[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>

1 files changed, 49 insertions, 0 deletions

diff --git a/net/bridge/br_sysfs_br.c b/net/bridge/br_sysfs_br.c
index 6f577f16c4c0..96bcb2ff59ab 100644
--- a/net/bridge/br_sysfs_br.c
+++ b/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
 };