linux-kernel - Re: [PATCH] md/raid5: fix possible null-pointer dereferences in raid5_store_group_thread

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Message-ID: <CADm8TekmvebrapiVCUA8D7tJPdDBGG1cS4sV0-ymqMHNG4JnSA@mail.gmail.com>
Date: Thu, 25 Dec 2025 20:34:42 +0800
From: Tuo Li <islituo@...il.com>
To: yukuai@...as.com
Cc: song@...nel.org, linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org, 
	xni@...hat.com
Subject: Re: [PATCH] md/raid5: fix possible null-pointer dereferences in raid5_store_group_thread_cnt()

Hi Kuai,

On Thu, Dec 25, 2025 at 3:40 PM Yu Kuai <yukuai@...as.com> wrote:
>
> Hi,
>
> 在 2025/12/10 15:41, Tuo Li 写道:
> > The variable mddev->private is first assigned to conf and then checked:
> >
> >    conf = mddev->private;
> >    if (!conf) ...
> >
> > If conf is NULL, then mddev->private is also NULL. However, the function
> > does not return at this point, and raid5_quiesce() is later called with
> > mddev as the argument. Inside raid5_quiesce(), mddev->private is again
> > assigned to conf, which is then dereferenced in multiple places, for
> > example:
> >
> >    conf->quiesce = 0;
> >    wake_up(&conf->wait_for_quiescent);
> >    ...
> >
> > This can lead to several null-pointer dereferences.
> >
> > To fix these issues, the function should unlock mddev and return early when
> > conf is NULL, following the pattern in raid5_change_consistency_policy().
> >
> > Signed-off-by: Tuo Li <islituo@...il.com>
> > ---
> >   drivers/md/raid5.c | 7 ++++---
> >   1 file changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> > index e57ce3295292..be3f9a127212 100644
> > --- a/drivers/md/raid5.c
> > +++ b/drivers/md/raid5.c
> > @@ -7190,9 +7190,10 @@ raid5_store_group_thread_cnt(struct mddev *mddev, const char *page, size_t len)
> >       raid5_quiesce(mddev, true);
> >
> >       conf = mddev->private;
> > -     if (!conf)
> > -             err = -ENODEV;
> > -     else if (new != conf->worker_cnt_per_group) {
> > +     if (!conf) {
> > +             mddev_unlock_and_resume(mddev);
> > +             return -ENODEV;
>
> +CC Xiao
>
> This is still wrong, please add the NULL check and return early before raid5_quise().
> And also add a fix tag:
>
> fa1944bbe622 md/raid5: Wait sync io to finish before changing group cnt
>
> > +     } else if (new != conf->worker_cnt_per_group) {
> >               old_groups = conf->worker_groups;
> >               if (old_groups)
> >                       flush_workqueue(raid5_wq);
>
> --
> Thansk,
> Kuai

Thanks for your reply!
I’ll prepare and submit a v2 patch shortly following your advice.

Sincerely,
Tuo