Subject: Re: [PATCH net-next] ipv6: addrconf: fix mcast route for GRE devices

From: Hannes Frederic Sowa <[email-masked]>
Date: Wed, 30 Jul 2014 17:14:42 +0200

Hi,

On Mi, 2014-07-30 at 02:55 +0200, David Lamparter wrote:
> GRE devices, for some reason, were coming up with an autoconfigured
> address, but no ff00::/8 route in the local table.  This breaks any kind
> of multicast, in particular OSPFv3, mDNS, - and ND.  In fact, IPv6 only
> works at all because there is little need for ND on PtP devices.
> 
> Adding any other IPv6 address on the device would rectify this issue
> through inet6_addr_add()/addrconf_add_dev() - and would leave the route
> around even if the address was later removed.  (This is probably why
> this issue was not discovered earlier.  AFAICS it has been there from
> the beginning, e.g. aee80b5 "generate link local address for GRE
> tunnel")

Yep, this is poor, but changing this will break user space...

> (Note: multicast is supported on GRE devices of all kinds, including PtP
> GRE, P-t-Mcast GRE and NBMA-GRE.)
> 
> Fixes: aee80b54b235 (ipv6: generate link local address for GRE tunnel)
> Signed-off-by: David Lamparter <[email-masked]>
> Cc: Stephen Hemminger <[email-masked]>

We should install routes before joining LL, I would go with

        idev = addrconf_add_dev(dev);
        if (IS_ERR(idev))
                return;

in addrconf_gre_config etc.

Looks like we don't correctly configure ARPHRD_IP6GRE gre tunnels...

> ---
>  net/ipv6/addrconf.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index 0b239fc..655a0df 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -2824,6 +2824,7 @@ static void addrconf_gre_config(struct net_device *dev)
>  	}
>  
>  	addrconf_addr_gen(idev, true);
> +	addrconf_add_mroute(dev);
>  }
>  #endif
>  

Thanks,
Hannes