Re: [libvirt] [PATCH] conf: Fix parsing of seclabels without model

On 08/30/2012 03:20 PM, Daniel P. Berrange wrote: >On Thu, Aug 30, 2012 at 03:17:09PM -0300, Marcelo Cerri wrote: >>On 08/30/2012 03:03 PM, Daniel P. Berrange wrote: >>>On Thu, Aug 30, 2012 at 07:12:26PM +0200, Jiri Denemark wrote: >>>>On Thu, Aug 30, 2012 at 13:19:31 -0300, Marcelo Cerri wrote: >>>>>With this patch libvirt tries to assign a model to seclabels when model >>>>>is missing. Libvirt will look up at host's capabilities and assign a >>>>>model in order to each seclabel that doesn't have a model assigned. >>>>> >>>>>This patch fixes: >>>>> >>>>>1. The problem with existing guests that have a seclabel defined in its XML. >>>>>2. A XML parse error when a guest is restored. >>>>> >>>>>Signed-off-by: Marcelo Cerri <mhcerri(a)linux.vnet.ibm.com&gt; >>>>>--- >>>>> src/conf/domain_conf.c | 56 ++++++++++++++++++++++++++------------------------ >>>>> 1 file changed, 29 insertions(+), 27 deletions(-) >>>> >>>>I think this is trying to fix the issue at a wrong place. It's not that XML >>>>generated by older libvirtd is not correctly parsed by current libvirtd. The >>>>problem is that *current* libvirtd creates an XML that it cannot parse back. >>>>Thus we should rather fix the code that formats the XML. >>>> >>>>On that front, I'm concerned about migration compatibility of this new >>>>security driver code. If we just blindly emit <seclabel type='dynamic' >>>>model='dac' relabel='yes'> element into the XML, I'm pretty sure an older >>>>libvirtd will complain about it even though the element was not used to do >>>>anything special that would be done anyway (that is, if labels are the default >>>>qemu_user:qemu_group). >>> >>>Yes, we should not auto-add a <seclabel> for model=dac unless we have >>>configured it to auto-assign a private uid:gid pair per guest. If it is >>>operating in the mode where it just uses a fixed uid:gid pair we should >>>not emit the seclabel. >>> >> >>Can you explain which problem this auto-added <seclabel> for >>model=dac can create? I really can see a migration compatibility >>issue with it. When a <seclabel> for model=selinux is not defined >>for a guest, and SELinux driver is in use, a <seclabel> is also >>auto-added to this guest. > >An old libvirtd (ie < 0.10.0) already knows how to parse & accept >a <seclabel> for model=selinux. It will reject a <seclabel> >which has model=dac, if that is the first <seclabe> element present. >(it will of course ignore the 2nd/3rd/etc <seclabel> element, since >it only expected one to exist). So if model=dac is added as the >second <seclabel> back compat is ok. If the selinux/apparmour >security drivers are disabled though, the <seclabel> with model=dac >will be the first & only element. This will confuse old libvirtd. > Ok. But in which scenario would this happen? It doesn't seem to make sense to save a guest with an earlier libvirt version and restore it in an older libvirt.