netdev - [PATCH net-next 2/6] ipip: allow redirecting ipip and mplsip packets to eth devices

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Date:   Fri, 25 Jun 2021 15:33:04 +0200
From:   Guillaume Nault <gnault@...hat.com>
To:     David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Simon Horman <simon.horman@...ronome.com>
Subject: [PATCH net-next 2/6] ipip: allow redirecting ipip and mplsip packets
 to eth devices

Even though ipip transports IPv4 or MPLS packets, it needs to reset the
mac_header pointer, so that other parts of the stack don't mistakenly
access the outer header after the packet has been decapsulated.

This allows to push an Ethernet header to ipip or mplsip packets and
redirect them to an Ethernet device:

  $ tc filter add dev ipip0 ingress matchall         \
      action vlan push_eth dst_mac 00:00:5e:00:53:01 \
                           src_mac 00:00:5e:00:53:00 \
      action mirred egress redirect dev eth0

Without this patch, push_eth refuses to add an ethernet header because
the skb appears to already have a MAC header.

Signed-off-by: Guillaume Nault <gnault@...hat.com>
---
 net/ipv4/ipip.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/ipv4/ipip.c b/net/ipv4/ipip.c
index d5bfa087c23a..266c65577ba6 100644
--- a/net/ipv4/ipip.c
+++ b/net/ipv4/ipip.c
@@ -242,6 +242,8 @@ static int ipip_tunnel_rcv(struct sk_buff *skb, u8 ipproto)
 			if (!tun_dst)
 				return 0;
 		}
+		skb_reset_mac_header(skb);
+
 		return ip_tunnel_rcv(tunnel, skb, tpi, tun_dst, log_ecn_error);
 	}
 
-- 
2.21.3