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

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

[Patrick McHardy]

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.

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

[Mario 'BitKoenig' Holbe]

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

[Patrick McHardy]

Am 24.01.2011 18:02, schrieb Mario 'BitKoenig' Holbe:
> 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...

No, ip6_route_me_harder() only attaches a new route to the packet,
the packets contents are not changed.

> 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.

No, what is happening is that radvd sends the packet with a specified
ifindex using IPV6_PKTINFO. The mangle table notices that the mark
changes and calls ip6_route_me_harder(), which performs a new route
lookup without taking the specified oif into account. It therefore
chooses the first of your two routes and sends the packet out eth1.