netdev - Re: [PATCH net] vhost: correctly remove wait queue during poll failure

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Message-ID: <b1576bcf-652a-7c1a-9d77-db54931ab979@redhat.com>
Date:   Tue, 27 Mar 2018 17:43:14 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     mst@...hat.com, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] vhost: correctly remove wait queue during poll
 failure



On 2018年03月27日 17:28, Darren Kenny wrote:
> Hi Jason,
>
> On Tue, Mar 27, 2018 at 11:47:22AM +0800, Jason Wang wrote:
>> We tried to remove vq poll from wait queue, but do not check whether
>> or not it was in a list before. This will lead double free. Fixing
>> this by checking poll->wqh to make sure it was in a list.
>
> This text seems at odds with the code below, instead of checking
> poll-whq, you are removing that check...
>
> Maybe the text needs rewording?

Yes, I admit it's bad, thanks for pointing out.

How about:

"Fixing this by switching to use vhost_poll_stop() which zeros poll->wqh 
after removing poll from waitqueue to make sure it won't be freed twice."

Thanks

>
> Thanks,
>
> Darren.
>
>>
>> Reported-by: syzbot+c0272972b01b872e604a@...kaller.appspotmail.com
>> Fixes: 2b8b328b61c79 ("vhost_net: handle polling errors when setting 
>> backend")
>> Signed-off-by: Jason Wang <jasowang@...hat.com>
>> ---
>> drivers/vhost/vhost.c | 3 +--
>> 1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
>> index 1b3e8d2d..5d5a9d9 100644
>> --- a/drivers/vhost/vhost.c
>> +++ b/drivers/vhost/vhost.c
>> @@ -212,8 +212,7 @@ int vhost_poll_start(struct vhost_poll *poll, 
>> struct file *file)
>>     if (mask)
>>         vhost_poll_wakeup(&poll->wait, 0, 0, poll_to_key(mask));
>>     if (mask & EPOLLERR) {
>> -        if (poll->wqh)
>> -            remove_wait_queue(poll->wqh, &poll->wait);
>> +        vhost_poll_stop(poll);
>>         ret = -EINVAL;
>>     }
>>
>> -- 
>> 2.7.4
>>