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

[Andrea Righi]

On Thu, May 30, 2019 at 03:31:13PM -0700, Connor Kuehl wrote:
> From: Jason Yan <yanaijie at huawei.com>
> 
> CVE-2018-20836
> 
> BugLink: https://bugs.launchpad.net/bugs/1808912
> 
> 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>

Clean upstream cherry pick. Fix already applied to the other kernel
relases. Looks good.

Acked-by: Andrea Righi <andrea.righi at canonical.com>