linux-kernel - Re: [PATCH] vsock: initialize the_virtio

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Message-ID: <f2d0aaad-70ca-4417-bf8e-0d7006be6ebc@linux.dev>
Date:   Thu, 19 Oct 2023 01:12:34 +0100
From:   Vadim Fedorenko <vadim.fedorenko@...ux.dev>
To:     Alexandru Matei <alexandru.matei@...ath.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     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>
Subject: Re: [PATCH] vsock: initialize the_virtio_vsock before using VQs

On 18/10/2023 19:32, 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>
> ---
>   net/vmw_vsock/virtio_transport.c | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
> index e95df847176b..eae0867133f8 100644
> --- a/net/vmw_vsock/virtio_transport.c
> +++ b/net/vmw_vsock/virtio_transport.c
> @@ -658,12 +658,13 @@ static int virtio_vsock_probe(struct virtio_device *vdev)
>   		vsock->seqpacket_allow = true;
>   
>   	vdev->priv = vsock;
> +	rcu_assign_pointer(the_virtio_vsock, vsock);
>   
>   	ret = virtio_vsock_vqs_init(vsock);
> -	if (ret < 0)
> +	if (ret < 0) {
> +		rcu_assign_pointer(the_virtio_vsock, NULL);
>   		goto out;
> -
> -	rcu_assign_pointer(the_virtio_vsock, vsock);
> +	}
>   
>   	mutex_unlock(&the_virtio_vsock_mutex);
>   

Looks like virtio_vsock_restore() needs the same changes. But
virtio_vsock_vqs_init() can fail only in virtio_find_vqs(). Maybe it can 
be split into 2 functions to avoid second rcu_assign_pointer() in case
of error?