transfer: reply with refused (#4510)

* transfer: reply with refused

When the *transfer* plugin is not loaded and of the handlers will still
see the AXFR/IXFR request because it is not intercepted.

They need to reply with REFUSED in that case. Update file, auto and k8s
to do this. Add testcase in the file plugin.

Ideally *erratic* should be moved over as well, but maybe that's
*erratic*

This is a bug fix.
Signed-off-by: Miek Gieben <miek@miek.nl>

* import path
Signed-off-by: Miek Gieben <miek@miek.nl>

plugin/auto/auto.go

@@ -62,6 +62,11 @@ func (a Auto) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (i
 		return dns.RcodeServerFailure, nil
 	}
 
+	// If transfer is not loaded, we'll see these, answer with refused (no transfer allowed).
+	if state.QType() == dns.TypeAXFR || state.QType() == dns.TypeIXFR {
+		return dns.RcodeRefused, nil
+	}
+
 	answer, ns, extra, result := z.Lookup(ctx, state, qname)
 
 	m := new(dns.Msg)

plugin/file/file.go

@@ -47,6 +47,11 @@ func (f File) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (i
 		return dns.RcodeServerFailure, nil
 	}
 
+	// If transfer is not loaded, we'll see these, answer with refused (no transfer allowed).
+	if state.QType() == dns.TypeAXFR || state.QType() == dns.TypeIXFR {
+		return dns.RcodeRefused, nil
+	}
+
 	// This is only for when we are a secondary zones.
 	if r.Opcode == dns.OpcodeNotify {
 		if z.isNotify(state) {

plugin/file/xfr_test.go

 package file
 
 import (
+	"context"
 	"fmt"
 	"strings"
 	"testing"
+
+	"github.com/coredns/coredns/plugin/pkg/dnstest"
+	"github.com/coredns/coredns/plugin/test"
+
+	"github.com/miekg/dns"
 )
 
 func ExampleZone_All() {
@@ -41,3 +47,26 @@ func TestAllNewZone(t *testing.T) {
 		t.Errorf("Expected %d records in empty zone, got %d", 0, len(records))
 	}
 }
+
+func TestAXFRWithOutTransferPlugin(t *testing.T) {
+	zone, err := Parse(strings.NewReader(dbMiekNL), testzone, "stdin", 0)
+	if err != nil {
+		t.Fatalf("Expected no error when reading zone, got %q", err)
+	}
+
+	fm := File{Next: test.ErrorHandler(), Zones: Zones{Z: map[string]*Zone{testzone: zone}, Names: []string{testzone}}}
+	ctx := context.TODO()
+
+	m := new(dns.Msg)
+	m.SetQuestion("miek.nl.", dns.TypeAXFR)
+
+	rec := dnstest.NewRecorder(&test.ResponseWriter{})
+	code, err := fm.ServeDNS(ctx, rec, m)
+	if err != nil {
+		t.Errorf("Expected no error, got %v", err)
+		return
+	}
+	if code != dns.RcodeRefused {
+		t.Errorf("Expecting REFUSED, got %d", code)
+	}
+}

plugin/kubernetes/handler.go

@@ -44,6 +44,8 @@ func (k Kubernetes) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.M
 		records, extra, err = plugin.SRV(ctx, &k, zone, state, plugin.Options{})
 	case dns.TypeSOA:
 		records, err = plugin.SOA(ctx, &k, zone, state, plugin.Options{})
+	case dns.TypeAXFR, dns.TypeIXFR:
+		return dns.RcodeRefused, nil
 	case dns.TypeNS:
 		if state.Name() == zone {
 			records, extra, err = plugin.NS(ctx, &k, zone, state, plugin.Options{})