[release-branch.go1.16] net: don't reject null mx records
Bypass hostname validity checking when a null mx record is returned as,
defined in RFC 7505.
Updates #46979
Updates #46999
Change-Id: Ibe683bd6b47333a8ff30909fb2680ec8e10696ef
Reviewed-on: https://go-review.googlesource.com/c/go/+/332094
Trust: Roland Shoemaker <roland@golang.org>
Trust: Katie Hockman <katie@golang.org>
Run-TryBot: Roland Shoemaker <roland@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Katie Hockman <katie@golang.org>
(cherry picked from commit 03761ede028d811dd7d7cf8a2690d4bfa2771d85)
Reviewed-on: https://go-review.googlesource.com/c/go/+/332371
Run-TryBot: Katie Hockman <katie@golang.org>
diff --git a/src/net/dnsclient_unix_test.go b/src/net/dnsclient_unix_test.go
index d51113f..8cd383c 100644
--- a/src/net/dnsclient_unix_test.go
+++ b/src/net/dnsclient_unix_test.go
@@ -1956,3 +1956,43 @@
t.Errorf("LookupAddr returned unexpected error, got %q, want %q", err, expected)
}
}
+
+func TestNullMX(t *testing.T) {
+ fake := fakeDNSServer{
+ rh: func(n, _ string, q dnsmessage.Message, _ time.Time) (dnsmessage.Message, error) {
+ r := dnsmessage.Message{
+ Header: dnsmessage.Header{
+ ID: q.Header.ID,
+ Response: true,
+ RCode: dnsmessage.RCodeSuccess,
+ },
+ Questions: q.Questions,
+ Answers: []dnsmessage.Resource{
+ {
+ Header: dnsmessage.ResourceHeader{
+ Name: q.Questions[0].Name,
+ Type: dnsmessage.TypeMX,
+ Class: dnsmessage.ClassINET,
+ },
+ Body: &dnsmessage.MXResource{
+ MX: dnsmessage.MustNewName("."),
+ },
+ },
+ },
+ }
+ return r, nil
+ },
+ }
+ r := Resolver{PreferGo: true, Dial: fake.DialContext}
+ rrset, err := r.LookupMX(context.Background(), "golang.org")
+ if err != nil {
+ t.Fatalf("LookupMX: %v", err)
+ }
+ if want := []*MX{&MX{Host: "."}}; !reflect.DeepEqual(rrset, want) {
+ records := []string{}
+ for _, rr := range rrset {
+ records = append(records, fmt.Sprintf("%v", rr))
+ }
+ t.Errorf("records = [%v]; want [%v]", strings.Join(records, " "), want[0])
+ }
+}
diff --git a/src/net/lookup.go b/src/net/lookup.go
index 0660268..01c81db 100644
--- a/src/net/lookup.go
+++ b/src/net/lookup.go
@@ -488,7 +488,9 @@
if mx == nil {
continue
}
- if !isDomainName(mx.Host) {
+ // Bypass the hostname validity check for targets which contain only a dot,
+ // as this is used to represent a 'Null' MX record.
+ if mx.Host != "." && !isDomainName(mx.Host) {
return nil, &DNSError{Err: "MX target is invalid", Name: name}
}
}