[PATCH net] ipvlan: fix RX byte accounting for local traffic

For traffic between ipvlan devices on the same lower device,
skb->len already includes the Ethernet header. Adding ETH_HLEN
again in ipvlan_rcv_frame() overcounts rx_bytes by 14 bytes per
packet. ipvlan_process_multicast() does the same for local broadcast
and multicast traffic.

Packets received from the lower device have had the Ethernet header
pulled by eth_type_trans(), so their counters still need ETH_HLEN.

Use the existing local and tx_pkt flags to distinguish these paths.

Sending five IPv4 UDP packets with 32-byte payloads between ipvlan
devices in separate network namespaces increases rx_bytes by 440
instead of 370. With this change the count is 370, while external
traffic is still counted correctly.

Fixes: 2ad7bf363841 ("ipvlan: Initial check-in of the IPVLAN driver.")
Cc: stable@vger.kernel.org
Signed-off-by: Xia Yan <redacted>
---
Tests:
  UML: 34 cases, three runs before and after, covering IPv4/IPv6,
  L2/L3/L3S unicast, L2 broadcast and joined multicast. Payloads,
  sources and RX counters were checked.

  x86_64 W=1: full builds completed before and after the fix with
  no new diagnostics, using adjusted allmodconfig and allyesconfig
  configurations with WERROR, KASAN and KCSAN disabled. The latter
  also disabled KUNIT_ALL_TESTS and dependent tests to work around
  an existing MCTP assertion. Configuration dependency changes
  were retained.

 drivers/net/ipvlan/ipvlan_core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ipvlan/ipvlan_core.c b/drivers/net/ipvlan/ipvlan_core.c
index 7ad12dc7..ba646293 100644
--- a/drivers/net/ipvlan/ipvlan_core.c
+++ b/drivers/net/ipvlan/ipvlan_core.c

@@ -276,7 +276,7 @@ void ipvlan_process_multicast(struct work_struct *work)
 			if (!(ipvlan->dev->flags & IFF_UP))
 				continue;
 			ret = NET_RX_DROP;
-			len = skb->len + ETH_HLEN;
+			len = skb->len + (tx_pkt ? 0 : ETH_HLEN);
 			nskb = skb_clone(skb, GFP_ATOMIC);
 			local_bh_disable();
 			if (nskb) {

@@ -331,7 +331,7 @@ static int ipvlan_rcv_frame(struct ipvl_addr *addr, struct sk_buff **pskb,
 	bool success = false;
 	struct sk_buff *skb = *pskb;
 
-	len = skb->len + ETH_HLEN;
+	len = skb->len + (local ? 0 : ETH_HLEN);
 	/* Only packets exchanged between two local slaves need to have
 	 * device-up check as well as skb-share check.
 	 */

base-commit: 734bef548a96e8774d6eef5dfa2026c6edc4e80b