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: 7589238a8cf3 ("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>

diff --git a/lib/kobject.c b/lib/kobject.c
index 1e4b738..3afb939 100644 (file)
--- a/lib/kobject.c
+++ b/lib/kobject.c
@@ -599,14 +599,7 @@ out:
 }
 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