linux-kernel - Re: [PATCH v2] vsock/virtio: initialize the_virtio

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Date:   Mon, 23 Oct 2023 17:59:45 +0300
From:   Alexandru Matei <alexandru.matei@...ath.com>
To:     Stefano Garzarella <sgarzare@...hat.com>
Cc:     Stefan Hajnoczi <stefanha@...hat.com>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Mihai Petrisor <mihai.petrisor@...ath.com>,
        Viorel Canja <viorel.canja@...ath.com>,
        Alexandru Matei <alexandru.matei@...ath.com>
Subject: Re: [PATCH v2] vsock/virtio: initialize the_virtio_vsock before using
 VQs

On 10/23/2023 5:52 PM, Alexandru Matei wrote:
> On 10/23/2023 5:29 PM, Stefano Garzarella wrote:
>> On Mon, Oct 23, 2023 at 05:08:33PM +0300, Alexandru Matei wrote:
>>> Once VQs are filled with empty buffers and we kick the host,
>>> it can send connection requests.  If 'the_virtio_vsock' is not
>>> initialized before, replies are silently dropped and do not reach the host.
>>>
>>> Fixes: 0deab087b16a ("vsock/virtio: use RCU to avoid use-after-free on the_virtio_vsock")
>>> Signed-off-by: Alexandru Matei <alexandru.matei@...ath.com>
>>> ---
>>> v2:
>>> - split virtio_vsock_vqs_init in vqs_init and vqs_fill and moved
>>>  the_virtio_vsock initialization after vqs_init
>>>
>>> net/vmw_vsock/virtio_transport.c | 9 +++++++--
>>> 1 file changed, 7 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
>>> index e95df847176b..92738d1697c1 100644
>>> --- a/net/vmw_vsock/virtio_transport.c
>>> +++ b/net/vmw_vsock/virtio_transport.c
>>> @@ -559,6 +559,11 @@ static int virtio_vsock_vqs_init(struct virtio_vsock *vsock)
>>>     vsock->tx_run = true;
>>>     mutex_unlock(&vsock->tx_lock);
>>>
>>> +    return 0;
>>> +}
>>> +
>>> +static void virtio_vsock_vqs_fill(struct virtio_vsock *vsock)
>>
>> What about renaming this function in virtio_vsock_vqs_start() and move also the setting of `tx_run` here?
> 
> It works but in this case we also need to move rcu_assign_pointer in virtio_vsock_vqs_start(), 
> the assignment needs to be right after setting tx_run to true and before filling the VQs.
> 

And if we move rcu_assign_pointer then there is no need to split the function in two,
We can move rcu_assign_pointer() directly inside virtio_vsock_vqs_init() after setting tx_run.

>>
>> Thanks,
>> Stefano
>>
>>> +{
>>>     mutex_lock(&vsock->rx_lock);
>>>     virtio_vsock_rx_fill(vsock);
>>>     vsock->rx_run = true;
>>> @@ -568,8 +573,6 @@ static int virtio_vsock_vqs_init(struct virtio_vsock *vsock)
>>>     virtio_vsock_event_fill(vsock);
>>>     vsock->event_run = true;
>>>     mutex_unlock(&vsock->event_lock);
>>> -
>>> -    return 0;
>>> }
>>>
>>> static void virtio_vsock_vqs_del(struct virtio_vsock *vsock)
>>> @@ -664,6 +667,7 @@ static int virtio_vsock_probe(struct virtio_device *vdev)
>>>         goto out;
>>>
>>>     rcu_assign_pointer(the_virtio_vsock, vsock);
>>> +    virtio_vsock_vqs_fill(vsock);
>>>
>>>     mutex_unlock(&the_virtio_vsock_mutex);
>>>
>>> @@ -736,6 +740,7 @@ static int virtio_vsock_restore(struct virtio_device *vdev)
>>>         goto out;
>>>
>>>     rcu_assign_pointer(the_virtio_vsock, vsock);
>>> +    virtio_vsock_vqs_fill(vsock);
>>>
>>> out:
>>>     mutex_unlock(&the_virtio_vsock_mutex);
>>> -- 
>>> 2.34.1
>>>
>>