Re: [PATCH v2] md/raid5: fix possible null-pointer dereferences in raid5_store_group_thread_cnt()

[Xiao Ni]

On Thu, Dec 25, 2025 at 9:04 PM Tuo Li <islituo@xxxxxxxxx> wrote:
>
> 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. In this case,
> null-pointer dereferences can occur when calling raid5_quiesce():
>
>   raid5_quiesce(mddev, true);
>   raid5_quiesce(mddev, false);
>
> since mddev->private is assigned to conf again in raid5_quiesce(), and conf
> is dereferenced in several places, for example:
>
>   conf->quiesce = 0;
>   wake_up(&conf->wait_for_quiescent);
>
> To fix this issue, the function should unlock mddev and return before
> invoking raid5_quiesce() when conf is NULL, following the existing pattern
> in raid5_change_consistency_policy().
>
> Fixes: fa1944bbe622 ("md/raid5: Wait sync io to finish before changing group cnt")
> Signed-off-by: Tuo Li <islituo@xxxxxxxxx>
> ---
> v2:
> * Move the NULL check and early return ahead of the first call to
>   raid5_quiesce().
>   Thanks to Yu Kuai for helpful advice.
> ---
>  drivers/md/raid5.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index e57ce3295292..8dc98f545969 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -7187,12 +7187,14 @@ raid5_store_group_thread_cnt(struct mddev *mddev, const char *page, size_t len)
>         err = mddev_suspend_and_lock(mddev);
>         if (err)
>                 return err;
> +       conf = mddev->private;
> +       if (!conf) {
> +               mddev_unlock_and_resume(mddev);
> +               return -ENODEV;
> +       }
>         raid5_quiesce(mddev, true);
>
> -       conf = mddev->private;
> -       if (!conf)
> -               err = -ENODEV;
> -       else if (new != conf->worker_cnt_per_group) {
> +       if (new != conf->worker_cnt_per_group) {
>                 old_groups = conf->worker_groups;
>                 if (old_groups)
>                         flush_workqueue(raid5_wq);
> --
> 2.43.0
>
>

Thanks for the patch. It looks good to me.

Reviewed-by: Xiao Ni <xni@xxxxxxxxxx>