[ 02/40] virtio: rng: disallow multiple device registrations, fixes crashes

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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

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

From: Amit Shah <amit.shah@redhat.com>

commit e84e7a56a3aa2963db506299e29a5f3f09377f9b upstream.

The code currently only supports one virtio-rng device at a time.
Invoking guests with multiple devices causes the guest to blow up.

Check if we've already registered and initialised the driver.  Also
cleanup in case of registration errors or hot-unplug so that a new
device can be used.

Reported-by: Peter Krempa <pkrempa@redhat.com>
Reported-by: <yunzheng@redhat.com>
Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/char/hw_random/virtio-rng.c |   13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

--- a/drivers/char/hw_random/virtio-rng.c
+++ b/drivers/char/hw_random/virtio-rng.c
@@ -88,14 +88,22 @@ static int virtrng_probe(struct virtio_d
 {
 	int err;
 
+	if (vq) {
+		/* We only support one device for now */
+		return -EBUSY;
+	}
 	/* We expect a single virtqueue. */
 	vq = virtio_find_single_vq(vdev, random_recv_done, "input");
-	if (IS_ERR(vq))
-		return PTR_ERR(vq);
+	if (IS_ERR(vq)) {
+		err = PTR_ERR(vq);
+		vq = NULL;
+		return err;
+	}
 
 	err = hwrng_register(&virtio_hwrng);
 	if (err) {
 		vdev->config->del_vqs(vdev);
+		vq = NULL;
 		return err;
 	}
 
@@ -107,6 +115,7 @@ static void __devexit virtrng_remove(str
 	vdev->config->reset(vdev);
 	hwrng_unregister(&virtio_hwrng);
 	vdev->config->del_vqs(vdev);
+	vq = NULL;
 }
 
 static struct virtio_device_id id_table[] = {