Re: [libvirt] [Qemu-devel] [PATCH v4] Add support for fd: protocol

On 08/22/2011 03:25 PM, Anthony Liguori wrote: > On 08/22/2011 01:22 PM, Daniel P. Berrange wrote: >> On Mon, Aug 22, 2011 at 12:25:25PM -0500, Anthony Liguori wrote: >>> On 08/22/2011 11:50 AM, Daniel P. Berrange wrote: >>>> On Mon, Aug 22, 2011 at 11:29:12AM -0500, Anthony Liguori wrote: >>>>> I don't think it makes sense to have qemu-fe do dynamic labelling. >>>>> You certainly could avoid the fd passing by having qemu-fe do the >>>>> open though and just let qemu-fe run without the restricted security >>>>> context. >>>> >>>> qemu-fe would also not be entirely simple, >>> >>> Indeed. >>> >>>> because it will need to act >>>> as a proxy for the monitor, in order to make hotplug work. ie the mgmt >>>> app would be sending 'drive_add file:/foo/bar' to qemu-fe, which would >>>> then have to open the file and send 'drive_add fd:NN' onto the real >>>> QEMU, >>>> and then pass the results on back. >>>> >>>> In addition qemu-fe would still have to be under some kind of >>>> restricted >>>> security context for it to be acceptable. This is going to want to >>>> be as >>>> locked down as possible. >>> >>> I think there's got to be some give and take here. >>> >>> It should at least be as locked down as libvirtd. From a security >>> point of view, we should be able to agree that we want libvirtd to >>> be as locked down as possible. >>> >>> But there shouldn't be a hard requirement to lock down qemu-fe more >>> than libvirtd. Instead, the requirement should be for qemu-fe to be >>> as/more vigilant in not trusting qemu-system-x86_64 as libvirtd is. >>> >>> The fundamental problem here, is that there is some logic in >>> libvirtd that rightly belongs in QEMU. In order to preserve the >>> security model, that means that we're going to have to take a >>> subsection of QEMU and trust it more. >> >> Well we have a process that makes security decisions, and a process >> which applies those security decisions and a process which is confined >> by those decisions. Currently libvirtd makes& applies the decisions, >> and qemu is confined. A qemu-fe model would mean that libvirt is making >> the decisions, but is then relying on qemu-fe to apply them. IMHO that >> split is undesirable, but that's besides the point, since this is not >> a decision that needs to be made now. >> >> 'qemu-fe' needs to have a way to communicate with the confined process >> ('qemu-system-XXX') to supply it the resources (file FDs) it needs to >> access. The requirements of such a comms channel for qemu-fe are going >> to be the same as those needed by libvirtd talking to QEMU today, or >> indeed by any process that is applying security decisions to QEMU. > > But the fundamental difference is that libvirtd uses what's ostensible a > public, supported interface. That means when we add things like this, > we're stuck supporting it for general use cases. > > It's much more palatable to do these things using a private interface > such that we can change these things down the road without worrying > about compatibility with third-party tools. > > Regards, > > Anthony Liguori > Is this a nack for the fd: protocol?

protocol as a stepping stone on the way to a privilege-separated qemu model? I know the fd: protocol is not ideal, but it does provide NFS image isolation, perhaps much sooner than privilege-separated qemu can.