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

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, May 14, 2026 at 04:57:16PM +0200, Stefano Garzarella wrote:
> 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
> > 


And so the bag of hacks grows. I feel this is energy not well spent.
Please, let us fix this properly *first*. And then worry about how to
backport.  Maybe it will not be so terrible to backport after all.