[SRU][Xenial][CVE-2018-20836][PATCH] scsi: libsas: fix a race condition when smp task timeout

[Connor Kuehl]

On 6/4/19 7:20 AM, Kleber Souza wrote:
> On 5/31/19 12:31 AM, Connor Kuehl wrote:
>> From: Jason Yan <yanaijie at huawei.com>
>>
>> CVE-2018-20836
>>
>> BugLink: https://bugs.launchpad.net/bugs/1808912
> 
> Hi Connor,
> 
> You have added the above BugLink as well for this CVE fix but this bug
> report has been marked as invalid for Xenial.
> 
> Generally we don't need to add a BugLink for a CVE fix, the CVE ID
> is enough. Is this BugLink really needed?

No, sorry, my mistake. The BugLink isn't needed.

Connor

> 
> 
> Thanks,
> Kleber
> 
>>
>> 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 at hisilicon.com>
>> Signed-off-by: Jason Yan <yanaijie at huawei.com>
>> CC: John Garry <john.garry at huawei.com>
>> CC: Johannes Thumshirn <jthumshirn at suse.de>
>> CC: Ewan Milne <emilne at redhat.com>
>> CC: Christoph Hellwig <hch at lst.de>
>> CC: Tomas Henzl <thenzl at redhat.com>
>> CC: Dan Williams <dan.j.williams at intel.com>
>> CC: Hannes Reinecke <hare at suse.com>
>> Reviewed-by: Hannes Reinecke <hare at suse.com>
>> Reviewed-by: John Garry <john.garry at huawei.com>
>> Reviewed-by: Johannes Thumshirn <jthumshirn at suse.de>
>> Signed-off-by: Martin K. Petersen <martin.petersen at oracle.com>
>> (cherry picked from commit b90cd6f2b905905fb42671009dc0e27c310a16ae)
>> Signed-off-by: Connor Kuehl <connor.kuehl at canonical.com>
>> ---
>>  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 7be581f7c35d..1a6f65db615e 100644
>> --- a/drivers/scsi/libsas/sas_expander.c
>> +++ b/drivers/scsi/libsas/sas_expander.c
>> @@ -47,17 +47,16 @@ static void smp_task_timedout(unsigned long _task)
>>  	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);
>>  }
>>  
>>
> 


-- 
Connor
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