFixedCidr2(c *testing.T) {
 func (s *DockerDaemonSuite) TestDaemonBridgeFixedCIDREqualBridgeNetwork(c *testing.T) {
 	d := s.d
 
+	// make sure the default docker0 bridge doesn't interfere with the test,
+	// which may happen if it was created with the same IP range.
+	deleteInterface(c, "docker0")
+
 	bridgeName := "external-bridge"
 	bridgeIP := "172.27.42.1/16"
 
@@ -843,6 +859,10 @@ func (s *DockerDaemonSuite) TestDaemonDefaultNetworkInvalidClusterConfig(c *test
 func (s *DockerDaemonSuite) TestDaemonIP(c *testing.T) {
 	d := s.d
 
+	// make sure the default docker0 bridge doesn't interfere with the test,
+	// which may happen if it was created with the same IP range.
+	deleteInterface(c, "docker0")
+
 	ipStr := "192.170.1.1/24"
 	ip, _, _ := net.ParseCIDR(ipStr)
 	args := []string{"--ip", ip.String()}
@@ -871,6 +891,10 @@ func (s *DockerDaemonSuite) TestDaemonICCPing(c *testing.T) {
 	testRequires(c, bridgeNfIptables)
 	d := s.d
 
+	// make sure the default docker0 bridge doesn't interfere with the test,
+	// which may happen if it was created with the same IP range.
+	deleteInterface(c, "docker0")
+
 	bridgeName := "external-bridge"
 	bridgeIP := "192.169.1.1/24"
 
@@ -893,6 +917,7 @@ func (s *DockerDaemonSuite) TestDaemonICCPing(c *testing.T) {
 	ifName := "icc-dummy"
 
 	createInterface(c, "dummy", ifName, ipStr)
+	defer deleteInterface(c, ifName)
 
 	// But, Pinging external or a Host interface must succeed
 	pingCmd := fmt.Sprintf("ping -c 1 %s -W 1", ip.String())
@@ -904,6 +929,10 @@ func (s *DockerDaemonSuite) TestDaemonICCPing(c *testing.T) {
 func (s *DockerDaemonSuite) TestDaemonICCLinkExpose(c *testing.T) {
 	d := s.d
 
+	// make sure the default docker0 bridge doesn't interfere with the test,
+	// which may happen if it was created with the same IP range.
+	deleteInterface(c, "docker0")
+
 	bridgeName := "external-bridge"
 	bridgeIP := "192.169.1.1/24"
 
@@ -926,6 +955,10 @@ func (s *DockerDaemonSuite) TestDaemonICCLinkExpose(c *testing.T) {
 }
 
 func (s *DockerDaemonSuite) TestDaemonLinksIpTablesRulesWhenLinkAndUnlink(c *testing.T) {
+	// make sure the default docker0 bridge doesn't interfere with the test,
+	// which may happen if it was created with the same IP range.
+	deleteInterface(c, "docker0")
+
 	bridgeName := "external-bridge"
 	bridgeIP := "192.169.1.1/24"