linux-kernel - Re: [PATCH v2] md/raid5: fix possible null-pointer dereferences in raid5_store_group_thread

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Message-ID: <19395340-acad-4e2f-938f-874c92b209bc@molgen.mpg.de>
Date: Fri, 26 Dec 2025 12:09:57 +0500
From: Paul Menzel <pmenzel@...gen.mpg.de>
To: Tuo Li <islituo@...il.com>
Cc: song@...nel.org, yukuai@...as.com, linux-raid@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] md/raid5: fix possible null-pointer dereferences in
 raid5_store_group_thread_cnt()

Dear Tuo,


Thank you for your patch.


Am 25.12.25 um 18:03 schrieb Tuo Li:
> The variable mddev->private is first assigned to conf and then checked:
> 
>     conf = mddev->private;
>      if (!conf) ...

Should you resend, please align conf` and `if`.

> 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@...il.com>
> ---
> 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);

Reviewed-by: Paul Menzel <pmenzel@...gen.mpg.de>


Kind regards,

Paul