Reject overlaps with wildcards. (#3542)

Requesting a certificate with "*.example.com" and "www.example.com" as
separate SANs doesn't make sense, because "www.example.com" is covered
by the wildcard.

#3524

ra/ra.go

@@ -1708,6 +1708,10 @@ func (ra *RegistrationAuthorityImpl) NewOrder(ctx context.Context, req *rapb.New
 		}
 	}
 
+	if err := wildcardOverlap(order.Names); err != nil {
+		return nil, err
+	}
+
 	// See if there is an existing, pending, unexpired order that can be reused
 	// for this account
 	existingOrder, err := ra.SA.GetOrderForNames(ctx, &sapb.GetOrderForNamesRequest{
@@ -1910,3 +1914,23 @@ func (ra *RegistrationAuthorityImpl) authzValidChallengeEnabled(authz *core.Auth
 	}
 	return false
 }
+
+// wildcardOverlap takes a slice of domain names and returns an error if any of
+// them is a non-wildcard FQDN that overlaps with a wildcard domain in the map.
+func wildcardOverlap(dnsNames []string) error {
+	nameMap := make(map[string]bool, len(dnsNames))
+	for _, v := range dnsNames {
+		nameMap[v] = true
+	}
+	for name := range nameMap {
+		if name[0] == '*' {
+			continue
+		}
+		labels := strings.Split(name, ".")
+		labels[0] = "*"
+		if nameMap[strings.Join(labels, ".")] {
+			return fmt.Errorf("Domain name %q is redundant with a wildcard domain in the same request. Remove one or the other from the certificate request.", name)
+		}
+	}
+	return nil
+}

ra/ra_test.go

@@ -3345,6 +3345,32 @@ func TestCTPolicyMeasurements(t *testing.T) {
 	test.AssertEquals(t, test.CountHistogramSamples(ra.ctpolicyResults.With(prometheus.Labels{"result": "failure"})), 1)
 }
 
+func TestWildcardOverlap(t *testing.T) {
+	err := wildcardOverlap([]string{
+		"*.example.com",
+		"*.example.net",
+	})
+	if err != nil {
+		t.Errorf("Got error %q, expected none", err)
+	}
+	err = wildcardOverlap([]string{
+		"*.example.com",
+		"*.example.net",
+		"www.example.com",
+	})
+	if err == nil {
+		t.Errorf("Got no error, expected one")
+	}
+	err = wildcardOverlap([]string{
+		"*.foo.example.com",
+		"*.example.net",
+		"www.example.com",
+	})
+	if err != nil {
+		t.Errorf("Got error %q, expected none", err)
+	}
+}
+
 var CAkeyPEM = `
 -----BEGIN RSA PRIVATE KEY-----
 MIIJKQIBAAKCAgEAqmM0dEf/J9MCk2ItzevL0dKJ84lVUtf/vQ7AXFi492vFXc3b