linux-kernel - Re: netfilter: marking IPv6 packets sends them to the wrong interface

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Message-ID: <20110124170213.GB2616@darkside.kls.lan>
Date:	Mon, 24 Jan 2011 18:02:13 +0100
From:	"Mario 'BitKoenig' Holbe" <Mario.Holbe@...Ilmenau.DE>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	netfilter-devel@...r.kernel.org, linux-kernel@...r.kernel.org,
	NetDev <netdev@...r.kernel.org>
Subject: Re: netfilter: marking IPv6 packets sends them to the wrong
 interface

On Mon, Jan 24, 2011 at 05:10:50PM +0100, Patrick McHardy wrote:
> > Yes, disabling the ip6_route_me_harder() call in ip6t_mangle_out()
> > results in the advertisements being transmitted on the correct
> > interfaces
> Thanks. The problem appears to be that ip6_route_me_harder()
> only uses the socket's oif for the route lookup when the
> socket is bound to an interface, but radvd uses IPV6_PKTINFO
> to specify the outgoing interface.
> 
> I guess netfilter shouldn't be overriding IPV6_PKTINFO, but
> we unfortunately have neither an indication of this nor the
> original route lookup keys available at the time the packet
> is rerouted.

Mh, I'm not sure, but I guess an indication of netfilter not overriding
IPV6_PKTINFO could be the fact that the source address does not
change...

From my 1st mail:
| # ip6tables -t mangle -A OUTPUT -o eth0 -j MARK --set-mark 1
| # /etc/init.d/radvd start
| -> eth0: <no traffic>
| -> eth1: fe80::2a0:c9ff:fee6:90ce > ff02::1: prefix 2001:6f8:90c:10::/64
| -> eth1: fe80::2d0:b7ff:fe06:6b36 > ff02::1: prefix 2001:6f8:90c:12::/64

fe80::2d0:b7ff:fe06:6b36 is the link-local address of eth0 set by radvd
in IPV6_PKTINFO as well. This, of course, is no guarantee for
ipi6_ifindex not being changed, but I believe if something would have
changed it, it would also have changed ipi6_addr.


Mario
-- 
Doing it right is no excuse for not meeting the schedule.
                                -- Plant Manager, Delphi Corporation

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