Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH] IB/cm: Fix possible use-after-free in ib_cm_cleanup()
To:     Jason Gunthorpe <jgg@nvidia.com>
CC:     <dledford@redhat.com>, <leon@kernel.org>, <markzhang@nvidia.com>,
        <liangwenpeng@huawei.com>, <liweihang@huawei.com>,
        <haakon.bugge@oracle.com>, <rolandd@cisco.com>,
        <sean.hefty@intel.com>, <linux-rdma@vger.kernel.org>,
        <linux-ide@vger.kernel.org>, <linux-kernel@vger.kernel.org>
References: <20211013093016.3869299-1-wanghai38@huawei.com>
 <20211013182448.GA3489723@nvidia.com>
From:   "wanghai (M)" <wanghai38@huawei.com>
Message-ID: <787f463c-85e9-c1f3-c772-1233e82a71b5@huawei.com>
Date:   Thu, 14 Oct 2021 21:19:07 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101
 Thunderbird/60.8.0
MIME-Version: 1.0
In-Reply-To: <20211013182448.GA3489723@nvidia.com>
Content-Type: text/plain; charset="gbk"; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk


?? 2021/10/14 2:24, Jason Gunthorpe д??:
> On Wed, Oct 13, 2021 at 05:30:16PM +0800, Wang Hai wrote:
>> This module's remove path calls cancel_delayed_work(). However, that
>> function does not wait until the work function finishes. This means
>> that the callback function may still be running after the driver's
>> remove function has finished, which would result in a use-after-free.
>>
>> Fix by calling cancel_delayed_work_sync(), which ensures that
>> the work is properly cancelled, no longer running, and unable
>> to re-schedule itself.
>>
>> Fixes: 8575329d4f85 ("IB/cm: Fix timewait crash after module unload")
>> Reported-by: Hulk Robot <hulkci@huawei.com>
>> Signed-off-by: Wang Hai <wanghai38@huawei.com>
>>   drivers/infiniband/core/cm.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/infiniband/core/cm.c b/drivers/infiniband/core/cm.c
>> index c903b74f46a4..ae0af63f3271 100644
>> +++ b/drivers/infiniband/core/cm.c
>> @@ -4508,7 +4508,7 @@ static void __exit ib_cm_cleanup(void)
>>   
>>   	spin_lock_irq(&cm.lock);
>>   	list_for_each_entry(timewait_info, &cm.timewait_list, list)
>> -		cancel_delayed_work(&timewait_info->work.work);
>> +		cancel_delayed_work_sync(&timewait_info->work.work);
>>   	spin_unlock_irq(&cm.lock);
> No, this will deadlock:
>
> static int cm_timewait_handler(struct cm_work *work)
> {
> 	struct cm_timewait_info *timewait_info;
> 	struct cm_id_private *cm_id_priv;
>
> 	timewait_info = container_of(work, struct cm_timewait_info, work);
> 	spin_lock_irq(&cm.lock);
>           ^^^^^^^^^^^^
>
> Holds the same lock
>
> What is your bug? The destroy_wq() a few lines below will flush out
> all the work so it is already not possible that work can still exist
> after the driver's remove function has finished.
>
> Jason
> .
Sorry, this is a wrong bugfix, thank you for pointing it out.

I was studying the code here and thought there might be a null
pointer reference problem.

You are right, I didn't take into account destroy_workqueue().
There are no bugs here. sorry for making this problematic patch.

Please ignore this patch.

-- 
Wang Hai