[BRIDGE]: allow show/store of group multicast address

Bridge's communicate with each other using Spanning Tree Protocol
over a standard multicast address. There are times when testing or
layering bridges over existing topologies or tunnels, when it is
useful to use alternative multicast addresses for STP packets.

The 802.1d standard has some unused addresses, that can be used for this.
This patch is restrictive in that it only allows one of the possible
addresses in the standard.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br_input.c

@@ -19,7 +19,8 @@
 #include <linux/netfilter_bridge.h>
 #include "br_private.h"
 
-const unsigned char bridge_ula[6] = { 0x01, 0x80, 0xc2, 0x00, 0x00, 0x00 };
+/* Bridge group multicast address 802.1d (pg 51). */
+const u8 br_group_address[ETH_ALEN] = { 0x01, 0x80, 0xc2, 0x00, 0x00, 0x00 };
 
 static void br_pass_frame_up(struct net_bridge *br, struct sk_buff *skb)
 {
@@ -108,9 +109,9 @@ static int br_handle_local_finish(struct sk_buff *skb)
 /* Does address match the link local multicast address.
  * 01:80:c2:00:00:0X
  */
-static inline int is_link_local(const unsigned char *dest)
+static inline int is_link_local(const const unsigned char *dest)
 {
-	return memcmp(dest, bridge_ula, 5) == 0 && (dest[5] & 0xf0) == 0;
+	return memcmp(dest, br_group_address, 5) == 0 && (dest[5] & 0xf0) == 0;
 }
 
 /*

net/bridge/br_private.h

@@ -109,6 +109,7 @@ struct net_bridge
 	unsigned long			bridge_hello_time;
 	unsigned long			bridge_forward_delay;
 
+	u8				group_addr[ETH_ALEN];
 	u16				root_port;
 	unsigned char			stp_enabled;
 	unsigned char			topology_change;
@@ -122,7 +123,7 @@ struct net_bridge
 };
 
 extern struct notifier_block br_device_notifier;
-extern const unsigned char bridge_ula[6];
+extern const u8 br_group_address[ETH_ALEN];
 
 /* called under bridge lock */
 static inline int br_is_root_bridge(const struct net_bridge *br)

net/bridge/br_stp_bpdu.c

@@ -47,7 +47,7 @@ static void br_send_bpdu(struct net_bridge_port *p, unsigned char *data, int len
 	skb->dev = dev;
 	skb->protocol = htons(ETH_P_802_2);
 	skb->mac.raw = skb_put(skb, size);
-	memcpy(skb->mac.raw, bridge_ula, ETH_ALEN);
+	memcpy(skb->mac.raw, p->br->group_addr, ETH_ALEN);
 	memcpy(skb->mac.raw+ETH_ALEN, dev->dev_addr, ETH_ALEN);
 	skb->mac.raw[2*ETH_ALEN] = 0;
 	skb->mac.raw[2*ETH_ALEN+1] = length;
@@ -171,7 +171,7 @@ int br_stp_rcv(struct sk_buff *skb, struct net_device *dev,
 	    || !(br->dev->flags & IFF_UP))
 		goto out;
 
-	if (compare_ether_addr(dest, bridge_ula) != 0)
+	if (compare_ether_addr(dest, br->group_addr) != 0)
 		goto out;
 
 	buf = skb_pull(skb, 3);

net/bridge/br_sysfs_br.c

@@ -242,6 +242,54 @@ static ssize_t show_gc_timer(struct class_device *cd, char *buf)
 }
 static CLASS_DEVICE_ATTR(gc_timer, S_IRUGO, show_gc_timer, NULL);
 
+static ssize_t show_group_addr(struct class_device *cd, char *buf)
+{
+	struct net_bridge *br = to_bridge(cd);
+	return sprintf(buf, "%x:%x:%x:%x:%x:%x\n",
+		       br->group_addr[0], br->group_addr[1],
+		       br->group_addr[2], br->group_addr[3],
+		       br->group_addr[4], br->group_addr[5]);
+}
+
+static ssize_t store_group_addr(struct class_device *cd, const char *buf,
+				    size_t len)
+{
+	struct net_bridge *br = to_bridge(cd);
+	unsigned new_addr[6];
+	int i;
+
+	if (!capable(CAP_NET_ADMIN))
+		return -EPERM;
+
+	if (sscanf(buf, "%x:%x:%x:%x:%x:%x",
+		   &new_addr[0], &new_addr[1], &new_addr[2],
+		   &new_addr[3], &new_addr[4], &new_addr[5]) != 6)
+		return -EINVAL;
+
+	/* Must be 01:80:c2:00:00:0X */
+	for (i = 0; i < 5; i++)
+		if (new_addr[i] != br_group_address[i])
+			return -EINVAL;
+
+	if (new_addr[5] & ~0xf)
+		return -EINVAL;
+
+	if (new_addr[5] == 1 	/* 802.3x Pause address */
+	    || new_addr[5] == 2 /* 802.3ad Slow protocols */
+	    || new_addr[5] == 3) /* 802.1X PAE address */
+		return -EINVAL;
+
+	spin_lock_bh(&br->lock);
+	for (i = 0; i < 6; i++)
+		br->group_addr[i] = new_addr[i];
+	spin_unlock_bh(&br->lock);
+	return len;
+}
+
+static CLASS_DEVICE_ATTR(group_addr, S_IRUGO | S_IWUSR,
+			 show_group_addr, store_group_addr);
+
+
 static struct attribute *bridge_attrs[] = {
 	&class_device_attr_forward_delay.attr,
 	&class_device_attr_hello_time.attr,
@@ -259,6 +307,7 @@ static struct attribute *bridge_attrs[] = {
 	&class_device_attr_tcn_timer.attr,
 	&class_device_attr_topology_change_timer.attr,
 	&class_device_attr_gc_timer.attr,
+	&class_device_attr_group_addr.attr,
 	NULL
 };