Date: Tue, 21 Mar 2017 01:09:47 +0100
From: Linus =?utf-8?Q?L=C3=BCssing?= <linus.luessing@c0d3.blue>
To: Pablo Neira Ayuso <pablo@netfilter.org>
Cc: netdev@vger.kernel.org, bridge@lists.linux-foundation.org,
        Florian Westphal <fw@strlen.de>, linux-kernel@vger.kernel.org,
        coreteam@netfilter.org, netfilter-devel@vger.kernel.org,
        Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>,
        "David S . Miller" <davem@davemloft.net>
Subject: Re: [Bridge] [PATCH net] bridge: ebtables: fix reception of frames
 DNAT-ed to bridge device
Message-ID: <20170321000947.GA31709@otheros>
References: <20170315031811.22714-1-linus.luessing@c0d3.blue>
 <20170315102608.GB24366@breakpoint.cc>
 <20170315104211.GA24409@salvia>
 <20170315142720.GU15692@otheros>
 <20170315181539.GA31875@salvia>
 <20170315211619.GA3464@otheros>
 <20170315220605.GA1766@salvia>
 <20170317131044.GA11995@salvia>
 <20170319165506.GA15475@otheros>
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On Sun, Mar 19, 2017 at 05:55:06PM +0100, Linus Lüssing wrote:
> On Fri, Mar 17, 2017 at 02:10:44PM +0100, Pablo Neira Ayuso wrote:
> > Wait.
> > 
> > May this break local multicast listener that are bound to the bridge
> > interface? Assuming the bridge interface got an IP address, and that
> > there is local multicast listener.
> > 
> > Missing anything here?
> 
> Hm, for multicast packets usually the code path a few lines
> later in br_handle_frame_finish() should be taken instead.
> 
> But you might be right for IP multicast packets with a unicast MAC
> destination (due to whatever reason, for instance via DNAT'ing
> again).
> 
> Will check that - thanks!

Ok, I tested DNAT'ing an IP multicast packet to the unicast MAC address
of the bridge interface.

Both ping-ing to an IPv4 and IPv6 multicast listener on br0 worked
and was replied to fine, both with or without changing skb->pkt_type
from PACKET_MULTICAST to PACKET_HOST.
("$ ping 224.1.0.123" and "$ ping6 ff02::1:ff40:707c%in0" from a
 network namespace, tied into the bridge via veth)

Also, a DNAT'ed PACKET_BROADCAST worked, with or without changing
it to PACKET_HOST.

I also checked via tcpdump that the destination MAC was changed
successfully.


So, so far I wasn't able to find any bugs with the current
patch. But I think I like the idea of leaving the skb->pkt_type
unaltered for PACKET_MULTICAST and PACKET_BROADCAST, seems cleaner.

I'd just add an "if (skb->pkt_type == PACKET_OTHERHOST)" check
then and resend a PATCH v2.