Virtualization - Mar 2011 - [PATCH] virtio_pci: Prevent double-free of pci regions after device hot-unplug

In the case where a virtio-console port is in use (opened by a program)
and a virtio-console device is removed, the port is kept around but all
the virtio-related state is assumed to be gone.

When the port is finally released (close() called), we call
device_destroy() on the port's device.  This results in the parent
device's structures to be freed as well.  This includes the PCI regions
for the virtio-console PCI device.

Once this is done, however, virtio_pci_release_dev() kicks in, as the
last ref to the virtio device is now gone, and attempts to do

     pci_iounmap(pci_dev, vp_dev->ioaddr);
     pci_release_regions(pci_dev);
     pci_disable_device(pci_dev);

which results in a double-free warning.

Move the code that releases regions, etc., to the virtio_pci_remove()
function, and all that's now left in release_dev is the final freeing of
the vp_dev.

Signed-off-by: Amit Shah <amit.shah at redhat.com>
---
 drivers/virtio/virtio_pci.c |   15 ++++++++-------
 1 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
index 4fb5b2b..4bcc8b8 100644
--- a/drivers/virtio/virtio_pci.c
+++ b/drivers/virtio/virtio_pci.c
@@ -590,15 +590,10 @@ static struct virtio_config_ops virtio_pci_config_ops = {
 
 static void virtio_pci_release_dev(struct device *_d)
 {
-	struct virtio_device *dev = container_of(_d, struct virtio_device, dev);
+	struct virtio_device *dev = container_of(_d, struct virtio_device,
+						 dev);
 	struct virtio_pci_device *vp_dev = to_vp_device(dev);
-	struct pci_dev *pci_dev = vp_dev->pci_dev;
 
-	vp_del_vqs(dev);
-	pci_set_drvdata(pci_dev, NULL);
-	pci_iounmap(pci_dev, vp_dev->ioaddr);
-	pci_release_regions(pci_dev);
-	pci_disable_device(pci_dev);
 	kfree(vp_dev);
 }
 
@@ -681,6 +676,12 @@ static void __devexit virtio_pci_remove(struct pci_dev
*pci_dev)
 	struct virtio_pci_device *vp_dev = pci_get_drvdata(pci_dev);
 
 	unregister_virtio_device(&vp_dev->vdev);
+
+	vp_del_vqs(&vp_dev->vdev);
+	pci_set_drvdata(pci_dev, NULL);
+	pci_iounmap(pci_dev, vp_dev->ioaddr);
+	pci_release_regions(pci_dev);
+	pci_disable_device(pci_dev);
 }
 
 #ifdef CONFIG_PM
-- 
1.7.4

On Mon, 14 Mar 2011 17:45:02 +0530, Amit Shah <amit.shah at redhat.com>
wrote:
> In the case where a virtio-console port is in use (opened by a program)
> and a virtio-console device is removed, the port is kept around but all
> the virtio-related state is assumed to be gone.
> 
> When the port is finally released (close() called), we call
> device_destroy() on the port's device.  This results in the parent
> device's structures to be freed as well.  This includes the PCI regions
> for the virtio-console PCI device.
> 
> Once this is done, however, virtio_pci_release_dev() kicks in, as the
> last ref to the virtio device is now gone, and attempts to do
> 
>      pci_iounmap(pci_dev, vp_dev->ioaddr);
>      pci_release_regions(pci_dev);
>      pci_disable_device(pci_dev);
> 
> which results in a double-free warning.
> 
> Move the code that releases regions, etc., to the virtio_pci_remove()
> function, and all that's now left in release_dev is the final freeing
of
> the vp_dev.
> 
> Signed-off-by: Amit Shah <amit.shah at redhat.com>
Applied.

Thanks,
Rusty.