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