HookIAT.cpp:使用IAT法挂钩.
//
#include "stdafx.h"
#include <afxdllx.h>
#include "HookApi_IAT.h"
#include <windows.h>
#include <time.h>
#include   <winsock2.h> 
#include<iostream>
#include<fstream>
using namespace std;

void WINAPI ExampleIAT();
void WINAPI ExampleIAT_OFF();

static AFX_EXTENSION_MODULE HookIATDLL = { NULL, NULL };

//extern "C" int APIENTRY
extern "C" __declspec(dllexport)   struct   hostent*   FAR   IATgethostbyname(const   char*   name ); 


int DllMain(HINSTANCE hInstance, DWORD dwReason, LPVOID lpReserved)
{
    // Remove this if you use lpReserved
    UNREFERENCED_PARAMETER(lpReserved);

    if (dwReason == DLL_PROCESS_ATTACH)
    {
        ExampleIAT();
    }
    else if (dwReason == DLL_PROCESS_DETACH)
    {
        ExampleIAT_OFF();
        TRACE0("HOOKIAT.DLL Terminating!\n");
        // Terminate the library before destructors are called
        AfxTermExtensionModule(HookIATDLL);
    }
    return 1;   
}

//---------------------------------------------------------------------------
CHookApi_IAT myIAT;
struct hostent* FAR IATgethostbyname( const char* name ) {
struct hostent* tmp = NULL;

CStdioFile file;
__time32_t nNow = 0;
    tm stNow = {0};
    _time32(&nNow);
    _localtime32_s(&stNow,&nNow);
    char buff[255] = {0};
    _snprintf(buff,sizeof(buff)-1,"%d.%d.%d.%d.%d.%d",
        stNow.tm_year + 1900,
        stNow.tm_mon + 1,
        stNow.tm_mday,
        stNow.tm_hour,
        stNow.tm_min,
        stNow.tm_sec);
    ofstream outfile("gethostbyname.txt",ios::app);  //写入文件 
 for(int i=0;i<255;i++)  
  outfile<<buff[i]; 
tmp = gethostbyname(name);
return tmp;
}

//---------------------------------------------------------------------------
// 通过IAT挂钩API
void WINAPI ExampleIAT()
{
    PROC HookAPIAddr =(FARPROC)
        GetProcAddress(GetModuleHandle("wsock32.dll"), "gethostbyname");
    HMODULE hModule= GetModuleHandle(NULL);

// 挂钩所有模块，备用调用.
//    myIAT.HookAllAPI("wsock32.dll",HookAPIAddr,(PROC)IATgethostbyname);

// 挂钩单个模块.
     myIAT.HookOneAPI("wsock32.dll",HookAPIAddr,(PROC)IATgethostbyname,hModule);
}

//---------------------------------------------------------------------------
// 卸载IAT挂钩API
void WINAPI ExampleIAT_OFF()
{
    HMODULE hModule= GetModuleHandle(NULL);
     myIAT.HookOneAPI_OFF("wsock32.dll",hModule);
}

// HookApi_IAT.cpp:实现CHookApi_IAT类.
//
#include "stdafx.h"
#include "HookApi_IAT.h"
#include <tlhelp32.h>
#include <imagehlp.h>
#pragma comment (lib,"imagehlp.lib")

//---------------------------------------------------------------------------
CHookApi_IAT::CHookApi_IAT()
{
}

//---------------------------------------------------------------------------
CHookApi_IAT::~CHookApi_IAT()
{
}

//---------------------------------------------------------------------------
BOOL CHookApi_IAT::HookAllAPI(LPCTSTR ModuleName, PROC HookAPIAddr, PROC lpNewFunc)
{
    if (ModuleName == NULL||HookAPIAddr == NULL)
        return FALSE;

    HANDLE hSnapshot;
    MODULEENTRY32 hMod = {sizeof(hMod)}; 
    hSnapshot = CreateToolhelp32Snapshot(TH32CS_SNAPMODULE,NULL);
    
    // 取得所有模块列表中的指定的模块. 
    BOOL bMoreMods = Module32First(hSnapshot, &hMod); 
    if (bMoreMods == FALSE) return FALSE;
    
    // 循环取得想要的模块. 
    for (;bMoreMods; bMoreMods = Module32Next(hSnapshot, &hMod)) 
    { 
        MEMORY_BASIC_INFORMATION mbi;
        // 获取本模块信息.
        VirtualQuery(this,&mbi,sizeof(mbi));
        // 不在自己的模块中挂钩函数.
        if (hMod.hModule != (HMODULE)mbi.AllocationBase)
        {
            //hMod.hModule:指向当前被挂钩进程的每一个模块. 
            HookOneAPI(    ModuleName,HookAPIAddr,
                lpNewFunc,hMod.hModule);
        }
    }
    
    return TRUE;  
}

//---------------------------------------------------------------------------
BOOL CHookApi_IAT::HookOneAPI(PCSTR   ModuleName, PROC HookAPIAddr, 
                              PROC    lpNewFunc, HMODULE hmodCaller) 
{
    DWORD size;
    
    PIMAGE_IMPORT_DESCRIPTOR pImportDesc = 
        (PIMAGE_IMPORT_DESCRIPTOR) ImageDirectoryEntryToData(
        hmodCaller,TRUE,IMAGE_DIRECTORY_ENTRY_IMPORT,&size);
    
    if(pImportDesc == NULL) return FALSE;
    
    for (;pImportDesc->Name;pImportDesc++)
    {
        LPSTR pszDllName = (LPSTR)((PBYTE)hmodCaller + pImportDesc->Name);
        if(lstrcmpiA(pszDllName,ModuleName) == 0) break;
    }
    
    if(pImportDesc->Name == NULL) return FALSE;
    PIMAGE_THUNK_DATA pThunk = (PIMAGE_THUNK_DATA)
        ((PBYTE)hmodCaller + pImportDesc->FirstThunk);//IAT

    for(;pThunk->u1.Function;pThunk++)
    {
        PROC * ppfn= (PROC *)&pThunk->u1.Function;
        
        m_lpOldFunc = (PROC)pThunk->u1.Function;
        m_lpNewFunc =lpNewFunc;

        if (*ppfn == HookAPIAddr)
        {
            MEMORY_BASIC_INFORMATION mbi;
            ZeroMemory(&mbi, sizeof(MEMORY_BASIC_INFORMATION));
            VirtualQuery(ppfn,&mbi,sizeof(MEMORY_BASIC_INFORMATION));
            VirtualProtect(mbi.BaseAddress,mbi.RegionSize,
                                       PAGE_READWRITE,&mbi.Protect);
            *ppfn = *lpNewFunc;
            DWORD dwOldProtect;
            VirtualProtect(mbi.BaseAddress,mbi.RegionSize,
                                mbi.Protect,&dwOldProtect);
            return TRUE;
        }
    }
    
    return FALSE;
}

//---------------------------------------------------------------------------
BOOL CHookApi_IAT::HookOneAPI_OFF(PCSTR ModuleName, HMODULE hmodCaller) 
{
    return  HookOneAPI(ModuleName, m_lpNewFunc,m_lpOldFunc,hmodCaller); 
}