|
| 1 | +package networking |
| 2 | + |
| 3 | +import ( |
| 4 | + "net" |
| 5 | + "os" |
| 6 | + "testing" |
| 7 | + |
| 8 | + containertypes "github.com/docker/docker/api/types/container" |
| 9 | + "github.com/docker/docker/integration/internal/container" |
| 10 | + "github.com/docker/docker/integration/internal/network" |
| 11 | + "github.com/docker/docker/testutil/daemon" |
| 12 | + "github.com/miekg/dns" |
| 13 | + "gotest.tools/v3/assert" |
| 14 | + is "gotest.tools/v3/assert/cmp" |
| 15 | + "gotest.tools/v3/skip" |
| 16 | +) |
| 17 | + |
| 18 | +// writeTempResolvConf writes a resolv.conf that only contains a single |
| 19 | +// nameserver line, with address addr. |
| 20 | +// It returns the name of the temp file. |
| 21 | +func writeTempResolvConf(t *testing.T, addr string) string { |
| 22 | + t.Helper() |
| 23 | + // Not using t.TempDir() here because in rootless mode, while the temporary |
| 24 | + // directory gets mode 0777, it's a subdir of an 0700 directory owned by root. |
| 25 | + // So, it's not accessible by the daemon. |
| 26 | + f, err := os.CreateTemp("", "resolv.conf") |
| 27 | + assert.NilError(t, err) |
| 28 | + t.Cleanup(func() { os.Remove(f.Name()) }) |
| 29 | + err = f.Chmod(0644) |
| 30 | + assert.NilError(t, err) |
| 31 | + f.Write([]byte("nameserver " + addr + "\n")) |
| 32 | + return f.Name() |
| 33 | +} |
| 34 | + |
| 35 | +const dnsRespAddr = "10.11.12.13" |
| 36 | + |
| 37 | +// startDaftDNS starts and returns a really, really daft DNS server that only |
| 38 | +// responds to type-A requests, and always with address dnsRespAddr. |
| 39 | +func startDaftDNS(t *testing.T, addr string) *dns.Server { |
| 40 | + serveDNS := func(w dns.ResponseWriter, query *dns.Msg) { |
| 41 | + if query.Question[0].Qtype == dns.TypeA { |
| 42 | + resp := &dns.Msg{} |
| 43 | + resp.SetReply(query) |
| 44 | + answer := &dns.A{ |
| 45 | + Hdr: dns.RR_Header{ |
| 46 | + Name: query.Question[0].Name, |
| 47 | + Rrtype: dns.TypeA, |
| 48 | + Class: dns.ClassINET, |
| 49 | + Ttl: 600, |
| 50 | + }, |
| 51 | + } |
| 52 | + answer.A = net.ParseIP(dnsRespAddr) |
| 53 | + resp.Answer = append(resp.Answer, answer) |
| 54 | + _ = w.WriteMsg(resp) |
| 55 | + } |
| 56 | + } |
| 57 | + |
| 58 | + conn, err := net.ListenUDP("udp", &net.UDPAddr{ |
| 59 | + IP: net.ParseIP(addr), |
| 60 | + Port: 53, |
| 61 | + }) |
| 62 | + assert.NilError(t, err) |
| 63 | + |
| 64 | + server := &dns.Server{Handler: dns.HandlerFunc(serveDNS), PacketConn: conn} |
| 65 | + go func() { |
| 66 | + _ = server.ActivateAndServe() |
| 67 | + }() |
| 68 | + |
| 69 | + return server |
| 70 | +} |
| 71 | + |
| 72 | +// Check that when a container is connected to an internal network, DNS |
| 73 | +// requests sent to daemon's internal DNS resolver are not forwarded to |
| 74 | +// an upstream resolver listening on a localhost address. |
| 75 | +// (Assumes the host does not already have a DNS server on 127.0.0.1.) |
| 76 | +func TestInternalNetworkDNS(t *testing.T) { |
| 77 | + skip.If(t, testEnv.DaemonInfo.OSType == "windows", "No resolv.conf on Windows") |
| 78 | + skip.If(t, testEnv.IsRootless, "Can't use resolver on host in rootless mode") |
| 79 | + ctx := setupTest(t) |
| 80 | + |
| 81 | + // Start a DNS server on the loopback interface. |
| 82 | + server := startDaftDNS(t, "127.0.0.1") |
| 83 | + defer server.Shutdown() |
| 84 | + |
| 85 | + // Set up a temp resolv.conf pointing at that DNS server, and a daemon using it. |
| 86 | + tmpFileName := writeTempResolvConf(t, "127.0.0.1") |
| 87 | + d := daemon.New(t, daemon.WithEnvVars("DOCKER_TEST_RESOLV_CONF_PATH="+tmpFileName)) |
| 88 | + d.StartWithBusybox(ctx, t, "--experimental", "--ip6tables") |
| 89 | + defer d.Stop(t) |
| 90 | + |
| 91 | + c := d.NewClientT(t) |
| 92 | + defer c.Close() |
| 93 | + |
| 94 | + intNetName := "intnet" |
| 95 | + network.CreateNoError(ctx, t, c, intNetName, |
| 96 | + network.WithDriver("bridge"), |
| 97 | + network.WithInternal(), |
| 98 | + ) |
| 99 | + defer network.RemoveNoError(ctx, t, c, intNetName) |
| 100 | + |
| 101 | + extNetName := "extnet" |
| 102 | + network.CreateNoError(ctx, t, c, extNetName, |
| 103 | + network.WithDriver("bridge"), |
| 104 | + ) |
| 105 | + defer network.RemoveNoError(ctx, t, c, extNetName) |
| 106 | + |
| 107 | + // Create a container, initially with external connectivity. |
| 108 | + // Expect the external DNS server to respond to a request from the container. |
| 109 | + ctrId := container.Run(ctx, t, c, container.WithNetworkMode(extNetName)) |
| 110 | + defer c.ContainerRemove(ctx, ctrId, containertypes.RemoveOptions{Force: true}) |
| 111 | + res, err := container.Exec(ctx, c, ctrId, []string{"nslookup", "test.example"}) |
| 112 | + assert.NilError(t, err) |
| 113 | + assert.Check(t, is.Equal(res.ExitCode, 0)) |
| 114 | + assert.Check(t, is.Contains(res.Stdout(), dnsRespAddr)) |
| 115 | + |
| 116 | + // Connect the container to the internal network as well. |
| 117 | + // External DNS should still be used. |
| 118 | + err = c.NetworkConnect(ctx, intNetName, ctrId, nil) |
| 119 | + assert.NilError(t, err) |
| 120 | + res, err = container.Exec(ctx, c, ctrId, []string{"nslookup", "test.example"}) |
| 121 | + assert.NilError(t, err) |
| 122 | + assert.Check(t, is.Equal(res.ExitCode, 0)) |
| 123 | + assert.Check(t, is.Contains(res.Stdout(), dnsRespAddr)) |
| 124 | + |
| 125 | + // Disconnect from the external network. |
| 126 | + // Expect no access to the external DNS. |
| 127 | + err = c.NetworkDisconnect(ctx, extNetName, ctrId, true) |
| 128 | + assert.NilError(t, err) |
| 129 | + res, err = container.Exec(ctx, c, ctrId, []string{"nslookup", "test.example"}) |
| 130 | + assert.NilError(t, err) |
| 131 | + assert.Check(t, is.Equal(res.ExitCode, 1)) |
| 132 | + assert.Check(t, is.Contains(res.Stdout(), "SERVFAIL")) |
| 133 | + |
| 134 | + // Reconnect the external network. |
| 135 | + // Check that the external DNS server is used again. |
| 136 | + err = c.NetworkConnect(ctx, extNetName, ctrId, nil) |
| 137 | + assert.NilError(t, err) |
| 138 | + res, err = container.Exec(ctx, c, ctrId, []string{"nslookup", "test.example"}) |
| 139 | + assert.NilError(t, err) |
| 140 | + assert.Check(t, is.Equal(res.ExitCode, 0)) |
| 141 | + assert.Check(t, is.Contains(res.Stdout(), dnsRespAddr)) |
| 142 | +} |
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