[virtiofs] Self-symlink causes crash in virtiofs share

[Sirius902]

Describe the bug Opening a mounted virtiofs share in Windows Explorer with a self-symlink inside will cause the guest's virtiofs driver to crash.

To Reproduce Steps to reproduce the behaviour:

• On the host create a new directory, cd into it, and create a self-symlink in it with ln -s bruh bruh.
• Share the directory with a Windows vm guest using virtiofs.
• Mount the virtiofs share to a drive (here's my script for reference).

  & "C:\Program Files (x86)\WinFsp\bin\launchctl-x64.exe" start virtiofs viofsZ VMShared \\.\Z:

• In Windows Explorer open the drive mounted with virtiofs (in my case drive Z) and the virtiofs driver will crash.

Expected behavior I would expect the virtiofs driver not to crash and possibly show the offending self-symlink as a shortcut.

Screenshots

Event Viewer error text:

Faulting application name: virtiofs.exe, version: 0.0.0.0, time stamp: 0x66952d29
Faulting module name: ntdll.dll, version: 10.0.22621.4111, time stamp: 0x518e67bb
Exception code: 0xc00000fd
Fault offset: 0x000000000002145a
Faulting process id: 0x0x1E28
Faulting application start time: 0x0x1DB07A4D7DEDDB8
Faulting application path: C:\Program Files\Virtio-Win\VioFS\virtiofs.exe
Faulting module path: C:\Windows\SYSTEM32\ntdll.dll
Report Id: bab05ad6-1799-40c1-894d-9ae2ca09894e
Faulting package full name: 
Faulting package-relative application ID: 

Host:

• Disto: NixOS
• Kernel version: Linux 6.10.9

VM:

• Windows version: Windows 11 22631.4169
• Which driver has a problem: virtiofs.exe
• Driver version or commit hash that was used to build the driver: Virtio-win-guest-tools 0.1.262

[YanVugenfirer]

Thank you for reporting the issue!

Symlinks are a known place for the corner cases due to the different handling by Linux and Windows. We will look into this, but unfortunately not in a very near future

[xiagao]

@Sirius902 I didn't reproduce this issue in my env with your steps, could you tell the virtiofsd version? Host/guest info: 5.14.0-494.el9.x86_64 virtiofsd-1.11.1-1.el9.x86_64 virtio-win-prewhql-0.1-262 Win11 23h3(os build 22631.3447)

Steps:

1. Create virtiofsd with root privilege:

   mkdir /root/avocado/data/avocado-vt/virtio_fs_test/ &
   /usr/libexec/virtiofsd --socket-path=/var/tmp/avocado-vt-vm1-fs-virtiofsd.sock -o source=/root/avocado/data/avocado-vt/virtio_fs_test/ -o cache=auto &

2. Create a symlink for a file

   ln -s tmp.sh tmp-link.sh
   lrwxrwxrwx 1 root root        6 Sep 18 08:34  tmp-link.sh -> tmp.sh

3. Start Win11 guest and start virtiofs service.

   
   C:\>"C:\Program Files (x86)\WinFsp\bin\fsreg.bat" virtiofs C:\virtiofs.exe "-t %1 -m %2"
   The operation completed successfully.
   The operation completed successfully.
   The operation completed successfully.

C:>"C:\Program Files (x86)\WinFsp\bin\launchctl-x64.exe" start virtiofs xiagao_fs1 myfs Y: OK

4.  Opening the mounted virtiofs share in Windows Explorer, in my case it is Y: volume.

Results: No driver crash.
![image](https://github.com/user-attachments/assets/d5d655de-402c-4263-a73d-cd65b47b4526)

[xiagao]

Ignore my last comment. It wasn't for self-symlink. The self-symlink indeed makes the virtiofs volume crash inside guest. I'll create an internal issue to track it.