drop all integrity protected NAS messages whose check is failing

- also enables integrity check for messages that are only integrity
  protected but not ciphered

srsue/src/upper/nas.cc

@@ -308,7 +308,6 @@ void nas::write_pdu(uint32_t lcid, byte_buffer_t *pdu) {
   uint8 pd = 0;
   uint8 msg_type = 0;
   uint8 sec_hdr_type = 0;
-  bool  mac_valid = false;
 
   nas_log->info_hex(pdu->msg, pdu->N_bytes, "DL %s PDU", rrc->get_rb_name(lcid).c_str());
 
@@ -319,11 +318,13 @@ void nas::write_pdu(uint32_t lcid, byte_buffer_t *pdu) {
     case LIBLTE_MME_SECURITY_HDR_TYPE_PLAIN_NAS:
     case LIBLTE_MME_SECURITY_HDR_TYPE_INTEGRITY_WITH_NEW_EPS_SECURITY_CONTEXT:
     case LIBLTE_MME_SECURITY_HDR_TYPE_SERVICE_REQUEST:
-    case LIBLTE_MME_SECURITY_HDR_TYPE_INTEGRITY:
       break;
+    case LIBLTE_MME_SECURITY_HDR_TYPE_INTEGRITY:
     case LIBLTE_MME_SECURITY_HDR_TYPE_INTEGRITY_AND_CIPHERED:
-        if((mac_valid = integrity_check(pdu))) {
+      if((integrity_check(pdu))) {
+        if (sec_hdr_type == LIBLTE_MME_SECURITY_HDR_TYPE_INTEGRITY_AND_CIPHERED) {
           cipher_decrypt(pdu);
+        }
         break;
       } else {
         nas_log->error("Not handling NAS message with integrity check error\n");