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

On 08/22/2011 01:25 PM, 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. > I do like the idea of a privileged qemu-fe performing the open and passing the fd to a restricted qemu.

 However, I get the impression that this won't get delivered nearly as quickly as fd: passing could be.  How soon do we need image isolation for NFS? Btw, this sounds similar to what Blue Swirl recommended here on v1 of this patch: http://lists.gnu.org/archive/html/qemu-devel/2011-05/msg02187.html

Regards, Corey >> 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. > >> So I'd see that you'd likely end up with the >> qemu-fe security policy being identical to the qemu security policy, > > Then there's no point in doing qemu-fe. qemu-fe should be thought of as > QEMU supplied libvirtd plugin. > >> with the exception that it would be allowed to open files on NFS without >> needing them to be labelled. So I don't really see that all this gives us >> any tangible benefits over just allowing the mgmt app to pass in the FDs >> directly. >> >>> But libvirt would still need to parse image files. >> >> Not neccessarily. As mentioned below, it is entirely possible to >> enable the mgmt app to pass in details of the backing files, at >> which point no image parsing is required by libvirt. Hence my >> assertion that the question of who does image parsing is irrelevant >> to this discussion. > > That's certainly true. > > Regards, > > Anthony Liguori