virtiofs=true: file created by non-root user on Windows bind mount is exposed as root-owned and cannot be reopened for write #40719

Windows Version

Microsoft Windows [Version 10.0.26200.8457]

WSL Version

2.7.7.0

Are you using WSL 1 or WSL 2?

• WSL 2
• WSL 1

Kernel Version

6.18.26.1-1

Distro Version

No response

Other Software

Docker Desktop 4.76.0 (228118)
Docker Engine 29.5.2

Repro Steps

Set %USERPROFILE%\.wslconfig:

[wsl2]
virtiofs=true

Restart WSL:

wsl --shutdown

From a PowerShell prompt in any Windows directory, create a local repro directory:

$repro = Join-Path (Get-Location) 'wsl-virtiofs-repro'
New-Item -ItemType Directory -Force -Path (Join-Path $repro 'data') | Out-Null

Run this container as UID 1000:

docker run --rm -u 1000:100 --mount "type=bind,source=$repro,target=/config" alpine sh -c 'id; mount | grep " /config "; f=/config/data/file-to-reopen.txt; rm -f "$f" 2>/dev/null || true; printf first > "$f"; echo after_create; ls -ln "$f"; if printf second >> "$f"; then echo append=ok; else echo append=failed; fi; echo after_append_attempt; ls -ln "$f"; printf "contents="; cat "$f"; echo'

Expected Behavior

The file created by UID 1000 should remain writable by UID 1000, or the mount should otherwise preserve behavior compatible with the default Windows-backed WSL/Docker bind mount path.

With virtiofs=true commented out and WSL restarted, the same command succeeds. The Windows drive letter in the mount output is generalized below:

uid=1000 gid=100(users) groups=100(users)
<Windows drive> on /config type 9p (rw,noatime,aname=drvfs;path=<Windows drive>\;uid=0;gid=0;metadata;symlinkroot=/mnt/host/,cache=0x5,access=client,msize=65536,trans=fd,rfd=5,wfd=5)
after_create
-rw-r--r--    1 1000     100              5 Jun  5 19:33 /config/data/file-to-reopen.txt
append=ok
after_append_attempt
-rw-r--r--    1 1000     100             11 Jun  5 19:33 /config/data/file-to-reopen.txt
contents=firstsecond

Actual Behavior

With virtiofs=true, the file is created, but it is immediately exposed as root:root with mode 0644. The same UID that created it cannot reopen it for append/write:

uid=1000 gid=100(users) groups=100(users)
60d56c4b-d352-468b-8ba2-4a96cfd9b211 on /config type virtiofs (rw,noatime)
after_create
-rw-r--r--    1 0        0                5 Jun  5 19:32 /config/data/file-to-reopen.txt
append=failed
after_append_attempt
-rw-r--r--    1 0        0                5 Jun  5 19:32 /config/data/file-to-reopen.txt
contents=first
sh: can't create /config/data/file-to-reopen.txt: Permission denied

Diagnostic Logs

WslLogs-2026-06-05_13-23-13.tar.gz