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

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Date:   Wed, 15 Mar 2017 11:26:08 +0100
From:   Florian Westphal <fw@...len.de>
To:     Linus Lüssing <linus.luessing@...3.blue>
Cc:     netdev@...r.kernel.org, "David S . Miller" <davem@...emloft.net>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
        bridge@...ts.linux-foundation.org, netfilter-devel@...r.kernel.org,
        coreteam@...filter.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] bridge: ebtables: fix reception of frames DNAT-ed to
 bridge device

Linus Lüssing <linus.luessing@...3.blue> wrote:
> When trying to redirect bridged frames to the bridge device itself
> via the ebtables nat-prerouting chain and the dnat target then this
> currently fails:
> 
> The ethernet destination of the frame is dnat'ed to the MAC address of
> the bridge itself just fine and the correctly altered frame can even
> be captured via a tcpdump on br0 (with or without promisc mode).
>
> However, the IP code drops it in the beginning of ip_input.c/ip_rcv()
> as the dnat target did not update the skb->pkt_type.

Right, thats the reason why ebtables also has ebt_redirect target
which does this pkt_type fixup.

> -		if (dst->is_local)
> +		if (dst->is_local) {
> +			/* fix up potential DNAT mess */
> +			skb->pkt_type = PACKET_HOST;
> +
>  			return br_pass_frame_up(skb);
> +		}

I don't mind this change though (i.e. I don't see how this would
bite us later).