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Date:   Mon, 23 Oct 2023 17:13:07 +0200
From:   Stefano Garzarella <sgarzare@redhat.com>
To:     Alexandru Matei <alexandru.matei@uipath.com>
Cc:     Stefan Hajnoczi <stefanha@redhat.com>,
        "David S . Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>, kvm@vger.kernel.org,
        virtualization@lists.linux-foundation.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Mihai Petrisor <mihai.petrisor@uipath.com>,
        Viorel Canja <viorel.canja@uipath.com>
Subject: Re: [PATCH v2] vsock/virtio: initialize the_virtio_vsock before
 using VQs
Message-ID: <dynlbzmgtr35byn5etbar33ufhweii6gk2pct5wpqxpqubchce@cltop4aar7r6>
References: <20231023140833.11206-1-alexandru.matei@uipath.com>
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 <0624137c-85cf-4086-8256-af2b8405f434@uipath.com>
 <632465d0-e04c-4e10-abb9-a740d6e3dc30@uipath.com>
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On Mon, Oct 23, 2023 at 05:59:45PM +0300, Alexandru Matei wrote:
>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@uipath.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.

Why?

If `rx_run` is false, we shouldn't need to send replies to the host 
IIUC.

If we need this instead, please add a comment in the code, but also in 
the commit, because it's not clear why.

>>
>
>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.

Yep, this could be another option, but we need to change the name of 
that function in this case.

Stefano

>
>>>
>>> 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
>>>>
>>>
>