netdev - Re: [PATCH net] netfilter: bridge: Don't sabotage nf

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Date:   Thu, 20 Sep 2018 18:25:28 +0200
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     dsahern@...nel.org
Cc:     netdev@...r.kernel.org, netfilter-devel@...r.kernel.org,
        ndsouza@...na.com, idosch@...lanox.com, fw@...len.de,
        David Ahern <dsahern@...il.com>
Subject: Re: [PATCH net] netfilter: bridge: Don't sabotage nf_hook calls from
 an l3mdev

On Mon, Sep 17, 2018 at 08:20:36AM -0700, dsahern@...nel.org wrote:
> From: David Ahern <dsahern@...il.com>
> 
> For starters, the bridge netfilter code registers operations that
> are invoked any time nh_hook is called. Specifically, ip_sabotage_in
> watches for nested calls for NF_INET_PRE_ROUTING when a bridge is in
> the stack.
> 
> Packet wise, the bridge netfilter hook runs first. br_nf_pre_routing
> allocates nf_bridge, sets in_prerouting to 1 and calls NF_HOOK for
> NF_INET_PRE_ROUTING. It's finish function, br_nf_pre_routing_finish,
> then resets in_prerouting flag to 0 and the packet continues up the
> stack. The packet eventually makes it to the VRF driver and it invokes
> nf_hook for NF_INET_PRE_ROUTING in case any rules have been added against
> the vrf device.
> 
> Because of the registered operations the call to nf_hook causes
> ip_sabotage_in to be invoked. That function sees the nf_bridge on the
> skb and that in_prerouting is not set. Thinking it is an invalid nested
> call it steals (drops) the packet.
> 
> Update ip_sabotage_in to recognize that the bridge or one of its upper
> devices (e.g., vlan) can be enslaved to a VRF (L3 master device) and
> allow the packet to go through the nf_hook a second time.

Applied.