On Thu, 11 Jul 2019 10:07:11 +0200 Pavel Hrdina <phrdina@redhat.com> wrote:
On Wed, Jul 10, 2019 at 11:56:38AM +0200, Stephan von Krawczynski wrote:
On Wed, 10 Jul 2019 09:56:35 +0200 Pavel Hrdina <phrdina@redhat.com> wrote:
On Wed, Jul 10, 2019 at 12:01:18AM +0200, Stephan von Krawczynski wrote:
On Tue, 9 Jul 2019 14:26:08 +0200 Pavel Hrdina <phrdina@redhat.com> wrote:
[...]
In addition if you would like to have only one VM as root:root you should keep the default config as nobody:kvm and use the root:root for that specific VM.
Pavel
Let me answer this part in another post. Generally I agree with you. But there is one question: if I configure libvirt to use nobody:kvm as user, how is it possible to start a qemu with root privileges? I thought it not to be possible that it runs a root process while its config says it should be nobody ...?
That configuration is in /etc/libvirt/qemu.conf which configures things related to QEMU process and the user:group configuration tells how the QEMU process will be started. The system libvirtd daemon runs always as root:root in order to have permissions to execute QEMU process under any user and to configure a lot of other things when starting a VM.
I thought it can only _drop_ privileges from root to nobody, because its primary user is root. Or is it in fact always running as root, and only "fake-dropping" to the configured user (maybe a spawned child), while still being able to spawn other root processes?
I'm not sure what do you mean by "fake-dropping", libvirt forks itself in order to create a new process where the QEMU binary is executed and the permissions are configured for that newly created process.
All of this is true only for the system libvirt, that means if you use qemu:///system connection, for the session libvirt everything runs as your user and there is no session libvirt for root user.
The XML and configuration that I've suggested should work as I've tried it before sending the mail.
Pavel
Thank you for clearing things up a bit for me. I am using arch linux (see OP) and the libvirt version gives:
virsh # version Kompiliert gegen die Bibliothek: libvirt 5.4.0 Verwende Bibliothek: libvirt 5.4.0
Verwende API: QEMU 5.4.0 Laufender Hypervisor: QEMU 4.0.0
Using your seclabel with root:root in libvirt/qemu.conf throws:
virsh # start collabora Fehler: Domain collabora konnte nicht gestartet werden Fehler: Interner Fehler: process exited while connecting to monitor: 2019-07-10T09:49:52.519211Z qemu-system-x86_64: -object secret,id=masterKey0,format=raw,file=/var/lib/libvirt/qemu/domain-18-collabora/master-key.aes: Unable to read /var/lib/libvirt/qemu/domain-18-collabora/master-key.aes: Failed to open file “/var/lib/libvirt/qemu/domain-18-collabora/master-key.aes”: Permission denied
Unfortunately I cannot verify what file permissions the requested file has, as it is vanished as soon as the crash happens. I bet though that it has root:root and the correctly set qemu user nobody:kvm has no read rights. So obviously relabel does not work. As it works on your side question is what's different? You are sure that you did not try the other way round and seclabel to root:root for a setup with standard user nobody:kvm. This would explain why you do not get this error... I generally try not to patch around in libvirt or qemu or the hosts' arch system. Which makes this probably at least a bug in the distro...
Since the conversation of solution for the issue continues in different part of this thread I would like to just point out that you should try doing it the other way around.
You've stated in previous mails that you would like to have only one VM as root:root and the rest of the VMs as the default nobody:kvm. In general it's really bad idea to configure root:root as the default, as it creates unnecessary security risk for all of the VMs.
Regardless of that, if there is a bug in libvirt when having root:root as default we should fix it.
Pavel
Hello Pavel, I totally agree with you that root:root is not the right choice for the global setup. I was thinking falsely that root:root would be required to be able to drop the rights to nobody for some qemus instead of increasing from nobody to root for one qemu. Since I learned libvirt is running as root anyways obviously setting global user to nobody is the right choice (which I did in the meantime). And since we found (elsewhere in the thread) that it is indeed a dir permission problem my trust in the libvirt project is at least 99% restored :-) Could be 100% if libvirt would check and set the permissions correctly ... ;-) -- Regards, Stephan