[PATCH] scsi: libsas: fix use-after-free bug in smp_execute_task_sg

[Duoming Zhou]

When executing SMP task failed, the smp_execute_task_sg()
calls del_timer() to delete the "slow_task->timer". However,
if the timer handler sas_task_internal_timedout() is running,
the del_timer() in smp_execute_task_sg() will not stop it
and the UAF bug will happen. The process is shown below:

      (thread 1)               |        (thread 2)
smp_execute_task_sg()          | sas_task_internal_timedout()
 ...                           |
 del_timer()                   |
 ...                           |  ...
 sas_free_task(task)           |
  kfree(task->slow_task) //FREE|
                               |  task->slow_task->... //USE

Fix by calling del_timer_sync() in smp_execute_task_sg(),
which makes sure the timer handler have finished before
the "task->slow_task" is deallocated.

Fixes: 2908d778ab3e ("[SCSI] aic94xx: new driver")
Signed-off-by: Duoming Zhou <duoming@xxxxxxxxxx>
---
 drivers/scsi/libsas/sas_expander.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/scsi/libsas/sas_expander.c b/drivers/scsi/libsas/sas_expander.c
index fa2209080cc..5ce25183010 100644
--- a/drivers/scsi/libsas/sas_expander.c
+++ b/drivers/scsi/libsas/sas_expander.c
@@ -67,7 +67,7 @@ static int smp_execute_task_sg(struct domain_device *dev,
 		res = i->dft->lldd_execute_task(task, GFP_KERNEL);
 
 		if (res) {
-			del_timer(&task->slow_task->timer);
+			del_timer_sync(&task->slow_task->timer);
 			pr_notice("executing SMP task failed:%d\n", res);
 			break;
 		}
-- 
2.17.1