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>

diff --git a/drivers/vfio/pci/vfio_pci_intrs.c b/drivers/vfio/pci/vfio_pci_intrs.c
index e9ea3fe..15ecfc9 100644 (file)
--- a/drivers/vfio/pci/vfio_pci_intrs.c
+++ b/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);