Re: [PATCH 4/6] usbip: fix stub_dev usbip_sockfd_store() races leading to gpf

From: Shuah Khan <skhan@linuxfoundation.org>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
	shuah@kernel.org, valentina.manea.m@gmail.com,
	gregkh@linuxfoundation.org
Cc: linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
	Shuah Khan <skhan@linuxfoundation.org>
Subject: Re: [PATCH 4/6] usbip: fix stub_dev usbip_sockfd_store() races leading to gpf
Date: Tue, 9 Mar 2021 16:52:22 -0700	[thread overview]
Message-ID: <05e8e744-0847-cde2-b978-0bfd7ef93a9f@linuxfoundation.org> (raw)
In-Reply-To: <7b9465aa-213e-a513-d033-12c048df15d6@i-love.sakura.ne.jp>

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