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 #include <linux/bug.h>
10 #include <linux/compiler_types.h>
11 #include <linux/err.h>
12 #include <linux/kernel.h>
13 #include <linux/rcupdate.h>
14 #include <linux/refcount.h>
15 #include <linux/slab.h>
16 #include <linux/spinlock.h>
17
18 #include "object.h"
19
20 struct landlock_object *
21 landlock_create_object(const struct landlock_object_underops *const underops,
22 void *const underobj)
23 {
24 struct landlock_object *new_object;
25
26 if (WARN_ON_ONCE(!underops || !underobj))
27 return ERR_PTR(-ENOENT);
28 new_object = kzalloc(sizeof(*new_object), GFP_KERNEL_ACCOUNT);
29 if (!new_object)
30 return ERR_PTR(-ENOMEM);
31 refcount_set(&new_object->usage, 1);
32 spin_lock_init(&new_object->lock);
33 new_object->underops = underops;
34 new_object->underobj = underobj;
35 return new_object;
36 }
37
38 /*
39 * The caller must own the object (i.e. thanks to object->usage) to safely put
40 * it.
41 */
42 void landlock_put_object(struct landlock_object *const object)
43 {
44 /*
45 * The call to @object->underops->release(object) might sleep, e.g.
46 * because of iput().
47 */
48 might_sleep();
49 if (!object)
50 return;
51
52 /*
53 * If the @object's refcount cannot drop to zero, we can just decrement
54 * the refcount without holding a lock. Otherwise, the decrement must
55 * happen under @object->lock for synchronization with things like
56 * get_inode_object().
57 */
58 if (refcount_dec_and_lock(&object->usage, &object->lock)) {
59 __acquire(&object->lock);
60 /*
61 * With @object->lock initially held, remove the reference from
62 * @object->underobj to @object (if it still exists).
63 */
64 object->underops->release(object);
65 kfree_rcu(object, rcu_free);
66 }
67 }
68
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