From mboxrd@z Thu Jan 1 00:00:00 1970 From: Antonio Quartulli Subject: [RFC net] bridge: clean the nf_bridge status when forwarding the skb Date: Thu, 26 Sep 2013 22:19:50 +0200 Message-ID: <1380226790-513-1-git-send-email-antonio@meshcoding.com> Cc: "David S. Miller" , bridge@lists.linux-foundation.org, netdev@vger.kernel.org, Antonio Quartulli To: Stephen Hemminger Return-path: Received: from s2.neomailbox.net ([178.209.62.154]:25981 "EHLO s2.neomailbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752951Ab3IZVBB (ORCPT ); Thu, 26 Sep 2013 17:01:01 -0400 Sender: netdev-owner@vger.kernel.org List-ID: From: Antonio Quartulli Even if enslaving a bridge interface into another bridge is forbidden, it is still possible to create a chain of virtual interfaces including two distinct bridges. In this case, the skb entering the second bridge could have the nf_bridge field already set due to a previous operation and consequently lead to a wrong processing of the packet itself. To prevent this behaviour release and set to NULL the nf_bridge field of the skb when exiting the bridge interface. Signed-off-by: Antonio Quartulli --- I am not sure if this is a wanted behaviour or a real BUG. I found this "misbehaviour" while testing batman-adv with the following configuration: - br0 (bridge interface) having bat0 and eth0 as slaves - bat0 (which is a virtual interface provided by the batman-adv module and that works similarly to a bridge - to some extends) having br1 as slave - br1 (second bridge interface) having eth1 as slave Then follow these events: - a broadcast packet arrives on eth0 - the skb enters br0 and skb->nf_bridge gets initialised and used - the skb enters bat0 and the packet *gets encapsulated in the batman-adv packet which adds a batman-adv header and another Ethernet header* - the skb enters br1 and gets ruined because nf_bridge_maybe_copy_header() (in br_dev_queue_push_xmit()) will try to restore an header that does not make sense anymore. With this patch the nf_bridge gets de-initialised before exiting br0 and therefore it is processed properly inside br1: nf_bridge_maybe_copy_header() does not take place at all because nf_bridge is never initialised (the packet is non-IP since it is a batman-adv packet) To the developers of the bridge module I would like to ask: 1) is skb->nf_bridge allowed to be non NULL when entering br_dev_xmit() ? If so, when is this supposed to happen? 2) do you think this patch is logically correct but the nf_bridge release should be done in batman-adv since it is the one re-encapsulating the packet? I hope I have made the problem clear. Best regards, net/bridge/br_forward.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/net/bridge/br_forward.c b/net/bridge/br_forward.c index 4b81b14..65864bc 100644 --- a/net/bridge/br_forward.c +++ b/net/bridge/br_forward.c @@ -49,6 +49,11 @@ int br_dev_queue_push_xmit(struct sk_buff *skb) } else { skb_push(skb, ETH_HLEN); br_drop_fake_rtable(skb); + + /* clean the NF bridge data */ + nf_bridge_put(skb->nf_bridge); + skb->nf_bridge = NULL; + dev_queue_xmit(skb); } -- 1.8.1.5