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[Xash]

#include <windows.h>

#include <string.h>

#include <stdio.h>



void HookFunction(char* funcName, LPDWORD function);

LPDWORD FoundIAT(char* funcName);



int WINAPI HookMessageBoxA(HWND hWnd, LPCTSTR lpText, LPCTSTR lpCaption, UINT uType);  



BOOL APIENTRY DllMain (HINSTANCE hInstance, DWORD dwReason, LPVOID lpReserved)

{

    if(dwReason == DLL_PROCESS_ATTACH)

    {

		HookFunction("MessageBoxA", (LPDWORD)&HookMessageBoxA);

    }



	return true;

}



void HookFunction(char* funcName, LPDWORD function)

{

	LPDWORD pOldFunction = FoundIAT(funcName);

    DWORD accessProtectionValue , accessProtec;



    int vProtect = VirtualProtect(pOldFunction, sizeof(LPDWORD), PAGE_EXECUTE_READWRITE, &accessProtectionValue);

    *pOldFunction = (DWORD)function;

    vProtect = VirtualProtect(pOldFunction, sizeof(LPDWORD), accessProtectionValue, &accessProtec);

}



int WINAPI HookMessageBoxA(HWND hWnd, LPCTSTR lpText, LPCTSTR lpCaption, UINT uType)

{

	return MessageBoxA(hWnd, "hi!", "how are you?", uType);

}



LPDWORD FoundIAT(char* funcName)

{

	DWORD test = 0;



	LPVOID pMapping = GetModuleHandle(NULL);

	if (pMapping == NULL)

		exit(-1);



	PIMAGE_DOS_HEADER DosHeader = (PIMAGE_DOS_HEADER) pMapping;



	if (DosHeader->e_magic != IMAGE_DOS_SIGNATURE)

		exit(-1);



	PIMAGE_NT_HEADERS NtHeaders = (PIMAGE_NT_HEADERS) ((char*) DosHeader + DosHeader->e_lfanew);



	if (NtHeaders->Signature != IMAGE_NT_SIGNATURE)

		exit(-1);



	PIMAGE_DATA_DIRECTORY DataDirectory = &NtHeaders->OptionalHeader.DataDirectory[1]; // Import symbols

	PIMAGE_IMPORT_DESCRIPTOR ImportDescriptor = (PIMAGE_IMPORT_DESCRIPTOR) ((char*) DosHeader + DataDirectory->VirtualAddress);



	PIMAGE_THUNK_DATA32 OriginalFirstThunk = (PIMAGE_THUNK_DATA32)((char*) DosHeader + ImportDescriptor->OriginalFirstThunk);



	while(OriginalFirstThunk != 0)

	{

		DWORD name = (DWORD)((char*) pMapping + ImportDescriptor->Name);

		

		OriginalFirstThunk = (PIMAGE_THUNK_DATA32)((char*) DosHeader + ImportDescriptor->OriginalFirstThunk);

		PIMAGE_THUNK_DATA32 FirstThunk = (PIMAGE_THUNK_DATA32)((char*) DosHeader + ImportDescriptor->FirstThunk);



		while(OriginalFirstThunk->u1.AddressOfData != 0)

        {

            PIMAGE_IMPORT_BY_NAME NameImg = (PIMAGE_IMPORT_BY_NAME)((char*) DosHeader + (DWORD)OriginalFirstThunk->u1.AddressOfData);



			test = (DWORD)OriginalFirstThunk->u1.Function & (DWORD)IMAGE_ORDINAL_FLAG32;

			if (test == 0)

			{

				if(strcmp(funcName, (const char*)NameImg->Name) == 0)

				{

					return (LPDWORD)&(FirstThunk->u1.Function);

				}

			}

	

            OriginalFirstThunk++;

			FirstThunk++;

        }



		ImportDescriptor++;

	}



	return 0;

}