[Qemu-devel] [PATCH V2] virtio: validate the existence of handle_output before calling it

[Jason Wang <jasowang@redhat.com>]

We don't validate the existence of handle_output which may let a buggy
guest to trigger a SIGSEV easily. E.g:

1) write 10 to queue_sel to a virtio net device with only 1 queue
2) setup an arbitrary pfn
3) then notify queue 10

Fixing this by validating the existence of handle_output before.

Cc: qemu-stable@nongnu.org
Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
Changes from V1:
- check the existence of both vring.desc and handle_output in the same
  line
- describe the reproducer in the commit log
---
 hw/virtio/virtio.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 3c6e430..17c1260 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -759,8 +759,9 @@ void virtio_queue_set_align(VirtIODevice *vdev, int n, int align)
 
 void virtio_queue_notify_vq(VirtQueue *vq)
 {
-    if (vq->vring.desc) {
+    if (vq->vring.desc && vq->handle_output) {
         VirtIODevice *vdev = vq->vdev;
+
         trace_virtio_queue_notify(vdev, vq - vdev->vq, vq);
         vq->handle_output(vdev, vq);
     }
-- 
2.1.0