[RFC] bridge: add netfilter hook for forwarding 802.1D group addresses

The IEEE standard expects that link local multicast packets will not
be forwarded by a bridge. But there are cases like 802.1X which may
require that packets be forwarded. For maximum flexibilty implement
this via netfilter.

The netfilter chain is slightly different from other chains in that
if packet is ACCEPTED by the chain, it means it should be forwarded.
And if the packet verdict result is DROP, the packet is processed
as a local packet. The default result for this chain is DROP and
therefore users who do not install any rules will get the same
result as before; ie. packets are only processed on the local host
and not forwarded.

Spanning Tree Packets are treated specially and do not
go through the new chain.

This code is conceptual design concept only. It compiles but
hasn't been tested.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>

---
 include/linux/netfilter_bridge.h      |    5 ++++-
 net/bridge/br_input.c                 |   15 ++++++++++++---
 net/bridge/netfilter/ebtable_filter.c |   18 ++++++++++++++++--
 3 files changed, 32 insertions(+), 6 deletions(-)

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The patch description and the code are clearly saying that STP is
an exception, but I am just worried about the users.
Maybe a proper description in the iptables help is sufficient.

Users may otherwise try to use this new hook for STP too
(for example to generate logs or produce statistics/counters
or divert STP traffic to userspace, etc).

Out of curiosity, ... if this gets accepted, shouldn't you provide
NF_BR_LINK_LOCAL_OUT too?
Or maybe you should call it NF_BR_LINK_LOCAL_FWD instead of
NF_BR_LINK_LOCAL_IN?

/Chris

> -----Original Message-----
> From: netfilter-devel-owner@vger.kernel.org [mailto:netfilter-devel-
> owner@vger.kernel.org] On Behalf Of Stephen Hemminger
> Sent: Friday, August 19, 2011 1:58 PM
> To: David Lamparter
> Cc: Nick Carter; Ed Swierk; netdev@vger.kernel.org; bridge@linux-
> foundation.org; netfilter-devel@vger.kernel.org
> Subject: [RFC] bridge: add netfilter hook for forwarding 802.1D group
> addresses
> 
> The IEEE standard expects that link local multicast packets will not
> be forwarded by a bridge. But there are cases like 802.1X which may
> require that packets be forwarded. For maximum flexibilty implement
> this via netfilter.
> 
> The netfilter chain is slightly different from other chains in that
> if packet is ACCEPTED by the chain, it means it should be forwarded.
> And if the packet verdict result is DROP, the packet is processed
> as a local packet. The default result for this chain is DROP and
> therefore users who do not install any rules will get the same
> result as before; ie. packets are only processed on the local host
> and not forwarded.
> 
> Spanning Tree Packets are treated specially and do not
> go through the new chain.
> 
> This code is conceptual design concept only. It compiles but
> hasn't been tested.
> 
> Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
> 
> ---
>  include/linux/netfilter_bridge.h      |    5 ++++-
>  net/bridge/br_input.c                 |   15 ++++++++++++---
>  net/bridge/netfilter/ebtable_filter.c |   18 ++++++++++++++++--
>  3 files changed, 32 insertions(+), 6 deletions(-)
> 
> --- a/include/linux/netfilter_bridge.h	2011-08-19
13:11:51.972125670
> -0700
> +++ b/include/linux/netfilter_bridge.h	2011-08-19
13:13:36.452130443
> -0700
> @@ -22,7 +22,10 @@
>  #define NF_BR_POST_ROUTING	4
>  /* Not really a hook, but used for the ebtables broute table */
>  #define NF_BR_BROUTING		5
> -#define NF_BR_NUMHOOKS		6
> +/* Packets to link local multicast addresses (01-80-C2-00-00-XX) */
> +#define NF_BR_LINK_LOCAL_IN	6
> +
> +#define NF_BR_NUMHOOKS		7
> 
>  #ifdef __KERNEL__
> 
> --- a/net/bridge/br_input.c	2011-08-18 16:12:02.576672548 -0700
> +++ b/net/bridge/br_input.c	2011-08-19 13:28:13.696170518 -0700
> @@ -166,10 +166,19 @@ rx_handler_result_t br_handle_frame(stru
>  		if (skb->protocol == htons(ETH_P_PAUSE))
>  			goto drop;
> 
> -		/* If STP is turned off, then forward */
> -		if (p->br->stp_enabled == BR_NO_STP && dest[5] == 0)
> -			goto forward;
> +		/* If this is Spanning Tree Protocol packet */
> +		if (dest[5] == 0) {
> +			/* and STP is turned off, then forward */
> +			if (p->br->stp_enabled == BR_NO_STP)
> +				goto forward;
> +		}
> +		/* Hook to allow forwarding other group MAC addresses */
> +		else if (p->state == BR_STATE_FORWARDING &&
> +			 NF_HOOK(NFPROTO_BRIDGE, NF_BR_LINK_LOCAL_IN,
skb,
> skb->dev,
> +				 NULL, br_handle_frame_finish))
> +			return RX_HANDLER_CONSUMED;	/* forwarded */
> 
> +		/* Packet will go only to the local host. */
>  		if (NF_HOOK(NFPROTO_BRIDGE, NF_BR_LOCAL_IN, skb,
skb->dev,
>  			    NULL, br_handle_local_finish)) {
>  			return RX_HANDLER_CONSUMED; /* consumed by
filter */
> --- a/net/bridge/netfilter/ebtable_filter.c	2011-08-19
> 13:14:46.232133631 -0700
> +++ b/net/bridge/netfilter/ebtable_filter.c	2011-08-19
> 13:27:33.436168679 -0700
> @@ -11,8 +11,10 @@
>  #include <linux/netfilter_bridge/ebtables.h>
>  #include <linux/module.h>
> 
> -#define FILTER_VALID_HOOKS ((1 << NF_BR_LOCAL_IN) | (1 <<
> NF_BR_FORWARD) | \
> -   (1 << NF_BR_LOCAL_OUT))
> +#define FILTER_VALID_HOOKS ((1 << NF_BR_LOCAL_IN) | \
> +			    (1 << NF_BR_FORWARD) | \
> +			    (1 << NF_BR_LOCAL_OUT) | \
> +			    (1 << NF_BR_LINK_LOCAL_IN))
> 
>  static struct ebt_entries initial_chains[] =
>  {
> @@ -28,6 +30,10 @@ static struct ebt_entries initial_chains
>  		.name	= "OUTPUT",
>  		.policy	= EBT_ACCEPT,
>  	},
> +	{
> +		.name	= "LINKLOCAL",
> +		.policy = EBT_DROP,
> +	},
>  };
> 
>  static struct ebt_replace_kernel initial_table =
> @@ -39,6 +45,7 @@ static struct ebt_replace_kernel initial
>  		[NF_BR_LOCAL_IN]	= &initial_chains[0],
>  		[NF_BR_FORWARD]		= &initial_chains[1],
>  		[NF_BR_LOCAL_OUT]	= &initial_chains[2],
> +		[NF_BR_LINK_LOCAL_IN]	= &initial_chains[3],
>  	},
>  	.entries	= (char *)initial_chains,
>  };
> @@ -95,6 +102,13 @@ static struct nf_hook_ops ebt_ops_filter
>  		.hooknum	= NF_BR_LOCAL_OUT,
>  		.priority	= NF_BR_PRI_FILTER_OTHER,
>  	},
> +	{
> +		.hook		= ebt_in_hook,
> +		.owner		= THIS_MODULE,
> +		.pf		= NFPROTO_BRIDGE,
> +		.hooknum	= NF_BR_LINK_LOCAL_IN,
> +		.priority	= NF_BR_PRI_FILTER_BRIDGED,
> +	},
>  };
> 
>  static int __net_init frame_filter_net_init(struct net *net)
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On Fri, 19 Aug 2011 17:18:04 -0500
"Christian Benvenuti (benve)" <benve@cisco.com> wrote:

> The patch description and the code are clearly saying that STP is
> an exception, but I am just worried about the users.
> Maybe a proper description in the iptables help is sufficient.
> 
> Users may otherwise try to use this new hook for STP too
> (for example to generate logs or produce statistics/counters
> or divert STP traffic to userspace, etc).

STP traffic already goes to userspace. And gets processed
by the LOCAL_IN chain. So I don't think it is needed.


> Out of curiosity, ... if this gets accepted, shouldn't you provide
> NF_BR_LINK_LOCAL_OUT too?
> Or maybe you should call it NF_BR_LINK_LOCAL_FWD instead of
> NF_BR_LINK_LOCAL_IN?

Thanks, that is a better name, I'll change it in next version.
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Op 19/08/2011 22:58, Stephen Hemminger schreef:

> Signed-off-by: Stephen Hemminger<shemminger@vyatta.com>
>
> ---
>   include/linux/netfilter_bridge.h      |    5 ++++-
>   net/bridge/br_input.c                 |   15 ++++++++++++---
>   net/bridge/netfilter/ebtable_filter.c |   18 ++++++++++++++++--
>   3 files changed, 32 insertions(+), 6 deletions(-)
>
> --- a/include/linux/netfilter_bridge.h	2011-08-19 13:11:51.972125670 -0700
> +++ b/include/linux/netfilter_bridge.h	2011-08-19 13:13:36.452130443 -0700
> @@ -22,7 +22,10 @@
>   #define NF_BR_POST_ROUTING	4
>   /* Not really a hook, but used for the ebtables broute table */
>   #define NF_BR_BROUTING		5
> -#define NF_BR_NUMHOOKS		6
> +/* Packets to link local multicast addresses (01-80-C2-00-00-XX) */
> +#define NF_BR_LINK_LOCAL_IN	6
> +
> +#define NF_BR_NUMHOOKS		7
>

You will need to make sure you don't break backwards compatibility with 
the ebtables userspace tool. ebtables.h::struct ebt_replace is a 
structure used for communication between userspace and the kernel. It 
has the member hook_entry defined like this:
struct ebt_entries __user *hook_entry[NF_BR_NUMHOOKS];

cheers,
Bart

On Fri, Aug 19, 2011 at 01:58:10PM -0700, Stephen Hemminger wrote:
> The IEEE standard expects that link local multicast packets will not
> be forwarded by a bridge. But there are cases like 802.1X which may
> require that packets be forwarded. For maximum flexibilty implement
> this via netfilter.
> 
> The netfilter chain is slightly different from other chains in that
> if packet is ACCEPTED by the chain, it means it should be forwarded.
> And if the packet verdict result is DROP, the packet is processed
> as a local packet.

Exactly this functionality already exists by way of the BROUTING chain
in the broute table. Currently, link-local packets are hardcodedly
treated as local before they even reach that chain. Nick's patch, in
conjunction with BROUTING, provides exactly what you're trying to do.

Now, without bridge netfilter, your patch becomes rather useless while
Nick's patch still allows per-group (and therefore per-protocol)
control.

Further, Nick's patch is considerably less intrusive.

I would therefore ask for Nick's patch to be merged.


-David


P.S.: this whole issue is starting to get rather annoying
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