From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Hemminger Subject: Re: [RFC net] bridge: clean the nf_bridge status when forwarding the skb Date: Thu, 26 Sep 2013 14:08:31 -0700 Message-ID: <20130926140831.36063454@nehalam.linuxnetplumber.net> References: <1380226790-513-1-git-send-email-antonio@meshcoding.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: "David S. Miller" , bridge@lists.linux-foundation.org, netdev@vger.kernel.org, Antonio Quartulli To: Antonio Quartulli Return-path: Received: from mail-pa0-f49.google.com ([209.85.220.49]:62417 "EHLO mail-pa0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753387Ab3IZVIh (ORCPT ); Thu, 26 Sep 2013 17:08:37 -0400 Received: by mail-pa0-f49.google.com with SMTP id ld10so1857125pab.22 for ; Thu, 26 Sep 2013 14:08:36 -0700 (PDT) In-Reply-To: <1380226790-513-1-git-send-email-antonio@meshcoding.com> Sender: netdev-owner@vger.kernel.org List-ID: On Thu, 26 Sep 2013 22:19:50 +0200 Antonio Quartulli wrote: > 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); > } > You need to bracket this with CONFIG_BRIDGE_NETFILTER since nf_bridge is only in skbuff if that option is enabled.