Genie 2.4 breaks WSL interop on Windows 10

[Elberet]

Windows version (build number): Windows 10 21H2 (19044.1766)

Linux distribution: Ubuntu 20.04

Kernel version: 5.10.102.1-microsoft-standard-WSL2

Genie version: genie 2.4

Describe the bug
Genie 2.4 by default installs /usr/lib/binfmt.d/WSLInterop.conf. This file is used by systemd to register the miscellaneous binary wrapper for WSL interop in the kernel. The registration includes a set of flags that tell the kernel how to interact with the wrapper. At least for my local Windows machine, these flags are wrong and result in WSL Linux becoming unable to launch any Windows binaries through the WSL /init wrapper.

To Reproduce
Steps to reproduce the behavior:

1. Create new WSL space:

   wsl --unregister Ubuntu-20.04
   wsl --install -d Ubuntu-20.04
   

2. Install genie (wsl -u root or sudo su -):

   curl -Ls -o /etc/apt/trusted.gpg.d/wsl-transdebian.gpg "https://arkane-systems.github.io/wsl-transdebian/apt/wsl-transdebian.gpg"
   echo "deb https://arkane-systems.github.io/wsl-transdebian/apt/ $(lsb_release -cs) main" >/etc/apt/sources.list.d/wsl-transdebian.list
   echo "deb-src https://arkane-systems.github.io/wsl-transdebian/apt/ $(lsb_release -cs) main" >>/etc/apt/sources.list.d/wsl-transdebian.list
   ssh-keygen -A
   awk -i inplace '($2=="/" && /^[^#]/){ print "#"$0; next } 1' /etc/fstab
   systemctl mask getty.target
   systemctl mask multipathd.service
   systemctl mask multipathd.socket
   systemctl mask apport-forward.
   systemctl mask iscsid.socket
   systemctl mask apport-autoreport.path
   systemctl mask systemd-modules-load.service
   systemctl set-default multi-user.target
   systemctl disable sshd.service
   systemctl disable ModemManager.service
   systemctl disable ufw.service
   systemctl disable apport.service
   systemctl disable unattended-upgrades.service
   apt-get update && apt-get install -y systemd-genie
   

3. Check WSL interop binfmt_misc configuration:

   # genie -b
   no-bottle
   # cat /proc/sys/fs/binfmt_misc/WSLInterop
   enabled
   interpreter /tools/init
   flags: F
   offset 0
   magic 4d5a
   

4. Start genie and repeat above:

   # genie -s
   Waiting for systemd....!!
   # genie -b
   inside
   # cat /proc/sys/fs/binfmt_misc/WSLInterop
   enabled
   interpreter /init
   flags: PF
   offset 0
   magic 4d5a
   

   Note that the flags have changed.
5. Attempt to run any Windows binary from within WSL:

   $ genie -b
   inside
   $ /mnt/c/Windows/System32/reg.exe "HKLM\\SYSTEM\\CurrentControlSet\\Control\\Nls\\CodePage"
   FEHLER: Ungültiges Argument/Option - '/mnt/c/Windows/System32/reg.exe'.
   Geben Sie "REG /?" ein, um die Syntax anzuzeigen.
   

   Due to the altered binfmt flags, reg.exe ended up being called with the Linux argv[0] as an additional command line argument, preceding the expected arguments, and failed with an error message.

Expected behavior
Genie should not break WSL interop. Specifically, if the binfmt misc configuration depends on the Windows version, Genie should detect the version it is running on and adjust the binfmt configuration to match. If the Windows version is not or no longer supported, Genie should at least emit a noticeable warning.

Additional context
The change to /usr/lib/binfmt.d/WSLInterop.conf was introduced in response to #267, where a user on Windows 10.0.22598.200 reported a problem with WSL interop. Build 22598 is a Windows 11 insider preview build, not a full release.

I confirm that I have read the ENTIRE supplied readme file and checked for relevant information on the repository wiki before raising this issue, and that if the solution to this issue is found in either location, it will be closed without further comment:

• Yes.

[Elberet]

I just noticed #264. Apparently, the binfmt wrapper's behaviour is inconsistent between Windows 10 and release versions of Windows 11, not just insider previews. So for Windows 10 users (like myself, because my perfectly good i7 7700K is not recent enough for Windows 11 😖), the change introduced in ebca3e3 straight up breaks WSL, while it is absolutely required on Windows 11...

[denskh]

Manual update of /usr/lib/binfmt.d/WSLInterop.conf to revert change mentioned above seems to fix issue on Win10/Debian.

[NotTheDr01ds]

@Elberet Not that it has anything to do with your issue, but I'm curious about the following in your installation procedure:

systemctl mask apport-forward.

Where does that come from? I see the same in another bug report, but is that the correct syntax? Shouldn't it be?

systemctl mask apport-forward.socket
# or
systemctl mask apport-forward@

The line as it is creates:

/etc/systemd/system/apport-forward..service -> /dev/null

With double-dots, which doesn't seem correct, right?

[Elberet]

You're right, that's probably a simple typo in my script. It shouldn't have any effect on the interop issue, tho.

[YenLegion]

Trying to parse this, so to fix /usr/lib/binfmt.d/WSLInterop.conf is set with P or PF?

[Elberet]

The correct set of flags depends on the Windows version:

• Windows 10 21H2 requires F.
• Windows 11 requires PF.

Genie 2.4 now defaults to PF. If you are running Windows 10, set the flags field in /usr/lib/binfmt.d/WSLInterop.conf to F.

The reason for this difference is that the behaviour of the WSL helper binary (/init) changes. It is not known exactly when that change was or will be introduced, only that it's sometime between Windows versions 19044.1826 (mine) and 22598.200 (as per #267).

A full explanation of what these flags mean can be found at https://www.kernel.org/doc/Documentation/admin-guide/binfmt-misc.rst.

[cerebrate]

Fixed in 2.5, shipping as soon as a psutil issue is resolved.