| /* 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 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; |
| } |
| |
| /* 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 1; |
| } |
| |
| static struct xt_match xt_limit_match[] = { |
| { |
| .name = "limit", |
| .family = AF_INET, |
| .checkentry = ipt_limit_checkentry, |
| .match = ipt_limit_match, |
| .matchsize = sizeof(struct xt_rateinfo), |
| .me = THIS_MODULE, |
| }, |
| { |
| .name = "limit", |
| .family = AF_INET6, |
| .checkentry = ipt_limit_checkentry, |
| .match = ipt_limit_match, |
| .matchsize = sizeof(struct xt_rateinfo), |
| .me = THIS_MODULE, |
| }, |
| }; |
| |
| static int __init xt_limit_init(void) |
| { |
| return xt_register_matches(xt_limit_match, ARRAY_SIZE(xt_limit_match)); |
| } |
| |
| static void __exit xt_limit_fini(void) |
| { |
| xt_unregister_matches(xt_limit_match, ARRAY_SIZE(xt_limit_match)); |
| } |
| |
| module_init(xt_limit_init); |
| module_exit(xt_limit_fini); |