C++ DLL not executing function after injection

Question

Okay so I made a DLL injector in VB.net a while ago. It works fine with any DLL except for mine. So I know the problem is with the DLL. Here is the injector's code:

Private Function Inject(ByVal pID As Integer, ByVal dllLocation As String) As Boolean
    Dim hProcess As Integer = OpenProcess(&H1F0FFF, 1, pID)
    If hProcess = 0 Then
        Return False
        MessageBox.Show("Could not open process!")
    End If
    Dim dllBytes As Byte() = System.Text.Encoding.ASCII.GetBytes(dllLocation)
    Dim allocAddress As Integer = VirtualAllocEx(hProcess, 0, dllBytes.Length, &H1000, &H4)
    If allocAddress = Nothing Then
        Return False
        MessageBox.Show("Could not allocate the address!")
    End If
    Dim kernelMod As Integer = GetModuleHandle("kernel32.dll")
    Dim loadLibAddr = GetProcAddress(kernelMod, "LoadLibraryA")
    If (kernelMod = 0) Then
        MessageBox.Show("Could not get the Module")
        Return False
    End If
    If (loadLibAddr = 0) Then
        MessageBox.Show("get the Process address!")
        Return False
    End If
    WriteProcessMemory(hProcess, allocAddress, dllBytes, dllBytes.Length, 0)
    Dim libThread As Integer = CreateRemoteThread(hProcess, 0, 0, loadLibAddr, allocAddress, 0, 0)

    If libThread = 0 Then
        Return False
        MessageBox.Show("Error Creating thread!")
    Else
        WaitForSingleObject(libThread, 5000)
        CloseHandle(libThread)
    End If
    CloseHandle(hProcess)
    Threading.Thread.Sleep(1000)
    Return True
End Function

This writes the process memory and creates a remote thread.

Now my project has two files: the header and the CPP File.

Header:

#ifdef MAINLIB_EXPORTS
#define MAINLIB_API __declspec(dllexport)
#else
#define MAINLIB_API __declspec(dllexport)
#endif

extern "C" MAINLIB_API DWORD TestFunction();

And the CPP:

#define WIN32_LEAN_AND_MEAN

#include <windows.h>
#include <stdio.h>
#include "dll.h"
#include "Urlmon.h"

BOOL APIENTRY DllMain( HANDLE hModule, DWORD  ul_reason_for_call, LPVOID lpReserved)
{
        hModule;
        lpReserved;

    switch (ul_reason_for_call)
        {
                case DLL_PROCESS_ATTACH:
                case DLL_THREAD_ATTACH:
                case DLL_THREAD_DETACH:
                case DLL_PROCESS_DETACH:
                        break;
    }

    return TRUE;
}

DWORD TestFunction()
{     
        MessageBox(0, TEXT("LOL"), TEXT("LMAO"), MB_OK);
        return 1;
}

From what I understand is that this should run TestFunction on injection. But it doesn't. Any solutions/helpful pages I could use?

Answer 1

There is nothing in your code that specifies TestFunction needs to be called. Once the DLL is attached to the process only DllMain and global objects needing initialization are called. You need to call TestFunction when processing DLL_PROCESS_ATTACH.

DWORD TestFunction();

BOOL APIENTRY DllMain( HANDLE hModule, DWORD  ul_reason_for_call, LPVOID lpReserved)
{
    hModule;
    lpReserved;

    switch (ul_reason_for_call)
    {
    case DLL_PROCESS_ATTACH:
        TestFunction(); // < call TestFunction ONCE when dll is loaded
        break;

    case DLL_THREAD_ATTACH:
    case DLL_THREAD_DETACH:
    case DLL_PROCESS_DETACH:
        break;
    }

    return TRUE;
}

DWORD TestFunction()
{     
        MessageBox(0, TEXT("LOL"), TEXT("LMAO"), MB_OK);
        return 1;
}