security/landlock/object.c

   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(
  21                 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 }