Nt Filesystem Dupe

A library for file & module redirection and hiding, by hooking various Nt APIs.
This project is inspired by CODEX Steam emu and based on reversing it. Credits to them.

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Solution structure

The solution is divided into 3 projects:

1. nt_file_dupe: The actual library, this is a static library (.lib)
2. dll_interface: A thin wrapper .dll project around the static library, exporting the necessary functions
3. testxxx: A simple console app to test the library + helpers

JSON file format:

{
  "myfile.txt": {
    "mode": "file_redirect",
    "to": "myfile.org",
    "file_must_exist": true
  },
  "path/myfile_22.txt": {
    "mode": "file_redirect",
    "to": "path/myfile_22.org",
  },
  "../../folder/some_file.txt": {
    "mode": "file_redirect",
    "to": "../../folder/some_file.org",
  },

  "hideme.txt": {
    "mode": "file_hide"
  },
  "../hideme_22.txt": {
    "mode": "file_hide"
  },

  "prevent_me.dll": {
    "mode": "module_prevent_load"
  },
  "prevent_me": {
    "mode": "module_prevent_load"
  },

  "my_module_org.dll": {
    "mode": "module_redirect",
    "to": "my_module_mod.dll"
  },
  "my_module_org": {
    "mode": "module_redirect",
    "to": "my_module_mod"
  }
}

Each JSON key is considered the original file, the value/object for that key defines the action for the original file.
The entry type is determined by the mode JSON key.

• mode

  ---

  • file_redirect
    Redirect original file creation/opening to a target file.
    Target files are always hidden.
  • file_hide
    Hide the file, as if it doesn't exist on disk.

  ---

  • module_prevent_load
    Prevent loading the module via LoadLibrary() and its variants.
  • module_redirect
    Redirect the loading operation to another target module.
    Target modules are always hidden and cannot be loaded by the process.
  • module_hide_handle
    Prevent GetModuleHandle() from succeeding, this won't affect LoadLibrary() and its variants.
    As if the module doesn't exist in the current process memory.

• to
  Defines which target file/module to redirect the original file/module to.
  Only useful when mode is:

  • file_redirect
  • module_redirect

• file_must_exist (default = false)
  When set to true, the JSON entry will be skipped if the original file doesn't exist, or the target file doesn't exist in file_redirect mode

Check the example sample.json

Behavior

In case this is a file entry, the paths to the original or target files could be absolute or relative.
Relative paths will be relative to the location of the current .exe, not the current directory.

In case this is a module entry, the paths to the original or target modules must be just their filenames.

Both the original and target files/modules must have the same filename length.
Additionally, if this is a file entry, they must exist in the same dir.

Target files/modules are hidden by default, for example, in the JSON file defined above:

• myfile.org Will be hidden and cannot be opened/created
• my_module_mod.dll Will be hidden and cannot be loaded

If file_must_exist = true, then this JSON entry will be ignored without an error if:

• The original file was missing
• The mode = file_redirect and the target file, defined by the JSON key to, is missing

The dll will try to load only one of the following files upon startup in that order:

• A JSON file with the same name as the .dll itself
• nt_file_dupe.json
• nt_file_dupe_config.json
• nt_fs_dupe.json
• nt_fs_dupe_config.json
• nt_dupe.json
• nt_dupe_config.json

Any of these files must exist beside the .dll, not the current running .exe

Upon startup, the dll will try to hide itself, both on disk and in memory.
Additionally in the debug build, it will try to hide the log file on disk.

How use the pre-built .dll:

1. Create a .json file with some entries as shown above
2. Rename the .json file to the same name of the .dll, for example if the .dll is called nt_file_dupe.dll, then the .json file must be named nt_file_dupe.json
3. Place both the .dll and the .json files beside each other in the same folder
4. Load the .dll inside your target, either modify the imports table with something like CFF Explorer, or use any dll loader/injector

Note that the functions to add entries are not thread safe.

How to link and use as a static lib (.lib):

1. Open the Visual Studio solution file nt_file_dupe.sln and build the project nt_file_dupe.
   Make sure to select the right architecture (x64 or x86) and build type (release or debug)
2. Assuming for example you've selected Debug | x64, the library will be built in

   bin\x64\nt_file_dupe\nt_file_dupe_static.lib
   

3. In your own Visual Studio project, you must use C++ language version >= C++17,
   add the static .lib file as an input to the linker: .lib files as linker input
4. Finally, add the folder nt_file_dupe\include as an extra include directory: Additional include directories
5. Everything will be under the namespace ntfsdupe::
6. Check how the .dll wrapper project is importing the required .hpp files, and using the library in its DllMain

How to link and use as a dynamic lib (.dll):

1. Open the Visual Studio solution file nt_file_dupe.sln and build the project dll_interface.
   Make sure to select the right architecture (x64 or x86) and build type (release or debug)
2. Assuming for example you've selected Debug | x64, the library will be built as 2 parts in

   bin\Debug\x64\dll_interface\nt_file_dupe.dll
   bin\Debug\x64\dll_interface\nt_file_dupe.lib
   

   Notice that the .dll file must be accompanied by a small-sized .lib file which we'll use next
3. In your own Visual Studio project, you must use C++ language version >= C++17,
   add the static .lib file as an input to the linker: .lib files as linker input
4. Finally, add the folder dll_interface\include as an extra include directory: Additional include directories
5. All available exports will have this prefix ntfsdupe_

   #include "nt_file_dupe.hpp"
   
   int main() {
       ntfsdupe_load_file(L"myfile.json");
       ntfsdupe_add_entry(ntfsdupe::itf::Mode::file_hide, L"some_file.dll", nullptr);
       return 0;
   }
   

6. The file nt_file_dupe.dll will be added to your imports table, so make sure to copy this .dll file beside your project's build output