From: Stephen Hemminger <stephen@networkplumber•org>
To: Antonio Quartulli <antonio@meshcoding•com>
Cc: "David S. Miller" <davem@davemloft•net>,
bridge@lists•linux-foundation.org, netdev@vger•kernel.org,
Antonio Quartulli <antonio@open-mesh•com>
Subject: Re: [RFC net] bridge: clean the nf_bridge status when forwarding the skb
Date: Thu, 26 Sep 2013 14:08:31 -0700 [thread overview]
Message-ID: <20130926140831.36063454@nehalam.linuxnetplumber.net> (raw)
In-Reply-To: <1380226790-513-1-git-send-email-antonio@meshcoding.com>
On Thu, 26 Sep 2013 22:19:50 +0200
Antonio Quartulli <antonio@meshcoding•com> wrote:
> From: Antonio Quartulli <antonio@open-mesh•com>
>
> 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 <antonio@open-mesh•com>
> ---
>
> 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.
next prev parent reply other threads:[~2013-09-26 21:08 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-26 20:19 [RFC net] bridge: clean the nf_bridge status when forwarding the skb Antonio Quartulli
2013-09-26 21:08 ` Stephen Hemminger [this message]
2013-09-26 21:10 ` Stephen Hemminger
2013-09-26 21:16 ` Antonio Quartulli
2013-09-26 21:32 ` Stephen Hemminger
2013-09-26 22:01 ` Antonio Quartulli
2013-10-14 22:20 ` Antonio Quartulli
2013-10-14 22:27 ` Stephen Hemminger
2013-10-14 22:35 ` Antonio Quartulli
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