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

[Casey Schaufler]

On 10/20/2023 8:58 AM, Maxime Coquelin 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.

Why do you think that there needs to be a special LSM check for virtio
devices? What can't existing device attributes be used?

>
> Signed-off-by: Maxime Coquelin <maxime.coquelin@xxxxxxxxxx>
> ---
>  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(+)
>
> diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> index 0243dee9cf0e..ca64eac11ddb 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>
> @@ -1443,6 +1444,10 @@ static int vduse_dev_open(struct inode *inode, struct file *file)
>  	if (dev->connected)
>  		goto unlock;
>  
> +	ret = -EPERM;
> +	if (security_vduse_dev_open(dev->device_id))
> +		goto unlock;
> +
>  	ret = 0;
>  	dev->connected = true;
>  	file->private_data = dev;
> @@ -1655,6 +1660,9 @@ static int vduse_destroy_dev(char *name)
>  	if (!dev)
>  		return -EINVAL;
>  
> +	if (security_vduse_dev_destroy(dev->device_id))
> +		return -EPERM;
> +
>  	mutex_lock(&dev->lock);
>  	if (dev->vdev || dev->connected) {
>  		mutex_unlock(&dev->lock);
> @@ -1819,6 +1827,10 @@ static int vduse_create_dev(struct vduse_dev_config *config,
>  	int ret;
>  	struct vduse_dev *dev;
>  
> +	ret = -EPERM;
> +	if (security_vduse_dev_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 ac962c4cb44b..0b3999ab3264 100644
> --- a/include/linux/lsm_hook_defs.h
> +++ b/include/linux/lsm_hook_defs.h
> @@ -419,3 +419,7 @@ 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_dev_create, u32 device_id)
> +LSM_HOOK(int, 0, vduse_dev_destroy, u32 device_id)
> +LSM_HOOK(int, 0, vduse_dev_open, u32 device_id)
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 5f16eecde00b..a650c500f841 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -484,6 +484,9 @@ 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_dev_create(u32 device_id);
> +int security_vduse_dev_destroy(u32 device_id);
> +int security_vduse_dev_open(u32 device_id);
>  #else /* CONFIG_SECURITY */
>  
>  static inline int call_blocking_lsm_notifier(enum lsm_event event, void *data)
> @@ -1395,6 +1398,18 @@ static inline int security_locked_down(enum lockdown_reason what)
>  {
>  	return 0;
>  }
> +static inline int security_vduse_dev_create(u32 device_id)
> +{
> +	return 0;
> +}
> +static inline int security_vduse_dev_destroy(u32 device_id)
> +{
> +	return 0;
> +}
> +static inline int security_vduse_dev_open(u32 device_id)
> +{
> +	return 0;
> +}
>  #endif	/* CONFIG_SECURITY */
>  
>  #if defined(CONFIG_SECURITY) && defined(CONFIG_WATCH_QUEUE)
> diff --git a/security/security.c b/security/security.c
> index 23b129d482a7..8d7d4d2eca0b 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -5337,3 +5337,45 @@ int security_uring_cmd(struct io_uring_cmd *ioucmd)
>  	return call_int_hook(uring_cmd, 0, ioucmd);
>  }
>  #endif /* CONFIG_IO_URING */
> +
> +/**
> + * security_vduse_dev_create() - Check if a VDUSE device type creation is allowed
> + * @device_id: the Virtio device ID
> + *
> + * Check whether the Virtio device creation is allowed
> + *
> + * Return: Returns 0 if permission is granted.
> + */
> +int security_vduse_dev_create(u32 device_id)
> +{
> +	return call_int_hook(vduse_dev_create, 0, device_id);
> +}
> +EXPORT_SYMBOL(security_vduse_dev_create);
> +
> +/**
> + * security_vduse_dev_destroy() - Check if a VDUSE device type destruction is allowed
> + * @device_id: the Virtio device ID
> + *
> + * Check whether the Virtio device destruction is allowed
> + *
> + * Return: Returns 0 if permission is granted.
> + */
> +int security_vduse_dev_destroy(u32 device_id)
> +{
> +	return call_int_hook(vduse_dev_destroy, 0, device_id);
> +}
> +EXPORT_SYMBOL(security_vduse_dev_destroy);
> +
> +/**
> + * security_vduse_dev_open() - Check if a VDUSE device type opening is allowed
> + * @device_id: the Virtio device ID
> + *
> + * Check whether the Virtio device opening is allowed
> + *
> + * Return: Returns 0 if permission is granted.
> + */
> +int security_vduse_dev_open(u32 device_id)
> +{
> +	return call_int_hook(vduse_dev_open, 0, device_id);
> +}
> +EXPORT_SYMBOL(security_vduse_dev_open);
> 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);
> +}
> +
> +static int selinux_vduse_dev_destroy(u32 device_id)
> +{
> +	u32 sid = current_sid();
> +	int ret;
> +
> +	ret = avc_has_perm(sid, sid, SECCLASS_VDUSE, VDUSE__DEVDESTROY, NULL);
> +	if (ret)
> +		return ret;
> +
> +	return vduse_check_device_type(sid, device_id);
> +}
> +
> +static int selinux_vduse_dev_open(u32 device_id)
> +{
> +	u32 sid = current_sid();
> +	int ret;
> +
> +	ret = avc_has_perm(sid, sid, SECCLASS_VDUSE, VDUSE__DEVOPEN, NULL);
> +	if (ret)
> +		return ret;
> +
> +	return vduse_check_device_type(sid, device_id);
> +}
> +
>  /*
>   * 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 +7295,9 @@ 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_dev_create, selinux_vduse_dev_create),
> +	LSM_HOOK_INIT(vduse_dev_destroy, selinux_vduse_dev_destroy),
> +	LSM_HOOK_INIT(vduse_dev_open, selinux_vduse_dev_open),
>  };
>  
>  static __init int selinux_init(void)
> diff --git a/security/selinux/include/classmap.h b/security/selinux/include/classmap.h
> index a3c380775d41..d3dc37fb03d4 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",
> +	  { "devcreate", "devdestroy", "devopen", "net", "block", NULL} },
>  	{ NULL }
>    };
>