From e469db25d6b2e5c71cd15451889226641c53a5cd Mon Sep 17 00:00:00 2001 From: P J P Date: Mon, 25 Jul 2016 17:37:18 +0530 Subject: [PATCH] virtio: error out if guest exceeds virtqueue size A broken or malicious guest can submit more requests than the virtqueue size permits. The guest can submit requests without bothering to wait for completion and is therefore not bound by virtqueue size. This requires reusing vring descriptors in more than one request, which is incorrect but possible. Processing a request allocates a VirtQueueElement and therefore causes unbounded memory allocation controlled by the guest. Exit with an error if the guest provides more requests than the virtqueue size permits. This bounds memory allocation and makes the buggy guest visible to the user. Reported-by: Zhenhao Hong Signed-off-by: Stefan Hajnoczi --- hw/virtio/virtio.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c index d24f775..f8ac0fb 100644 --- a/tools/qemu-xen/hw/virtio/virtio.c +++ b/tools/qemu-xen/hw/virtio/virtio.c @@ -483,6 +483,11 @@ int virtqueue_pop(VirtQueue *vq, VirtQueueElement *elem) max = vq->vring.num; + if (vq->inuse >= max) { + error_report("Virtqueue size exceeded"); + exit(1); + } + i = head = virtqueue_get_head(vq, vq->last_avail_idx++); if (virtio_vdev_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX)) { vring_set_avail_event(vq, vq->last_avail_idx); -- 2.1.4