netdev - Re: [**EXTERNAL**] Re: VRF with enslaved L3 enabled bridge

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Message-ID: <a32ada04-6dd6-3d09-19bf-8db4e1479e03@cumulusnetworks.com>
Date:   Fri, 7 Sep 2018 10:09:24 -0600
From:   David Ahern <dsa@...ulusnetworks.com>
To:     "D'Souza, Nelson" <ndsouza@...na.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Cc:     Ido Schimmel <idosch@...lanox.com>
Subject: Re: [**EXTERNAL**] Re: VRF with enslaved L3 enabled bridge

On 9/7/18 9:56 AM, D'Souza, Nelson wrote:

> ------------------------------------------------------------------------
> *From:* David Ahern <dsa@...ulusnetworks.com>
> *Sent:* Thursday, September 6, 2018 5:27 PM
> *To:* D'Souza, Nelson; netdev@...r.kernel.org
> *Subject:* Re: [**EXTERNAL**] Re: VRF with enslaved L3 enabled bridge
>  
> On 9/5/18 12:00 PM, D'Souza, Nelson wrote:
>> Just following up.... would you be able to confirm that this is a
> Linux VRF issue?
> 
> I can confirm that I can reproduce the problem. Need to find time to dig
> into it.

bridge's netfilter hook is dropping the packet.

bridge's netfilter code registers hook operations that are invoked when
nh_hook is called. It then sees all subsequent calls to nf_hook.

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. Any subsequent calls to nf_hook
invoke ip_sabotage_in. That function sees in_prerouting is not
set and steals (drops) the packet.

The simplest change is to have ip_sabotage_in recognize that the bridge
can be enslaved to a VRF (L3 master device) and allow the packet to
continue.

Thanks to Ido for the hint on ip_sabotage_in.

This patch works for me:

diff --git a/net/bridge/br_netfilter_hooks.c
b/net/bridge/br_netfilter_hooks.c
index 6e0dc6bcd32a..37278dc280eb 100644
--- a/net/bridge/br_netfilter_hooks.c
+++ b/net/bridge/br_netfilter_hooks.c
@@ -835,7 +835,8 @@ static unsigned int ip_sabotage_in(void *priv,
                                   struct sk_buff *skb,
                                   const struct nf_hook_state *state)
 {
-       if (skb->nf_bridge && !skb->nf_bridge->in_prerouting) {
+       if (skb->nf_bridge && !skb->nf_bridge->in_prerouting &&
+           !netif_is_l3_master(skb->dev)) {
                state->okfn(state->net, state->sk, skb);
                return NF_STOLEN;
        }