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

From: Michael S. Tsirkin
Date: Tue Dec 12 2023 - 13:00:16 EST

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

> >
> > 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 }
> > };
> >