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
16 struct landlock_object;
17
18 /**
19 * struct landlock_object_underops - Operations on an underlying object
20 */
21 struct 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 */
39 struct 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
79 struct landlock_object *
80 landlock_create_object(const struct landlock_object_underops *const underops,
81 void *const underobj);
82
83 void landlock_put_object(struct landlock_object *const object);
84
85 static 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
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