Re: [PATCH net v3 1/2] vsock/virtio: reset connection on receiving queue overflow

[Stefano Garzarella <sgarzare@redhat.com>]

On Wed, May 13, 2026 at 12:54:16PM +0200, Stefano Garzarella wrote:
>From: Stefano Garzarella <sgarzare@redhat.com>
>
>When there is no more space to queue an incoming packet, the packet is
>silently dropped. This causes data loss without any notification to
>either peer, since there is no retransmission.
>
>Under normal circumstances, this should never happen. However, it could
>happen if the other peer doesn't respect the credit, or if the skb
>overhead, which we recently began to take into account with commit
>059b7dbd20a6 ("vsock/virtio: fix potential unbounded skb queue"),
>is too high.
>
>Fix this by resetting the connection and setting the local socket error
>to ENOBUFS when virtio_transport_recv_enqueue() can no longer queue a
>packet, so both peers are explicitly notified of the failure rather than
>silently losing data.
>
>Fixes: ae6fcfbf5f03 ("vsock/virtio: discard packets if credit is not respected")
>Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
>---
> net/vmw_vsock/virtio_transport_common.c | 19 ++++++++++++++-----
> 1 file changed, 14 insertions(+), 5 deletions(-)
>
>diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
>index 989cc252d3d3..4a4ac69d1ad1 100644
>--- a/net/vmw_vsock/virtio_transport_common.c
>+++ b/net/vmw_vsock/virtio_transport_common.c
>@@ -1350,7 +1350,7 @@ virtio_transport_recv_connecting(struct sock *sk,
> 	return err;
> }
>
>-static void
>+static bool
> virtio_transport_recv_enqueue(struct vsock_sock *vsk,
> 			      struct sk_buff *skb)
> {
>@@ -1365,10 +1365,8 @@ virtio_transport_recv_enqueue(struct vsock_sock *vsk,
> 	spin_lock_bh(&vvs->rx_lock);
>
> 	can_enqueue = virtio_transport_inc_rx_pkt(vvs, len);
>-	if (!can_enqueue) {
>-		free_pkt = true;
>+	if (!can_enqueue)
> 		goto out;
>-	}
>
> 	if (le32_to_cpu(hdr->flags) & VIRTIO_VSOCK_SEQ_EOM)
> 		vvs->msg_count++;
>@@ -1408,6 +1406,8 @@ virtio_transport_recv_enqueue(struct vsock_sock *vsk,
> 	spin_unlock_bh(&vvs->rx_lock);
> 	if (free_pkt)
> 		kfree_skb(skb);
>+
>+	return can_enqueue;
> }
>
> static int
>@@ -1420,7 +1420,16 @@ virtio_transport_recv_connected(struct sock *sk,
>
> 	switch (le16_to_cpu(hdr->op)) {
> 	case VIRTIO_VSOCK_OP_RW:
>-		virtio_transport_recv_enqueue(vsk, skb);
>+		if (!virtio_transport_recv_enqueue(vsk, skb)) {
>+			/* There is no more space to queue the packet, so let's
>+			 * close the connection; otherwise, we'll lose data.
>+			 */
>+			(void)virtio_transport_reset(vsk, skb);
>+			sk->sk_state = TCP_CLOSE;
>+			sk->sk_err = ENOBUFS;
>+			sk_error_report(sk);

sashiko reported some issues related to setting TCP_CLOSE state and not 
removing the socket from the connect table:
https://sashiko.dev/#/patchset/20260513105417.56761-1-sgarzare%40redhat.com

I'll change this by calling virtio_transport_do_close() and 
vsock_remove_sock() in the next version.

Stefano

>+			break;
>+		}
> 		vsock_data_ready(sk);
> 		return err;
> 	case VIRTIO_VSOCK_OP_CREDIT_REQUEST:
>-- 
>2.54.0
>