Re: [libvirt] [PATCH 0/12] Improve security driver handling & QEMU DAC management

On Tue, Jan 26, 2010 at 12:56:00PM +0000, Daniel P. Berrange wrote: > On Tue, Jan 26, 2010 at 02:28:45PM +0200, Dan Kenigsberg wrote: > > On Tue, Jan 26, 2010 at 10:23:01AM +0000, Daniel P. Berrange wrote: > > > On Tue, Jan 26, 2010 at 12:06:58PM +0200, Dan Kenigsberg wrote: > > > > On Wed, Jan 20, 2010 at 03:14:57PM +0000, Daniel P. Berrange wrote: > > > > > This patch series does some work on te security drivers, and the QEMU code > > > > > for managing DAC permissions on files. > > > > > > > > > > The core goal is to turn the QEMU driver DAC file management code into a > > > > > security driver. Instead of QEMU calling into the SELinux/AppArmour drivers > > > > > directly, a stacked driver module is introduced. This delegates all operations > > > > > to first the QEMU DAC driver, and then the main SELinux/AppArmour driver. > > > > > The end result is that all the permissions management code is removed from > > > > > the QEMU driver, and we're left with just simple security driver calls. > > > > > > > > > > In the process of this a number of flaws in the current hotplug code were > > > > > found, and code was generally tidied up with a view to making it easier to > > > > > manage. > > > > > > > > > > Finally, we add the ability to turn off the QEMU DAC file managment code, > > > > > and also deal gracefully with failures to change ownership (eg on NFS with > > > > > root squash, or readonly FS). > > > > > > > > hmmm, there's another problem which this patch set does not address: > > > > error : virStorageFileGetMetadata:415 : cannot open file '/deep/into/my/root/squashing/export': Permission denied > > > > > > > > With dynamic_ownership = 0, libvirt down not mess with chown, but it now > > > > assumes that it can read disk images. > > > > > > That is a not unreasonable assumption. The model we want to support is one > > > where > > > > > > - App uses virStoragePool APIs to setup the NFS mount point on the host > > > - App uses virStorageVol APIs to create the new volume with correct > > > ownership at time of creation > > > - libvirt starts the guest, without needing chown() due to step 2 > > > getting ownership correct at time of creation. > > > > > > If libvirt can't read the directories leading upto the image, then it > > > would never have been able to create the volume in the first place. The > > > patchs we have done have aimed at avoiding root squash problems which > > > prevent chmod/chown of files between root & non-root. We still assume > > > that we can read files / browse directories. > > > > Understood. But if I am handling storage myself, I have a regression > > when I switch to libvirt from the sordid art of playing with qemu > > directly. I don't want to make my repository world-readable, and I don't > > want (yet) to use libvirt storage API. > > > > Do I have a third option? > > virStorageFileGetMetadata() is used to determine if the disk configured > for a guest has a backing file (eg qcow linked images). This is called > from the DAC driver to setup ownership, and from the SELinux driver to > setup labelling. You say you've already disabled the DAC driver ownership > so it shouldn't be hitting it there. Thus I assume it must the SELinux > driver that's causing the error. > > > Note that before this patchset, I could apply a patch disabling chown's > > and I managed to start domains over root squashing nfs. > > I'm surprised if that's true, because I don't believe my patches changed > this behaviour of the SELinux driver - it was always calling into the > virStorageFileGetMetadata() method to determine backing store, so should > always have hit the issue you describe Ok I was probably too hasty to blame this patchset, after all, I tested it earlier on a different machine with a different os and a different storage export. However my question still stands: what can I do to make this work when the storage is not readable by root?