[PATCH net 4/9] virtio-net: correctly handle XDP_PASS for linearized packets

[Jason Wang]

When XDP_PASS were determined for linearized packets, we try to get
new buffers in the virtqueue and build skbs from them. This is wrong,
we should create skbs based on existed buffers instead. Fixing them by
creating skb based on xdp_page.

With this patch "ping 192.168.100.4 -s 3900 -M do" works for XDP_PASS.

Cc: John Fastabend <john.r.fastabend@xxxxxxxxx>
Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
---
 drivers/net/virtio_net.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 58ad40e..470293e 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -578,8 +578,14 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
 		act = do_xdp_prog(vi, rq, xdp_prog, xdp_page, offset, len);
 		switch (act) {
 		case XDP_PASS:
-			if (unlikely(xdp_page != page))
-				__free_pages(xdp_page, 0);
+			/* We can only create skb based on xdp_page. */
+			if (unlikely(xdp_page != page)) {
+				rcu_read_unlock();
+				put_page(page);
+				head_skb = page_to_skb(vi, rq, xdp_page,
+						       0, len, PAGE_SIZE);
+				return head_skb;
+			}
 			break;
 		case XDP_TX:
 			if (unlikely(xdp_page != page))
-- 
2.7.4