fix(zwapi) Harden zwapi_connection_tx in zwapi_connection.c

Change is obvious, it prevent an overflow,
note that functions did not test all inputs params
specially when it is done in caller
(eg: in  zwave_api_send_data reject frames above limit).

Bug-SiliconLabs: UIC-3666
Bug-SLVDBBP: 3169925
Signed-off-by: Philippe Coval <[email protected]>

Author: rzr

applications/zpc/components/zwave_api/src/zwapi_connection.c

@@ -138,15 +138,21 @@ void zwapi_connection_tx(
   uint8_t len,        /* IN the length of DATA to transmit */
   bool ack_needed)
 {
-  uint8_t tx_buffer[255];
+  uint8_t tx_buffer[FRAME_LENGTH_MAX];
+  const size_t MAX_PAYLOAD_LEN_ALLOWED = sizeof(tx_buffer) - 4 - 1; // 255 - 5 = 250
   uint8_t *c;
   c = tx_buffer;
 
   *c++ = SOF;
   *c++ = len + 3;
   *c++ = type;
   *c++ = cmd;
-
+  if (len > MAX_PAYLOAD_LEN_ALLOWED) {
+    sl_log_error(LOG_TAG, "Buffer overflow prevented: Payload length (%u) exceeds maximum allowed (%zu).\n", len,
+		 MAX_PAYLOAD_LEN_ALLOWED);
+    assert(false);
+    return;
+  }
   memcpy(c, Buf, len);
   c += len;