Hooking PeekMessage crash

c++ / delphi package - dll injection and api hooking

Hooking PeekMessage crash

Postby SpiderVenom » Tue Jun 22, 2004 3:25 am

I'm using madCodeHook to write a system-wide keyhook by hooking PeekMessage (GetMessage will be implemented later). My DLL code looks like this:

Code: Select all
library KeyHandler;

uses Windows, Messages, madCodeHook;

  TParam = record
    WParam: WPARAM;
    LParam: LPARAM;

var PeekMessageCallNext: function (lpMsg: TMsg; hWnd: HWND; wMsgFilterMin, wMsgFilterMax, wRemoveMsg: UINT): BOOL; stdcall;

function PeekMessageCallBack(lpMsg: TMsg; hWnd: HWND; wMsgFilterMin, wMsgFilterMax, wRemoveMsg: UINT): BOOL; stdcall;
  Param: TParam;
  case lpMsg.message of
      Param.WParam := lpMsg.wParam;
      Param.LParam := lpMsg.lParam;
      SendIpcMessage('KYHNDLR', @Param, SizeOf(Param));
  Result := PeekMessageCallNext(lpMsg, hWnd, wMsgFilterMin, wMsgFilterMax, wRemoveMsg);

  HookAPI(user32, 'PeekMessageA', @PeekMessageCallBack, @PeekMessageCallNext);
  HookAPI(user32, 'PeekMessageW', @PeekMessageCallBack, @PeekMessageCallNext);

As soon as I inject it, it bring down every process, and the system reboots (XP). If I comment out the two HookAPI lines, everything is fine... so it seems the problem is in the DLL.

What am I doing wrong?

PS. I'm not using SetWindowsHookEx because I want to be able to inject/uninject and delete the DLL at any time. I suppose I could write a keyhook with SetWindowsHookEx, then use madRemote to execute a function in each remote process to force them to unload the DLL. Dunno if this would work though.
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Location: New Zealand

Postby madshi » Tue Jun 22, 2004 6:34 pm

PeekMessage is called so often by the OS that it's not funny. Calling SendIpcMessage for each and every PeekMessage call will either crash the system or dramatically slow down the OS. The problem is that SendIpcMessage does cost performance. Actually right now it's rather slow. I'll improve that in a later version. It's meant to be used only for a reasonable of message per second.

Another problem is that I don't know what your IPC handler does when receiving IPC messages. If you're doing something in your IPC handler which results in PeekMessage being called you have a classic recursive deadlock.

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