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

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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@xxxxxxxxxxxxxxx [mailto:netfilter-devel-
> owner@xxxxxxxxxxxxxxx] On Behalf Of Stephen Hemminger
> Sent: Friday, August 19, 2011 1:58 PM
> To: David Lamparter
> Cc: Nick Carter; Ed Swierk; netdev@xxxxxxxxxxxxxxx; bridge@linux-
> foundation.org; netfilter-devel@xxxxxxxxxxxxxxx
> 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@xxxxxxxxxx>
> 
> ---
>  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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