On Thursday, December 06, 2012 12:33:25 PM Michael S. Tsirkin wrote: > On Wed, Dec 05, 2012 at 03:26:19PM -0500, Paul Moore wrote: > > This patch corrects some problems with LSM/SELinux that were introduced > > with the multiqueue patchset. The problem stems from the fact that the > > multiqueue work changed the relationship between the tun device and its > > associated socket; before the socket persisted for the life of the > > device, however after the multiqueue changes the socket only persisted > > for the life of the userspace connection (fd open). For non-persistent > > devices this is not an issue, but for persistent devices this can cause > > the tun device to lose its SELinux label. > > > > We correct this problem by adding an opaque LSM security blob to the > > tun device struct which allows us to have the LSM security state, e.g. > > SELinux labeling information, persist for the lifetime of the tun > > device. In the process we tweak the LSM hooks to work with this new > > approach to TUN device/socket labeling and introduce a new LSM hook, > > security_tun_dev_create_queue(), to approve requests to create a new > > TUN queue via TUNSETQUEUE. > > > > The SELinux code has been adjusted to match the new LSM hooks, the > > other LSMs do not make use of the LSM TUN controls. This patch makes > > use of the recently added "tun_socket:create_queue" permission to > > restrict access to the TUNSETQUEUE operation. On older SELinux > > policies which do not define the "tun_socket:create_queue" permission > > the access control decision for TUNSETQUEUE will be handled according > > to the SELinux policy's unknown permission setting. > > > > Signed-off-by: Paul Moore <pmoore@xxxxxxxxxx> > > OK so just to verify: this can be used to ensure that qemu > process that has the queue fd can only attach it to > a specific device, right? Whenever a new queue is created via TUNSETQUEUE/tun_set_queue() the security_tun_dev_create_queue() LSM hook is called. When SELinux is enabled this hook ends up calling selinux_tun_dev_create_queue() which checks that the calling process (process_t) is allowed to create a new queue on the specified device (tundev_t) . If you are familiar with SELinux security policy, the allow rule would look like this: allow process_t tundev_t:tun_socket create_queue; In practice, if we assume libvirt is creating the TUN device and running with a SELinux label of virtd_t and that QEMU instances are running with a SELinux label of svirt_t then the allow rule would look like this: allow svirt_t virtd_t:tun_socket create_queue; There is also the matter of the MLS/MCS constraints providing additional separation but that is another level of detail which I don't believe is important for our discussion. -- 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.
