[ymodem] Check the file path's legitimacy of 'sy' command

components/utilities/ymodem/ry_sy.c

@@ -6,6 +6,7 @@
  * Change Logs:
  * Date           Author       Notes
  * 2019-12-09     Steven Liu   the first version
+ * 2021-04-14     Meco Man     Check the file path's legitimacy of 'sy' command
  */
 
 #include <rtthread.h>
@@ -219,6 +220,12 @@ static rt_err_t sy(uint8_t argc, char **argv)
     const char *file_path;
     rt_device_t dev;
 
+    if (argc < 2)
+    {
+        rt_kprintf("invalid file path.\n");
+        return -RT_ERROR;
+    }
+
     if (argc > 2)
         dev = rt_device_find(argv[2]);
     else