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Date:   Mon, 8 Oct 2018 10:20:24 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     stefanha@...hat.com, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, sergei.shtylyov@...entembedded.com
Subject: Re: [PATCH net V2] vhost-vsock: fix use after free



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@...kaller.appspotmail.com
>>>> Fixes: 16320f363ae1 ("vhost-vsock: add pkt cancel capability")
>>>> Fixes: 433fc58e6bf2 ("VSOCK: Introduce vhost_vsock.ko")
>>>> Cc: Stefan Hajnoczi<stefanha@...hat.com>
>>>> Signed-off-by: Jason Wang<jasowang@...hat.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

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