scsi: libsas: Fix use-after-free bug in smp_execute_task_sg()

In the Linux kernel, the following vulnerability has been resolved:

scsi: libsas: Fix use-after-free bug in smp_execute_task_sg()

When executing SMP task failed, the smp_execute_task_sg() calls del_timer()

to delete "slow_task->timer". However, if the timer handler

sas_task_internal_timedout() is running, the del_timer() in

smp_execute_task_sg() will not stop it and a UAF will happen. The process

is shown below:

(thread 1) | (thread 2)

smp_execute_task_sg() | sas_task_internal_timedout()

... |

del_timer() |

... | ...

sas_free_task(task) |

kfree(task->slow_task) //FREE|

| task->slow_task->... //USE

Fix by calling del_timer_sync() in smp_execute_task_sg(), which makes sure

the timer handler have finished before the "task->slow_task" is

deallocated.