"Permission denied" in Debian 11 without apparmor (opennebula) about virtnbdbackup

[abbbi]

seems libvirt is unable to create the scratch file required during backup due to permission errors. Try passing another path using the --scratchdir option
Check your /var/log/audit.log, maybe SELinux. Havent seen this happen without apparmor so it must either be a configuration or libvirt issue.

[abbbi]

Check the logfiles in /var/log/libvirt/qemu/ too, the scratch file is created by the qemu process. Maybe your qemu process does not have write access to /var/tmp/.

[gesielbernardes]

Hi,
I'm still having the same problem :-(

Below are more details about this error:

=> /var/log/syslog:

May 10 11:30:01 tcnvh12 libvirtd[28853]: libvirt version: 7.0.0, package: 3 (Andrea Bolognani [email protected] Fri, 26 Feb 2021 16:46:34 +0100)
May 10 11:30:01 tcnvh12 libvirtd[28853]: hostname: tcnvh12
May 10 11:30:01 tcnvh12 libvirtd[28853]: Domain id=3 name='one-8' uuid=0c214241-042c-4c05-a24c-0d717cd825b9 is tainted: custom-hypervisor-feature
May 10 11:30:01 tcnvh12 systemd[1]: Started Virtual Machine qemu-3-one-8.
May 10 11:30:05 tcnvh12 kernel: [ 6377.737274] kvm [29137]: vcpu0, guest rIP: 0xffffffff8fc6b2b4 disabled perfctr wrmsr: 0xc2 data 0xffff
May 10 11:30:44 tcnvh12 libvirtd[28853]: internal error: unable to execute QEMU "blockdev-add": Could not open '/var/tmp/backup.UWXYN.vda': Permission denied
May 10 11:30:44 tcnvh12 libvirtd[28853]: File '/var/tmp/backup.UWXYN.vda' not accessible: File or directory does not exist
May 10 11:30:44 tcnvh12 libvirtd[28853]: Unable to tear down cgroup access on /var/tmp/backup.UWXYN.vda

=> AppArmor disabled:

# cat /sys/module/apparmor/parameters/enabled
N

More info:

• No SELinux active (is Debian 11)
• /var/tmp with 777
• I've tried use "-S /tmp" or "-S /var/lib/libvirt/images" and result is the same problem
• Versions:
• • libvirt 7.0.0-3
• • qemu 5.2
• • virtnbdbackup 0.59

Any idea where I can look?

[abbbi]

Does /var/log/kern.log offer any audit related log entries? Has libvirtd been restarted after disabling apparmor? Are there still any rules existant in /etc/apparmor.d/libvirt/?

Which security driver is set in /etc/libvirt/qemu.conf?

Following logline looks strange too:

libvirtd[28853]: **Unable to tear down cgroup access on /var/tmp/backup.UWXYN.vda**

[gesielbernardes]

Hi @abbbi,

I found what causes the problem: Some modification/configuration done by Opennebula. I tested in Rocky Linux (Centos 8) and had the same problem. Even using virt-manager to create VM, the error is the same.
I will check with Opennebula team about any solution for this problem, and If it works, I'll post the solution here.

[gesielbernardes]

Hi @abbbi , I again!

I think that found a clue: The scratch file is created with "root" owner and 600 permission; But qemu/libvirt running as a user of Opennebula (oneadmin). Then is generated the error.

I think that to backup work will be necessary that the user that executes Qemu needs permission to access the scratch file, correct?

If running virtnbdbackup as "oneadmin" the scratch file is created as root owner too. Any idea about how to proceed?

[gesielbernardes]

Hi,

The problem are solved: Set "dynamic_ownership = 1" in /etc/libvirt/qemu.conf

[abbbi]

Hi,

The problem are solved: Set "dynamic_ownership = 1" in /etc/libvirt/qemu.conf

thanks for the feedback, yes, opennebula alters the qemu configuration.