vfio/fsl-mc: Re-order vfio_fsl_mc_probe()

vfio_add_group_dev() must be called only after all of the private data in
vdev is fully setup and ready, otherwise there could be races with user
space instantiating a device file descriptor and starting to call ops.

For instance vfio_fsl_mc_reflck_attach() sets vdev->reflck and
vfio_fsl_mc_open(), called by fops open, unconditionally derefs it, which
will crash if things get out of order.

This driver started life with the right sequence, but two commits added
stuff after vfio_add_group_dev().

Fixes: 2e0d29561f ("vfio/fsl-mc: Add irq infrastructure for fsl-mc devices")
Fixes: f2ba7e8c94 ("vfio/fsl-mc: Added lock support in preparation for interrupt handling")
Co-developed-by: Diana Craciun OSS <diana.craciun@oss.nxp.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Message-Id: <5-v3-225de1400dfc+4e074-vfio1_jgg@nvidia.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/fsl-mc/vfio_fsl_mc.c

@@ -568,25 +568,41 @@ static int vfio_fsl_mc_init_device(struct vfio_fsl_mc_device *vdev)
 		dev_err(&mc_dev->dev, "VFIO_FSL_MC: Failed to setup DPRC (%d)\n", ret);
 		goto out_nc_unreg;
 	}
-
-	ret = dprc_scan_container(mc_dev, false);
-	if (ret) {
-		dev_err(&mc_dev->dev, "VFIO_FSL_MC: Container scanning failed (%d)\n", ret);
-		goto out_dprc_cleanup;
-	}
-
 	return 0;
 
-out_dprc_cleanup:
-	dprc_remove_devices(mc_dev, NULL, 0);
-	dprc_cleanup(mc_dev);
 out_nc_unreg:
 	bus_unregister_notifier(&fsl_mc_bus_type, &vdev->nb);
-	vdev->nb.notifier_call = NULL;
-
 	return ret;
 }
 
+static int vfio_fsl_mc_scan_container(struct fsl_mc_device *mc_dev)
+{
+	int ret;
+
+	/* non dprc devices do not scan for other devices */
+	if (!is_fsl_mc_bus_dprc(mc_dev))
+		return 0;
+	ret = dprc_scan_container(mc_dev, false);
+	if (ret) {
+		dev_err(&mc_dev->dev,
+			"VFIO_FSL_MC: Container scanning failed (%d)\n", ret);
+		dprc_remove_devices(mc_dev, NULL, 0);
+		return ret;
+	}
+	return 0;
+}
+
+static void vfio_fsl_uninit_device(struct vfio_fsl_mc_device *vdev)
+{
+	struct fsl_mc_device *mc_dev = vdev->mc_dev;
+
+	if (!is_fsl_mc_bus_dprc(mc_dev))
+		return;
+
+	dprc_cleanup(mc_dev);
+	bus_unregister_notifier(&fsl_mc_bus_type, &vdev->nb);
+}
+
 static int vfio_fsl_mc_probe(struct fsl_mc_device *mc_dev)
 {
 	struct iommu_group *group;
@@ -607,29 +623,39 @@ static int vfio_fsl_mc_probe(struct fsl_mc_device *mc_dev)
 	}
 
 	vdev->mc_dev = mc_dev;
-
-	ret = vfio_add_group_dev(dev, &vfio_fsl_mc_ops, vdev);
-	if (ret) {
-		dev_err(dev, "VFIO_FSL_MC: Failed to add to vfio group\n");
-		goto out_group_put;
-	}
+	mutex_init(&vdev->igate);
 
 	ret = vfio_fsl_mc_reflck_attach(vdev);
 	if (ret)
-		goto out_group_dev;
+		goto out_group_put;
 
 	ret = vfio_fsl_mc_init_device(vdev);
 	if (ret)
 		goto out_reflck;
 
-	mutex_init(&vdev->igate);
+	ret = vfio_add_group_dev(dev, &vfio_fsl_mc_ops, vdev);
+	if (ret) {
+		dev_err(dev, "VFIO_FSL_MC: Failed to add to vfio group\n");
+		goto out_device;
+	}
 
+	/*
+	 * This triggers recursion into vfio_fsl_mc_probe() on another device
+	 * and the vfio_fsl_mc_reflck_attach() must succeed, which relies on the
+	 * vfio_add_group_dev() above. It has no impact on this vdev, so it is
+	 * safe to be after the vfio device is made live.
+	 */
+	ret = vfio_fsl_mc_scan_container(mc_dev);
+	if (ret)
+		goto out_group_dev;
 	return 0;
 
-out_reflck:
-	vfio_fsl_mc_reflck_put(vdev->reflck);
 out_group_dev:
 	vfio_del_group_dev(dev);
+out_device:
+	vfio_fsl_uninit_device(vdev);
+out_reflck:
+	vfio_fsl_mc_reflck_put(vdev->reflck);
 out_group_put:
 	vfio_iommu_group_put(group, dev);
 	return ret;
@@ -646,16 +672,10 @@ static int vfio_fsl_mc_remove(struct fsl_mc_device *mc_dev)
 
 	mutex_destroy(&vdev->igate);
 
+	dprc_remove_devices(mc_dev, NULL, 0);
+	vfio_fsl_uninit_device(vdev);
 	vfio_fsl_mc_reflck_put(vdev->reflck);
 
-	if (is_fsl_mc_bus_dprc(mc_dev)) {
-		dprc_remove_devices(mc_dev, NULL, 0);
-		dprc_cleanup(mc_dev);
-	}
-
-	if (vdev->nb.notifier_call)
-		bus_unregister_notifier(&fsl_mc_bus_type, &vdev->nb);
-
 	vfio_iommu_group_put(mc_dev->dev.iommu_group, dev);
 
 	return 0;