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

[Bart Van Assche]

On 3/7/19 11:37 PM, Kefeng Wang wrote:
> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: 669de8bda87b ("kernel/workqueue: Use dynamic lockdep keys for workqueues")
> Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
> ---
>   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;

Hi Kefeng,

Five days ago I had posted a similar but slightly different patch. Can 
you have a look at it? See also 
https://lore.kernel.org/lkml/20190303220046.29448-1-bvanassche@xxxxxxx/

Thanks,

Bart.