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

[Jason Yan]

On 2018/9/17 17:47, John Garry wrote:
> 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()

OK

> > Reported-by: chenxiang <chenxiang66@xxxxxxxxxxxxx>
> > Signed-off-by: Jason Yan <yanaijie@xxxxxxxxxx>
> > CC: John Garry <john.garry@xxxxxxxxxx>
> > CC: Johannes Thumshirn <jthumshirn@xxxxxxx>
> > CC: Ewan Milne <emilne@xxxxxxxxxx>
> > CC: Christoph Hellwig <hch@xxxxxx>
> > CC: Tomas Henzl <thenzl@xxxxxxxxxx>
> > CC: Dan Williams <dan.j.williams@xxxxxxxxx>
> > CC: Hannes Reinecke <hare@xxxxxxxx>
> > ---
> >  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.

Is it necessary to add a variable just for consistency with other places?

> > +    }
> >      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.

This changes the logic a bit. To be safe, maybe we shall do this with 
another patch after some tests.

> >
>
> Thanks,
> John
>
>
>
> .