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

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

[Kefeng Wang]

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

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@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;

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@acm.org/

Thanks,

Bart.

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

[Kefeng Wang]

On 2019/3/8 22:45, Bart Van Assche wrote:
> 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@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;
>
> 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@acm.org/  
I don't notice your patch due to no subscribe lkml,  that is better, wq->lock_name should be freed too; )
>
> Thanks,
>
> Bart.
>
>
>
> .
>