linux-kernel - Re: [PATCH v2 5/5] scsi: libsas: fix a race condition when smp task timeout

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Date:   Wed, 19 Sep 2018 09:42:45 +0100
From:   John Garry <john.garry@...wei.com>
To:     Jason Yan <yanaijie@...wei.com>, <martin.petersen@...cle.com>,
        <jejb@...ux.vnet.ibm.com>
CC:     <linux-scsi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <zhaohongjiang@...wei.com>, <hare@...e.com>,
        <dan.j.williams@...el.com>, <jthumshirn@...e.de>, <hch@....de>,
        <huangdaode@...ilicon.com>, <chenxiang66@...ilicon.com>,
        <miaoxie@...wei.com>, Ewan Milne <emilne@...hat.com>,
        Tomas Henzl <thenzl@...hat.com>
Subject: Re: [PATCH v2 5/5] scsi: libsas: fix a race condition when smp task
 timeout

On 19/09/2018 04:32, Jason Yan wrote:
> When the lldd is processing the complete sas task in interrupt and set
> the task stat as SAS_TASK_STATE_DONE, the smp timeout timer is able to
> be triggered at the same time. And smp_task_timedout() will complete the
> task wheter the SAS_TASK_STATE_DONE is set or not. Then the sas task may
> freed before lldd end the interrupt process. Thus a use-after-free will
> happen.
>
> Fix this by calling the complete() only when SAS_TASK_STATE_DONE is not
> set. And remove the check of the return value of the del_timer(). Once
> the LLDD sets DONE, it must call task->done(), which will call
> smp_task_done()->complete() and the task will be completed and freed
> correctly.
>
> Reported-by: chenxiang <chenxiang66@...ilicon.com>
> Signed-off-by: Jason Yan <yanaijie@...wei.com>
> CC: John Garry <john.garry@...wei.com>
> CC: Johannes Thumshirn <jthumshirn@...e.de>
> CC: Ewan Milne <emilne@...hat.com>
> CC: Christoph Hellwig <hch@....de>
> CC: Tomas Henzl <thenzl@...hat.com>
> CC: Dan Williams <dan.j.williams@...el.com>
> CC: Hannes Reinecke <hare@...e.com>

Uh, I should have added this for my last comment on v1:
Reviewed-by: John Garry <john.garry@...wei.com>

> Reviewed-by: Hannes Reinecke <hare@...e.com>
> ---
>  drivers/scsi/libsas/sas_expander.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/scsi/libsas/sas_expander.c b/drivers/scsi/libsas/sas_expander.c
> index 52222940d398..0d1f72752ca2 100644
> --- a/drivers/scsi/libsas/sas_expander.c
> +++ b/drivers/scsi/libsas/sas_expander.c
> @@ -48,17 +48,16 @@ static void smp_task_timedout(struct timer_list *t)
>  	unsigned long flags;
>
>  	spin_lock_irqsave(&task->task_state_lock, flags);
> -	if (!(task->task_state_flags & SAS_TASK_STATE_DONE))
> +	if (!(task->task_state_flags & SAS_TASK_STATE_DONE)) {
>  		task->task_state_flags |= SAS_TASK_STATE_ABORTED;
> +		complete(&task->slow_task->completion);
> +	}
>  	spin_unlock_irqrestore(&task->task_state_lock, flags);
> -
> -	complete(&task->slow_task->completion);
>  }
>
>  static void smp_task_done(struct sas_task *task)
>  {
> -	if (!del_timer(&task->slow_task->timer))
> -		return;
> +	del_timer(&task->slow_task->timer);
>  	complete(&task->slow_task->completion);
>  }
>
>