linux-kernel - Re: [PATCH v4 4/4] vduse: Add LSM hooks to check Virtio device type

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Message-ID: <20231208072649-mutt-send-email-mst@kernel.org>
Date:   Fri, 8 Dec 2023 07:26:59 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Maxime Coquelin <maxime.coquelin@...hat.com>
Cc:     Paul Moore <paul@...l-moore.com>,
        Casey Schaufler <casey@...aufler-ca.com>, jasowang@...hat.com,
        xuanzhuo@...ux.alibaba.com, jmorris@...ei.org, serge@...lyn.com,
        stephen.smalley.work@...il.com, eparis@...isplace.org,
        xieyongji@...edance.com, virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org, selinux@...r.kernel.org,
        david.marchand@...hat.com, lulu@...hat.com
Subject: Re: [PATCH v4 4/4] vduse: Add LSM hooks to check Virtio device type

On Fri, Dec 08, 2023 at 01:23:00PM +0100, Maxime Coquelin wrote:
> 
> 
> On 12/8/23 12:05, Michael S. Tsirkin wrote:
> > On Fri, Dec 08, 2023 at 12:01:15PM +0100, Maxime Coquelin wrote:
> > > Hello Paul,
> > > 
> > > On 11/8/23 03:31, Paul Moore wrote:
> > > > On Oct 20, 2023 "Michael S. Tsirkin" <mst@...hat.com> wrote:
> > > > > 
> > > > > This patch introduces LSM hooks for devices creation,
> > > > > destruction and opening operations, checking the
> > > > > application is allowed to perform these operations for
> > > > > the Virtio device type.
> > > > > 
> > > > > Signed-off-by: Maxime Coquelin <maxime.coquelin@...hat.com>
> > > > > ---
> > > > >    drivers/vdpa/vdpa_user/vduse_dev.c  | 12 +++++++
> > > > >    include/linux/lsm_hook_defs.h       |  4 +++
> > > > >    include/linux/security.h            | 15 ++++++++
> > > > >    security/security.c                 | 42 ++++++++++++++++++++++
> > > > >    security/selinux/hooks.c            | 55 +++++++++++++++++++++++++++++
> > > > >    security/selinux/include/classmap.h |  2 ++
> > > > >    6 files changed, 130 insertions(+)
> > > > 
> > > > My apologies for the late reply, I've been trying to work my way through
> > > > the review backlog but it has been taking longer than expected; comments
> > > > below ...
> > > 
> > > No worries, I have also been busy these days.
> > > 
> > > > > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> > > > > index 2aa0e219d721..65d9262a37f7 100644
> > > > > --- a/security/selinux/hooks.c
> > > > > +++ b/security/selinux/hooks.c
> > > > > @@ -21,6 +21,7 @@
> > > > >     *  Copyright (C) 2016 Mellanox Technologies
> > > > >     */
> > > > > +#include "av_permissions.h"
> > > > >    #include <linux/init.h>
> > > > >    #include <linux/kd.h>
> > > > >    #include <linux/kernel.h>
> > > > > @@ -92,6 +93,7 @@
> > > > >    #include <linux/fsnotify.h>
> > > > >    #include <linux/fanotify.h>
> > > > >    #include <linux/io_uring.h>
> > > > > +#include <uapi/linux/virtio_ids.h>
> > > > >    #include "avc.h"
> > > > >    #include "objsec.h"
> > > > > @@ -6950,6 +6952,56 @@ static int selinux_uring_cmd(struct io_uring_cmd *ioucmd)
> > > > >    }
> > > > >    #endif /* CONFIG_IO_URING */
> > > > > +static int vduse_check_device_type(u32 sid, u32 device_id)
> > > > > +{
> > > > > +	u32 requested;
> > > > > +
> > > > > +	if (device_id == VIRTIO_ID_NET)
> > > > > +		requested = VDUSE__NET;
> > > > > +	else if (device_id == VIRTIO_ID_BLOCK)
> > > > > +		requested = VDUSE__BLOCK;
> > > > > +	else
> > > > > +		return -EINVAL;
> > > > > +
> > > > > +	return avc_has_perm(sid, sid, SECCLASS_VDUSE, requested, NULL);
> > > > > +}
> > > > > +
> > > > > +static int selinux_vduse_dev_create(u32 device_id)
> > > > > +{
> > > > > +	u32 sid = current_sid();
> > > > > +	int ret;
> > > > > +
> > > > > +	ret = avc_has_perm(sid, sid, SECCLASS_VDUSE, VDUSE__DEVCREATE, NULL);
> > > > > +	if (ret)
> > > > > +		return ret;
> > > > > +
> > > > > +	return vduse_check_device_type(sid, device_id);
> > > > > +}
> > > > 
> > > > I see there has been some discussion about the need for a dedicated
> > > > create hook as opposed to using the existing ioctl controls.  I think
> > > > one important point that has been missing from the discussion is the
> > > > idea of labeling the newly created device.  Unfortunately prior to a
> > > > few minutes ago I hadn't ever looked at VDUSE so please correct me if
> > > > I get some things wrong :)
> > > > 
> > > >   From what I can see userspace creates a new VDUSE device with
> > > > ioctl(VDUSE_CREATE_DEV), which trigger the creation of a new
> > > > /dev/vduse/XXX device which will be labeled according to the udev
> > > > and SELinux configuration, likely with a generic udev label.  My
> > > > question is if we want to be able to uniquely label each VDUSE
> > > > device based on the process that initiates the device creation
> > > > with the call to ioctl()?  If that is the case, we would need a
> > > > create hook not only to control the creation of the device, but to
> > > > record the triggering process' label in the new device; this label
> > > > would then be used in subsequent VDUSE open and destroy operations.
> > > > The normal device file I/O operations would still be subject to the
> > > > standard SELinux file I/O permissions using the device file label
> > > > assigned by systemd/udev when the device was created.
> > > 
> > > I don't think we need a unique label for VDUSE devices, but maybe
> > > Michael thinks otherwise?
> > 
> > I don't know.
> > All this is consumed by libvirt, you need to ask these guys.
> 
> I think it is not consumed by libvirt, at least not in the usecases I
> have in mind. For networking devices, it will be consumed by OVS.
> 
> Maxime

OK, ovs then :)

-- 
MST