luavgl: avoid wild pointer in lua context

Monitor if the root obj is deleted, and change the ctx->root pointer correspondingly to avoid accessing wild pointer

Signed-off-by: Neo Xu <[email protected]>

src/luavgl.c

@@ -87,10 +87,17 @@ static int root_clean(lua_State *L)
 {
   LV_LOG_INFO("enter");
   luavgl_ctx_t *ctx = luavgl_context(L);
-  lv_obj_clean(ctx->root);
+  if (ctx->root)
+    lv_obj_clean(ctx->root);
   return 0;
 }
 
+static void root_delete_cb(lv_event_t *e)
+{
+  luavgl_ctx_t *ctx = e->user_data;
+  ctx->root = NULL;
+}
+
 LUALIB_API int luaopen_lvgl(lua_State *L)
 {
   luavgl_ctx_t *ctx = luavgl_context(L);
@@ -148,7 +155,7 @@ LUALIB_API int luaopen_lvgl(lua_State *L)
 
 #ifdef LUAVGL_EXPOSE_WIDGET_API
   const luaL_Reg *reg;
-  for (int i = 0; ;i++) {
+  for (int i = 0;; i++) {
     reg = &widget_create_methods[i];
     if (reg->name == NULL)
       break;
@@ -158,6 +165,8 @@ LUALIB_API int luaopen_lvgl(lua_State *L)
   }
 #endif
 
+  lv_obj_add_event_cb(root, root_delete_cb, LV_EVENT_DELETE, ctx);
+
   (void)dumpstack;
   (void)dumptable;
   (void)dumpvalue;