xref: /openbmc/linux/security/landlock/object.h (revision 695c7c06)
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 
landlock_get_object(struct landlock_object * const object)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