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libnet: Don't forward to upstream resolvers on internal nw
This commit makes sure the embedded resolver doesn't try to forward to upstream servers when a container is only attached to an internal network. Co-authored-by: Albin Kerouanton <albinker@gmail.com> Signed-off-by: Rob Murray <rob.murray@docker.com> (cherry picked from commit 790c303) Signed-off-by: Cory Snider <csnider@mirantis.com>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,142 @@ | ||
| package networking | ||
|
|
||
| import ( | ||
| "net" | ||
| "os" | ||
| "testing" | ||
|
|
||
| "github.com/docker/docker/api/types" | ||
| "github.com/docker/docker/integration/internal/container" | ||
| "github.com/docker/docker/integration/internal/network" | ||
| "github.com/docker/docker/testutil/daemon" | ||
| "github.com/miekg/dns" | ||
| "gotest.tools/v3/assert" | ||
| is "gotest.tools/v3/assert/cmp" | ||
| "gotest.tools/v3/skip" | ||
| ) | ||
|
|
||
| // writeTempResolvConf writes a resolv.conf that only contains a single | ||
| // nameserver line, with address addr. | ||
| // It returns the name of the temp file. | ||
| func writeTempResolvConf(t *testing.T, addr string) string { | ||
| t.Helper() | ||
| // Not using t.TempDir() here because in rootless mode, while the temporary | ||
| // directory gets mode 0777, it's a subdir of an 0700 directory owned by root. | ||
| // So, it's not accessible by the daemon. | ||
| f, err := os.CreateTemp("", "resolv.conf") | ||
| assert.NilError(t, err) | ||
| t.Cleanup(func() { os.Remove(f.Name()) }) | ||
| err = f.Chmod(0644) | ||
| assert.NilError(t, err) | ||
| f.Write([]byte("nameserver " + addr + "\n")) | ||
| return f.Name() | ||
| } | ||
|
|
||
| const dnsRespAddr = "10.11.12.13" | ||
|
|
||
| // startDaftDNS starts and returns a really, really daft DNS server that only | ||
| // responds to type-A requests, and always with address dnsRespAddr. | ||
| func startDaftDNS(t *testing.T, addr string) *dns.Server { | ||
| serveDNS := func(w dns.ResponseWriter, query *dns.Msg) { | ||
| if query.Question[0].Qtype == dns.TypeA { | ||
| resp := &dns.Msg{} | ||
| resp.SetReply(query) | ||
| answer := &dns.A{ | ||
| Hdr: dns.RR_Header{ | ||
| Name: query.Question[0].Name, | ||
| Rrtype: dns.TypeA, | ||
| Class: dns.ClassINET, | ||
| Ttl: 600, | ||
| }, | ||
| } | ||
| answer.A = net.ParseIP(dnsRespAddr) | ||
| resp.Answer = append(resp.Answer, answer) | ||
| _ = w.WriteMsg(resp) | ||
| } | ||
| } | ||
|
|
||
| conn, err := net.ListenUDP("udp", &net.UDPAddr{ | ||
| IP: net.ParseIP(addr), | ||
| Port: 53, | ||
| }) | ||
| assert.NilError(t, err) | ||
|
|
||
| server := &dns.Server{Handler: dns.HandlerFunc(serveDNS), PacketConn: conn} | ||
| go func() { | ||
| _ = server.ActivateAndServe() | ||
| }() | ||
|
|
||
| return server | ||
| } | ||
|
|
||
| // Check that when a container is connected to an internal network, DNS | ||
| // requests sent to daemon's internal DNS resolver are not forwarded to | ||
| // an upstream resolver listening on a localhost address. | ||
| // (Assumes the host does not already have a DNS server on 127.0.0.1.) | ||
| func TestInternalNetworkDNS(t *testing.T) { | ||
| skip.If(t, testEnv.DaemonInfo.OSType == "windows", "No resolv.conf on Windows") | ||
| skip.If(t, testEnv.IsRootless, "Can't use resolver on host in rootless mode") | ||
| ctx := setupTest(t) | ||
|
|
||
| // Start a DNS server on the loopback interface. | ||
| server := startDaftDNS(t, "127.0.0.1") | ||
| defer server.Shutdown() | ||
|
|
||
| // Set up a temp resolv.conf pointing at that DNS server, and a daemon using it. | ||
| tmpFileName := writeTempResolvConf(t, "127.0.0.1") | ||
| d := daemon.New(t, daemon.WithEnvVars("DOCKER_TEST_RESOLV_CONF_PATH="+tmpFileName)) | ||
| d.StartWithBusybox(t, "--experimental", "--ip6tables") | ||
| defer d.Stop(t) | ||
|
|
||
| c := d.NewClientT(t) | ||
| defer c.Close() | ||
|
|
||
| intNetName := "intnet" | ||
| network.CreateNoError(ctx, t, c, intNetName, | ||
| network.WithDriver("bridge"), | ||
| network.WithInternal(), | ||
| ) | ||
| defer network.RemoveNoError(ctx, t, c, intNetName) | ||
|
|
||
| extNetName := "extnet" | ||
| network.CreateNoError(ctx, t, c, extNetName, | ||
| network.WithDriver("bridge"), | ||
| ) | ||
| defer network.RemoveNoError(ctx, t, c, extNetName) | ||
|
|
||
| // Create a container, initially with external connectivity. | ||
| // Expect the external DNS server to respond to a request from the container. | ||
| ctrId := container.Run(ctx, t, c, container.WithNetworkMode(extNetName)) | ||
| defer c.ContainerRemove(ctx, ctrId, types.ContainerRemoveOptions{Force: true}) | ||
| res, err := container.Exec(ctx, c, ctrId, []string{"nslookup", "test.example"}) | ||
| assert.NilError(t, err) | ||
| assert.Check(t, is.Equal(res.ExitCode, 0)) | ||
| assert.Check(t, is.Contains(res.Stdout(), dnsRespAddr)) | ||
|
|
||
| // Connect the container to the internal network as well. | ||
| // External DNS should still be used. | ||
| err = c.NetworkConnect(ctx, intNetName, ctrId, nil) | ||
| assert.NilError(t, err) | ||
| res, err = container.Exec(ctx, c, ctrId, []string{"nslookup", "test.example"}) | ||
| assert.NilError(t, err) | ||
| assert.Check(t, is.Equal(res.ExitCode, 0)) | ||
| assert.Check(t, is.Contains(res.Stdout(), dnsRespAddr)) | ||
|
|
||
| // Disconnect from the external network. | ||
| // Expect no access to the external DNS. | ||
| err = c.NetworkDisconnect(ctx, extNetName, ctrId, true) | ||
| assert.NilError(t, err) | ||
| res, err = container.Exec(ctx, c, ctrId, []string{"nslookup", "test.example"}) | ||
| assert.NilError(t, err) | ||
| assert.Check(t, is.Equal(res.ExitCode, 1)) | ||
| assert.Check(t, is.Contains(res.Stdout(), "SERVFAIL")) | ||
|
|
||
| // Reconnect the external network. | ||
| // Check that the external DNS server is used again. | ||
| err = c.NetworkConnect(ctx, extNetName, ctrId, nil) | ||
| assert.NilError(t, err) | ||
| res, err = container.Exec(ctx, c, ctrId, []string{"nslookup", "test.example"}) | ||
| assert.NilError(t, err) | ||
| assert.Check(t, is.Equal(res.ExitCode, 0)) | ||
| assert.Check(t, is.Contains(res.Stdout(), dnsRespAddr)) | ||
| } |
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