subconsciouscompute/minifilter-rs

An example of Windows minifilter in C++/Rust

Have a look at https://github.com/SubconsciousCompute/fsfilter-rs

minifilter-rs

Use cargo doc --no-deps --document-private-items --open to read Documentation

Table of Contents

Table of Contents

• Minifilter Driver
  • Building Driver
  • Installing Driver
  • Loading/Removing Driver
• Rust Application
  • Building Rust App
  • Running Rust App
• What and the How

Minifilter Driver

Building Driver

1. Open VS 2022 as Administrator
2. Goto minifilter-rs -> minifilter -> RWatch.sln
3. Build solution in Debug mode with x64

NOTE: Enable Loading of Test Signed Drivers by executing Bcdedit.exe -set TESTSIGNING ON in administrative cmd

Installing Driver

1. Open Powershell or command prompt as Administrator
2. RUNDLL32.EXE SETUPAPI.DLL,InstallHinfSection DefaultInstall 132 <path-to>\minifilter-rs\minifilter\x64\Debug\FsFilter.inf

You should be able to see the driver at "C:\Windows\System32\drivers\FsFilter.sys"

Loading/Removing Driver

1. Open Powershell or command prompt as Administrator
2. Start the driver using sc start FSFilter, expected output:

   SERVICE_NAME: FSFilter
       TYPE               : 2  FILE_SYSTEM_DRIVER
       STATE              : 4  RUNNING
                               (STOPPABLE, NOT_PAUSABLE, IGNORES_SHUTDOWN)
       WIN32_EXIT_CODE    : 0  (0x0)
       SERVICE_EXIT_CODE  : 0  (0x0)
       CHECKPOINT         : 0x0
       WAIT_HINT          : 0x0
       PID                : 0
       FLAGS              :
   

3. Stop the driver using sc stop FSFilter, should give the following output:

   SERVICE_NAME: FSFilter
       TYPE               : 2  FILE_SYSTEM_DRIVER
       STATE              : 1  STOPPED
       WIN32_EXIT_CODE    : 0  (0x0)
       SERVICE_EXIT_CODE  : 0  (0x0)
       CHECKPOINT         : 0x0
       WAIT_HINT          : 0x0
   

4. Remove it by sc delete FSFilter, should give the following output:

   [SC] DeleteService SUCCESS
   

You can also run Fltmc.exe to see the currently loaded drivers:

Filter Name                     Num Instances    Altitude    Frame
------------------------------  -------------  ------------  -----
bindflt                                 1       409800         0
FSFilter                                4       378781         0   // our minifilter driver
WdFilter                                5       328010         0
storqosflt                              0       244000         0
wcifs                                   0       189900         0
CldFlt                                  0       180451         0
FileCrypt                               0       141100         0
luafv                                   1       135000         0
npsvctrig                               1        46000         0
Wof                                     3        40700         0
FileInfo                                5        40500         0

Rust Application

Building Rust App

Simply use cargo build --release to build the application

Running Rust App

Use cargo run --bin minifilter --release to run the application

The program starts to print the IOMessage which is defined like:

#[repr(C)]
pub struct IOMessage {
    pub extension: [wchar_t; 12],
    pub file_id_vsn: c_ulonglong,
    pub file_id_id: [u8; 16],
    pub mem_sized_used: c_ulonglong,
    pub entropy: f64,
    pub pid: c_ulong,
    pub irp_op: c_uchar,
    pub is_entropy_calc: u8,
    pub file_change: c_uchar,
    pub file_location_info: c_uchar,
    pub filepathstr: String,
    pub gid: c_ulonglong,
    pub runtime_features: RuntimeFeatures,
    pub file_size: i64,
}

We end the process using ctrl + c in the example video:

NOTE:

• Might fail if not ran with administrative privileges
• You need to load and start the driver before running the program or else it will error out

What and the How

We basically share definition between the mini-filter and Rust using #[repr(C)]

We use channels to process all IRPs.

minifilter-rs's Issues

VCRUNTIME140.dll missing on target machine

Maybe the solution is here: https://www.reddit.com/r/rust/comments/ekts0d/how_to_link_crt_statically_when_building_with_msvc/