Re: [libvirt] [Qemu-devel] [PATCH v4 0/5] Per-guest configurable user/group for QEMU processes

On Fri, Sep 14, 2012 at 09:31:26AM -0400, Corey Bryant wrote: > > > On 09/14/2012 04:40 AM, Daniel P. Berrange wrote: >> On Tue, Sep 11, 2012 at 02:13:38PM -0400, Corey Bryant wrote: >>> Are there any other requirements that need to be taken care of to >>> enable execution of QEMU guests under separate unprivileged user IDs >>> (ie. DAC isolation)? >>> >>> At this point, this patch series (Per-guest configurable user/group >>> for QEMU processes) is upstream, allowing libvirt to execute guests >>> under separate unprivileged user IDs. Additionally, the QEMU bridge >>> helper series is upstream, allowing QEMU to allocate a tap device >>> and attach it to a bridge when run under an unprivileged user ID (http://www.redhat.com/archives/libvir-list/2012-August/msg00277.html). >>> >>> Is there any other feature in QEMU that requires QEMU to be run as root? >> >> Well those features you mention are for two separate issues. When >> running libvirt privileged (qemu:///system), QEMU was already run >> as non-root (qemu:qemu). The per-guest user/group was just making >> sure that QEMU VMs were isolated from each other using user IDs. >> Since libvirtd is running privileged, it can either set permissions >> or open things on QEMU's behalf. All this side of things really >> works already. > > Ok good. This is really what I was getting at and you answered my > question. So we now have DAC isolation of QEMU guests when running > with the qemu:///system URI and there shouldn't be any issues > running unprivileged guests from a privileged libvirt. > >> >> The TAP device bridge helper is something that's needed when running >> libvirtd itself unprivileged (eg the per user qemu:///session libvirtd). >> In this case libvirtd can't access privileged resources at all, hence >> the setuid TAP helper was required. >> > > Ah, that's right, the bridge helper is really only benefiting > libvirt when running with the qemu:///session URI. > > Is there a desire to get to a point where libvirt can do everything > under a session URI that it can do today under a system URI? Then > libvirt and guests could all run unprivileged. I'm sure it's a lot > of work.. I'm just asking. :) Well if you want to give a VM a raw block device someone/thing needs to be running privileged to set an ACL on the device to le the unprivileged VM use it. Similarly for PCI device passthrough. Traditionally in the qemu:///system case, libvirt can deal with this. In a qemu:///session case the sysadmin would have had to setup ACLs/permissions on the devices / files ahead of time.