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

[Casey Schaufler]

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. 

>
> 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 }
>    };
>