[client] Forward non-address DNS record types through route forwarders (#6455)

client/internal/routemanager/dnsinterceptor/handler.go

@@ -226,12 +226,11 @@ func (d *DnsInterceptor) ServeDNS(w dns.ResponseWriter, r *dns.Msg) {
 		return
 	}
 
-	// pass if non A/AAAA query
-	if r.Question[0].Qtype != dns.TypeA && r.Question[0].Qtype != dns.TypeAAAA {
-		d.continueToNextHandler(w, r, logger, "non A/AAAA query")
-		return
-	}
-
+	// All query types for an intercepted domain are forwarded to the peer's
+	// DNS forwarder, which owns the name. Falling through to the system
+	// resolver would let it answer NXDOMAIN for a name it isn't authoritative
+	// for, poisoning the whole name (including the A/AAAA records the route
+	// does serve). The forwarder answers NODATA for types it cannot resolve.
 	d.mu.RLock()
 	peerKey := d.currentPeerKey
 	d.mu.RUnlock()
@@ -293,19 +292,6 @@ func (d *DnsInterceptor) writeDNSError(w dns.ResponseWriter, r *dns.Msg, logger
 	}
 }
 
-// continueToNextHandler signals the handler chain to try the next handler
-func (d *DnsInterceptor) continueToNextHandler(w dns.ResponseWriter, r *dns.Msg, logger *log.Entry, reason string) {
-	logger.Tracef("continuing to next handler for domain=%s reason=%s", r.Question[0].Name, reason)
-
-	resp := new(dns.Msg)
-	resp.SetRcode(r, dns.RcodeNameError)
-	// Set Zero bit to signal handler chain to continue
-	resp.MsgHdr.Zero = true
-	if err := w.WriteMsg(resp); err != nil {
-		logger.Errorf("failed writing DNS continue response: %v", err)
-	}
-}
-
 func (d *DnsInterceptor) getUpstreamIP(peerKey string) (netip.Addr, error) {
 	peerAllowedIP, exists := d.peerStore.AllowedIP(peerKey)
 	if !exists {