minigui/mgncs 1.20 ncsCreateModalDialogFromID函数的隐患

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mgncs(1.2.0) 的ncsCreateModalDialogFromID函数存在一个隐患，原代码很简单，如下：

int ncsCreateModalDialogFromID (HPACKAGE package, Uint32 dlgId,
                    HWND owner, HICON hIcon, HMENU hMenu,
                    NCS_EVENT_HANDLER_INFO* handlers, NCS_EVENT_CONNECT_INFO* connects)
{
    int ret = 0;
    mDialogBox * dialog = SAFE_CAST(mDialogBox,
            ncsCreateMainWindowIndirectFromID(package, dlgId, owner, hIcon, hMenu, handlers, connects, 0));

    if (dialog) {
        ret = _c(dialog)->doModal(dialog, TRUE);
        MainWindowThreadCleanup(dialog->hwnd);
    }
    return ret;
}

上面的代码中在调用doModal成员函数后，又调用MainWindowThreadCleanup函数清除主窗口所使用的消息队列，内存等系统资源，看着好像没错。
下面是MiniGUI中MainWindowThreadCleanup函数的实现代码，可以看到函数最后释放了hMainWnd(pWin)指向的内存，这也没错：

void GUIAPI MainWindowThreadCleanup (HWND hMainWnd)
{
    PMAINWIN pWin = (PMAINWIN)hMainWnd;

    _MG_PRINTF ("GUI>Window: MainWindowThreadCleanup called: %p (%s)\n", pWin, pWin->spCaption);

    if (!MG_IS_DESTROYED_WINDOW (hMainWnd)) {
        _MG_PRINTF ("GUI>Window: Unexpected calling of "
                "(MainWindowThreadCleanup); Window (%p) "
                "not destroyed yet!\n", hMainWnd);
        return;
    }

#ifdef _MGRM_THREADS
    if (pWin->pHosting == NULL) {
        mg_FreeMsgQueueThisThread ();
        _MG_PRINTF ("GUI>Window: Message queure is freed: %p (%s)\n", pWin, pWin->spCaption);
    }
#endif

#ifdef __THREADX__ 
    /* to avoid threadx keep pWin's value,which will lead to wrong way */
    memset (pWin, 0xcc, sizeof(MAINWIN));
#endif
    free (pWin);
}

但是如果进一步剖析doModal成员函数的代码，就会发现当doModal的bAutoDestroy参数为TRUE时，会在doModal结束的时候调用MainWindowThreadCleanup函数。
下面是doModal成员函数的实现代码节选：

static DWORD mMainWnd_doModal(mMainWnd*self, BOOL bAutoDestroy)
{
	HWND hwnd;

	IncludeWindowStyle(self->hwnd, NCSS_MNWND_MODE);
	// 。。。。
	hwnd = self->hwnd;
	// 。。。。
	if((GetWindowStyle(self->hwnd)&NCSS_MNWND_MODE) && bAutoDestroy)
	{
		HWND hwnd = self->hwnd;
		//destroy
		DestroyMainWindow(self->hwnd);
		// 本文作者注:MainWindowCleanup 为宏定义，等价于MainWindowThreadCleanup
		MainWindowCleanup(hwnd);
	}
	else
	{
		ExcludeWindowStyle(self->hwnd, NCSS_MNWND_MODE);
	}

	return ret;
}

那么问题就来了：bAutoDestroy为TRUE调用doModal成员函数之后，dialog->hwnd指向的内存已经被释放，dialog->hwnd已经是个野指针(wild pointer),再调用MainWindowThreadCleanup函数就可能会产生不可预知的后果。

所以ncsCreateModalDialogFromID函数中调用doModal成员函数之后，就没有必要也不能再调用MainWindowThreadCleanup函数，删除之就可以解决这个隐患。修正的代码如下：

int ncsCreateModalDialogFromID (HPACKAGE package, Uint32 dlgId,
                    HWND owner, HICON hIcon, HMENU hMenu,
                    NCS_EVENT_HANDLER_INFO* handlers, NCS_EVENT_CONNECT_INFO* connects)
{
    int ret = 0;
    mDialogBox * dialog = SAFE_CAST(mDialogBox,
            ncsCreateMainWindowIndirectFromID(package, dlgId, owner, hIcon, hMenu, handlers, connects, 0));

    if (dialog) {
        ret = _c(dialog)->doModal(dialog, TRUE);
    }
    return ret;
}