linux-kernel - Re: [PATCH 4/6] usbip: fix stub_dev usbip_sockfd

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Date:   Tue, 9 Mar 2021 16:52:22 -0700
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        shuah@...nel.org, valentina.manea.m@...il.com,
        gregkh@...uxfoundation.org
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH 4/6] usbip: fix stub_dev usbip_sockfd_store() races
 leading to gpf

On 3/9/21 4:40 PM, Tetsuo Handa wrote:
> On 2021/03/10 4:50, Shuah Khan wrote:
>> On 3/9/21 4:04 AM, Tetsuo Handa wrote:
>>> On 2021/03/09 1:27, Shuah Khan wrote:
>>>> Yes. We might need synchronization between events, threads, and shutdown
>>>> in usbip_host side and in connection polling and threads in vhci.
>>>>
>>>> I am also looking at the shutdown sequences closely as well since the
>>>> local state is referenced without usbip_device lock in these paths.
>>>>
>>>> I am approaching these problems as peeling the onion an expression so
>>>> we can limit the changes and take a spot fix approach. We have the
>>>> goal to address these crashes and not introduce regressions.
>>>
>>> I think my [PATCH v4 01/12]-[PATCH v4 06/12] simplify your further changes
>>> without introducing regressions. While ud->lock is held when checking ud->status,
>>> current attach/detach code is racy about read/update of ud->status . I think we
>>> can close race in attach/detach code via a simple usbip_event_mutex serialization.
>>>
>>
>> Do you mean patches 1,2,3,3,4,5,6?
> 
> Yes, my 1,2,3,4,5,6.
> 
> Since you think that usbip_prepare_threads() does not worth introducing, I'm fine with
> replacing my 7,8,9,10,11,12 with your "[PATCH 0/6] usbip fixes to crashes found by syzbot".
> 

Using event lock isn't the right approach to solve the race. It is a
large grain lock. I am not looking to replace patches.

I still haven't seen any response from you about if you were able to
verify the fixes I sent in fix the problem you are seeing.

thanks,
-- Shuah