dns: improve handling of tx pick up on response

src/app-layer-dns-udp.c

@@ -277,11 +277,16 @@ static int DNSUDPResponseParse(Flow *f, void *dstate,
         }
     }
 
+    /* if we previously didn't have a tx, it could have been created by the
+     * above code, so lets check again */
+    if (tx == NULL) {
+        tx = DNSTransactionFindByTxId(dns_state, ntohs(dns_header->tx_id));
+    }
+    if (tx != NULL) {
         /* parse rcode, e.g. "noerror" or "nxdomain" */
         uint8_t rcode = ntohs(dns_header->flags) & 0x0F;
         if (rcode <= DNS_RCODE_NOTZONE) {
             SCLogDebug("rcode %u", rcode);
-        if (tx != NULL)
             tx->rcode = rcode;
         } else {
             /* this is not invalid, rcodes can be user defined */
@@ -290,14 +295,11 @@ static int DNSUDPResponseParse(Flow *f, void *dstate,
 
         if (ntohs(dns_header->flags) & 0x0080) {
             SCLogDebug("recursion desired");
-        if (tx != NULL)
             tx->recursion_desired = 1;
         }
 
-    if (tx != NULL) {
         tx->replied = 1;
     }
-
     SCReturnInt(1);
 
 bad_data: