Re: [PATCH v5 4/4] vduse: Add LSM hook to check Virtio device type

From: Casey Schaufler
Date: Tue Dec 12 2023 - 17:55:44 EST

On 12/12/2023 9:59 AM, Michael S. Tsirkin wrote:
> On Tue, Dec 12, 2023 at 08:33:39AM -0800, Casey Schaufler wrote:
>> On 12/12/2023 5:17 AM, Maxime Coquelin wrote:
>>> This patch introduces a LSM hook for devices creation,
>>> destruction (ioctl()) and opening (open()) operations,
>>> checking the application is allowed to perform these
>>> operations for the Virtio device type.
>> My earlier comments on a vduse specific LSM hook still hold.
>> I would much prefer to see a device permissions hook(s) that
>> are useful for devices in general. Not just vduse devices.
>> I know that there are already some very special purpose LSM
>> hooks, but the experience with maintaining them is why I don't
>> want more of them.
> What exactly does this mean?

You have proposed an LSM hook that is only useful for vduse.
You want to implement a set of controls that only apply to vduse.
I can't help but think that if someone (i.e. you) wants to control
device creation for vduse that there could well be a use case for
control over device creation for some other set of devices. It is
quite possible that someone out there is desperately trying to
solve the same problem you have, but with a different device.

I have no desire to have to deal with
security_vduse_perm_check()
security_odddev_perm_check()
...
security_evendev_perm_check()

when we should be able to have
security_device_perm_check()

that can service them all.


> Devices like tap etc? How do we
> find them all though?

I'm not suggesting you find them all. I'm suggesting that you provide
an interface that someone could use if they wanted to. I think you
will be surprised how many will appear (with complaints about the
interface you propose, of course) if you implement a generally useful
LSM hook.

>
>>> Signed-off-by: Maxime Coquelin <maxime.coquelin@xxxxxxxxxx>
>>> ---
>>> MAINTAINERS | 1 +
>>> drivers/vdpa/vdpa_user/vduse_dev.c | 13 ++++++++++++
>>> include/linux/lsm_hook_defs.h | 2 ++
>>> include/linux/security.h | 6 ++++++
>>> include/linux/vduse.h | 14 +++++++++++++
>>> security/security.c | 15 ++++++++++++++
>>> security/selinux/hooks.c | 32 +++++++++++++++++++++++++++++
>>> security/selinux/include/classmap.h | 2 ++
>>> 8 files changed, 85 insertions(+)
>>> create mode 100644 include/linux/vduse.h
>>>
>>> diff --git a/MAINTAINERS b/MAINTAINERS
>>> index a0fb0df07b43..4e83b14358d2 100644
>>> --- a/MAINTAINERS
>>> +++ b/MAINTAINERS
>>> @@ -23040,6 +23040,7 @@ F: drivers/net/virtio_net.c
>>> F: drivers/vdpa/
>>> F: drivers/virtio/
>>> F: include/linux/vdpa.h
>>> +F: include/linux/vduse.h
>>> F: include/linux/virtio*.h
>>> F: include/linux/vringh.h
>>> F: include/uapi/linux/virtio_*.h
>>> diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
>>> index fa62825be378..59ab7eb62e20 100644
>>> --- a/drivers/vdpa/vdpa_user/vduse_dev.c
>>> +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
>>> @@ -8,6 +8,7 @@
>>> *
>>> */
>>>
>>> +#include "linux/security.h"
>>> #include <linux/init.h>
>>> #include <linux/module.h>
>>> #include <linux/cdev.h>
>>> @@ -30,6 +31,7 @@
>>> #include <uapi/linux/virtio_blk.h>
>>> #include <uapi/linux/virtio_ring.h>
>>> #include <linux/mod_devicetable.h>
>>> +#include <linux/vduse.h>
>>>
>>> #include "iova_domain.h"
>>>
>>> @@ -1442,6 +1444,10 @@ static int vduse_dev_open(struct inode *inode, struct file *file)
>>> if (dev->connected)
>>> goto unlock;
>>>
>>> + ret = -EPERM;
>>> + if (security_vduse_perm_check(VDUSE_PERM_OPEN, dev->device_id))
>>> + goto unlock;
>>> +
>>> ret = 0;
>>> dev->connected = true;
>>> file->private_data = dev;
>>> @@ -1664,6 +1670,9 @@ static int vduse_destroy_dev(char *name)
>>> if (!dev)
>>> return -EINVAL;
>>>
>>> + if (security_vduse_perm_check(VDUSE_PERM_DESTROY, dev->device_id))
>>> + return -EPERM;
>>> +
>>> mutex_lock(&dev->lock);
>>> if (dev->vdev || dev->connected) {
>>> mutex_unlock(&dev->lock);
>>> @@ -1828,6 +1837,10 @@ static int vduse_create_dev(struct vduse_dev_config *config,
>>> int ret;
>>> struct vduse_dev *dev;
>>>
>>> + ret = -EPERM;
>>> + if (security_vduse_perm_check(VDUSE_PERM_CREATE, config->device_id))
>>> + goto err;
>>> +
>>> ret = -EEXIST;
>>> if (vduse_find_dev(config->name))
>>> goto err;
>>> diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
>>> index ff217a5ce552..3930ab2ae974 100644
>>> --- a/include/linux/lsm_hook_defs.h
>>> +++ b/include/linux/lsm_hook_defs.h
>>> @@ -419,3 +419,5 @@ LSM_HOOK(int, 0, uring_override_creds, const struct cred *new)
>>> LSM_HOOK(int, 0, uring_sqpoll, void)
>>> LSM_HOOK(int, 0, uring_cmd, struct io_uring_cmd *ioucmd)
>>> #endif /* CONFIG_IO_URING */
>>> +
>>> +LSM_HOOK(int, 0, vduse_perm_check, enum vduse_op_perm op_perm, u32 device_id)
>>> diff --git a/include/linux/security.h b/include/linux/security.h
>>> index 1d1df326c881..2a2054172394 100644
>>> --- a/include/linux/security.h
>>> +++ b/include/linux/security.h
>>> @@ -32,6 +32,7 @@
>>> #include <linux/string.h>
>>> #include <linux/mm.h>
>>> #include <linux/sockptr.h>
>>> +#include <linux/vduse.h>
>>>
>>> struct linux_binprm;
>>> struct cred;
>>> @@ -484,6 +485,7 @@ int security_inode_notifysecctx(struct inode *inode, void *ctx, u32 ctxlen);
>>> int security_inode_setsecctx(struct dentry *dentry, void *ctx, u32 ctxlen);
>>> int security_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen);
>>> int security_locked_down(enum lockdown_reason what);
>>> +int security_vduse_perm_check(enum vduse_op_perm op_perm, u32 device_id);
>>> #else /* CONFIG_SECURITY */
>>>
>>> static inline int call_blocking_lsm_notifier(enum lsm_event event, void *data)
>>> @@ -1395,6 +1397,10 @@ static inline int security_locked_down(enum lockdown_reason what)
>>> {
>>> return 0;
>>> }
>>> +static inline int security_vduse_perm_check(enum vduse_op_perm op_perm, u32 device_id)
>>> +{
>>> + return 0;
>>> +}
>>> #endif /* CONFIG_SECURITY */
>>>
>>> #if defined(CONFIG_SECURITY) && defined(CONFIG_WATCH_QUEUE)
>>> diff --git a/include/linux/vduse.h b/include/linux/vduse.h
>>> new file mode 100644
>>> index 000000000000..7a20dcc43997
>>> --- /dev/null
>>> +++ b/include/linux/vduse.h
>>> @@ -0,0 +1,14 @@
>>> +/* SPDX-License-Identifier: GPL-2.0 */
>>> +#ifndef _LINUX_VDUSE_H
>>> +#define _LINUX_VDUSE_H
>>> +
>>> +/*
>>> + * The permission required for a VDUSE device operation.
>>> + */
>>> +enum vduse_op_perm {
>>> + VDUSE_PERM_CREATE,
>>> + VDUSE_PERM_DESTROY,
>>> + VDUSE_PERM_OPEN,
>>> +};
>>> +
>>> +#endif /* _LINUX_VDUSE_H */
>>> diff --git a/security/security.c b/security/security.c
>>> index dcb3e7014f9b..150abf85f97d 100644
>>> --- a/security/security.c
>>> +++ b/security/security.c
>>> @@ -5337,3 +5337,18 @@ int security_uring_cmd(struct io_uring_cmd *ioucmd)
>>> return call_int_hook(uring_cmd, 0, ioucmd);
>>> }
>>> #endif /* CONFIG_IO_URING */
>>> +
>>> +/**
>>> + * security_vduse_perm_check() - Check if a VDUSE device type operation is allowed
>>> + * @op_perm: the operation type
>>> + * @device_id: the Virtio device ID
>>> + *
>>> + * Check whether the Virtio device creation is allowed
>>> + *
>>> + * Return: Returns 0 if permission is granted.
>>> + */
>>> +int security_vduse_perm_check(enum vduse_op_perm op_perm, u32 device_id)
>>> +{
>>> + return call_int_hook(vduse_perm_check, 0, op_perm, device_id);
>>> +}
>>> +EXPORT_SYMBOL(security_vduse_perm_check);
>>> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
>>> index feda711c6b7b..18845e4f682f 100644
>>> --- a/security/selinux/hooks.c
>>> +++ b/security/selinux/hooks.c
>>> @@ -21,6 +21,8 @@
>>> * Copyright (C) 2016 Mellanox Technologies
>>> */
>>>
>>> +#include "av_permissions.h"
>>> +#include "linux/vduse.h"
>>> #include <linux/init.h>
>>> #include <linux/kd.h>
>>> #include <linux/kernel.h>
>>> @@ -92,6 +94,7 @@
>>> #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 +6953,34 @@ static int selinux_uring_cmd(struct io_uring_cmd *ioucmd)
>>> }
>>> #endif /* CONFIG_IO_URING */
>>>
>>> +static int selinux_vduse_perm_check(enum vduse_op_perm op_perm, u32 device_id)
>>> +{
>>> + u32 requested_op, requested_type, sid = current_sid();
>>> + int ret;
>>> +
>>> + if (op_perm == VDUSE_PERM_CREATE)
>>> + requested_op = VDUSE__CREATE;
>>> + else if (op_perm == VDUSE__DESTROY)
>>> + requested_op = VDUSE__DESTROY;
>>> + else if (op_perm == VDUSE_PERM_OPEN)
>>> + requested_op = VDUSE__OPEN;
>>> + else
>>> + return -EINVAL;
>>> +
>>> + ret = avc_has_perm(sid, sid, SECCLASS_VDUSE, requested_op, NULL);
>>> + if (ret)
>>> + return ret;
>>> +
>>> + if (device_id == VIRTIO_ID_NET)
>>> + requested_type = VDUSE__NET;
>>> + else if (device_id == VIRTIO_ID_BLOCK)
>>> + requested_type = VDUSE__BLOCK;
>>> + else
>>> + return -EINVAL;
>>> +
>>> + return avc_has_perm(sid, sid, SECCLASS_VDUSE, requested_type, NULL);
>>> +}
>>> +
>>> /*
>>> * IMPORTANT NOTE: When adding new hooks, please be careful to keep this order:
>>> * 1. any hooks that don't belong to (2.) or (3.) below,
>>> @@ -7243,6 +7274,7 @@ static struct security_hook_list selinux_hooks[] __ro_after_init = {
>>> #ifdef CONFIG_PERF_EVENTS
>>> LSM_HOOK_INIT(perf_event_alloc, selinux_perf_event_alloc),
>>> #endif
>>> + LSM_HOOK_INIT(vduse_perm_check, selinux_vduse_perm_check),
>>> };
>>>
>>> static __init int selinux_init(void)
>>> diff --git a/security/selinux/include/classmap.h b/security/selinux/include/classmap.h
>>> index a3c380775d41..b0a358cbac1c 100644
>>> --- a/security/selinux/include/classmap.h
>>> +++ b/security/selinux/include/classmap.h
>>> @@ -256,6 +256,8 @@ const struct security_class_mapping secclass_map[] = {
>>> { "override_creds", "sqpoll", "cmd", NULL } },
>>> { "user_namespace",
>>> { "create", NULL } },
>>> + { "vduse",
>>> + { "create", "destroy", "open", "net", "block", NULL} },
>>> { NULL }
>>> };
>>>
>