net: veth: Account total xdp_frame len running ndo_xdp_xmit

Even if this is a theoretical issue since it is not possible to perform
XDP_REDIRECT on a non-linear xdp_frame, veth driver does not account
paged area in ndo_xdp_xmit function pointer.
Introduce xdp_get_frame_len utility routine to get the xdp_frame full
length and account total frame size running XDP_REDIRECT of a
non-linear xdp frame into a veth device.

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Toke Hoiland-Jorgensen <toke@redhat.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/54f9fd3bb65d190daf2c0bbae2f852ff16cfbaa0.1646989407.git.lorenzo@kernel.org

drivers/net/veth.c

@@ -494,7 +494,7 @@ static int veth_xdp_xmit(struct net_device *dev, int n,
 		struct xdp_frame *frame = frames[i];
 		void *ptr = veth_xdp_to_ptr(frame);
 
-		if (unlikely(frame->len > max_len ||
+		if (unlikely(xdp_get_frame_len(frame) > max_len ||
 			     __ptr_ring_produce(&rq->xdp_ring, ptr)))
 			break;
 		nxmit++;
@@ -855,7 +855,7 @@ static int veth_xdp_rcv(struct veth_rq *rq, int budget,
 			/* ndo_xdp_xmit */
 			struct xdp_frame *frame = veth_ptr_to_xdp(ptr);
 
-			stats->xdp_bytes += frame->len;
+			stats->xdp_bytes += xdp_get_frame_len(frame);
 			frame = veth_xdp_rcv_one(rq, frame, bq, stats);
 			if (frame) {
 				/* XDP_PASS */

include/net/xdp.h

@@ -343,6 +343,20 @@ out:
 	__xdp_release_frame(xdpf->data, mem);
 }
 
+static __always_inline unsigned int xdp_get_frame_len(struct xdp_frame *xdpf)
+{
+	struct skb_shared_info *sinfo;
+	unsigned int len = xdpf->len;
+
+	if (likely(!xdp_frame_has_frags(xdpf)))
+		goto out;
+
+	sinfo = xdp_get_shared_info_from_frame(xdpf);
+	len += sinfo->xdp_frags_size;
+out:
+	return len;
+}
+
 int __xdp_rxq_info_reg(struct xdp_rxq_info *xdp_rxq,
 		       struct net_device *dev, u32 queue_index,
 		       unsigned int napi_id, u32 frag_size);