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libnetwork: reply SERVFAIL on resolve error

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...instead of silently dropping the DNS query.

Signed-off-by: Cory Snider <csnider@mirantis.com>
This commit is contained in:
Cory Snider
2022-12-13 18:54:43 -05:00
parent 92aa6e6282
commit 0bd30e90bb
2 changed files with 35 additions and 8 deletions
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2
libnetwork/resolver.go
View File

@@ -399,7 +399,7 @@ func (r *resolver) ServeDNS(w dns.ResponseWriter, query *dns.Msg) {
if err != nil {
logrus.WithError(err).Errorf("[resolver] failed to handle query: %s (%s)", queryName, dns.TypeToString[queryType])
return
resp = new(dns.Msg).SetRcode(query, dns.RcodeServerFailure)
}
if resp == nil {

41
libnetwork/resolver_test.go
View File

@@ -59,12 +59,14 @@ func (w *tstwriter) GetResponse() *dns.Msg { return w.msg }
func (w *tstwriter) ClearResponse() { w.msg = nil }
func checkNonNullResponse(t *testing.T, m *dns.Msg) {
t.Helper()
if m == nil {
t.Fatal("Null DNS response found. Non Null response msg expected.")
}
}
func checkDNSAnswersCount(t *testing.T, m *dns.Msg, expected int) {
t.Helper()
answers := len(m.Answer)
if answers != expected {
t.Fatalf("Expected number of answers in response: %d. Found: %d", expected, answers)
@@ -72,12 +74,14 @@ func checkDNSAnswersCount(t *testing.T, m *dns.Msg, expected int) {
}
func checkDNSResponseCode(t *testing.T, m *dns.Msg, expected int) {
t.Helper()
if m.MsgHdr.Rcode != expected {
t.Fatalf("Expected DNS response code: %d. Found: %d", expected, m.MsgHdr.Rcode)
}
}
func checkDNSRRType(t *testing.T, actual, expected uint16) {
t.Helper()
if actual != expected {
t.Fatalf("Expected DNS Rrtype: %d. Found: %d", expected, actual)
}
@@ -373,13 +377,7 @@ func TestOversizedDNSReply(t *testing.T) {
// The resolver logs lots of valuable info at level debug. Redirect it
// to t.Log() so the log spew is emitted only if the test fails.
oldLevel, oldOut := logrus.StandardLogger().Level, logrus.StandardLogger().Out
defer func() {
logrus.StandardLogger().SetLevel(oldLevel)
logrus.StandardLogger().SetOutput(oldOut)
}()
logrus.StandardLogger().SetLevel(logrus.DebugLevel)
logrus.SetOutput(tlogWriter{t})
defer redirectLogrusTo(t)()
w := &tstwriter{localAddr: srv.LocalAddr()}
q := new(dns.Msg).SetQuestion("s3.amazonaws.com.", dns.TypeA)
@@ -392,6 +390,16 @@ func TestOversizedDNSReply(t *testing.T) {
checkDNSRRType(t, resp.Answer[0].Header().Rrtype, dns.TypeA)
}
func redirectLogrusTo(t *testing.T) func() {
oldLevel, oldOut := logrus.StandardLogger().Level, logrus.StandardLogger().Out
logrus.StandardLogger().SetLevel(logrus.DebugLevel)
logrus.SetOutput(tlogWriter{t})
return func() {
logrus.StandardLogger().SetLevel(oldLevel)
logrus.StandardLogger().SetOutput(oldOut)
}
}
type tlogWriter struct{ t *testing.T }
func (w tlogWriter) Write(p []byte) (n int, err error) {
@@ -408,3 +416,22 @@ func (noopDNSBackend) ExecFunc(f func()) error { f(); return nil }
func (noopDNSBackend) NdotsSet() bool { return false }
func (noopDNSBackend) HandleQueryResp(name string, ip net.IP) {}
func TestReplySERVFAILOnInternalError(t *testing.T) {
defer redirectLogrusTo(t)
rsv := NewResolver("", false, badSRVDNSBackend{}).(*resolver)
w := &tstwriter{}
q := new(dns.Msg).SetQuestion("_sip._tcp.example.com.", dns.TypeSRV)
rsv.ServeDNS(w, q)
resp := w.GetResponse()
checkNonNullResponse(t, resp)
t.Log("Response: ", resp.String())
checkDNSResponseCode(t, resp, dns.RcodeServerFailure)
}
type badSRVDNSBackend struct{ noopDNSBackend }
func (badSRVDNSBackend) ResolveService(name string) ([]*net.SRV, []net.IP) {
return []*net.SRV{nil, nil, nil}, nil // Mismatched slice lengths
}