[Bug 1559317] [NEW] [xenial] No write access to VirtFS (p9) in qemu VM run by libvirt

[Harald Hetzner]

Public bug reported:

Using virt-manager and libvirtd, I added a VirtFS filesystem passthrough
to an existing qemu virtual machine also running Ubuntu.

The XML code generated by libvirt looks like this:

    <filesystem type='mount' accessmode='mapped'>
      <source dir='/p9test'/>
      <target dir='p9_mapped'/>
      <alias name='fs0'/>
      <address type='pci' domain='0x0000' bus='0x02' slot='0x06' function='0x0'/>
    </filesystem>

Inside the VM, I am able to mount the filesystem passthrough like this:

mount -t 9p -o trans=virtio,version=9p2000.L,rw p9_mapped /mnt

After mounting, it is possible to read the contents of the passthrough,
but it is not possible to write into the directory. E.g. 'touch
/mnt/test' results in the error:

touch: cannot touch ‘/mnt/test’: Permission denied

Using the other p9 access modes 'passthrough' and 'squash' also does not
work. Read is possible, write isn't.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: libvirt-bin 1.3.1-1ubuntu6
ProcVersionSignature: Ubuntu 4.4.0-13.29-generic 4.4.5
Uname: Linux 4.4.0-13-generic x86_64
ApportVersion: 2.20-0ubuntu3
Architecture: amd64
CurrentDesktop: Unity
Date: Fri Mar 18 22:12:34 2016
SourcePackage: libvirt
UpgradeStatus: Upgraded to xenial on 2016-02-06 (41 days ago)
modified.conffile..etc.libvirt.qemu.conf: [inaccessible: [Errno 13] Keine Berechtigung: '/etc/libvirt/qemu.conf']
modified.conffile..etc.libvirt.qemu.networks.default.xml: [inaccessible: [Errno 13] Keine Berechtigung: '/etc/libvirt/qemu/networks/default.xml']

** Affects: libvirt (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: amd64 apparmor apport-bug libvirt p9 qemu xenial

** Tags added: libvirt p9 qemu

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Title:
  [xenial] No write access to VirtFS (p9) in qemu VM run by libvirt

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