vfio/pci: Fix ordering of eventfd vs virqfd shutdown

Both the INTx and MSI/X disable paths do an eventfd_ctx_put() for the
trigger eventfd before calling vfio_virqfd_disable() any potential
mask and unmask eventfds.  This opens a use-after-free race where an
inopportune irqfd can reference the freed signalling eventfd.  Reorder
to avoid this possibility.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/pci/vfio_pci_intrs.c

@@ -228,9 +228,9 @@ static int vfio_intx_set_signal(struct vfio_pci_device *vdev, int fd)
 
 static void vfio_intx_disable(struct vfio_pci_device *vdev)
 {
-	vfio_intx_set_signal(vdev, -1);
 	vfio_virqfd_disable(&vdev->ctx[0].unmask);
 	vfio_virqfd_disable(&vdev->ctx[0].mask);
+	vfio_intx_set_signal(vdev, -1);
 	vdev->irq_type = VFIO_PCI_NUM_IRQS;
 	vdev->num_ctx = 0;
 	kfree(vdev->ctx);
@@ -401,13 +401,13 @@ static void vfio_msi_disable(struct vfio_pci_device *vdev, bool msix)
 	struct pci_dev *pdev = vdev->pdev;
 	int i;
 
-	vfio_msi_set_block(vdev, 0, vdev->num_ctx, NULL, msix);
-
 	for (i = 0; i < vdev->num_ctx; i++) {
 		vfio_virqfd_disable(&vdev->ctx[i].unmask);
 		vfio_virqfd_disable(&vdev->ctx[i].mask);
 	}
 
+	vfio_msi_set_block(vdev, 0, vdev->num_ctx, NULL, msix);
+
 	if (msix) {
 		pci_disable_msix(vdev->pdev);
 		kfree(vdev->msix);