text: /*
   *	Handle incoming frames
   *	Linux ethernet bridge
   *
   *	Authors:
   *	Lennert Buytenhek		<buytenh@gnu.org>
   *
   *	This program is free software; you can redistribute it and/or
   *	modify it under the terms of the GNU General Public License
   *	as published by the Free Software Foundation; either version
   *	2 of the License, or (at your option) any later version.
   */
  
  #include <linux/slab.h>
  #include <linux/kernel.h>
  #include <linux/netdevice.h>
  #include <linux/etherdevice.h>
  #include <linux/netfilter_bridge.h>
  #include "br_private.h"
  
  /* Bridge group multicast address 802.1d (pg 51). */
  const u8 br_group_address[ETH_ALEN] = { 0x01, 0x80, 0xc2, 0x00, 0x00, 0x00 };
  
  static int br_pass_frame_up(struct sk_buff *skb)
  {
  	struct net_device *indev, *brdev = BR_INPUT_SKB_CB(skb)->brdev;
  
  	brdev->stats.rx_packets++;
  	brdev->stats.rx_bytes += skb->len;
  
  	indev = skb->dev;
  	skb->dev = brdev;
  
  	return NF_HOOK(PF_BRIDGE, NF_BR_LOCAL_IN, skb, indev, NULL,
  		       netif_receive_skb);
  }
  
  /* note: already called with rcu_read_lock (preempt_disabled) */
  int br_handle_frame_finish(struct sk_buff *skb)
  {
  	const unsigned char *dest = eth_hdr(skb)->h_dest;
  	struct net_bridge_port *p = rcu_dereference(skb->dev->br_port);
  	struct net_bridge *br;
  	struct net_bridge_fdb_entry *dst;
  	struct net_bridge_mdb_entry *mdst;
  	struct sk_buff *skb2;
  
  	if (!p || p->state == BR_STATE_DISABLED)
  		goto drop;
  
  	/* insert into forwarding database after filtering to avoid spoofing */
  	br = p->br;
  	br_fdb_update(br, p, eth_hdr(skb)->h_source);
  
  	if (is_multicast_ether_addr(dest) &&
  	    br_multicast_rcv(br, p, skb))
  		goto drop;
  
  	if (p->state == BR_STATE_LEARNING)
  		goto drop;
  
  	BR_INPUT_SKB_CB(skb)->brdev = br->dev;
  
  	/* The packet skb2 goes to the local host (NULL to skip). */
  	skb2 = NULL;
  
  	if (br->dev->flags & IFF_PROMISC)
  		skb2 = skb;
  
  	dst = NULL;
  
  	if (is_multicast_ether_addr(dest)) {
  		mdst = br_mdb_get(br, skb);
  		if (mdst || BR_INPUT_SKB_CB_MROUTERS_ONLY(skb)) {
  			if ((mdst && !hlist_unhashed(&mdst->mglist)) ||
  			    br_multicast_is_router(br))
  				skb2 = skb;
  			br_multicast_forward(mdst, skb, skb2);
  			skb = NULL;
  			if (!skb2)
  				goto out;
  		} else
  			skb2 = skb;
  
  		br->dev->stats.multicast++;
  	} else if ((dst = __br_fdb_get(br, dest)) && dst->is_local) {
  		skb2 = skb;
  		/* Do not forward the packet since it's local. */
  		skb = NULL;
  	}
  
  	if (skb) {
  		if (dst)
  			br_forward(dst->dst, skb, skb2);
  		else
  			br_flood_forward(br, skb, skb2);
  	}
  
  	if (skb2)
  		return br_pass_frame_up(skb2);
  
  out:
  	return 0;
  drop:
  	kfree_skb(skb);
  	goto out;
  }
  
  /* note: already called with rcu_read_lock (preempt_disabled) */
  static int br_handle_local_finish(struct sk_buff *skb)
  {
  	struct net_bridge_port *p = rcu_dereference(skb->dev->br_port);
  
  	if (p)
  		br_fdb_update(p->br, p, eth_hdr(skb)->h_source);
  	return 0;	 /* process further */
  }
  
  /* Does address match the link local multicast address.
   * 01:80:c2:00:00:0X
   */
  static inline int is_link_local(const unsigned char *dest)
  {
  	__be16 *a = (__be16 *)dest;
  	static const __be16 *b = (const __be16 *)br_group_address;
  	static const __be16 m = cpu_to_be16(0xfff0);
  
  	return ((a[0] ^ b[0]) | (a[1] ^ b[1]) | ((a[2] ^ b[2]) & m)) == 0;
  }
  
  /*
   * Called via br_handle_frame_hook.
   * Return NULL if skb is handled
   * note: already called with rcu_read_lock (preempt_disabled)
   */
  struct sk_buff *br_handle_frame(struct net_bridge_port *p, struct sk_buff *skb)
  {
  	const unsigned char *dest = eth_hdr(skb)->h_dest;
  	int (*rhook)(struct sk_buff *skb);
  
  	if (!is_valid_ether_addr(eth_hdr(skb)->h_source))
  		goto drop;
  
  	skb = skb_share_check(skb, GFP_ATOMIC);
  	if (!skb)
  		return NULL;
  
  	if (unlikely(is_link_local(dest))) {
  		/* Pause frames shouldn't be passed up by driver anyway */
  		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 (NF_HOOK(PF_BRIDGE, NF_BR_LOCAL_IN, skb, skb->dev,
  			    NULL, br_handle_local_finish))
  			return NULL;	/* frame consumed by filter */
  		else
  			return skb;	/* continue processing */
  	}
  
  forward:
  	switch (p->state) {
  	case BR_STATE_FORWARDING:
  		rhook = rcu_dereference(br_should_route_hook);
  		if (rhook != NULL) {
  			if (rhook(skb))
  				return skb;
  			dest = eth_hdr(skb)->h_dest;
  		}
  		/* fall through */
  	case BR_STATE_LEARNING:
  		if (!compare_ether_addr(p->br->dev->dev_addr, dest))
  			skb->pkt_type = PACKET_HOST;
  
  		NF_HOOK(PF_BRIDGE, NF_BR_PRE_ROUTING, skb, skb->dev, NULL,
  			br_handle_frame_finish);
  		break;
  	default:
  drop:
  		kfree_skb(skb);
  	}
  	return NULL;
  }
  