Re: [Qemu-devel] [PATCH for 2.3 V2] virtio-net: validate backend queue numbers against bus limitation

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Fri, Mar 20, 2015 at 02:07:50PM +0800, Jason Wang wrote:
> We don't validate the backend queue numbers against bus limitation,
> this will easily crash qemu if it exceeds the limitation which will
> hit the abort() in virtio_del_queue(). An example is trying to
> starting a virtio-net device with 256 queues. E.g:
> 
> ./qemu-system-x86_64 -netdev tap,id=hn0,queues=256 -device
> virtio-net-pci,netdev=hn0
> 
> Fixing this by doing the validation and fail early.
> 
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: qemu-stable <qemu-stable@nongnu.org>
> Signed-off-by: Jason Wang <jasowang@redhat.com>
> ---
> Changes from V1:
> Tweak the commit log.
> ---
>  hw/net/virtio-net.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index 27adcc5..59f76bc 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -1588,6 +1588,13 @@ static void virtio_net_device_realize(DeviceState *dev, Error **errp)
>      virtio_init(vdev, "virtio-net", VIRTIO_ID_NET, n->config_size);
>  
>      n->max_queues = MAX(n->nic_conf.peers.queues, 1);
> +    if (n->max_queues * 2 + 1 > VIRTIO_PCI_QUEUE_MAX) {
> +        error_setg(errp, "Invalid number of queues (= %" PRIu32 "), "
> +                   "must be a postive integer less than %d.",
> +                   n->max_queues, (VIRTIO_PCI_QUEUE_MAX - 1) / 2);
> +        virtio_cleanup(vdev);
> +        return;
> +    }

If VIRTIO_PCI_QUEUE_MAX is really PCI-only then this is a layering
violation.  Virtio devices should not assume a particular transport
(PCI, CCW, etc).

Either the constant should be renamed if it truly applies to all
transports, or there should be a virtio_get_max_queues() function that
lets the transport pick a value.

That said, virtio-scsi.c already checks VIRTIO_PCI_QUEUE_MAX so maybe
this patch is fine and a cleanup should be written later:

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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