;;;;;截获API是个很有用的东西，比如你想分析一下别人的程序是怎样工作的。这里我介绍一下一种我自己试验通过的方法。;
首先，我们必须设法把自己的代码放到目标程序的进程空间里去。Windows Hook可以帮我们实现这一点。SetWindowsHookEx的声明如下：;
HHOOK SetWindowsHookEx(;
int idHook, // hook type;
HOOKPROC lpfn, // hook procedure;
HINSTANCE hMod, // handle to application instance;
DWORD dwThreadId // thread identifier;
)
具体的参数含义可以翻阅msdn，没有msdn可谓寸步难行。;
这里Hook本身的功能并不重要，我们使用它的目的仅仅只是为了能够让Windows把我们的代码植入别的进程里去。hook Type我们任选一种即可，只要保证是目标程序肯定会调用到就行，这里我用的是WH_CALLWNDPROC。lpfn和hMod分别指向我们的钩子代码及其所在的dll，dwThreadId设为0，表示对所有系统内的线程都挂上这样一个hook，这样我们才能把代码放到别的进程里去。;;
之后，我们的代码就已经进入了系统内的所有进程空间了。必须注意的是，我们只需要截获我们所关心的目标程序的调用，因此还必须区分一下进程号。我们自己的钩子函数中，第一次运行将进行最重要的API重定向的工作。也就是通过将所需要截获的API的开头几个字节改为一个跳转指令，使其跳转到我们的API中来。这是最关键的部分。这里我想截三个调用，ws2_32.dll中的send和recv、user32.dll中的GetMessageA。;
DWORD dwCurrentPID = 0
HHOOK hOldHook = NULL
DWORD pSend = 0
DWORD pRecv = 0
GETMESSAGE pGetMessage = NULL
BYTE btNewBytes[8] = { 0x0B8, 0x0, 0x0, 0x40, 0x0, 0x0FF, 0x0E0, 0 }
DWORD dwOldBytes[3][2]
HANDLE hDebug = INVALID_HANDLE_value
LRESULT CALLBACK CallWndProc( int nCode, WPARAM wParam, LPARAM lParam );
{;
DWORD dwSize
DWORD dwPIDWatched
HMODULE hLib
if( dwCurrentPID == 0 );
{;
dwCurrentPID = GetCurrentProcessId()
HWND hwndMainHook
wndMainHook = ::FindWindow( 0, "MainHook )
dwPIDWatched = ::SendMessage( hwndMainHook, (WM_USER+100), 0, 0 )
hOldHook = (HHOOK)::SendMessage( hwndMainHook, (WM_USER+101), 0, 0 )
if( dwCurrentPID == dwPIDWatched );
{;
Lib = LoadLibrary( "ws2_32.dll )
Send = (DWORD)GetProcAddress( hLib, "send )
Recv = (DWORD)GetProcAddress( hLib, "recv )
::ReadProcessMemory( INVALID_HANDLE_value, (void *)pSend, (void *)dwOldBytes[0], sizeof(DWORD)*2, &dwSize )
*(DWORD *)( btNewBytes + 1 ) = (DWORD)new_send
::WriteProcessMemory( INVALID_HANDLE_value, (void *)pSend, (void *)btNewBytes, sizeof(DWORD)*2, &dwSize )
::ReadProcessMemory( INVALID_HANDLE_value, (void *)pRecv, (void *)dwOldBytes[1], sizeof(DWORD)*2, &dwSize )
*(DWORD *)( btNewBytes + 1 ) = (DWORD)new_recv
::WriteProcessMemory( INVALID_HANDLE_value, (void *)pRecv, (void *)btNewBytes, sizeof(DWORD)*2, &dwSize )
Lib = LoadLibrary( "user32.dll )
GetMessage = (GETMESSAGE)GetProcAddress( hLib, "GetMessageA )
::ReadProcessMemory( INVALID_HANDLE_value, (void *)pGetMessage, (void *)dwOldBytes[2], sizeof(DWORD)*2, &dwSize )
*(DWORD *)( btNewBytes + 1 ) = (DWORD)new_GetMessage
::WriteProcessMemory( INVALID_HANDLE_value, (void *)pGetMessage, (void *)btNewBytes, sizeof(DWORD)*2, &dwSize )
Debug = ::CreateFile( "C:Trace.log, GENERIC_WRITE, 0, 0, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, 0 )
};
};
if( hOldHook != NULL );
{;
return CallNextHookEx( hOldHook, nCode, wParam, lParam )
};
return 0
};
上面的钩子函数，只有第一次运行时有用，就是把三个函数的首8字节修改一下（实际上只需要7个）。btNewBytes中的指令实际就是;
mov eax, 0x400000;
jmp eax;
这里的0x400000就是新的函数的地址，比如new_recv/new_send/new_GetMessage，此时，偷梁换柱已经完成。再看看我们的函数中都干了些什么。以GetMessageA为例：;
BOOL _stdcall new_GetMessage( LPMSG lpMsg, HWND hWnd, UINT wMsgFilterMin, UINT wMsgFilterMax );
{;
DWORD dwSize
char szTemp[256]
BOOL r = false
//Watch here before it"s executed.;
printf( szTemp, "Before GetMessage : HWND 0x%8.8X, msgMin 0x%8.8X, msgMax 0x%8.8x , hWnd, wMsgFilterMin, wMsgFilterMax )
::WriteFile( hDebug, szTemp, strlen(szTemp), &dwSize, 0 )
//Watch over;
// restore it at first;
::WriteProcessMemory( INVALID_HANDLE_value, (void *)pGetMessage, (void *)dwOldBytes[2], sizeof(DWORD)*2, &dwSize )
// execute it;
r = pGetMessage( lpMsg, hWnd, wMsgFilterMin, wMsgFilterMax )
// hook it again;
*(DWORD *)( btNewBytes + 1 ) = (DWORD)new_GetMessage
::WriteProcessMemory( INVALID_HANDLE_value, (void *)pGetMessage, (void *)btNewBytes, sizeof(DWORD)*2, &dwSize )
//Watch here after it"s executed;
printf( szTemp, "Result of GetMessage is %d., r )
::WriteFile( hDebug, szTemp, strlen( szTemp ), &dwSize, 0 )
if( r );
{;
printf( szTemp, "Msg : HWND 0x%8.8X, MSG 0x%8.8x, wParam 0x%8.8X, lParam 0x%8.8XTime 0x%8.8X, X %d, Y %d,;
lpMsg->hwnd, lpMsg->message,;
lpMsg->wParam, lpMsg->lParam, lpMsg->time,;
lpMsg->pt.x, lpMsg->pt.y )
::WriteFile( hDebug, szTemp, strlen( szTemp ), &dwSize, 0 )
};
trcpy( szTemp, " )
::WriteFile( hDebug, szTemp, strlen( szTemp ), &dwSize, 0 )
//Watch over;
return r
};
先将截获下来的参数，写入到一个log文件中，以便分析。然后恢复原先保留下来的GetMessageA的首8字节，然后执行真正的GetMessageA调用，完毕后再将执行结果也写入log文件，然后将GetMessageA的执行结果返回给调用者。;
整个截获的过程就是这样。你可以把其中的写log部分改成你自己想要的操作。这里有个不足的地方是，截获动作是不能够并发进行的，如果目标进程是多线程的，就会有问题。解决办法是，可以在每次new_GetMessage中加入一个CriticalSection的锁和解锁，以使调用变为串行进行，但这个我没有试验过。
