On Thu, Feb 02, 2023 at 04:14:51PM +0800, Heng Qi wrote:

在 2023/2/2 下午4:07, Michael S. Tsirkin 写道:

quoted

On Tue, Jan 31, 2023 at 04:50:04PM +0800, Heng Qi wrote:

quoted

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 <redacted>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
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.

Yes it would work without this, but I was keeping this because I wanted it
to handle 0 early and exit early.

Do you want to remove this?

Thanks.

why do you want to exit early?

quoted

quoted

@@ -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