Subject: Re: netfilter: marking IPv6 packets sends them to the wrong interface

From: Patrick McHardy <[email-masked]>
Date: Mon, 24 Jan 2011 17:10:50 +0100

Am 24.01.2011 15:35, schrieb Mario 'BitKoenig' Holbe:
> On Mon, Jan 24, 2011 at 02:46:57PM +0100, Patrick McHardy wrote:
>> On 23.01.2011 13:21, Mario 'BitKoenig' Holbe wrote:
>>> Without marking everything runs as it should be.
>>> Marking eth0 packets results in all advertisements transmitted via eth1.
>>> The behaviour goes back to normal as soon as the marking disappears.
>>> I also tried marking with 0xff00 instead of 1 - same results.
>> That probably means that we're not using the correct keys
>> when rerouting in ip6_route_me_harder(). Just for testing,
>> please try to disable the ip6_route_me_harder() call in
>> net/ipv6/netfilter/ip6table_mangle.c::ip6t_mangle_out().
> 
> 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.