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Date:   Tue, 25 Sep 2018 10:56:54 +0800
From:   Jason Yan <yanaijie@...wei.com>
To:     <martin.petersen@...cle.com>, <jejb@...ux.vnet.ibm.com>
CC:     <linux-scsi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <john.garry@...wei.com>, <zhaohongjiang@...wei.com>,
        <hare@...e.com>, <dan.j.williams@...el.com>, <jthumshirn@...e.de>,
        <hch@....de>, <huangdaode@...ilicon.com>,
        <chenxiang66@...ilicon.com>, <miaoxie@...wei.com>,
        Jason Yan <yanaijie@...wei.com>,
        Ewan Milne <emilne@...hat.com>, Tomas Henzl <thenzl@...hat.com>
Subject: [PATCH v3 5/5] scsi: libsas: fix a race condition when smp task timeout

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(). Once
the LLDD sets DONE, it must call task->done(), which will call
smp_task_done()->complete() and the task will be completed and freed
correctly.

Reported-by: chenxiang <chenxiang66@...ilicon.com>
Signed-off-by: Jason Yan <yanaijie@...wei.com>
CC: John Garry <john.garry@...wei.com>
CC: Johannes Thumshirn <jthumshirn@...e.de>
CC: Ewan Milne <emilne@...hat.com>
CC: Christoph Hellwig <hch@....de>
CC: Tomas Henzl <thenzl@...hat.com>
CC: Dan Williams <dan.j.williams@...el.com>
CC: Hannes Reinecke <hare@...e.com>
Reviewed-by: Hannes Reinecke <hare@...e.com>
Reviewed-by: John Garry <john.garry@...wei.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@...e.de>
---
 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);
+	}
 	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);
 }
 
-- 
2.14.4

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