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

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Date:   Fri, 8 Dec 2023 13:23:00 +0100
From:   Maxime Coquelin <maxime.coquelin@...hat.com>
To:     "Michael S. Tsirkin" <mst@...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 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