On Monday, December 10, 2012 07:26:56 PM Michael S. Tsirkin wrote: > On Mon, Dec 10, 2012 at 12:04:35PM -0500, Paul Moore wrote: > > On Friday, December 07, 2012 02:25:16 PM Michael S. Tsirkin wrote: > > > On Thu, Dec 06, 2012 at 04:09:51PM -0500, Paul Moore wrote: > > > > On Thursday, December 06, 2012 10:57:16 PM Michael S. Tsirkin wrote: > > > > > On Thu, Dec 06, 2012 at 11:56:45AM -0500, Paul Moore wrote: > > > > > > The SETQUEUE/tun_socket:create_queue permissions do not yet exist > > > > > > in any released SELinux policy as we are just now adding them with > > > > > > this patchset. With current policies loaded into a kernel with > > > > > > this patchset applied the SETQUEUE/tun_socket:create_queue > > > > > > permission would be treated according to the policy's unknown > > > > > > permission setting. > > > > > > > > > > OK I think we need to rethink what we are doing here: what you sent > > > > > addresses the problem as stated but I think we mis-stated it. Let > > > > > me try to restate the problem: it is not just selinux problem. Let's > > > > > assume qemu wants to use tun, I (libvirt) don't want to run it as > > > > > root. > > > > > > > > > > 1. TUNSETIFF: I can open tun, attach an fd and pass it to qemu. > > > > > Now, qemu does not invoke TUNSETIFF so it can run without > > > > > kernel priveledges. > > > > > > > > Correct me if I'm wrong, but I believe libvirt does this while running > > > > as root. Assuming that is the case, why not simply setuid()/setgid() > > > > to the same credentials as the QEMU instance before creating the TUN > > > > device? You can always (re)configure the device afterwards while > > > > running as root/CAP_NET_ADMIN. > > > > > > We want isolation between qemu instances. > > > > Understood, I agree. > > > > Achieving separation via SELinux is easily done, with libvirt/sVirt > > already doing this for us automatically in most cases; the only thing we > > will want to do is make sure the SELinux policy is aware of the new > > permission. > > > > Achieving separation via DAC should also be easily done, simply run each > > QEMU instance with a separate UID and/or GID. > > > > > Giving qemu right to open tun and SETIFF would give it rights > > > to access any tun device. > > > > I'm quickly looked at tun_chr_open() again and I don't see any special > > rights/privileges required, the same for tun_chr_ioctl() and > > __tun_chr_ioctl(). Looking at tun_set_queue() I see we call > > tun_not_capable() which does a simple DAC check; it must have the same > > UID/GID or have CAP_NET_ADMIN. > > > > I'm having a hard time seeing the problem you are describing; help me > > understand. > > The issue is guest controls the number of queues in use. > So qemu would be required to be allowed to call tun_set_queue. > If we allow this we have a problem as one qemu will be > able to access any tun. QEMU can call tun_set_queue() as long as it satisfies tun_not_capable(), which from a practical point of view means that the TUN device was created with the same UID/GID as the QEMU instance. If you want TUN device separation between QEMU instances using DAC you need to run each QEMU instance with a different UID/GID (which you should be doing anyway if you want DAC enforced general separation). I believe I've stated this point several times now and I don't feel you've addressed it properly. -- paul moore security and virtualization @ redhat -- This message was distributed to subscribers of the selinux mailing list. If you no longer wish to subscribe, send mail to majordomo@xxxxxxxxxxxxx with the words "unsubscribe selinux" without quotes as the message.
