Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH net V2] vhost-vsock: fix use after free
To:     "Michael S. Tsirkin" <mst@redhat.com>
Cc:     stefanha@redhat.com, kvm@vger.kernel.org,
        virtualization@lists.linux-foundation.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, sergei.shtylyov@cogentembedded.com
References: <20180927122204.4188-1-jasowang@redhat.com>
 <20180927123539-mutt-send-email-mst@kernel.org>
 <588ed28b-7e4b-9dc8-92ce-d75692836c9e@redhat.com>
 <20180927194734-mutt-send-email-mst@kernel.org>
From:   Jason Wang <jasowang@redhat.com>
Message-ID: <9ea5d616-8a78-b3c4-2a96-cbb6abb85c2c@redhat.com>
Date:   Mon, 8 Oct 2018 10:20:24 +0800
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.9.1
MIME-Version: 1.0
In-Reply-To: <20180927194734-mutt-send-email-mst@kernel.org>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit
Content-Language: en-US
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


On 2018年09月28日 07:50, Michael S. Tsirkin wrote:
> On Fri, Sep 28, 2018 at 07:37:37AM +0800, Jason Wang wrote:
>>
>> On 2018年09月28日 01:04, Michael S. Tsirkin wrote:
>>> On Thu, Sep 27, 2018 at 08:22:04PM +0800, Jason Wang wrote:
>>>> The access of vsock is not protected by vhost_vsock_lock. This may
>>>> lead to use after free since vhost_vsock_dev_release() may free the
>>>> pointer at the same time.
>>>>
>>>> Fix this by holding the lock during the access.
>>>>
>>>> Reported-by:syzbot+e3e074963495f92a89ed@syzkaller.appspotmail.com
>>>> Fixes: 16320f363ae1 ("vhost-vsock: add pkt cancel capability")
>>>> Fixes: 433fc58e6bf2 ("VSOCK: Introduce vhost_vsock.ko")
>>>> Cc: Stefan Hajnoczi<stefanha@redhat.com>
>>>> Signed-off-by: Jason Wang<jasowang@redhat.com>
>>> Wow is that really the best we can do?
>> For net/stable, probably yes.
>>
>>>    A global lock on a data path
>>> operation?
>> It's already there,
> &vhost_vsock_lock? were is it takes on data path?

Ok, but the current code use list which means a global lock is needed 
anyway here.

>
>> and the patch only increase the critical section.
>>
>>>    Granted use after free is nasty but Stefan said he sees
>>> a way to fix it using a per socket refcount. He's on vacation
>>> until Oct 4 though ...
>>>
>> Stefan has acked the pacth, so I think it's ok? We can do optimization for
>> -next on top.
>>
>> Thanks
>
> Well on high SMP serializing can drop performance as much as x100 so I'm
> not sure it's appropriate - seems to fix a bug but can introduce a
> regression. Let's see how does a proper fix look first?
>

It looks to me hlist + RCU is better. But I'm not sure it's suitable for 
-net/-stable.

Thanks