[PATCH 5.8 219/464] kobject: Avoid premature parent object freeing in kobject_cleanup()

From: Greg Kroah-Hartman
Date: Mon Aug 17 2020 - 11:32:31 EST


From: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>

[ Upstream commit 079ad2fb4bf9eba8a0aaab014b49705cd7f07c66 ]

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@xxxxxxxxxx>
Reported-by: kernel test robot <rong.a.chen@xxxxxxxxx>
Fixes: 7589238a8cf3 ("Revert "software node: Simplify software_node_release() function"")
Suggested-by: Rafael J. Wysocki <rafael@xxxxxxxxxx>
Signed-off-by: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Link: https://lore.kernel.org/r/1908555.IiAGLGrh1Z@kreacher
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
lib/kobject.c | 33 +++++++++++++++++++++++----------
1 file changed, 23 insertions(+), 10 deletions(-)

diff --git a/lib/kobject.c b/lib/kobject.c
index 1e4b7382a88ed..3afb939f2a1cc 100644
--- a/lib/kobject.c
+++ b/lib/kobject.c
@@ -599,14 +599,7 @@ int kobject_move(struct kobject *kobj, struct kobject *new_parent)
}
EXPORT_SYMBOL_GPL(kobject_move);

-/**
- * 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)
+static void __kobject_del(struct kobject *kobj)
{
struct kernfs_node *sd;
const struct kobj_type *ktype;
@@ -632,9 +625,23 @@ void kobject_del(struct kobject *kobj)

kobj->state_in_sysfs = 0;
kobj_kset_leave(kobj);
- kobject_put(kobj->parent);
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);

/**
@@ -670,6 +677,7 @@ EXPORT_SYMBOL(kobject_get_unless_zero);
*/
static void kobject_cleanup(struct kobject *kobj)
{
+ struct kobject *parent = kobj->parent;
struct kobj_type *t = get_ktype(kobj);
const char *name = kobj->name;

@@ -684,7 +692,10 @@ static void kobject_cleanup(struct kobject *kobj)
if (kobj->state_in_sysfs) {
pr_debug("kobject: '%s' (%p): auto cleanup kobject_del\n",
kobject_name(kobj), kobj);
- kobject_del(kobj);
+ __kobject_del(kobj);
+ } else {
+ /* avoid dropping the parent reference unnecessarily */
+ parent = NULL;
}

if (t && t->release) {
@@ -698,6 +709,8 @@ static void kobject_cleanup(struct kobject *kobj)
pr_debug("kobject: '%s': free name\n", name);
kfree_const(name);
}
+
+ kobject_put(parent);
}

#ifdef CONFIG_DEBUG_KOBJECT_RELEASE
--
2.25.1