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kobject: Avoid premature parent object freeing in kobject_cleanup() 

If kobject_del() is invoked by kobject_cleanup() to delete the
target kobject, it may cause its parent kobject to be freed
before invoking the target kobject's ->release() method, which
effectively means freeing the parent before dealing with the
child entirely.

That is confusing at best and it may also lead to functional
issues if the callers of kobject_cleanup() are not careful enough
about the order in which these calls are made, so avoid the
problem by making kobject_cleanup() drop the last reference to
the target kobject's parent at the end, after invoking the target
kobject's ->release() method.

[ rjw: Rewrite the subject and changelog, make kobject_cleanup()
  drop the parent reference only when __kobject_del() has been
  called. ]

Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Reported-by: kernel test robot <rong.a.chen@intel.com>
Fixes: 7589238a8c ("Revert "software node: Simplify software_node_release() function"")
Suggested-by: Rafael J. Wysocki <rafael@kernel.org>
Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lore.kernel.org/r/1908555.IiAGLGrh1Z@kreacher
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Heikki Krogerus 2020-06-04 19:46:46 +02:00 committed by Greg Kroah-Hartman
parent e5711945c6
commit 079ad2fb4b
1 changed files with 23 additions and 10 deletions
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33
lib/kobject.c
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@ -599,14 +599,7 @@ int kobject_move(struct kobject *kobj, struct kobject *new_parent)
} }
EXPORT_SYMBOL_GPL(kobject_move); EXPORT_SYMBOL_GPL(kobject_move);
/** static void __kobject_del(struct kobject *kobj)
* kobject_del() - Unlink kobject from hierarchy.
* @kobj: object.
*
* This is the function that should be called to delete an object
* successfully added via kobject_add().
*/
void kobject_del(struct kobject *kobj)
{ {
struct kernfs_node *sd; struct kernfs_node *sd;
const struct kobj_type *ktype; const struct kobj_type *ktype;
@ -632,9 +625,23 @@ void kobject_del(struct kobject *kobj)
kobj->state_in_sysfs = 0; kobj->state_in_sysfs = 0;
kobj_kset_leave(kobj); kobj_kset_leave(kobj);
kobject_put(kobj->parent);
kobj->parent = NULL; kobj->parent = NULL;
} }
/**
* kobject_del() - Unlink kobject from hierarchy.
* @kobj: object.
*
* This is the function that should be called to delete an object
* successfully added via kobject_add().
*/
void kobject_del(struct kobject *kobj)
{
struct kobject *parent = kobj->parent;
__kobject_del(kobj);
kobject_put(parent);
}
EXPORT_SYMBOL(kobject_del); EXPORT_SYMBOL(kobject_del);
/** /**
@ -670,6 +677,7 @@ EXPORT_SYMBOL(kobject_get_unless_zero);
*/ */
static void kobject_cleanup(struct kobject *kobj) static void kobject_cleanup(struct kobject *kobj)
{ {
struct kobject *parent = kobj->parent;
struct kobj_type *t = get_ktype(kobj); struct kobj_type *t = get_ktype(kobj);
const char *name = kobj->name; const char *name = kobj->name;
@ -684,7 +692,10 @@ static void kobject_cleanup(struct kobject *kobj)
if (kobj->state_in_sysfs) { if (kobj->state_in_sysfs) {
pr_debug("kobject: '%s' (%p): auto cleanup kobject_del\n", pr_debug("kobject: '%s' (%p): auto cleanup kobject_del\n",
kobject_name(kobj), kobj); kobject_name(kobj), kobj);
kobject_del(kobj); __kobject_del(kobj);
} else {
/* avoid dropping the parent reference unnecessarily */
parent = NULL;
} }
if (t && t->release) { if (t && t->release) {
@ -698,6 +709,8 @@ static void kobject_cleanup(struct kobject *kobj)
pr_debug("kobject: '%s': free name\n", name); pr_debug("kobject: '%s': free name\n", name);
kfree_const(name); kfree_const(name);
} }
kobject_put(parent);
} }
#ifdef CONFIG_DEBUG_KOBJECT_RELEASE #ifdef CONFIG_DEBUG_KOBJECT_RELEASE