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SubjectRe: [PATCH 5/5] scsi: libsas: fix a race condition when smp task timeout
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On 12/09/2018 09:29, 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().
>

Hi Jason,

Please mention that once the LLDD sets DONE, it must call task->done(),
which will call smp_task_done()->complete()

> Reported-by: chenxiang <chenxiang66@hisilicon.com>
> Signed-off-by: Jason Yan <yanaijie@huawei.com>
> CC: John Garry <john.garry@huawei.com>
> CC: Johannes Thumshirn <jthumshirn@suse.de>
> CC: Ewan Milne <emilne@redhat.com>
> CC: Christoph Hellwig <hch@lst.de>
> CC: Tomas Henzl <thenzl@redhat.com>
> CC: Dan Williams <dan.j.williams@intel.com>
> CC: Hannes Reinecke <hare@suse.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);

Nit: for consistency with any other time we use this lock, can we call
complete() outside the lock? Maybe just use a flag variable for this.

> + }
> 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);
> }

Do we also need this change or similar:
static int smp_execute_task_sg(struct domain_device *dev,
if ((task->task_state_flags & SAS_TASK_STATE_ABORTED)) {
SAS_DPRINTK("smp task timed out or aborted\n");
i->dft->lldd_abort_task(task);
- if (!(task->task_state_flags & SAS_TASK_STATE_DONE)) {
- SAS_DPRINTK("SMP task aborted and not done\n");
- break;
- }
+ break;

To me, the ABORTED and DONE states are mutually exclusive.

>
>

Thanks,
John


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