[PATCH 4.4 168/342] virtio_pci: fix use after free on release

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Michael S. Tsirkin <mst@redhat.com>

commit 2989be09a8a9d62a785137586ad941f916e08f83 upstream.

KASan detected a use-after-free error in virtio-pci remove code. In
virtio_pci_remove(), vp_dev is still used after being freed in
unregister_virtio_device() (in virtio_pci_release_dev() more
precisely).

To fix, keep a reference until cleanup is done.

Fixes: 63bd62a08ca4 ("virtio_pci: defer kfree until release callback")
Reported-by: Jerome Marchand <redacted>
Cc: Sasha Levin <redacted>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Jerome Marchand <redacted>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/virtio/virtio_pci_common.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/virtio/virtio_pci_common.c
+++ b/drivers/virtio/virtio_pci_common.c

@@ -545,6 +545,7 @@ err_enable_device:
 static void virtio_pci_remove(struct pci_dev *pci_dev)
 {
 	struct virtio_pci_device *vp_dev = pci_get_drvdata(pci_dev);
+	struct device *dev = get_device(&vp_dev->vdev.dev);
 
 	unregister_virtio_device(&vp_dev->vdev);
 

@@ -554,6 +555,7 @@ static void virtio_pci_remove(struct pci
 		virtio_pci_modern_remove(vp_dev);
 
 	pci_disable_device(pci_dev);
+	put_device(dev);
 }
 
 static struct pci_driver virtio_pci_driver = {