linux-kernel - [PATCH] ipv6: icmp6: Allow icmp messages to be looped back

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Message-Id: <1513163697-21136-1-git-send-email-redmcg@redmandi.dyndns.org>
Date:   Wed, 13 Dec 2017 22:14:57 +1100
From:   Brendan McGrath <redmcg@...mandi.dyndns.org>
To:     "David S . Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Brendan McGrath <redmcg@...mandi.dyndns.org>
Subject: [PATCH] ipv6: icmp6: Allow icmp messages to be looped back

One example of when an ICMPv6 packet is required to be looped back is
when a host acts as both a Multicast Listener and a Multicast Router.

A Multicast Router will listen on address ff02::16 for MLDv2 messages.

Currently, MLDv2 messages originating from a Multicast Listener running
on the same host as the Multicast Router are not being delivered to the
Multicast Router. This is due to dst.input being assigned the default
value of dst_discard.

This results in the packet being looped back but discarded before being
delivered to the Multicast Router.

This patch sets dst.input to ip6_input to ensure a looped back packet
is delivered to the Multicast Router.

Signed-off-by: Brendan McGrath <redmcg@...mandi.dyndns.org>
---

I considered putting this in mld_sendpack after the call to icmp6_dst_alloc
but it looks like igmp6_send could use this fix too.

In the end I followed the example set by addrconf_dst_alloc

 net/ipv6/route.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index b3f4d19..5c014ce 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -2336,6 +2336,7 @@ struct dst_entry *icmp6_dst_alloc(struct net_device *dev,
 	}

 	rt->dst.flags |= DST_HOST;
+	rt->dst.input = ip6_input;
 	rt->dst.output  = ip6_output;
 	rt->rt6i_gateway  = fl6->daddr;
 	rt->rt6i_dst.addr = fl6->daddr;
-- 
2.7.4