[PATCH v3] kset: fix memory leak when kset_register() returns error

[Yang Yingliang]

Inject fault while loading module, kset_register() may fail.
If it fails, the kset.kobj.name allocated by kobject_set_name()
which must be called before a call to kset_register() may be
leaked, since refcount of kobj was set in kset_init().

To mitigate this, we free the name in kset_register() when an
error is encountered, i.e. when kset_register() returns an error.

A kset may be embedded in a larger structure which may be dynamically
allocated in callers, it needs to be freed in ktype.release() or error
path in callers, in this case, we can not call kset_put() in kset_register(),
or it will cause double free, so just call kfree_const() to free the
name and set it to NULL to avoid accessing bad pointer in callers.

With this fix, the callers don't need care about freeing the name
and may call kset_put() if kset_register() fails.

Suggested-by: Luben Tuikov <luben.tuikov@xxxxxxx>
Signed-off-by: Yang Yingliang <yangyingliang@xxxxxxxxxx>
---
v2 -> v3:
  Update commit message and comment of kset_register().

v1 -> v2:
  Free name inside of kset_register() instead of calling kset_put()
  in drivers.
---
 lib/kobject.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/lib/kobject.c b/lib/kobject.c
index a0b2dbfcfa23..3cd19b9ca5ab 100644
--- a/lib/kobject.c
+++ b/lib/kobject.c
@@ -834,6 +834,9 @@ EXPORT_SYMBOL_GPL(kobj_sysfs_ops);
 /**
  * kset_register() - Initialize and add a kset.
  * @k: kset.
+ *
+ * NOTE: On error, the kset.kobj.name allocated by() kobj_set_name()
+ * is freed, it can not be used any more.
  */
 int kset_register(struct kset *k)
 {
@@ -844,8 +847,12 @@ int kset_register(struct kset *k)
 
 	kset_init(k);
 	err = kobject_add_internal(&k->kobj);
-	if (err)
+	if (err) {
+		kfree_const(k->kobj.name);
+		/* Set it to NULL to avoid accessing bad pointer in callers. */
+		k->kobj.name = NULL;
 		return err;
+	}
 	kobject_uevent(&k->kobj, KOBJ_ADD);
 	return 0;
 }
-- 
2.25.1