From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paul Moore Subject: Re: [RFC PATCH v2 3/3] tun: fix LSM/SELinux labeling of tun/tap devices Date: Thu, 06 Dec 2012 10:46:11 -0500 Message-ID: <7448004.siKCIqQqTi@sifl> References: <20121205202144.18626.61966.stgit@localhost> <20121205202619.18626.98778.stgit@localhost> <20121206103325.GG10837@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Cc: netdev@vger.kernel.org, linux-security-module@vger.kernel.org, selinux@tycho.nsa.gov, jasowang@redhat.com To: "Michael S. Tsirkin" Return-path: In-Reply-To: <20121206103325.GG10837@redhat.com> Sender: linux-security-module-owner@vger.kernel.org List-Id: netdev.vger.kernel.org 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 > > 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