EDNS: return error on wrong version. (#95)

Split up the previous changes a bit. This PR only returns the expected
error when the received packet has the wrong EDNS version.

EDNS0 handling in the middleware needs a nicer abstraction, like
ReflectEdns() or something.

middleware/edns.go

@@ -0,0 +1,34 @@
+package middleware
+
+import (
+	"errors"
+
+	"github.com/miekg/dns"
+)
+
+// Edns0Version checks the EDNS version in the request. If error
+// is nil everything is OK and we can invoke the middleware. If non-nil, the
+// returned Msg is valid to be returned to the client (and should). For some
+// reason this response should not contain a question RR in the question section.
+func Edns0Version(req *dns.Msg) (*dns.Msg, error) {
+	opt := req.IsEdns0()
+	if opt == nil {
+		return nil, nil
+	}
+	if opt.Version() == 0 {
+		return nil, nil
+	}
+	m := new(dns.Msg)
+	m.SetReply(req)
+	// zero out question section, wtf.
+	m.Question = nil
+
+	o := new(dns.OPT)
+	o.Hdr.Name = "."
+	o.Hdr.Rrtype = dns.TypeOPT
+	o.SetVersion(0)
+	o.SetExtendedRcode(dns.RcodeBadVers)
+	m.Extra = []dns.RR{o}
+
+	return m, errors.New("EDNS0 BADVERS")
+}

middleware/edns_test.go

@@ -0,0 +1,37 @@
+package middleware
+
+import (
+	"testing"
+
+	"github.com/miekg/dns"
+)
+
+func TestEdns0Version(t *testing.T) {
+	m := ednsMsg()
+	m.Extra[0].(*dns.OPT).SetVersion(2)
+
+	_, err := Edns0Version(m)
+	if err == nil {
+		t.Errorf("expected wrong version, but got OK")
+	}
+}
+
+func TestEdns0VersionNoEdns(t *testing.T) {
+	m := ednsMsg()
+	m.Extra = nil
+
+	_, err := Edns0Version(m)
+	if err != nil {
+		t.Errorf("expected no error, but got one: %s", err)
+	}
+}
+
+func ednsMsg() *dns.Msg {
+	m := new(dns.Msg)
+	m.SetQuestion("example.com.", dns.TypeA)
+	o := new(dns.OPT)
+	o.Hdr.Name = "."
+	o.Hdr.Rrtype = dns.TypeOPT
+	m.Extra = append(m.Extra, o)
+	return m
+}

middleware/rcode.go

@@ -0,0 +1,14 @@
+package middleware
+
+import (
+	"strconv"
+
+	"github.com/miekg/dns"
+)
+
+func RcodeToString(rcode int) string {
+	if str, ok := dns.RcodeToString[rcode]; ok {
+		return str
+	}
+	return "RCODE" + strconv.Itoa(rcode)
+}

middleware/recorder.go

@@ -1,7 +1,6 @@
 package middleware
 
 import (
-	"strconv"
 	"time"
 
 	"github.com/miekg/dns"
@@ -54,27 +53,16 @@ func (r *ResponseRecorder) Write(buf []byte) (int, error) {
 }
 
 // Size returns the size.
-func (r *ResponseRecorder) Size() int {
-	return r.size
-}
+func (r *ResponseRecorder) Size() int { return r.size }
 
 // Rcode returns the rcode.
-func (r *ResponseRecorder) Rcode() string {
-	if rcode, ok := dns.RcodeToString[r.rcode]; ok {
-		return rcode
-	}
-	return "RCODE" + strconv.Itoa(r.rcode)
-}
+func (r *ResponseRecorder) Rcode() string { return RcodeToString(r.rcode) }
 
 // Start returns the start time of the ResponseRecorder.
-func (r *ResponseRecorder) Start() time.Time {
-	return r.start
-}
+func (r *ResponseRecorder) Start() time.Time { return r.start }
 
 // Msg returns the written message from the ResponseRecorder.
-func (r *ResponseRecorder) Msg() *dns.Msg {
-	return r.msg
-}
+func (r *ResponseRecorder) Msg() *dns.Msg { return r.msg }
 
 // Hijack implements dns.Hijacker. It simply wraps the underlying
 // ResponseWriter's Hijack method if there is one, or returns an error.

server/server.go

@@ -12,10 +12,10 @@ import (
 	"net"
 	"os"
 	"runtime"
-	"strconv"
 	"sync"
 	"time"
 
+	"github.com/miekg/coredns/middleware"
 	"github.com/miekg/coredns/middleware/chaos"
 	"github.com/miekg/coredns/middleware/prometheus"
 
@@ -279,6 +279,14 @@ func (s *Server) ServeDNS(w dns.ResponseWriter, r *dns.Msg) {
 		}
 	}()
 
+	if m, err := middleware.Edns0Version(r); err != nil { // Wrong EDNS version, return at once.
+		qtype := dns.Type(r.Question[0].Qtype).String()
+		rc := middleware.RcodeToString(dns.RcodeBadVers)
+		metrics.Report(dropped, qtype, rc, m.Len(), time.Now())
+		w.WriteMsg(m)
+		return
+	}
+
 	// Execute the optional request callback if it exists
 	if s.ReqCallback != nil && s.ReqCallback(w, r) {
 		return
@@ -332,12 +340,7 @@ func (s *Server) ServeDNS(w dns.ResponseWriter, r *dns.Msg) {
 // of the specified HTTP status code.
 func DefaultErrorFunc(w dns.ResponseWriter, r *dns.Msg, rcode int) {
 	qtype := dns.Type(r.Question[0].Qtype).String()
-
-	// this code is duplicated a few times, TODO(miek)
-	rc := dns.RcodeToString[rcode]
-	if rc == "" {
-		rc = "RCODE" + strconv.Itoa(rcode)
-	}
+	rc := middleware.RcodeToString(rcode)
 
 	answer := new(dns.Msg)
 	answer.SetRcode(r, rcode)