Re: [PATCH V2] IPv6 : add multicast routing verify which net_device is lo

From: Gao feng <redacted>
Date: Tue, 20 Dec 2011 19:10:24 +0800

quoted

In currently routing subsystem, when we lookup a multicast routing
to send muticast packets to outside, rt6_device_match will return
the rt6_info which it's match first. If we add a multicast route on
loopback devices beforce the others interface, rt6_device_match will
retrun the rt6_info which rt6i_dev->name is "lo". But, obviously,
we can't send a muticast packet to outside using loopback devices.
It case all multicast packets blocking.

Commit 4af04aba93f47699e disabled kernel add multicast route on lo
automatically. However,  we can't surmise the routing-add order or
interdict add multicast routing on loopback devices in user space.
The bug still exist. So, i think, more stronger routing subsystem is
necessary.

Signed-off-by: Wang xingtong <redacted>

Ok, this is getting rediculious.  I want to revert all of this
stuff.

How about, instead, we stop userland adding explicit addresses to the
loopback device since that's what started behaving differently
recently and causes these problems in the first place?

OK, David, I reproduce this as following :

1) ip -6 route show | grep ff00
    unreachable ff00::/8 dev lo  metric 1024  error -101
    ff00::/8 dev eth1  metric 1024

2) ip -6 route del ff00::/8 dev eth1
    ip -6 route del ff00::/8 dev lo

3) ip -6 route add ff00::/8 dev lo
    ip -6 route add ff00::/8 dev eth1

now, if we join to the multicast group with the interface index is 
specified as 0, not restrict devices( oif == 0 ), not restrict saddr ( 
saddr == :: ), rt6_device_match  will return rt6_info which 
rt6i_dev->name is "lo" all the while, and rt6i_dev->error is
"-ENETUNREACH".  we got "ENODEV" at userspace,  all multicast packets 
will be blocked .

But, in fact, eth1 can be uesd and we missed. This is a bug in routing 
system， isn't it？

This patch add multicast routing check-up in rt6_device_match to arrest
it return loopback device when we isn't specified interface and saddr.

thanks,

wang xingtong