Re: [PATCH v2 3/4] vhost_net: validate virtio_net_hdr only if it exists

[Jason Wang <jasowang@redhat.com>]

在 2021/6/23 上午12:15, David Woodhouse 写道:
> From: David Woodhouse <dwmw@amazon.co.uk>
>
> When the underlying socket doesn't handle the virtio_net_hdr, the
> existing code in vhost_net_build_xdp() would attempt to validate stack
> noise, by copying zero bytes into the local copy of the header and then
> validating that. Skip the whole pointless pointer arithmetic and partial
> copy (of zero bytes) in this case.
>
> Fixes: 0a0be13b8fe2 ("vhost_net: batch submitting XDP buffers to underlayer sockets")
> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>


Acked-by: Jason Wang <jasowang@redhat.com>


> ---
>   drivers/vhost/net.c | 43 ++++++++++++++++++++++---------------------
>   1 file changed, 22 insertions(+), 21 deletions(-)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index df82b124170e..1e3652eb53af 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -690,7 +690,6 @@ static int vhost_net_build_xdp(struct vhost_net_virtqueue *nvq,
>   					     dev);
>   	struct socket *sock = vhost_vq_get_backend(vq);
>   	struct page_frag *alloc_frag = &net->page_frag;
> -	struct virtio_net_hdr *gso;
>   	struct xdp_buff *xdp = &nvq->xdp[nvq->batched_xdp];
>   	struct tun_xdp_hdr *hdr;
>   	size_t len = iov_iter_count(from);
> @@ -715,29 +714,31 @@ static int vhost_net_build_xdp(struct vhost_net_virtqueue *nvq,
>   		return -ENOMEM;
>   
>   	buf = (char *)page_address(alloc_frag->page) + alloc_frag->offset;
> -	copied = copy_page_from_iter(alloc_frag->page,
> -				     alloc_frag->offset +
> -				     offsetof(struct tun_xdp_hdr, gso),
> -				     sock_hlen, from);
> -	if (copied != sock_hlen)
> -		return -EFAULT;
> -
>   	hdr = buf;
> -	gso = &hdr->gso;
> -
> -	if ((gso->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) &&
> -	    vhost16_to_cpu(vq, gso->csum_start) +
> -	    vhost16_to_cpu(vq, gso->csum_offset) + 2 >
> -	    vhost16_to_cpu(vq, gso->hdr_len)) {
> -		gso->hdr_len = cpu_to_vhost16(vq,
> -			       vhost16_to_cpu(vq, gso->csum_start) +
> -			       vhost16_to_cpu(vq, gso->csum_offset) + 2);
> -
> -		if (vhost16_to_cpu(vq, gso->hdr_len) > len)
> -			return -EINVAL;
> +	if (sock_hlen) {
> +		struct virtio_net_hdr *gso = &hdr->gso;
> +
> +		copied = copy_page_from_iter(alloc_frag->page,
> +					     alloc_frag->offset +
> +					     offsetof(struct tun_xdp_hdr, gso),
> +					     sock_hlen, from);
> +		if (copied != sock_hlen)
> +			return -EFAULT;
> +
> +		if ((gso->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) &&
> +		    vhost16_to_cpu(vq, gso->csum_start) +
> +		    vhost16_to_cpu(vq, gso->csum_offset) + 2 >
> +		    vhost16_to_cpu(vq, gso->hdr_len)) {
> +			gso->hdr_len = cpu_to_vhost16(vq,
> +						      vhost16_to_cpu(vq, gso->csum_start) +
> +						      vhost16_to_cpu(vq, gso->csum_offset) + 2);
> +
> +			if (vhost16_to_cpu(vq, gso->hdr_len) > len)
> +				return -EINVAL;
> +		}
> +		len -= sock_hlen;
>   	}
>   
> -	len -= sock_hlen;
>   	copied = copy_page_from_iter(alloc_frag->page,
>   				     alloc_frag->offset + pad,
>   				     len, from);