Basic hook (thanks to Mhook)

SleepLock.cpp

/*
 * SleepLock: Simplest DLL ever to lock when resuming from sleep only. Designed to be injected into processes that call SetSuspendState.
 *
 * I feel dirty for attaching a license to something as simple as this. Nevertheless, the BSD licence is pretty much a free pass.
 *
 * Copyright (C) 2011 Faheem Pervez <trippin1@gmail.com>. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification, are
 * permitted provided that the following conditions are met:
 *
 *  1. Redistributions of source code must retain the above copyright notice, this list of
 *     conditions and the following disclaimer.
 *
 *  2. Redistributions in binary form must reproduce the above copyright notice, this list
 *     of conditions and the following disclaimer in the documentation and/or other materials
 *     provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY <COPYRIGHT HOLDER> ''AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
 * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT HOLDER> OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 * 
 * The views and conclusions contained in the software and documentation are those of the
 * authors and should not be interpreted as representing official policies, either expressed
 * or implied.
 *
 */

// SleepLock.cpp : Entry point for the DLL

#include "stdafx.h"
#include "mhook/mhook-lib/mhook.h"

//////////////////////////////////////////////////////////////////////////
// Defines and typedefs

typedef BOOLEAN (WINAPI *_SLSetSuspendState)(
  __in  BOOLEAN Hibernate,
  __in  BOOLEAN ForceCritical,
  __in  BOOLEAN DisableWakeEvent
);

//////////////////////////////////////////////////////////////////////////
// Original function

_SLSetSuspendState RealSetSuspendState = (_SLSetSuspendState) GetProcAddress(GetModuleHandle(TEXT("powrprof")), "SetSuspendState");

//////////////////////////////////////////////////////////////////////////
// Hooked function

BOOLEAN WINAPI HookedSetSuspendState(
  __in  BOOLEAN Hibernate,
  __in  BOOLEAN ForceCritical,
  __in  BOOLEAN DisableWakeEvent
)
{
	if (!Hibernate) // Run if we're going into sleep mode
		LockWorkStation();

	// We're done; call the OS' proper SetSuspendState function
	return RealSetSuspendState(Hibernate, ForceCritical, DisableWakeEvent);
}

//////////////////////////////////////////////////////////////////////////
// Entry point

BOOL APIENTRY DllMain( HMODULE hModule,
                       DWORD  ul_reason_for_call,
                       LPVOID lpReserved
					 )
{
	switch (ul_reason_for_call)
	{
	case DLL_PROCESS_ATTACH:
		if (RealSetSuspendState) //Check to see if GetProcAddress did actually give us a pointer to the original SetSuspendState
			(void) Mhook_SetHook((PVOID*)&RealSetSuspendState, HookedSetSuspendState);
		break;
	case DLL_PROCESS_DETACH:
		Mhook_Unhook((PVOID*)&RealSetSuspendState);
		break;
	default:
		break;
	}
	return TRUE;
}