netdev - Re: [RFC PATCH net] Revert "ipv6: ndisc: inherit metadata dst when creating ndisc requests"

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Message-ID: <20151130122038.26c5de6b@griffin>
Date:	Mon, 30 Nov 2015 12:20:38 +0100
From:	Jiri Benc <jbenc@...hat.com>
To:	Nicolas Dichtel <nicolas.dichtel@...nd.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	Thomas Graf <tgraf@...g.ch>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>
Subject: Re: [RFC PATCH net] Revert "ipv6: ndisc: inherit metadata dst when
 creating ndisc requests"

On Fri, 27 Nov 2015 18:17:05 +0100, Nicolas Dichtel wrote:
> This reverts commit ab450605b35caa768ca33e86db9403229bf42be4.
> 
> In IPv6, we cannot inherit the dst of the original dst. ndisc packets
> are IPv6 packets and may take another route than the original packet.
> 
> This patch breaks the following scenario: a packet comes from eth0 and
> is forwarded through vxlan1. The encapsulated packet triggers an NS
> which cannot be sent because of the wrong route.
> 
> CC: Jiri Benc <jbenc@...hat.com>
> CC: Thomas Graf <tgraf@...g.ch>
> Signed-off-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>
> ---
> 
> I know that this is not the right fix, it's why I've put RFC ;-)

I'm actually okay with applying the revert for now. The revert is not
the right fix but at least it is less wrong than the current state.

The problem is deeper. I fixed the IPv4 part in commit 63d008a4e9ee
("ipv4: send arp replies to the correct tunnel") but for IPv6, I don't
know how to fix it. We already have dst set for IPv6, thus we cannot
use it to carry lwtunnel metadata for ndisc replies.

I tried to consult this with a couple of people, haven't met with much
interest.

> Should the right fix only do a copy of dst metadata in the new dst?

Copy of the dst (I'm afraid we cannot just set the ->lwtstate field,
the same dst_entry may be shared between different tunnels) is pretty
much the only thing I could think of.

> Feedback is welcomed.

Yes.

Thanks,

 Jiri

-- 
Jiri Benc
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