PVOID WINAPI DetourGetEntryPoint()

in src/modules.cpp [297:368]
60 lines of code
15 McCabe index (conditional complexity)

PVOID WINAPI DetourGetEntryPoint(_In_opt_ HMODULE hModule)
{
    PIMAGE_DOS_HEADER pDosHeader = (PIMAGE_DOS_HEADER)hModule;
    if (hModule == NULL) {
        pDosHeader = (PIMAGE_DOS_HEADER)GetModuleHandleW(NULL);
    }

    __try {
#pragma warning(suppress:6011) // GetModuleHandleW(NULL) never returns NULL.
        if (pDosHeader->e_magic != IMAGE_DOS_SIGNATURE) {
            SetLastError(ERROR_BAD_EXE_FORMAT);
            return NULL;
        }

        PIMAGE_NT_HEADERS pNtHeader = (PIMAGE_NT_HEADERS)((PBYTE)pDosHeader +
                                                          pDosHeader->e_lfanew);
        if (pNtHeader->Signature != IMAGE_NT_SIGNATURE) {
            SetLastError(ERROR_INVALID_EXE_SIGNATURE);
            return NULL;
        }
        if (pNtHeader->FileHeader.SizeOfOptionalHeader == 0) {
            SetLastError(ERROR_EXE_MARKED_INVALID);
            return NULL;
        }

        PDETOUR_CLR_HEADER pClrHeader = NULL;
        if (pNtHeader->OptionalHeader.Magic == IMAGE_NT_OPTIONAL_HDR32_MAGIC) {
            if (((PIMAGE_NT_HEADERS32)pNtHeader)->CLR_DIRECTORY.VirtualAddress != 0 &&
                ((PIMAGE_NT_HEADERS32)pNtHeader)->CLR_DIRECTORY.Size != 0) {
                pClrHeader = (PDETOUR_CLR_HEADER)
                    (((PBYTE)pDosHeader)
                     + ((PIMAGE_NT_HEADERS32)pNtHeader)->CLR_DIRECTORY.VirtualAddress);
            }
        }
        else if (pNtHeader->OptionalHeader.Magic == IMAGE_NT_OPTIONAL_HDR64_MAGIC) {
            if (((PIMAGE_NT_HEADERS64)pNtHeader)->CLR_DIRECTORY.VirtualAddress != 0 &&
                ((PIMAGE_NT_HEADERS64)pNtHeader)->CLR_DIRECTORY.Size != 0) {
                pClrHeader = (PDETOUR_CLR_HEADER)
                    (((PBYTE)pDosHeader)
                     + ((PIMAGE_NT_HEADERS64)pNtHeader)->CLR_DIRECTORY.VirtualAddress);
            }
        }

        if (pClrHeader != NULL) {
            // For MSIL assemblies, we want to use the _Cor entry points.

            HMODULE hClr = GetModuleHandleW(L"MSCOREE.DLL");
            if (hClr == NULL) {
                return NULL;
            }

            SetLastError(NO_ERROR);
            return (PVOID)GetProcAddress(hClr, "_CorExeMain");
        }

        SetLastError(NO_ERROR);

        // Pure resource DLLs have neither an entry point nor CLR information
        // so handle them by returning NULL (LastError is NO_ERROR)
        if (pNtHeader->OptionalHeader.AddressOfEntryPoint == 0) {
            return NULL;
        }

        return ((PBYTE)pDosHeader) +
            pNtHeader->OptionalHeader.AddressOfEntryPoint;
    }
    __except(GetExceptionCode() == EXCEPTION_ACCESS_VIOLATION ?
             EXCEPTION_EXECUTE_HANDLER : EXCEPTION_CONTINUE_SEARCH) {
        SetLastError(ERROR_EXE_MARKED_INVALID);
        return NULL;
    }
}