为什么由“ CreateEvent”创建的HANDLE在另一个进程中无效？

Question

I am writing an ant-cheat Win32 loader and in it I need to create an event, wait for it to get signaled by another process in which I have stored it - but it's failing with ERROR_INVALID_HANDLE. I am creating an unnamed event and just passing it's HANDLE value into the other process which should set it to signaled state in certain condition. Any ideas why is this - isn't the HANDLE created by 'CreateEvent' valid for all proceses. Pseudo code illustrating this:

Process1, Thread1:

extern LPVOID pExternalMemory;

extern HANDLE hExternalProcess; //Process2 Handle

extern HANDLE hExternalThread; //In suspended state (Thread1)

extern HANDLE hEventDuplicate;

HANDLE hEvent = CreateEvent(nullptr, true, false, nullptr);

DuplicateHandle(GetCurrentProcess(), hEvent, hExternalProcess, &hEventDuplicate, STANDARD_RIGHTS_ALL, false, 0); //Wrong, check EDIT1

WriteProcessMemory(hProcess, pExternalMemory, &hEventDuplicate, sizeof(HANDLE), nullptr);

ResumeThread(hExternalThread);

WaitForSingleObject(hEvent, INFINITE);

Process2, Thread1:

EIP->

if(SomeCondition) SetEvent((HANDLE)ExternalMemory); //fails with 'ERROR_INVALID_HANDLE'

//Other code

EDIT: I used 'DuplicateHandle' to fix the problem but now 'SetEvent' call on second process fails with 'ERROR_ACCESS_DENIED'.

EDIT1: Solved the problem - it was with the 'DuplicateHandle' function call, it should be

DuplicateHandle(GetCurrentProcess(), hEvent, hExternalProcess, &hEventDuplicate, 0, false, DUPLICATE_SAME_ACCESS)

For some strange reason - anyone can explain why is this?

Answer 1

Handles are kinda like pointers in that they're usually process-specific. It takes special actions (like using DuplicateHandle) to share them.

Depending on the situation, it might just be easier to name the object and then have the other process access it that way. See the fourth parameter of CreateEvent .