Merge branch 'vsock-virtio-make-the-credit-mechanism-more-robust'

Stefano Garzarella says:

====================
vsock/virtio: make the credit mechanism more robust

This series makes the credit mechanism implemented in the
virtio-vsock devices more robust.
Patch 1 sends an update to the remote peer when the buf_alloc
change.
Patch 2 prevents a malicious peer (especially the guest) can
consume all the memory of the other peer, discarding packets
when the credit available is not respected.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

net/vmw_vsock/virtio_transport_common.c

@@ -204,10 +204,14 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
 	return virtio_transport_get_ops()->send_pkt(pkt);
 }
 
-static void virtio_transport_inc_rx_pkt(struct virtio_vsock_sock *vvs,
+static bool virtio_transport_inc_rx_pkt(struct virtio_vsock_sock *vvs,
 					struct virtio_vsock_pkt *pkt)
 {
+	if (vvs->rx_bytes + pkt->len > vvs->buf_alloc)
+		return false;
+
 	vvs->rx_bytes += pkt->len;
+	return true;
 }
 
 static void virtio_transport_dec_rx_pkt(struct virtio_vsock_sock *vvs,
@@ -458,6 +462,9 @@ void virtio_transport_set_buffer_size(struct vsock_sock *vsk, u64 val)
 		vvs->buf_size_max = val;
 	vvs->buf_size = val;
 	vvs->buf_alloc = val;
+
+	virtio_transport_send_credit_update(vsk, VIRTIO_VSOCK_TYPE_STREAM,
+					    NULL);
 }
 EXPORT_SYMBOL_GPL(virtio_transport_set_buffer_size);
 
@@ -876,14 +883,18 @@ virtio_transport_recv_enqueue(struct vsock_sock *vsk,
 			      struct virtio_vsock_pkt *pkt)
 {
 	struct virtio_vsock_sock *vvs = vsk->trans;
-	bool free_pkt = false;
+	bool can_enqueue, free_pkt = false;
 
 	pkt->len = le32_to_cpu(pkt->hdr.len);
 	pkt->off = 0;
 
 	spin_lock_bh(&vvs->rx_lock);
 
-	virtio_transport_inc_rx_pkt(vvs, pkt);
+	can_enqueue = virtio_transport_inc_rx_pkt(vvs, pkt);
+	if (!can_enqueue) {
+		free_pkt = true;
+		goto out;
+	}
 
 	/* Try to copy small packets into the buffer of last packet queued,
 	 * to avoid wasting memory queueing the entire buffer with a small