[PATCH bpf 3/6] bpf: Fix dev's rx stats for bpf_redirect_peer traffic

[Daniel Borkmann <daniel@iogearbox.net>]

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 supported devices (that is, veth
and netkit), confusing user space metrics collectors such as cAdvisor [0],
as reported by Youlun.

Fix it by calling dev_sw_netstats_rx_add() in skb_do_redirect(), to update
RX traffic counters. Devices that support ndo_get_peer_dev _must_ use the
@tstats per-CPU counters (instead of @lstats, or @dstats).

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

Fixes: 9aa1206e8f48 ("bpf: Add redirect_peer helper")
Reported-by: Youlun Zhang <zhangyoulun@bytedance.com>
Signed-off-by: Peilin Ye <peilin.ye@bytedance.com>
Co-developed-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
---
 include/linux/netdevice.h | 3 ++-
 net/core/filter.c         | 1 +
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index a16c9cc063fe..fcfeaedb1256 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1408,7 +1408,8 @@ struct netdev_net_notifier {
  *	Add, change, delete or get information on an IPv4 tunnel.
  * struct net_device *(*ndo_get_peer_dev)(struct net_device *dev);
  *	If a device is paired with a peer device, return the peer instance.
- *	The caller must be under RCU read context.
+ *	The caller must be under RCU read context. The driver implementing
+ *	ndo_get_peer_dev must support @tstats packet accounting!
  * int (*ndo_fill_forward_path)(struct net_device_path_ctx *ctx, struct net_device_path *path);
  *     Get the forwarding path to reach the real device from the HW destination address
  * ktime_t (*ndo_get_tstamp)(struct net_device *dev,
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 ?
-- 
2.34.1