ACK: [PATCH 1/1] scsi: libsas: fix a race condition when smp task timeout

[Kleber Souza]

On 12/18/18 7:09 AM, Ike Panhc wrote:
> From: Jason Yan <yanaijie at huawei.com>
>
> Buglink: http://bugs.launchpad.net/bugs/1808912
>
> 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 at hisilicon.com>
> Signed-off-by: Jason Yan <yanaijie at huawei.com>
> CC: John Garry <john.garry at huawei.com>
> CC: Johannes Thumshirn <jthumshirn at suse.de>
> CC: Ewan Milne <emilne at redhat.com>
> CC: Christoph Hellwig <hch at lst.de>
> CC: Tomas Henzl <thenzl at redhat.com>
> CC: Dan Williams <dan.j.williams at intel.com>
> CC: Hannes Reinecke <hare at suse.com>
> Reviewed-by: Hannes Reinecke <hare at suse.com>
> Reviewed-by: John Garry <john.garry at huawei.com>
> Reviewed-by: Johannes Thumshirn <jthumshirn at suse.de>
> Signed-off-by: Martin K. Petersen <martin.petersen at oracle.com>
> (cherry picked from commit b90cd6f2b905905fb42671009dc0e27c310a16ae)
> Signed-off-by: Ike Panhc <ike.pan at canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza at canonical.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 6a4f8198b78e..0ebed2a86b97 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);
>  }
>