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

[John Garry]

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 <chenxian...@hisilicon.com>
Signed-off-by: Jason Yan <yanai...@huawei.com>
CC: John Garry <john.ga...@huawei.com>
CC: Johannes Thumshirn <jthumsh...@suse.de>
CC: Ewan Milne <emi...@redhat.com>
CC: Christoph Hellwig <h...@lst.de>
CC: Tomas Henzl <the...@redhat.com>
CC: Dan Williams <dan.j.willi...@intel.com>
CC: Hannes Reinecke <h...@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