tsdns: lowercase the name in parseQuery.

Domains in DNS should be case-insensitive.

Signed-off-by: Dmytro Shynkevych <dmytro@tailscale.com>

wgengine/tsdns/tsdns.go

@@ -293,6 +293,14 @@ func (r *Resolver) parseQuery(query []byte, resp *response) error {
 		return err
 	}
 
+	// Lowercase the name: DOMAIN.COM. should resolve the same as domain.com.
+	name := resp.Question.Name.Data[:resp.Question.Name.Length]
+	for i, b := range name {
+		if 'A' <= b && b <= 'Z' {
+			name[i] = b - 'A' + 'a'
+		}
+	}
+
 	return nil
 }
 

wgengine/tsdns/tsdns_test.go

@@ -550,6 +550,7 @@ func TestFull(t *testing.T) {
 	}{
 		{"ipv4", dnspacket("test1.ipn.dev.", dns.TypeA), validIPv4Response},
 		{"ipv6", dnspacket("test2.ipn.dev.", dns.TypeAAAA), validIPv6Response},
+		{"upper", dnspacket("TEST1.IPN.DEV.", dns.TypeA), validIPv4Response},
 		{"ptr", dnspacket("4.3.2.1.in-addr.arpa.", dns.TypePTR), validPTRResponse},
 		{"error", dnspacket("test3.ipn.dev.", dns.TypeA), nxdomainResponse},
 	}