Hi German,
I tried to repoduce just under qemu kvm env, but didn't reproduce, I would list my steps.
1. start virtiofsd
[root@dell-per440-06 bbbbk]# /usr/libexec/virtiofsd -o source=/home/test  --socket-path=/tmp/sock1  --modcaps=+sys_admin &

2. start rhel920 guest.
     -chardev socket,id=char_virtiofs_fs,path=/tmp/sock1 \
     -device vhost-user-fs-pci,id=vufs_virtiofs_fs,chardev=char_virtiofs_fs,tag=myfs,queue-size=1024,bus=pcie-root-port-3,addr=0x0 \


3. in guest, mount the virtiofs
[root@bootp-73-75-109 mnt]#  mount -t virtiofs myfs mmm/

4. add a user and change it's group to wheel
 184  useradd u1
  185  passwd u1
  186  usermod -g wheel u1

5. switch to u1 user and try to mkdir on shared directory, it shows me 'Permission denied.' 
[root@bootp-73-75-109 mmm]# su u1
[u1@bootp-73-75-109 mnt]$ mkdir -m 0770 mmm/testdir
mkdir: cannot create directory ‘mmm/testdir’: Permission denied


So I failed on the step 1 in your #c0, I'm wondering what's the virtiofs cmd line do you have?

Thanks,
Xiaoling

(In reply to xiagao from comment #1)
> Hi German,
> I tried to repoduce just under qemu kvm env, but didn't reproduce, I would
> list my steps.
> 1. start virtiofsd
> [root@dell-per440-06 bbbbk]# /usr/libexec/virtiofsd -o source=/home/test 
> --socket-path=/tmp/sock1  --modcaps=+sys_admin &
> 
> 2. start rhel920 guest.
>      -chardev socket,id=char_virtiofs_fs,path=/tmp/sock1 \
>      -device
> vhost-user-fs-pci,id=vufs_virtiofs_fs,chardev=char_virtiofs_fs,tag=myfs,
> queue-size=1024,bus=pcie-root-port-3,addr=0x0 \
> 
> 
> 3. in guest, mount the virtiofs
> [root@bootp-73-75-109 mnt]#  mount -t virtiofs myfs mmm/
> 
> 4. add a user and change it's group to wheel
>  184  useradd u1
>   185  passwd u1
>   186  usermod -g wheel u1
> 
> 5. switch to u1 user and try to mkdir on shared directory, it shows me
> 'Permission denied.' 
> [root@bootp-73-75-109 mmm]# su u1
> [u1@bootp-73-75-109 mnt]$ mkdir -m 0770 mmm/testdir
> mkdir: cannot create directory ‘mmm/testdir’: Permission denied
> 

Sorry for confusion, these command are intended to be run as root and the user
"u1" must have the wheel group as a supplementary, not as a main group.

> 
> So I failed on the step 1 in your #c0, I'm wondering what's the virtiofs cmd
> line do you have?

I updated the comment #0 with clearer instructions

Thanks German for your update.
I can reproduce then, the difference is the previous group is the main group, while the error occurred on the supplementary steps.

Thank you very much.

Test passed, so set bug status to verified.
1, create u1 and change it to the wheel group (as a supplementary group)
[root@bootp-73-75-32 mm]# useradd u1
[root@bootp-73-75-32 mm]# passwd u1
[root@bootp-73-75-32 mm]# usermod -G wheel u1

2. mkdir testdir and set rwx premission for owner and group.
[root@bootp-73-75-32 mm]# mkdir -m 0770 testdir
[root@bootp-73-75-32 mm]# chgrp wheel testdir
[root@bootp-73-75-32 mm]# ll
drwxrwx---. 2 root wheel    6 Dec 29 17:02 testdir

3. switch to u1 and try to create a file under testdir, it
[u1@bootp-73-75-32 mm]$ touch testdir/file
[u1@bootp-73-75-32 mm]$ ls -l testdir/file
-rw-r--r--. 1 u1 u1 0 Dec 29 17:02 testdir/file



pkg:
virtiofsd-1.5.0-1.el9.x86_64
qemu-kvm-7.2.0-1.el9
5.14.0-219.el9.x86_64(host)
5.14.0-226.el9.x86_64(guest)

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (virtiofsd bug fix and enhancement update), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2023:2334