Re: [PATCH net] bridge: ebtables: fix reception of frames DNAT-ed to bridge device

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:

quoted

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.