Re: [libvirt] Problem configuring selective dropping of root (SOLVED)

On Wed, Jul 10, 2019 at 03:44:54PM +0200, Stephan von Krawczynski wrote: >On Wed, 10 Jul 2019 14:48:14 +0200 >Martin Kletzander <mkletzan(a)redhat.com&gt; wrote: > >> On Tue, Jul 09, 2019 at 02:45:18PM +0200, Stephan von Krawczynski wrote: >> >On Tue, 9 Jul 2019 14:26:08 +0200 >> >Pavel Hrdina <phrdina(a)redhat.com&gt; wrote: >> > >> >> On Tue, Jul 09, 2019 at 02:03:15PM +0200, Stephan von Krawczynski wrote: >> >> > On Tue, 9 Jul 2019 09:40:23 +0100 >> >> > Daniel P. Berrangé <berrange(a)redhat.com&gt; wrote: >> >> > >> >> > > On Mon, Jul 08, 2019 at 09:47:24PM +0200, Stephan von Krawczynski >> >> > > wrote: >> >> > > > Hello list, >> >> > > > >> >> > > > I came across a fundamental flaw in the libvirt user configuration >> >> > > > lately and try to find a solution now. Here is the problem: >> >> > > > I run several qemu instances on arch linux all configured via libvirt. >> >> > > > The default config as user nobody:kvm was fine up to the day I tried >> >> > > > to use a host filesystem via 9p. If you want to gain all user rights >> >> > > > on the guest inside that fs you have to run qemu as root. So far so >> >> > > > good. But if you have several qemus running and only one needs to be >> >> > > > root, what to do? You can try to give a -runas by using <qemu:args>. >> >> > > > But that does not work, qemu instantly crashes. I think this is >> >> > > > because to have _one_ root qemu, you have to configure libvirt to use >> >> > > > root user. This means all rights to fs and so on are set to root and >> >> > > > this is what lets qemu probably go crazy if dropping root by -runas. >> >> > > > The whole thing would be a lot easier and more transparent if the user >> >> > > > in libvirt wouldn't be a global config, but instead be part of the >> >> > > > domain xml. This way every qemu started could use a different user and >> >> > > > have different rights. In my case all but one could be nobody:kvm, and >> >> > > > one root:root. This should not be to complicated based on whats >> >> > > > already there, is it? >> >> > > >> >> > > Libvirt needs to know about the user/group QEMU is running at in order to >> >> > > ensure it gets given access to the various files it needs to use. If you >> >> > > look at the XML of the running guest you should see a <seclabel> >> >> > > describing the user/group it is running as currently. >> >> > > >> >> > > If no <seclabel> is in the offline config, libvirt adds the default >> >> > > seclabel, but if you want a different user/group, you can add the >> >> > > <seclabel> yourself. >> >> > > >> >> > > Regards, >> >> > > Daniel >> >> > >> >> > Hello Daniel, >> >> > >> >> > well, tried that (as good as the docs are) by adding: >> >> > >> >> > <seclabel type='dynamic' model='dac'> >> >> > <label>nobody:kvm</label> >> >> > </seclabel> >> >> > >> >> > This edit worked in virsh without giving errors. >> >> > Starting the domain and then looking into the xml showed: >> >> > >> >> > <seclabel type='dynamic' model='dac' relabel='yes'/> >> >> > >> >> > Consequently qemu runs still as root. My user:group setting simply >> >> > vanished. >> >> > >> >> > I think at least some better docs are needed with a striking example of >> >> > how to change user and group ... >> >> > I may be biased, but how to set user and group is probably the most basic >> >> > example of how to use seclabel - and I cannot find one. >> >> >> >> I agree that the documentation is not the best one. >> >> >> >> You need to use type='static' relabel='yes': >> >> >> >> <seclabel type='static' model='dac' relabel='yes'> >> >> <label>nobody:kvm</label> >> >> </seclabel> >> >> >> >> To achieve that. >> >> >> >> 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 >> > >> >Hello Pavel, >> > >> >thank you for taking up the thread, but unfortunately your suggestion does not >> >work: >> > >> >virsh # start collabora >> >Fehler: Domain collabora konnte nicht gestartet werden >> >Fehler: Interner Fehler: process exited while connecting to monitor: >> >2019-07-09T12:34:00.735392Z qemu-system-x86_64: -object >> >secret,id=masterKey0,format=raw,file=/var/lib/libvirt/qemu/domain-17-collabora/master-key.aes: >> >Unable to read /var/lib/libvirt/qemu/domain-17-collabora/master-key.aes: >> >Failed to open file >> >“/var/lib/libvirt/qemu/domain-17-collabora/master-key.aes”: Permission denied >> > >> >Obviously this is because "type='static'" means that libvirt does not care >> >about setting the user rights for qemu, which then leads to this. >> >> No, 'static' means you tell libvirt what the label should be, 'dynamic' means >> libvirt will generate it automatically. >> >> >I did think "relabel='yes'" should do that, but does not - or I have a deep >> >misunderstanding concerning the seclabel parameters ... >> >Thanks for any help to solve this, if there is no bug involved. >> > >> >> Relabel definitely does that and unless there is a bug it uses the seclabel for >> the domain. What could be happening is that one of the parent directories is >> missing a browse permission for others (the last 'x' in rwxrwxrwx). Could you >> run the following commands and reply with the output? >> >> ls -ld /var/lib/ >> ls -ld /var/lib/libvirt/ >> ls -ld /var/lib/libvirt/qemu/ >> >> Also what distribution are you using? I remember there were some differences in >> packaging related to the directory permissions. >> >> Martin >> >> >Dumpxml shows this btw: >> > >> > <seclabel type='static' model='dac' relabel='yes'> >> > <label>nobody:kvm</label> >> > </seclabel> >> > >> >which at least is what was configured. >> >-- >> >Regards, >> >Stephan > >Hello Martin, > >thanks for picking up. Here is the output you requested: > >[root@vserver-a01 /]# ls -ld /var/lib/ >drwxr-xr-x 21 root root 4096 10. Jul 00:00 /var/lib/ >[root@vserver-a01 /]# ls -ld /var/lib/libvirt/ >drwxr-xr-x 11 root root 4096 4. Jul 10:08 /var/lib/libvirt/ >[root@vserver-a01 /]# ls -ld /var/lib/libvirt/qemu/ >drwxrwx--- 11 root root 4096 10. Jul 15:36 /var/lib/libvirt/qemu/ > >It seems your guess is right. After > >[root@vserver-a01 /]# chmod a+x /var/lib/libvirt/qemu/ >[root@vserver-a01 /]# ls -ld /var/lib/libvirt/qemu/ >drwxrwx--x 11 root root 4096 10. Jul 15:41 /var/lib/libvirt/qemu/ > >it started: > >virsh # start collabora >Domain collabora gestartet > >So that's a bug in the Arch Linux packaging? >Who to tell? > Our Makefile specifies what to do on installation: $(MKDIR_P) -m 0751 "$(DESTDIR)$(localstatedir)/lib/libvirt/qemu" so I guess this is a packaging issue. No idea where/how the arch packaging works, sorry. >Thank you Martin, Pavel and Daniel for tracking that down. > >-- >Regards, >Stephan