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 *
landlock_create_object(const struct landlock_object_underops * const underops,void * const underobj)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  */
landlock_put_object(struct landlock_object * const object)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