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Re: virtiofs mounted filesystems & SELinux



Adding the <binary xattr='on'> element to the <filesystem> device does seem to spawn virtiofsd with the option string "source=/home,xattr". My guest can no longer mount the device though.

It errors with:

[ 170.225553] 9pnet_virtio: no channels available
mount: mount(2) failed: No such file or directory

I think what this is doing is causing libvirt to create the device as a virtiofs device instead of a 9p device. The EL7 kernel doesn't have a virtiofs driver, so it can't mount virtiofs devices.

My knowledge is unfortunately limited about the nuances between 9p and virtiofs. So I'm mostly experimenting by trial-and-error here.

On Wed, Jun 2 2021 at 03:55:40 PM -0500, Connor Kuehl <ckuehl redhat com> wrote:
On 5/21/21 11:59 AM, Link Dupont wrote:

Adding the virtio-fs mailing list.

 I am mounting a filesystem into a domain using the virtiofs driver.

 <filesystem accessmode="passthrough" type="mount">
       <source dir="/home"/>
       <target dir="/home"/>
       <driver type="virtiofs"/>
 </filesystem>

Both my host (Fedora 34) and guest (CentOS 8.4) are running with SELinux enforcing. From my host, I can see that the SELinux context type is set to
 user_home_dir_t.

 $ ls -ldZ /home/link
drwxr-xr-x. 61 link link system_u:object_r:user_home_dir_t:s0 8192 May 21
 12:41 /home/link

From within the guest however, the volume is unlabeled_t

 $ ls -lZd /home/link
drwxr-xr-x. 61 link link system_u:object_r:unlabeled_t:s0 8192 May 21 12:53 /
 home/link

Is there a way to pass the SELinux context through to the guest? Or mount the
 volume with the correct options to map SELinux contexts?



Hi,

I'm afraid I actually don't know that much about SELinux but I read
that it relies on using extended attributes in the file system to
accomplish its labeling.

Do you still experience this issue when you enable extended attribute
support[1] in virtiofsd? The example in the optional parameters snippet
enables extended attributes with the xattr='on' element.

Connor

[1] https://libvirt.org/kbase/virtiofs.html#optional-parameters




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