在C++中钩取IDispatch的虚函数表

Question

我试图修改系统中已存在的IDispatch接口的行为。为了实现这一点，我的计划是在运行时钩入对象的v-table并修改指针，使其指向一个自定义的钩子方法。

如果我能让它起作用，我就可以向已有的对象添加新的方法和属性。很好。

首先，我尝试钩入IUnknown的v-table（IDispatch继承自IUnknown），这很顺利。然而，尝试更改IDispatch中的条目根本不起作用。什么都没有发生，代码的工作方式与没有钩子时完全相同。

下面是代码，非常简单，因此应该没有理解上的问题。

#include <iostream>
#include <windows.h>
#include <Objbase.h>
#pragma comment (lib,"Ole32.lib")
using namespace std;

HRESULT __stdcall typecount(IDispatch *self,UINT*u)
{
    cout << "hook" << endl;
    *u=1;
    return S_OK;
}


int main()
{
    CoInitialize(NULL);

    // Get clsid from name
    CLSID clsid;
    CLSIDFromProgID(L"shell.application",&clsid);

    // Create instance
    IDispatch *obj=NULL;
    CoCreateInstance(clsid,NULL,CLSCTX_INPROC_SERVER,__uuidof(IDispatch),(void**)&obj);

    // Get vtable and offset in vtable for idispatch
    void* iunknown_vtable= (void*)*((unsigned int*)obj);
    // There are three entries in IUnknown, therefore add 12 to go to IDispatch
    void* idispatch_vtable = (void*)(((unsigned int)iunknown_vtable)+12);

    // Get pointer of first emtry in IDispatch vtable (GetTypeInfoCount)
    unsigned int* v1 = (unsigned int*)iunknown_vtable;

    // Change memory permissions so address can be overwritten
    DWORD old;
    VirtualProtect(v1,4,PAGE_EXECUTE_READWRITE,&old);

    // Override v-table pointer
    *v1 = (unsigned int) typecount;

    // Try calling GetTypeInfo count, should now be hooked. But isn't works as usual
    UINT num=0;
    obj->GetTypeInfoCount(&num);

/*
    HRESULT hresult;
    OLECHAR FAR* szMember = (OLECHAR*)L"MinimizeAll";
    DISPID dispid;
    DISPPARAMS dispparamsNoArgs = {NULL, NULL, 0, 0};
    hresult = obj->GetIDsOfNames(IID_NULL, &szMember, 1,
    LOCALE_SYSTEM_DEFAULT, &dispid) ;
    hresult = obj->Invoke(dispid,IID_NULL,LOCALE_SYSTEM_DEFAULT,DISPATCH_METHOD,&dispparamsNoArgs, NULL, NULL, NULL); 
*/

}

- monoceres

Answer 1

// Get pointer of first emtry in IDispatch vtable (GetTypeInfoCount)
unsigned int* v1 = (unsigned int*)iunknown_vtable;

这实际上钩取了 IUnknown 的 QueryInterface。

接下来的调用将路由到您的 typecount。

//obj->GetTypeInfoCount(&num);
LPVOID dummy;
obj->QueryInterface(IID_NULL, &dummy);

- whunmr

---

糟糕！我不小心打错了iunknown_vtable而不是idispatch_vtable。感谢您的敏锐视力！ - monoceres

Answer 2

我认为你应该重新编码，使其在32位和64位之间可移植。

原文：

   // There are three entries in IUnknown, therefore add 12 to go to IDispatch
    void* idispatch_vtable = (void*)(((unsigned int)iunknown_vtable)+12);

便携式：

   // There are three entries in IUnknown, therefore add 3 pointers to go to IDispatch
    void* idispatch_vtable = (void*)(((DWORD_PTR)iunknown_vtable) + (sizeof(void *) * 3));

- Stephen Kellett