Hook and unhook one file DLL - c++

Question

I try hook file DLL into console app. This code
#include "pch.h"
#include <vector>
#include <string>
#include <windows.h>
#include <Tlhelp32.h>
using std::vector;
using std::string;
int main(void)
{
while (true)
{
vector<string>processNames;
PROCESSENTRY32 pe32;
pe32.dwSize = sizeof(PROCESSENTRY32);
HANDLE hTool32 = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, NULL);
BOOL bProcess = Process32First(hTool32, &pe32);
if (bProcess == TRUE)
{
while ((Process32Next(hTool32, &pe32)) == TRUE)
{
processNames.push_back(pe32.szExeFile);
if (strcmp(pe32.szExeFile, "ConsoleApplication4.exe") == 0)
{
char* DirPath = new char[MAX_PATH];
char* FullPath = new char[MAX_PATH];
GetCurrentDirectory(MAX_PATH, DirPath);
sprintf_s(FullPath, MAX_PATH, "%s\\..\\ConsoleApplication1\\ConsoleApplication1.dll", DirPath);
FILE *pFile;
if (fopen_s(&pFile, FullPath, "r") || !pFile)
{
OutputDebugString("[Hook] File name or file does not exist");
OutputDebugString(FullPath);
return -1;
}
fclose(pFile);
HANDLE hProcess = OpenProcess(PROCESS_ALL_ACCESS, FALSE, pe32.th32ProcessID);
if (!hProcess)
{
OutputDebugString("[Hook] Open process fail");
return -1;
}
//attach
LPVOID LoadLibraryAddr = (LPVOID)GetProcAddress(GetModuleHandle("kernel32.dll"), "LoadLibraryA");
if (!LoadLibraryAddr)
{
OutputDebugString("[Hook] Load LoadLibraryA fail");
return -1;
}
LPVOID LLParam = (LPVOID)VirtualAllocEx(hProcess, NULL, strlen(FullPath), MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE);
if (!WriteProcessMemory(hProcess, LLParam, FullPath, strlen(FullPath), NULL))
{
OutputDebugString("[Hook] Write process fail");
return -1;
}
HANDLE hHandle = CreateRemoteThread(hProcess, NULL, NULL, (LPTHREAD_START_ROUTINE)LoadLibraryAddr, LLParam, NULL, NULL);
if (!hHandle)
{
OutputDebugString("[Hook] Hooked fail");
return -1;
}
system("pause");
//detach
LoadLibraryAddr = (LPVOID)GetProcAddress(GetModuleHandle("kernel32.dll"), "FreeLibrary");
if (!LoadLibraryAddr)
{
OutputDebugString("[Hook] Load FreeLibrary fail");
return -1;
}
hHandle = CreateRemoteThread(hProcess, NULL, NULL, (LPTHREAD_START_ROUTINE)LoadLibraryAddr, LLParam, NULL, NULL);
if (!hHandle)
{
OutputDebugString("[Hook] detach fail");
return -1;
}
CloseHandle(hProcess);
delete[] DirPath;
delete[] FullPath;
system("pause");
return 0;
}
}
}
CloseHandle(hTool32);
}
return 0;
}
I have some question for this:
- Why this code can not detach file dll ?
- Why I change LoadLibraryA -> LoadLibrary : load LoadLibrary fail ?
- Why I change LoadLibraryA -> LoadLibraryW : file dll no attach ?
- Code in Mutibyte run is good, but convert to Unicode, file dll no attach ?
Thanks,

Answer 1

The reason this works in multibyte but won't compile with unicode character set is because you're passing a regular c string which is a regular char array. When you set your build type to use multibyte LoadLibrary() resolves to the ansi version which is LoadLibraryA(). If you want to use Unicode in your project properties it will resolve to LoadLibraryW() and you will need to pass a unicode char array, typically wchar_t[].
Even while compiling in unicode mode, you can still call LoadLibraryA() and pass a c string but you must specifically call the A (ansi) version of the function rather than rely on the #ifdef preprocessor statements which resolve them for you.