Re: [RFC PATCH 2/2] tun: fix LSM/SELinux labeling of tun/tap devices

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Dec 05, 2012 at 02:19:22PM +0800, Jason Wang wrote:
> On 12/05/2012 02:17 AM, Paul Moore wrote:
> > On Tuesday, December 04, 2012 07:36:26 PM Michael S. Tsirkin wrote:
> >> On Tue, Dec 04, 2012 at 11:18:57AM -0500, Paul Moore wrote:
> >>> Okay, based on your explanation of TUNSETQUEUE, the steps below are what I
> >>> believe we need to do ... if you disagree speak up quickly please.
> >>>
> >>> A. TUNSETIFF (new, non-persistent device)
> >>>
> >>> [Allocate and initialize the tun_struct LSM state based on the calling
> >>> process, use this state to label the TUN socket.]
> >>>
> >>> 1. Call security_tun_dev_create() which authorizes the action.
> >>> 2. Call security_tun_dev_alloc_security() which allocates the tun_struct
> >>> LSM blob and SELinux sets some internal blob state to record the label of
> >>> the calling process.
> >>> 3. Call security_tun_dev_attach() which sets the label of the TUN socket
> >>> to match the label stored in the tun_struct LSM blob during A2.  No
> >>> authorization is done at this point since the socket is new/unlabeled.
> >>>
> >>> B. TUNSETIFF (existing, persistent device)
> >>>
> >>> [Relabel the existing tun_struct LSM state based on the calling process,
> >>> use this state to label the TUN socket.]
> >>>
> >>> 1. Attempt to relabel/reset the tun_struct LSM blob from the currently
> >>> stored value, set during A2, to the label of the current calling process.
> >>> *** THIS IS NOT CURRENTLY DONE IN THE RFC PATCH ***
> >>> 2. Call security_tun_dev_attach() which sets the label of the TUN socket
> >>> to match the label stored in the tun_struct LSM blob during B1. No
> >>> authorization is done at this point since the socket is new/unlabeled.
> >>>
> >>> C. TUNSETQUEUE
> >>>
> >>> [Use the existing tun_struct LSM state to label the new TUN socket.]
> >>>
> >>> 1. Call security_tun_dev_attach() which sets the label of the TUN socket
> >>> to match the label stored in the tun_struct LSM blob set during either A2
> >>> or B1. No authorization is done at this point since the socket is
> >>> new/unlabeled.
> >> Here's what bothers me. libvirt currently opens tun and passes
> >> fd to qemu. What would prevent qemu from attaching fd using TUNSETQUEUE
> >> to another device it does not own?
> > True, assuming all the above is correct and that I'm understanding it 
> > correctly (Jason?), we should probably add a new SELinux access control for 
> > TUNSETQUEUE.
> 
> Yes, we need make sure qemu can call TUNSETQUEUE for the device it does
> not own.

Meaning can *not* call?

> >
> > The current DAC code exists in tun_not_capable().
> >