--- /dev/null
+/* 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 struct xt_match *match,
+ 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,
+ const struct xt_match *match,
+ void *matchinfo,
+ unsigned int matchsize,
+ unsigned int hook_mask)
+{
+ struct xt_rateinfo *r = 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 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,
+ .matchsize = sizeof(struct xt_rateinfo),
+ .checkentry = ipt_limit_checkentry,
+ .family = AF_INET,
+ .me = THIS_MODULE,
+};
+static struct xt_match limit6_reg = {
+ .name = "limit",
+ .match = ipt_limit_match,
+ .matchsize = sizeof(struct xt_rateinfo),
+ .checkentry = ipt_limit_checkentry,
+ .family = AF_INET6,
+ .me = THIS_MODULE,
+};
+
+static int __init xt_limit_init(void)
+{
+ int ret;
+
+ ret = xt_register_match(&ipt_limit_reg);
+ if (ret)
+ return ret;
+
+ ret = xt_register_match(&limit6_reg);
+ if (ret)
+ xt_unregister_match(&ipt_limit_reg);
+
+ return ret;
+}
+
+static void __exit xt_limit_fini(void)
+{
+ xt_unregister_match(&ipt_limit_reg);
+ xt_unregister_match(&limit6_reg);
+}
+
+module_init(xt_limit_init);
+module_exit(xt_limit_fini);
git://git.onelab.eu / linux-2.6.git / blobdiff