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    Subject[PATCH 4.4 143/266] scsi: libsas: fix a race condition when smp task timeout
    Date
    From: Jason Yan <yanaijie@huawei.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@hisilicon.com>
    Signed-off-by: Jason Yan <yanaijie@huawei.com>
    CC: John Garry <john.garry@huawei.com>
    CC: Johannes Thumshirn <jthumshirn@suse.de>
    CC: Ewan Milne <emilne@redhat.com>
    CC: Christoph Hellwig <hch@lst.de>
    CC: Tomas Henzl <thenzl@redhat.com>
    CC: Dan Williams <dan.j.williams@intel.com>
    CC: Hannes Reinecke <hare@suse.com>
    Reviewed-by: Hannes Reinecke <hare@suse.com>
    Reviewed-by: John Garry <john.garry@huawei.com>
    Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
    Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
    Cc: Guenter Roeck <linux@roeck-us.net
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    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);
    }


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