linux-kernel - [PATCH] vsock/virtio: fix packet delivery to tap device

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Date: Mon, 25 Mar 2024 18:12:38 +0100
From: Marco Pinna <marco.pinn95@...il.com>
To: stefanha@...hat.com,
	sgarzare@...hat.com
Cc: 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,
	Marco Pinna <marco.pinn95@...il.com>
Subject: [PATCH] vsock/virtio: fix packet delivery to tap device

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). This may cause timing issues since
the sending of the packet may fail, causing it to be re-queued
(possibly multiple times), while the tap device would show the
packet being sent correctly.

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

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