Re: [libvirt] [PATCH v2] qemu: Introduce caching whether /dev/kvm is accessible

On 10/30/2018 04:07 PM, Daniel P. Berrangé wrote: > On Tue, Oct 30, 2018 at 03:45:36PM +0100, Michal Privoznik wrote: >> On 10/30/2018 02:46 PM, Michal Privoznik wrote: >>> On 10/30/2018 01:55 PM, Daniel P. Berrangé wrote: >>>> On Tue, Oct 30, 2018 at 10:32:08AM +0000, Daniel P. Berrangé wrote: >>>>> On Tue, Oct 30, 2018 at 11:08:45AM +0100, Michal Privoznik wrote: >>>>>> On 10/30/2018 10:35 AM, Daniel P. Berrangé wrote: >>>>>>> On Tue, Oct 30, 2018 at 09:13:50AM +0100, Michal Privoznik wrote: >>>>>>>> On 10/29/2018 06:34 PM, Marc Hartmayer wrote: >>>>>>>>> Introduce caching whether /dev/kvm is usable as the QEMU user:QEMU >>>>>>>>> group. This reduces the overhead of the QEMU capabilities cache >>>>>>>>> lookup. Before this patch there were many fork() calls used for >>>>>>>>> checking whether /dev/kvm is accessible. Now we store the result >>>>>>>>> whether /dev/kvm is accessible or not and we only need to re-run the >>>>>>>>> virFileAccessibleAs check if the ctime of /dev/kvm has changed. >>>>>>>>> >>>>>>>>> Suggested-by: Daniel P. Berrangé <berrange(a)redhat.com&gt; >>>>>>>>> Signed-off-by: Marc Hartmayer <mhartmay(a)linux.ibm.com&gt; >>>>>>>>> --- >>>>>>>>> src/qemu/qemu_capabilities.c | 54 ++++++++++++++++++++++++++++++++++-- >>>>>>>>> 1 file changed, 52 insertions(+), 2 deletions(-) >>>>>>>>> > Not really. Udev is in use everywhere, so this behaviour makes the > patch useless in practice, even though it is technically right in > theory :-( > Well, caching owner + seclabels + ACLs won't help either. What if user loads some profile into AppArmor or something that denies previously allowed access to /dev/kvm (or vice versa)? What I am saying is that there are some security models which base their decisions on something else than file attributes.