[PATCH 1/2] hw/virtio/virtio: Don't allow guests to add/remove queues

[Peter Maydell <peter.maydell@xxxxxxxxxx>]

A queue size of 0 is used to indicate a nonexistent queue, so
don't allow the guest to flip a queue between zero-size and
non-zero-size. Don't permit setting of negative queue sizes
either.

Signed-off-by: Peter Maydell <peter.maydell@xxxxxxxxxx>
---
 hw/virtio/virtio.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 09f62c6..d5b0502 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -673,10 +673,14 @@ hwaddr virtio_queue_get_addr(VirtIODevice *vdev, int n)
 
 void virtio_queue_set_num(VirtIODevice *vdev, int n, int num)
 {
-    if (num <= VIRTQUEUE_MAX_SIZE) {
-        vdev->vq[n].vring.num = num;
-        virtqueue_init(&vdev->vq[n]);
+    if ((num == 0 && vdev->vq[n].vring.num != 0) ||
+        (num != 0 && vdev->vq[n].vring.num == 0) ||
+        (num > VIRTQUEUE_MAX_SIZE) ||
+        (num < 0)) {
+        return;
     }
+    vdev->vq[n].vring.num = num;
+    virtqueue_init(&vdev->vq[n]);
 }
 
 int virtio_queue_get_num(VirtIODevice *vdev, int n)
-- 
1.7.9.5

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