scsi: libsas: Fix use-after-free bug in smp_execute_task_sg()

[ Upstream commit 46ba53c ]

When executing SMP task failed, the smp_execute_task_sg() calls del_timer()
to delete "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 a UAF 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.

Link: https://lore.kernel.org/r/[email protected]
Fixes: 2908d77 ("[SCSI] aic94xx: new driver")
Reviewed-by: Jason Yan <[email protected]>
Signed-off-by: Duoming Zhou <[email protected]>
Signed-off-by: Martin K. Petersen <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>

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;
 		}