[PATCH 1/1] virtio: rng: disallow multiple device registrations, fixes crashes

[Amit Shah <amit.shah@redhat.com>]

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>
---

Also valid for stable?

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

diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c
index 10fd71c..6bf4d47 100644
--- a/drivers/char/hw_random/virtio-rng.c
+++ b/drivers/char/hw_random/virtio-rng.c
@@ -92,14 +92,22 @@ static int probe_common(struct virtio_device *vdev)
 {
 	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;
 	}
 
@@ -112,6 +120,7 @@ static void remove_common(struct virtio_device *vdev)
 	busy = false;
 	hwrng_unregister(&virtio_hwrng);
 	vdev->config->del_vqs(vdev);
+	vq = NULL;
 }
 
 static int virtrng_probe(struct virtio_device *vdev)
-- 
1.8.1.2