[SRU][Xenial][CVE-2018-20836] Fix a race condition when smp task timeout

[Connor Kuehl]

https://people.canonical.com/~ubuntu-security/cve/2018/CVE-2018-20836.html

CVE description taken from the link above: An issue was discovered in 
the Linux kernel before 4.20. There is a race condition in smp_task_timedout() 
and smp_task_done() in drivers/scsi/libsas/sas_expander.c, leading to a 
use-after-free.

Clean cherry pick. No context adjustments required. Compiled all architectures.
Boot-tested in an amd64 virtual machine and verified the module loaded
properly.

Regression potential: Low. This patch was released to bionic and cosmic
several months ago. It's been upstream since September 2018.

Jason Yan (1):
  scsi: libsas: fix a race condition when smp task timeout

 drivers/scsi/libsas/sas_expander.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

-- 
2.20.1