linux-kernel - [PATCH 3.16 157/157] scsi: libsas: fix a race condition when smp task timeout

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Message-ID: <lsq.1565469607.672530587@decadent.org.uk>
Date:   Sat, 10 Aug 2019 21:40:07 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "chenxiang" <chenxiang66@...ilicon.com>,
        "John Garry" <john.garry@...wei.com>,
        "Johannes Thumshirn" <jthumshirn@...e.de>,
        "Ewan Milne" <emilne@...hat.com>,
        "Dan Williams" <dan.j.williams@...el.com>,
        "Tomas Henzl" <thenzl@...hat.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        "Hannes Reinecke" <hare@...e.com>,
        "Christoph Hellwig" <hch@....de>, "Jason Yan" <yanaijie@...wei.com>
Subject: [PATCH 3.16 157/157] scsi: libsas: fix a race condition when smp
 task timeout

3.16.72-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jason Yan <yanaijie@...wei.com>

commit b90cd6f2b905905fb42671009dc0e27c310a16ae upstream.

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>
Signed-off-by: Martin K. Petersen <martin.petersen@...cle.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/scsi/libsas/sas_expander.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

--- a/drivers/scsi/libsas/sas_expander.c
+++ b/drivers/scsi/libsas/sas_expander.c
@@ -47,17 +47,16 @@ static void smp_task_timedout(unsigned l
 	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);
 }