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Subject: Re: [PATCH] scsi: libsas: fix use-after-free bug in
 smp_execute_task_sg
To:     Duoming Zhou <duoming@zju.edu.cn>, <linux-kernel@vger.kernel.org>
CC:     <linux-scsi@vger.kernel.org>, <jejb@linux.ibm.com>,
        <martin.petersen@oracle.com>, <kuba@kernel.org>,
        <john.garry@huawei.com>, <gregkh@linuxfoundation.org>,
        <davem@davemloft.net>
References: <20220920144213.10536-1-duoming@zju.edu.cn>
From:   Jason Yan <yanaijie@huawei.com>
Message-ID: <9cd0b0ae-c6c7-a5bc-a834-a84010702bbc@huawei.com>
Date:   Thu, 22 Sep 2022 22:06:30 +0800
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On 2022/9/20 22:42, Duoming Zhou wrote:
> When executing SMP task failed, the smp_execute_task_sg()
> calls del_timer() to delete the "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 the UAF bug 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.
> 
> Fixes: 2908d778ab3e ("[SCSI] aic94xx: new driver")
> Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
> ---
>   drivers/scsi/libsas/sas_expander.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/libsas/sas_expander.c b/drivers/scsi/libsas/sas_expander.c
> index fa2209080cc..5ce25183010 100644
> --- a/drivers/scsi/libsas/sas_expander.c
> +++ b/drivers/scsi/libsas/sas_expander.c
> @@ -67,7 +67,7 @@ static int smp_execute_task_sg(struct domain_device *dev,
>   		res = i->dft->lldd_execute_task(task, GFP_KERNEL);
>   
>   		if (res) {
> -			del_timer(&task->slow_task->timer);
> +			del_timer_sync(&task->slow_task->timer);
>   			pr_notice("executing SMP task failed:%d\n", res);
>   			break;
>   		}
> 

The timer should be triggered 10 seconds later. I am curious why we stay
this long before del_timer().

However this change looks good to me.
Reviewed-by: Jason Yan <yanaijie@huawei.com>