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

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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@xxxxxxxxxxxxxx
Signed-off-by: Marco Pinna <marco.pinn95@xxxxxxxxx>
net/vmw_vsock/virtio_transport.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

Reviewed-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>

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)

-		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)

+		virtio_transport_deliver_tap_pkt(skb);
		if (reply) {
			struct virtqueue *rx_vq = vsock->vqs[VSOCK_VQ_RX];
			int val;

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