Re: [PATCH] usbnet: smsc95xx: Fix use-after-free after removal

[David Miller]

From: Tuomas Tynkkynen <tuomas.tynkkynen@xxxxxx>
Date: Sun, 21 Jun 2020 13:43:26 +0300

> Syzbot reports an use-after-free in workqueue context:
> 
> BUG: KASAN: use-after-free in mutex_unlock+0x19/0x40 kernel/locking/mutex.c:737
>  mutex_unlock+0x19/0x40 kernel/locking/mutex.c:737
>  __smsc95xx_mdio_read drivers/net/usb/smsc95xx.c:217 [inline]
>  smsc95xx_mdio_read+0x583/0x870 drivers/net/usb/smsc95xx.c:278
>  check_carrier+0xd1/0x2e0 drivers/net/usb/smsc95xx.c:644
>  process_one_work+0x777/0xf90 kernel/workqueue.c:2274
>  worker_thread+0xa8f/0x1430 kernel/workqueue.c:2420
>  kthread+0x2df/0x300 kernel/kthread.c:255
> 
> It looks like that smsc95xx_unbind() is freeing the structures that are
> still in use by the concurrently running workqueue callback. Thus switch
> to using cancel_delayed_work_sync() to ensure the work callback really
> is no longer active.
> 
> Reported-by: syzbot+29dc7d4ae19b703ff947@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Tuomas Tynkkynen <tuomas.tynkkynen@xxxxxx>

Applied, thanks.