On Tue, Jan 31, 2023 at 04:50:04PM +0800, Heng Qi wrote:
> When the single-buffer xdp is loaded and after xdp_linearize_page()
> is called, *num_buf becomes 0 and (*num_buf - 1) may overflow into
> a large integer in virtnet_build_xdp_buff_mrg(), resulting in
> unexpected packet dropping.
>
> Fixes: ef75cb51f139 ("virtio-net: build xdp_buff with multi buffers")
> Signed-off-by: Heng Qi <hengqi@xxxxxxxxxxxxxxxxx>
> Reviewed-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> ---
> v1->v2:
> - Change the type of num_buf from unsigned int to int. @Michael S . Tsirkin
> - Some cleaner codes. @Michael S . Tsirkin
>
> drivers/net/virtio_net.c | 15 +++++++++------
> 1 file changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index aaa6fe9b214a..8102861785a2 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -716,7 +716,7 @@ static unsigned int virtnet_get_headroom(struct virtnet_info *vi)
> * have enough headroom.
> */
> static struct page *xdp_linearize_page(struct receive_queue *rq,
> - u16 *num_buf,
> + int *num_buf,
> struct page *p,
> int offset,
> int page_off,
> @@ -816,7 +816,7 @@ static struct sk_buff *receive_small(struct net_device *dev,
> if (unlikely(xdp_headroom < virtnet_get_headroom(vi))) {
> int offset = buf - page_address(page) + header_offset;
> unsigned int tlen = len + vi->hdr_len;
> - u16 num_buf = 1;
> + int num_buf = 1;
>
> xdp_headroom = virtnet_get_headroom(vi);
> header_offset = VIRTNET_RX_PAD + xdp_headroom;
> @@ -989,7 +989,7 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
> void *buf,
> unsigned int len,
> unsigned int frame_sz,
> - u16 *num_buf,
> + int *num_buf,
> unsigned int *xdp_frags_truesize,
> struct virtnet_rq_stats *stats)
> {
> @@ -1007,6 +1007,9 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
> xdp_prepare_buff(xdp, buf - VIRTIO_XDP_HEADROOM,
> VIRTIO_XDP_HEADROOM + vi->hdr_len, len - vi->hdr_len, true);
>
> + if (!*num_buf)
> + return 0;
> +
> if (*num_buf > 1) {
> /* If we want to build multi-buffer xdp, we need
> * to specify that the flags of xdp_buff have the
Ouch. Why is this here? Merged so pls remove by a follow up patch, the
rest of the code handles 0 fine. I'm not sure this introduces a bug by
we don't want spaghetti code.
> @@ -1020,10 +1023,10 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
> shinfo->xdp_frags_size = 0;
> }
>
> - if ((*num_buf - 1) > MAX_SKB_FRAGS)
> + if (*num_buf > MAX_SKB_FRAGS + 1)
> return -EINVAL;
>
> - while ((--*num_buf) >= 1) {
> + while (--*num_buf > 0) {
> buf = virtqueue_get_buf_ctx(rq->vq, &len, &ctx);
> if (unlikely(!buf)) {
> pr_debug("%s: rx error: %d buffers out of %d missing\n",
> @@ -1076,7 +1079,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> struct virtnet_rq_stats *stats)
> {
> struct virtio_net_hdr_mrg_rxbuf *hdr = buf;
> - u16 num_buf = virtio16_to_cpu(vi->vdev, hdr->num_buffers);
> + int num_buf = virtio16_to_cpu(vi->vdev, hdr->num_buffers);
> struct page *page = virt_to_head_page(buf);
> int offset = buf - page_address(page);
> struct sk_buff *head_skb, *curr_skb;
> --
> 2.19.1.6.gb485710b
