[PATCH] workqueue: unregister wq lockdep on error path in alloc_workqueue()

[Kefeng Wang <wangkefeng.wang@huawei.com>]

syzkaller report an issue "KASAN: use-after-free Read in alloc_workqueue",

alloc_workqueue
 - kzalloc wq
 - wq_init_lockdep(wq);
   - lockdep_register_key(&wq->key);  // add to hlist
 - kfree wq

But forget to call wq_unregister_lockdep()->lockdep_unregister_key(), it
will delete the entry from hlist.

Reported-by: syzbot+17335689e239ce135d8b@syzkaller.appspotmail.com
Fixes: 669de8bda87b ("kernel/workqueue: Use dynamic lockdep keys for workqueues")
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
---
 kernel/workqueue.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 7abbeed13421..9209d25dfade 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -4291,6 +4291,7 @@ struct workqueue_struct *alloc_workqueue(const char *fmt,
 	return wq;
 
 err_free_wq:
+	wq_unregister_lockdep(wq);
 	free_workqueue_attrs(wq->unbound_attrs);
 	kfree(wq);
 	return NULL;
-- 
2.20.1