Re: [PATCH -next v7 5/5] md: protect md_thread with rcu

[Song Liu]

On Sat, Apr 22, 2023 at 7:42 PM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
>
> Hi,
>
> 在 2023/04/14 9:32, Yu Kuai 写道:
> > From: Yu Kuai <yukuai3@xxxxxxxxxx>
> >
> > Our test reports a uaf for 'mddev->sync_thread':
> >
> > T1                      T2
> > md_start_sync
> >   md_register_thread
> >   // mddev->sync_thread is set
> >                       raid1d
> >                        md_check_recovery
> >                         md_reap_sync_thread
> >                          md_unregister_thread
> >                           kfree
> >
> >   md_wakeup_thread
> >    wake_up
> >    ->sync_thread was freed
> >
> > Root cause is that there is a small windown between register thread and
> > wake up thread, where the thread can be freed concurrently.
> >
> > Currently, a global spinlock 'pers_lock' is borrowed to protect
> > 'mddev->thread', this problem can be fixed likewise, however, there are
> > similar problems elsewhere, and use a global lock for all the cases is
> > not good.
> >
> > This patch protect all md_thread with rcu.
>
> Friendly ping... Or do I need to resend the whole patchset for v7?

Sorry for the delay. But yes, please resend the whole patchset.

Song