[EBTABLES]: Add ebt_limit match.

The patch below adds the ebt_limit match, which is the equivalent of
the iptables limit match. This enables limiting the number of frames
processed per time unit.

The patch is from Tom Marshall <tommy_at_home.tig-grr.com>.

include/linux/netfilter_bridge/ebt_limit.h

+#ifndef __LINUX_BRIDGE_EBT_LIMIT_H
+#define __LINUX_BRIDGE_EBT_LIMIT_H
+
+#define EBT_LIMIT_MATCH "limit"
+
+/* timings are in milliseconds. */
+#define EBT_LIMIT_SCALE 10000
+
+/* 1/10,000 sec period => max of 10,000/sec.  Min rate is then 429490
+   seconds, or one every 59 hours. */
+
+struct ebt_limit_info
+{
+	u_int32_t avg;    /* Average secs between packets * scale */
+	u_int32_t burst;  /* Period multiplier for upper limit. */
+
+	/* Used internally by the kernel */
+	unsigned long prev;
+	u_int32_t credit;
+	u_int32_t credit_cap, cost;
+};
+
+#endif

net/bridge/netfilter/Kconfig

@@ -73,6 +73,17 @@ config BRIDGE_EBT_IP
 
 	  To compile it as a module, choose M here.  If unsure, say N.
 
+config BRIDGE_EBT_LIMIT
+	tristate "ebt: limit match support"
+	depends on BRIDGE_NF_EBTABLES
+	help
+	  This option adds the limit match, which allows you to control
+	  the rate at which a rule can be matched. This match is the
+	  equivalent of the iptables limit match.
+
+	  If you want to compile it as a module, say M here and read
+	  <file:Documentation/modules.txt>.  If unsure, say `N'.
+
 config BRIDGE_EBT_MARK
 	tristate "ebt: mark filter support"
 	depends on BRIDGE_NF_EBTABLES

net/bridge/netfilter/Makefile

@@ -13,6 +13,7 @@ obj-$(CONFIG_BRIDGE_EBT_T_NAT) += ebtable_nat.o
 obj-$(CONFIG_BRIDGE_EBT_802_3) += ebt_802_3.o
 obj-$(CONFIG_BRIDGE_EBT_ARP) += ebt_arp.o
 obj-$(CONFIG_BRIDGE_EBT_IP) += ebt_ip.o
+obj-$(CONFIG_BRIDGE_EBT_LIMIT) += ebt_limit.o
 obj-$(CONFIG_BRIDGE_EBT_MARK) += ebt_mark_m.o
 obj-$(CONFIG_BRIDGE_EBT_PKTTYPE) += ebt_pkttype.o
 obj-$(CONFIG_BRIDGE_EBT_STP) += ebt_stp.o

net/bridge/netfilter/ebt_limit.c

+/*
+ *  ebt_limit
+ *
+ *	Authors:
+ *	Tom Marshall <tommy@home.tig-grr.com>
+ *
+ *	Mostly copied from netfilter's ipt_limit.c, see that file for
+ *	more explanation
+ *
+ *  September, 2003
+ *
+ */
+
+#include <linux/netfilter_bridge/ebtables.h>
+#include <linux/netfilter_bridge/ebt_limit.h>
+#include <linux/module.h>
+
+#include <linux/netdevice.h>
+#include <linux/spinlock.h>
+
+static spinlock_t limit_lock = SPIN_LOCK_UNLOCKED;
+
+#define CREDITS_PER_JIFFY 128
+
+static int ebt_limit_match(const struct sk_buff *skb,
+   const struct net_device *in, const struct net_device *out,
+   const void *data, unsigned int datalen)
+{
+	struct ebt_limit_info *info = (struct ebt_limit_info *)data;
+	unsigned long now = jiffies;
+
+	spin_lock_bh(&limit_lock);
+	info->credit += (now - xchg(&info->prev, now)) * CREDITS_PER_JIFFY;
+	if (info->credit > info->credit_cap)
+		info->credit = info->credit_cap;
+
+	if (info->credit >= info->cost) {
+		/* We're not limited. */
+		info->credit -= info->cost;
+		spin_unlock_bh(&limit_lock);
+		return EBT_MATCH;
+	}
+
+	spin_unlock_bh(&limit_lock);
+	return EBT_NOMATCH;
+}
+
+/* Precision saver. */
+static u_int32_t
+user2credits(u_int32_t user)
+{
+	/* If multiplying would overflow... */
+	if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY))
+		/* Divide first. */
+		return (user / EBT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY;
+
+	return (user * HZ * CREDITS_PER_JIFFY) / EBT_LIMIT_SCALE;
+}
+
+static int ebt_limit_check(const char *tablename, unsigned int hookmask,
+   const struct ebt_entry *e, void *data, unsigned int datalen)
+{
+	struct ebt_limit_info *info = (struct ebt_limit_info *)data;
+
+	if (datalen != EBT_ALIGN(sizeof(struct ebt_limit_info)))
+		return -EINVAL;
+
+	/* Check for overflow. */
+	if (info->burst == 0 ||
+	    user2credits(info->avg * info->burst) < user2credits(info->avg)) {
+		printk("Overflow in ebt_limit: %u/%u\n",
+			info->avg, info->burst);
+		return -EINVAL;
+	}
+
+	/* User avg in seconds * EBT_LIMIT_SCALE: convert to jiffies * 128. */
+	info->prev = jiffies;
+	info->credit = user2credits(info->avg * info->burst);
+	info->credit_cap = user2credits(info->avg * info->burst);
+	info->cost = user2credits(info->avg);
+	return 0;
+}
+
+static struct ebt_match ebt_limit_reg =
+{
+	.name		= EBT_LIMIT_MATCH,
+	.match		= ebt_limit_match,
+	.check		= ebt_limit_check,
+	.me		= THIS_MODULE,
+};
+
+static int __init init(void)
+{
+	return ebt_register_match(&ebt_limit_reg);
+}
+
+static void __exit fini(void)
+{
+	ebt_unregister_match(&ebt_limit_reg);
+}
+
+module_init(init);
+module_exit(fini);
+MODULE_LICENSE("GPL");