Make multicast trusting configurable in CmakeLists

Author: FrankZRS

CMakeLists.txt

@@ -31,6 +31,7 @@ set(CLANG_TIDY_ENABLED OFF CACHE BOOL "Enable clang-tidy analysis during compila
 set(OC_USE_STORAGE ON CACHE BOOL "Persistent storage of data.")
 set(OC_USE_MULTICAST_SCOPE_2 ON CACHE BOOL "devices send also group multicast events with scope2.")
 set(OC_REPLAY_PROTECTION_ENABLED ON CACHE BOOL "Enable replay protection using the Echo option")
+set(OC_TRUST_FIRST_MCAST ON CACHE BOOL "Trust first multicast message from an unsynchronised client")
 
 set(KNX_BUILTIN_MBEDTLS ON CACHE BOOL "Use built-in mbedTLS, as opposed to external lib from different project")
 set(KNX_BUILTIN_TINYCBOR ON CACHE BOOL "Use built-in TinyCBOR, as opposed to external lib from different project")

api/oc_replay.c

@@ -159,12 +159,16 @@ oc_replay_check_client(uint64_t rx_ssn, oc_string_t rx_kid,
 
   struct oc_replay_record *rec = get_record(rx_kid, rx_kid_ctx);
   if (rec == NULL) {
+#if OC_TRUST_FIRST_MCAST
     if (is_mcast) {
       oc_replay_add_client(rx_ssn, rx_kid, rx_kid_ctx);
       return true;
     } else {
       return false;
     }
+#else
+    return false;
+#endif
   }
   // received message matched existing record, so this record is useful &
   // should be kept around - thus we update the time here