netdev - Re: [PATCH net v2] vsock/virtio: fix packet delivery to tap device

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Message-ID: <tglqxtqa47wu53idfssswmrb6ulhnkdlavt27qoxhp2hniwgxc@j3fmzh5wowbc>
Date: Fri, 29 Mar 2024 17:22:00 +0100
From: Stefano Garzarella <sgarzare@...hat.com>
To: Marco Pinna <marco.pinn95@...il.com>
Cc: stefanha@...hat.com, davem@...emloft.net, edumazet@...gle.com, 
	kuba@...nel.org, pabeni@...hat.com, ggarcia@...c.uab.cat, jhansen@...are.com, 
	kvm@...r.kernel.org, virtualization@...ts.linux.dev, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org, stable@....kernel.org
Subject: Re: [PATCH net v2] vsock/virtio: fix packet delivery to tap device

On Fri, Mar 29, 2024 at 05:12:59PM +0100, Marco Pinna wrote:
>Commit 82dfb540aeb2 ("VSOCK: Add virtio vsock vsockmon hooks") added
>virtio_transport_deliver_tap_pkt() for handing packets to the
>vsockmon device. However, in virtio_transport_send_pkt_work(),
>the function is called before actually sending the packet (i.e.
>before placing it in the virtqueue with virtqueue_add_sgs() and checking
>whether it returned successfully).
>Queuing the packet in the virtqueue can fail even multiple times.
>However, in virtio_transport_deliver_tap_pkt() we deliver the packet
>to the monitoring tap interface only the first time we call it.
>This certainly avoids seeing the same packet replicated multiple times
>in the monitoring interface, but it can show the packet sent with the
>wrong timestamp or even before we succeed to queue it in the virtqueue.
>
>Move virtio_transport_deliver_tap_pkt() after calling virtqueue_add_sgs()
>and making sure it returned successfully.
>
>Fixes: 82dfb540aeb2 ("VSOCK: Add virtio vsock vsockmon hooks")
>Cc: stable@....kernel.org
>Signed-off-by: Marco Pinna <marco.pinn95@...il.com>
>---
> net/vmw_vsock/virtio_transport.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)

Reviewed-by: Stefano Garzarella <sgarzare@...hat.com>

>
>diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
>index 1748268e0694..ee5d306a96d0 100644
>--- a/net/vmw_vsock/virtio_transport.c
>+++ b/net/vmw_vsock/virtio_transport.c
>@@ -120,7 +120,6 @@ virtio_transport_send_pkt_work(struct work_struct *work)
> 		if (!skb)
> 			break;
>
>-		virtio_transport_deliver_tap_pkt(skb);
> 		reply = virtio_vsock_skb_reply(skb);
> 		sgs = vsock->out_sgs;
> 		sg_init_one(sgs[out_sg], virtio_vsock_hdr(skb),
>@@ -170,6 +169,8 @@ virtio_transport_send_pkt_work(struct work_struct *work)
> 			break;
> 		}
>
>+		virtio_transport_deliver_tap_pkt(skb);
>+
> 		if (reply) {
> 			struct virtqueue *rx_vq = vsock->vqs[VSOCK_VQ_RX];
> 			int val;
>-- 
>2.44.0
>