Re: [Qemu-devel] [PATCH 1/1] virtio-net: check guest header length is valid

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Jul 16, 2019 at 03:38:09AM +0000, Oleinik, Alexander wrote:
> virtio-net checks that the "out" sg is longer than the guest header, but
> this check can be skipped if has_net_hdr is 0. Also perform this check
> if host_hdr_len != guest_hdr_len

This explanation is way less clear than what you have in 0/1.
I suggest you just move the log here.

> 
> Signed-off-by: Alexander Oleinik <alxndr@bu.edu>
> ---
>  hw/net/virtio-net.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index b9e1cd71cf..46d715b4f5 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -2064,7 +2064,18 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q)
>           */
>          assert(n->host_hdr_len <= n->guest_hdr_len);
>          if (n->host_hdr_len != n->guest_hdr_len) {
> -            unsigned sg_num = iov_copy(sg, ARRAY_SIZE(sg),
> +            unsigned sg_num;
> +
> +            if (!n->has_vnet_hdr) {
> +                if (iov_to_buf(out_sg, out_num, 0, &mhdr, n->guest_hdr_len) <
> +                    n->guest_hdr_len) {
> +                    virtio_error(vdev, "virtio-net header incorrect");
> +                    virtqueue_detach_element(q->tx_vq, elem, 0);
> +                    g_free(elem);
> +                    return -EINVAL;
> +                }
> +            }

This code is duplicated from above. I also suspect some parts are missing
here (such as header endian-ness swap).
Pls find a way not to duplicate the code.


> +            sg_num = iov_copy(sg, ARRAY_SIZE(sg),
>                                         out_sg, out_num,
>                                         0, n->host_hdr_len);
>              sg_num += iov_copy(sg + sg_num, ARRAY_SIZE(sg) - sg_num,
> -- 
> 2.20.1