1 files changed, 190 insertions, 0 deletions
diff --git a/net/netfilter/xt_limit.c b/net/netfilter/xt_limit.c
new file mode 100644
index 0000000..c908d69
--- /dev/null
+++ b/net/netfilter/xt_limit.c
@@ -0,0 +1,190 @@
+/* (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("Xtables: 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 bool
+limit_mt(const struct sk_buff *skb, const struct xt_match_param *par)
+{
+	struct xt_rateinfo *r =
+		((const struct xt_rateinfo *)par->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 true;
+	}
+
+	spin_unlock_bh(&limit_lock);
+	return false;
+}
+
+/* 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 bool limit_mt_check(const struct xt_mtchk_param *par)
+{
+	struct xt_rateinfo *r = par->matchinfo;
+
+	/* 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 false;
+	}
+
+	/* For SMP, we only want to use one set of counters. */
+	r->master = r;
+	if (r->cost == 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);
+	}
+	return true;
+}
+
+#ifdef CONFIG_COMPAT
+struct compat_xt_rateinfo {
+	u_int32_t avg;
+	u_int32_t burst;
+
+	compat_ulong_t prev;
+	u_int32_t credit;
+	u_int32_t credit_cap, cost;
+
+	u_int32_t master;
+};
+
+/* To keep the full "prev" timestamp, the upper 32 bits are stored in the
+ * master pointer, which does not need to be preserved. */
+static void limit_mt_compat_from_user(void *dst, void *src)
+{
+	const struct compat_xt_rateinfo *cm = src;
+	struct xt_rateinfo m = {
+		.avg		= cm->avg,
+		.burst		= cm->burst,
+		.prev		= cm->prev | (unsigned long)cm->master << 32,
+		.credit		= cm->credit,
+		.credit_cap	= cm->credit_cap,
+		.cost		= cm->cost,
+	};
+	memcpy(dst, &m, sizeof(m));
+}
+
+static int limit_mt_compat_to_user(void __user *dst, void *src)
+{
+	const struct xt_rateinfo *m = src;
+	struct compat_xt_rateinfo cm = {
+		.avg		= m->avg,
+		.burst		= m->burst,
+		.prev		= m->prev,
+		.credit		= m->credit,
+		.credit_cap	= m->credit_cap,
+		.cost		= m->cost,
+		.master		= m->prev >> 32,
+	};
+	return copy_to_user(dst, &cm, sizeof(cm)) ? -EFAULT : 0;
+}
+#endif /* CONFIG_COMPAT */
+
+static struct xt_match limit_mt_reg __read_mostly = {
+	.name             = "limit",
+	.revision         = 0,
+	.family           = NFPROTO_UNSPEC,
+	.match            = limit_mt,
+	.checkentry       = limit_mt_check,
+	.matchsize        = sizeof(struct xt_rateinfo),
+#ifdef CONFIG_COMPAT
+	.compatsize       = sizeof(struct compat_xt_rateinfo),
+	.compat_from_user = limit_mt_compat_from_user,
+	.compat_to_user   = limit_mt_compat_to_user,
+#endif
+	.me               = THIS_MODULE,
+};
+
+static int __init limit_mt_init(void)
+{
+	return xt_register_match(&limit_mt_reg);
+}
+
+static void __exit limit_mt_exit(void)
+{
+	xt_unregister_match(&limit_mt_reg);
+}
+
+module_init(limit_mt_init);
+module_exit(limit_mt_exit);