On Sun, Apr 16, 2023 at 10:46:07AM +0300, Alvaro Karsz wrote:
> Check vring size and fail probe if a transmit/receive vring size is
> smaller than MAX_SKB_FRAGS + 2.
>
> At the moment, any vring size is accepted. This is problematic because
> it may result in attempting to transmit a packet with more fragments
> than there are descriptors in the ring.
>
> Furthermore, it leads to an immediate bug:
>
> The condition: (sq->vq->num_free >= 2 + MAX_SKB_FRAGS) in
> virtnet_poll_cleantx and virtnet_poll_tx always evaluates to false,
> so netif_tx_wake_queue is not called, leading to TX timeouts.
>
> Signed-off-by: Alvaro Karsz <alvaro.karsz@xxxxxxxxxxxxx>
> ---
> drivers/net/virtio_net.c | 24 ++++++++++++++++++++++++
> 1 file changed, 24 insertions(+)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 2396c28c012..59676252c5c 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -3745,6 +3745,26 @@ static int init_vqs(struct virtnet_info *vi)
> return ret;
> }
>
> +static int virtnet_validate_vqs(struct virtnet_info *vi)
> +{
> + u32 i, min_size = roundup_pow_of_two(MAX_SKB_FRAGS + 2);
why power of two?
> +
> + /* Transmit/Receive vring size must be at least MAX_SKB_FRAGS + 2
> + * (fragments + linear part + virtio header)
> + */
> + for (i = 0; i < vi->max_queue_pairs; i++) {
> + if (virtqueue_get_vring_size(vi->sq[i].vq) < min_size ||
> + virtqueue_get_vring_size(vi->rq[i].vq) < min_size) {
> + dev_warn(&vi->vdev->dev,
> + "Transmit/Receive virtqueue vring size must be at least %u\n",
> + min_size);
> + return -EINVAL;
> + }
> + }
> +
> + return 0;
> +}
> +
> #ifdef CONFIG_SYSFS
> static ssize_t mergeable_rx_buffer_size_show(struct netdev_rx_queue *queue,
> char *buf)
> @@ -4056,6 +4076,10 @@ static int virtnet_probe(struct virtio_device *vdev)
> if (err)
> goto free;
>
> + err = virtnet_validate_vqs(vi);
> + if (err)
> + goto free_vqs;
> +
> #ifdef CONFIG_SYSFS
> if (vi->mergeable_rx_bufs)
> dev->sysfs_rx_queue_group = &virtio_net_mrg_rx_group;
> --
> 2.34.1
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