netdev - [PATCH net-next v2 07/14] net: ipv6: ip6mr: Fix in/out netdev to pass to the FORWARD chain

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Message-ID: <c169efdd39667586bec562c9734080e1ba7da255.1749757582.git.petrm@nvidia.com>
Date: Thu, 12 Jun 2025 22:10:41 +0200
From: Petr Machata <petrm@...dia.com>
To: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
	<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, David Ahern <dsahern@...il.com>,
	<netdev@...r.kernel.org>
CC: Simon Horman <horms@...nel.org>, Nikolay Aleksandrov
	<razor@...ckwall.org>, Ido Schimmel <idosch@...dia.com>, Petr Machata
	<petrm@...dia.com>, <mlxsw@...dia.com>, YOSHIFUJI Hideaki
	<yoshfuji@...ux-ipv6.org>
Subject: [PATCH net-next v2 07/14] net: ipv6: ip6mr: Fix in/out netdev to pass to the FORWARD chain

The netfilter hook is invoked with skb->dev for input netdevice, and
vif_dev for output netdevice. However at the point of invocation, skb->dev
is already set to vif_dev, and MR-forwarded packets are reported with
in=out:

 # ip6tables -A FORWARD -j LOG --log-prefix '[forw]'
 # cd tools/testing/selftests/net/forwarding
 # ./router_multicast.sh
 # dmesg | fgrep '[forw]'
 [ 1670.248245] [forw]IN=v5 OUT=v5 [...]

For reference, IPv4 MR code shows in and out as appropriate.
Fix by caching skb->dev and using the updated value for output netdev.

Fixes: 7bc570c8b4f7 ("[IPV6] MROUTE: Support multicast forwarding.")
Signed-off-by: Petr Machata <petrm@...dia.com>
Reviewed-by: Ido Schimmel <idosch@...dia.com>
Reviewed-by: Nikolay Aleksandrov <razor@...ckwall.org>
---

Notes:
    This never worked correctly, hence going through net-next.
---
CC: YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>

 net/ipv6/ip6mr.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
index 3276cde5ebd7..63c90dae6cbf 100644
--- a/net/ipv6/ip6mr.c
+++ b/net/ipv6/ip6mr.c
@@ -2039,6 +2039,7 @@ static int ip6mr_forward2(struct net *net, struct mr_table *mrt,
 			  struct sk_buff *skb, int vifi)
 {
 	struct vif_device *vif = &mrt->vif_table[vifi];
+	struct net_device *indev = skb->dev;
 	struct net_device *vif_dev;
 	struct ipv6hdr *ipv6h;
 	struct dst_entry *dst;
@@ -2101,7 +2102,7 @@ static int ip6mr_forward2(struct net *net, struct mr_table *mrt,
 	IP6CB(skb)->flags |= IP6SKB_FORWARDED;
 
 	return NF_HOOK(NFPROTO_IPV6, NF_INET_FORWARD,
-		       net, NULL, skb, skb->dev, vif_dev,
+		       net, NULL, skb, indev, skb->dev,
 		       ip6mr_forward2_finish);
 
 out_free:
-- 
2.49.0