[PATCH net] veth: Fix RX stats for bpf_redirect_peer() traffic

[Peilin Ye <yepeilin.cs@gmail.com>]

From: Peilin Ye <peilin.ye@bytedance.com>

Traffic redirected by bpf_redirect_peer() (used by recent CNIs like
Cilium) is not accounted for in the RX stats of veth devices, confusing
user space metrics collectors such as cAdvisor [1], as reported by
Youlun.

Currently veth devices use the @lstats per-CPU counters, which only
cover TX traffic.  veth_get_stats64() actually collects RX stats of a
veth device from its peer's TX (@lstats) counters, based on the
assumption that a veth device can _only_ receive packets from its peer,
which is no longer true.

Instead, use @tstats to maintain both per-CPU RX and TX traffic counters
for each veth device, and count bpf_redirect_peer() traffic in
skb_do_redirect().

veth_stats_rx() might need a name change (perhaps to "veth_stats_xdp()")
for less confusion, but let's leave it to a separate patch to keep this
fix minimal.

[1] Specifically, the "container_network_receive_{byte,packet}s_total"
    counters are affected.

Reported-by: Youlun Zhang <zhangyoulun@bytedance.com>
Fixes: 9aa1206e8f48 ("bpf: Add redirect_peer helper")
Cc: Jiang Wang <jiang.wang@bytedance.com>
Signed-off-by: Peilin Ye <peilin.ye@bytedance.com>
---
 drivers/net/veth.c | 36 ++++++++++++++----------------------
 net/core/filter.c  |  1 +
 2 files changed, 15 insertions(+), 22 deletions(-)

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index 9980517ed8b0..df7a7c21a46d 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -373,7 +373,7 @@ static netdev_tx_t veth_xmit(struct sk_buff *skb, struct net_device *dev)
 	skb_tx_timestamp(skb);
 	if (likely(veth_forward_skb(rcv, skb, rq, use_napi) == NET_RX_SUCCESS)) {
 		if (!use_napi)
-			dev_lstats_add(dev, length);
+			dev_sw_netstats_tx_add(dev, 1, length);
 		else
 			__veth_xdp_flush(rq);
 	} else {
@@ -387,14 +387,6 @@ static netdev_tx_t veth_xmit(struct sk_buff *skb, struct net_device *dev)
 	return ret;
 }
 
-static u64 veth_stats_tx(struct net_device *dev, u64 *packets, u64 *bytes)
-{
-	struct veth_priv *priv = netdev_priv(dev);
-
-	dev_lstats_read(dev, packets, bytes);
-	return atomic64_read(&priv->dropped);
-}
-
 static void veth_stats_rx(struct veth_stats *result, struct net_device *dev)
 {
 	struct veth_priv *priv = netdev_priv(dev);
@@ -432,24 +424,24 @@ static void veth_get_stats64(struct net_device *dev,
 	struct veth_priv *priv = netdev_priv(dev);
 	struct net_device *peer;
 	struct veth_stats rx;
-	u64 packets, bytes;
 
-	tot->tx_dropped = veth_stats_tx(dev, &packets, &bytes);
-	tot->tx_bytes = bytes;
-	tot->tx_packets = packets;
+	tot->tx_dropped = atomic64_read(&priv->dropped);
+	dev_fetch_sw_netstats(tot, dev->tstats);
 
 	veth_stats_rx(&rx, dev);
 	tot->tx_dropped += rx.xdp_tx_err;
 	tot->rx_dropped = rx.rx_drops + rx.peer_tq_xdp_xmit_err;
-	tot->rx_bytes = rx.xdp_bytes;
-	tot->rx_packets = rx.xdp_packets;
+	tot->rx_bytes += rx.xdp_bytes;
+	tot->rx_packets += rx.xdp_packets;
 
 	rcu_read_lock();
 	peer = rcu_dereference(priv->peer);
 	if (peer) {
-		veth_stats_tx(peer, &packets, &bytes);
-		tot->rx_bytes += bytes;
-		tot->rx_packets += packets;
+		struct rtnl_link_stats64 tot_peer = {};
+
+		dev_fetch_sw_netstats(&tot_peer, peer->tstats);
+		tot->rx_bytes += tot_peer.tx_bytes;
+		tot->rx_packets += tot_peer.tx_packets;
 
 		veth_stats_rx(&rx, peer);
 		tot->tx_dropped += rx.peer_tq_xdp_xmit_err;
@@ -1508,13 +1500,13 @@ static int veth_dev_init(struct net_device *dev)
 {
 	int err;
 
-	dev->lstats = netdev_alloc_pcpu_stats(struct pcpu_lstats);
-	if (!dev->lstats)
+	dev->tstats = netdev_alloc_pcpu_stats(struct pcpu_sw_netstats);
+	if (!dev->tstats)
 		return -ENOMEM;
 
 	err = veth_alloc_queues(dev);
 	if (err) {
-		free_percpu(dev->lstats);
+		free_percpu(dev->tstats);
 		return err;
 	}
 
@@ -1524,7 +1516,7 @@ static int veth_dev_init(struct net_device *dev)
 static void veth_dev_free(struct net_device *dev)
 {
 	veth_free_queues(dev);
-	free_percpu(dev->lstats);
+	free_percpu(dev->tstats);
 }
 
 #ifdef CONFIG_NET_POLL_CONTROLLER
diff --git a/net/core/filter.c b/net/core/filter.c
index 21d75108c2e9..7aca28b7d0fd 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2492,6 +2492,7 @@ int skb_do_redirect(struct sk_buff *skb)
 			     net_eq(net, dev_net(dev))))
 			goto out_drop;
 		skb->dev = dev;
+		dev_sw_netstats_rx_add(dev, skb->len);
 		return -EAGAIN;
 	}
 	return flags & BPF_F_NEIGH ?
-- 
2.20.1