From: Brian Foley Subject: virtio_mmio: Don't attempt to create empty virtqueues Date: Mon, 24 Sep 2012 14:33:42 +0100 If a virtio device reports a QueueNumMax of 0, vring_new_virtqueue() doesn't check this, and thanks to an unsigned (i < num - 1) loop guard, scribbles over memory when initialising the free list. Avoid by not trying to create zero-descriptor queues, as there's no way to do any I/O with one. Signed-off-by: Brian Foley Signed-off-by: Pawel Moll Signed-off-by: Rusty Russell --- drivers/virtio/virtio_mmio.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c index 58e2d78..6979c1b 100644 --- a/drivers/virtio/virtio_mmio.c +++ b/drivers/virtio/virtio_mmio.c @@ -332,6 +332,16 @@ static struct virtqueue *vm_setup_vq(struct virtio_device *vdev, unsigned index, * and two rings (which makes it "alignment_size * 2") */ info->num = readl(vm_dev->base + VIRTIO_MMIO_QUEUE_NUM_MAX); + + /* If the device reports a 0 entry queue, we won't be able to + * use it to perform I/O, and vring_new_virtqueue() can't create + * empty queues anyway, so don't bother to set up the device. + */ + if (info->num == 0) { + err = -ENOENT; + goto error_alloc_pages; + } + while (1) { size = PAGE_ALIGN(vring_size(info->num, VIRTIO_MMIO_VRING_ALIGN));