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

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Date:   Sun, 16 Sep 2018 21:14:42 -0700
From:   David Ahern <dsahern@...il.com>
To:     dsahern@...nel.org, netdev@...r.kernel.org, pablo@...filter.org,
        fw@...len.de
Cc:     ndsouza@...na.com, idosch@...lanox.com
Subject: Re: [PATCH net] netfilter: bridge: Don't sabotage nf_hook calls from
 an l3mdev

Pablo:

DaveM has this marked as waiting for upstream. Any comment on this patch?

Thanks,
David

On 9/7/18 3:08 PM, 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.
> 
> Fixes: 73e20b761acf ("net: vrf: Add support for PREROUTING rules on vrf device")
> Reported-by: D'Souza, Nelson <ndsouza@...na.com>
> Signed-off-by: David Ahern <dsahern@...il.com>
> ---
>  net/bridge/br_netfilter_hooks.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> 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;
>  	}
>