Linux Virtualization - Nov 2011 - [PATCH] virtio-pci: fix use after free

Commit 31a3ddda166cda86d2b5111e09ba4bda5239fae6 introduced
a use after free in virtio-pci. The main issue is
that the release method signals removal of the virtio device,
while remove signals removal of the pci device.

For example, on driver removal or hot-unplug,
virtio_pci_release_dev is called before virtio_pci_remove.
We then might get a crash as virtio_pci_remove tries to use the
device freed by virtio_pci_release_dev.

We allocate/free all resources together with the
pci device, so we can leave the release method empty.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
 drivers/virtio/virtio_pci.c |   11 ++++++-----
 1 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
index d4ed130..a989b41 100644
--- a/drivers/virtio/virtio_pci.c
+++ b/drivers/virtio/virtio_pci.c
@@ -730,11 +730,11 @@ 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_pci_device *vp_dev = to_vp_device(dev);
-
-	kfree(vp_dev);
+	/*
+	 * No need for a release method as we allocate/free
+	 * all devices together with the pci devices.
+	 * Provide an empty one to avoid getting a warning from core.
+	 */
 }
 
 /* the PCI probing function */
@@ -822,6 +822,7 @@ static void __devexit virtio_pci_remove(struct pci_dev
*pci_dev)
 	virtio_pci_iounmap(vp_dev);
 	pci_release_regions(pci_dev);
 	pci_disable_device(pci_dev);
+	kfree(vp_dev);
 }
 
 #ifdef CONFIG_PM
-- 
1.7.5.53.gc233e

On Mon, 7 Nov 2011 18:37:05 +0200, "Michael S. Tsirkin" <mst at
redhat.com> wrote:
> Commit 31a3ddda166cda86d2b5111e09ba4bda5239fae6 introduced
> a use after free in virtio-pci. The main issue is
> that the release method signals removal of the virtio device,
> while remove signals removal of the pci device.
> 
> For example, on driver removal or hot-unplug,
> virtio_pci_release_dev is called before virtio_pci_remove.
> We then might get a crash as virtio_pci_remove tries to use the
> device freed by virtio_pci_release_dev.
> 
> We allocate/free all resources together with the
> pci device, so we can leave the release method empty.
> 
> Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Applied, thanks.  Will push once it's spent a day in linux-next.

Thanks,
Rusty.

On (Mon) 07 Nov 2011 [18:37:05], Michael S. Tsirkin
wrote:
> Commit 31a3ddda166cda86d2b5111e09ba4bda5239fae6 introduced
> a use after free in virtio-pci. The main issue is
> that the release method signals removal of the virtio device,
> while remove signals removal of the pci device.
> 
> For example, on driver removal or hot-unplug,
> virtio_pci_release_dev is called before virtio_pci_remove.
> We then might get a crash as virtio_pci_remove tries to use the
> device freed by virtio_pci_release_dev.
> 
> We allocate/free all resources together with the
> pci device, so we can leave the release method empty.
> 
> Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: Amit Shah <amit.shah at redhat.com>

(note: Adding CC: stable at kernel.org to the commit log is the way
patches get automatically pulled from upstream when committed; CC'ing
stable on submissions won't help with that.)

		Amit