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

[Jason Wang]

We don't validate the existence of handle_output which may let a buggy
guest to trigger a SIGSEV easily. Fix this by validate its existence
before.

Cc: address@hidden
Cc: Anthony Liguori <address@hidden>
Cc: Michael S. Tsirkin <address@hidden>
Signed-off-by: Jason Wang <address@hidden>
---
 hw/virtio/virtio.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index d735343..ffc22e8 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -761,6 +761,10 @@ void virtio_queue_notify_vq(VirtQueue *vq)
 {
     if (vq->vring.desc) {
         VirtIODevice *vdev = vq->vdev;
+
+        if (!vq->handle_output) {
+            return;
+        }
         trace_virtio_queue_notify(vdev, vq - vdev->vq, vq);
         vq->handle_output(vdev, vq);
     }
-- 
1.9.1