LXR linux/security/landlock/object.h

   1/* SPDX-License-Identifier: GPL-2.0-only */
   2/*
   3 * Landlock LSM - Object management
   4 *
   5 * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
   6 * Copyright © 2018-2020 ANSSI
   7 */
   8
   9#ifndef _SECURITY_LANDLOCK_OBJECT_H
  10#define _SECURITY_LANDLOCK_OBJECT_H
  11
  12#include <linux/compiler_types.h>
  13#include <linux/refcount.h>
  14#include <linux/spinlock.h>
  15
  16struct landlock_object;
  17
  18/**
  19 * struct landlock_object_underops - Operations on an underlying object
  20 */
  21struct landlock_object_underops {
  22        /**
  23         * @release: Releases the underlying object (e.g. iput() for an inode).
  24         */
  25        void (*release)(struct landlock_object *const object)
  26                __releases(object->lock);
  27};
  28
  29/**
  30 * struct landlock_object - Security blob tied to a kernel object
  31 *
  32 * The goal of this structure is to enable to tie a set of ephemeral access
  33 * rights (pertaining to different domains) to a kernel object (e.g an inode)
  34 * in a safe way.  This implies to handle concurrent use and modification.
  35 *
  36 * The lifetime of a &struct landlock_object depends on the rules referring to
  37 * it.
  38 */
  39struct landlock_object {
  40        /**
  41         * @usage: This counter is used to tie an object to the rules matching
  42         * it or to keep it alive while adding a new rule.  If this counter
  43         * reaches zero, this struct must not be modified, but this counter can
  44         * still be read from within an RCU read-side critical section.  When
  45         * adding a new rule to an object with a usage counter of zero, we must
  46         * wait until the pointer to this object is set to NULL (or recycled).
  47         */
  48        refcount_t usage;
  49        /**
  50         * @lock: Protects against concurrent modifications.  This lock must be
  51         * held from the time @usage drops to zero until any weak references
  52         * from @underobj to this object have been cleaned up.
  53         *
  54         * Lock ordering: inode->i_lock nests inside this.
  55         */
  56        spinlock_t lock;
  57        /**
  58         * @underobj: Used when cleaning up an object and to mark an object as
  59         * tied to its underlying kernel structure.  This pointer is protected
  60         * by @lock.  Cf. landlock_release_inodes() and release_inode().
  61         */
  62        void *underobj;
  63        union {
  64                /**
  65                 * @rcu_free: Enables lockless use of @usage, @lock and
  66                 * @underobj from within an RCU read-side critical section.
  67                 * @rcu_free and @underops are only used by
  68                 * landlock_put_object().
  69                 */
  70                struct rcu_head rcu_free;
  71                /**
  72                 * @underops: Enables landlock_put_object() to release the
  73                 * underlying object (e.g. inode).
  74                 */
  75                const struct landlock_object_underops *underops;
  76        };
  77};
  78
  79struct landlock_object *landlock_create_object(
  80                const struct landlock_object_underops *const underops,
  81                void *const underobj);
  82
  83void landlock_put_object(struct landlock_object *const object);
  84
  85static inline void landlock_get_object(struct landlock_object *const object)
  86{
  87        if (object)
  88                refcount_inc(&object->usage);
  89}
  90
  91#endif /* _SECURITY_LANDLOCK_OBJECT_H */
  92