[NETFILTER] x_tables: Abstraction layer for {ip,ip6,arp}_tables

This monster-patch tries to do the best job for unifying the data
structures and backend interfaces for the three evil clones ip_tables,
ip6_tables and arp_tables.  In an ideal world we would never have
allowed this kind of copy+paste programming... but well, our world
isn't (yet?) ideal.

o introduce a new x_tables module
o {ip,arp,ip6}_tables depend on this x_tables module
o registration functions for tables, matches and targets are only
  wrappers around x_tables provided functions
o all matches/targets that are used from ip_tables and ip6_tables
  are now implemented as xt_FOOBAR.c files and provide module aliases
  to ipt_FOOBAR and ip6t_FOOBAR
o header files for xt_matches are in include/linux/netfilter/,
  include/linux/netfilter_{ipv4,ipv6} contains compatibility wrappers
  around the xt_FOOBAR.h headers

Based on this patchset we're going to further unify the code,
gradually getting rid of all the layer 3 specific assumptions.

Signed-off-by: Harald Welte <laforge@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 175 insertions, 0 deletions

diff --git a/net/netfilter/xt_limit.c b/net/netfilter/xt_limit.c
new file mode 100644
index 000000000000..15e40506bc3a
--- /dev/null
+++ b/net/netfilter/xt_limit.c
@@ -0,0 +1,175 @@
+/* Kernel module to control the rate
+ *
+ * 2 September 1999: Changed from the target RATE to the match
+ *                   `limit', removed logging.  Did I mention that
+ *                   Alexey is a fucking genius?
+ *                   Rusty Russell (rusty@rustcorp.com.au).  */
+
+/* (C) 1999 Jérôme de Vivie <devivie@info.enserb.u-bordeaux.fr>
+ * (C) 1999 Hervé Eychenne <eychenne@info.enserb.u-bordeaux.fr>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/spinlock.h>
+#include <linux/interrupt.h>
+
+#include <linux/netfilter/x_tables.h>
+#include <linux/netfilter/xt_limit.h>
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Herve Eychenne <rv@wallfire.org>");
+MODULE_DESCRIPTION("iptables rate limit match");
+MODULE_ALIAS("ipt_limit");
+MODULE_ALIAS("ip6t_limit");
+
+/* The algorithm used is the Simple Token Bucket Filter (TBF)
+ * see net/sched/sch_tbf.c in the linux source tree
+ */
+
+static DEFINE_SPINLOCK(limit_lock);
+
+/* Rusty: This is my (non-mathematically-inclined) understanding of
+   this algorithm.  The `average rate' in jiffies becomes your initial
+   amount of credit `credit' and the most credit you can ever have
+   `credit_cap'.  The `peak rate' becomes the cost of passing the
+   test, `cost'.
+
+   `prev' tracks the last packet hit: you gain one credit per jiffy.
+   If you get credit balance more than this, the extra credit is
+   discarded.  Every time the match passes, you lose `cost' credits;
+   if you don't have that many, the test fails.
+
+   See Alexey's formal explanation in net/sched/sch_tbf.c.
+
+   To get the maxmum range, we multiply by this factor (ie. you get N
+   credits per jiffy).  We want to allow a rate as low as 1 per day
+   (slowest userspace tool allows), which means
+   CREDITS_PER_JIFFY*HZ*60*60*24 < 2^32. ie. */
+#define MAX_CPJ (0xFFFFFFFF / (HZ*60*60*24))
+
+/* Repeated shift and or gives us all 1s, final shift and add 1 gives
+ * us the power of 2 below the theoretical max, so GCC simply does a
+ * shift. */
+#define _POW2_BELOW2(x) ((x)|((x)>>1))
+#define _POW2_BELOW4(x) (_POW2_BELOW2(x)|_POW2_BELOW2((x)>>2))
+#define _POW2_BELOW8(x) (_POW2_BELOW4(x)|_POW2_BELOW4((x)>>4))
+#define _POW2_BELOW16(x) (_POW2_BELOW8(x)|_POW2_BELOW8((x)>>8))
+#define _POW2_BELOW32(x) (_POW2_BELOW16(x)|_POW2_BELOW16((x)>>16))
+#define POW2_BELOW32(x) ((_POW2_BELOW32(x)>>1) + 1)
+
+#define CREDITS_PER_JIFFY POW2_BELOW32(MAX_CPJ)
+
+static int
+ipt_limit_match(const struct sk_buff *skb,
+		const struct net_device *in,
+		const struct net_device *out,
+		const void *matchinfo,
+		int offset,
+		unsigned int protoff,
+		int *hotdrop)
+{
+	struct xt_rateinfo *r = ((struct xt_rateinfo *)matchinfo)->master;
+	unsigned long now = jiffies;
+
+	spin_lock_bh(&limit_lock);
+	r->credit += (now - xchg(&r->prev, now)) * CREDITS_PER_JIFFY;
+	if (r->credit > r->credit_cap)
+		r->credit = r->credit_cap;
+
+	if (r->credit >= r->cost) {
+		/* We're not limited. */
+		r->credit -= r->cost;
+		spin_unlock_bh(&limit_lock);
+		return 1;
+	}
+
+       	spin_unlock_bh(&limit_lock);
+	return 0;
+}
+
+/* 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 / XT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY;
+
+	return (user * HZ * CREDITS_PER_JIFFY) / XT_LIMIT_SCALE;
+}
+
+static int
+ipt_limit_checkentry(const char *tablename,
+		     const void *inf,
+		     void *matchinfo,
+		     unsigned int matchsize,
+		     unsigned int hook_mask)
+{
+	struct xt_rateinfo *r = matchinfo;
+
+	if (matchsize != XT_ALIGN(sizeof(struct xt_rateinfo)))
+		return 0;
+
+	/* Check for overflow. */
+	if (r->burst == 0
+	    || user2credits(r->avg * r->burst) < user2credits(r->avg)) {
+		printk("Overflow in xt_limit, try lower: %u/%u\n",
+		       r->avg, r->burst);
+		return 0;
+	}
+
+	/* User avg in seconds * XT_LIMIT_SCALE: convert to jiffies *
+	   128. */
+	r->prev = jiffies;
+	r->credit = user2credits(r->avg * r->burst);	 /* Credits full. */
+	r->credit_cap = user2credits(r->avg * r->burst); /* Credits full. */
+	r->cost = user2credits(r->avg);
+
+	/* For SMP, we only want to use one set of counters. */
+	r->master = r;
+
+	return 1;
+}
+
+static struct xt_match ipt_limit_reg = {
+	.name		= "limit",
+	.match		= ipt_limit_match,
+	.checkentry	= ipt_limit_checkentry,
+	.me		= THIS_MODULE,
+};
+static struct xt_match limit6_reg = {
+	.name		= "limit",
+	.match		= ipt_limit_match,
+	.checkentry	= ipt_limit_checkentry,
+	.me		= THIS_MODULE,
+};
+
+static int __init init(void)
+{
+	int ret;
+	
+	ret = xt_register_match(AF_INET, &ipt_limit_reg);
+	if (ret)
+		return ret;
+	
+	ret = xt_register_match(AF_INET6, &limit6_reg);
+	if (ret)
+		xt_unregister_match(AF_INET, &ipt_limit_reg);
+
+	return ret;
+}
+
+static void __exit fini(void)
+{
+	xt_unregister_match(AF_INET, &ipt_limit_reg);
+	xt_unregister_match(AF_INET6, &limit6_reg);
+}
+
+module_init(init);
+module_exit(fini);