virtio: rng: disallow multiple device registrations, fixes crashes

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>
Cc: stable@kernel.org

1 files changed, 11 insertions, 2 deletions

diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c
index 10fd71ccf587..6bf4d47324eb 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)