xt_limit.c revision 55b69e91040c685a064198bd76e59885b7ad26c6
1/* (C) 1999 Jérôme de Vivie <devivie@info.enserb.u-bordeaux.fr> 2 * (C) 1999 Hervé Eychenne <eychenne@info.enserb.u-bordeaux.fr> 3 * 4 * This program is free software; you can redistribute it and/or modify 5 * it under the terms of the GNU General Public License version 2 as 6 * published by the Free Software Foundation. 7 */ 8 9#include <linux/module.h> 10#include <linux/skbuff.h> 11#include <linux/spinlock.h> 12#include <linux/interrupt.h> 13 14#include <linux/netfilter/x_tables.h> 15#include <linux/netfilter/xt_limit.h> 16 17MODULE_LICENSE("GPL"); 18MODULE_AUTHOR("Herve Eychenne <rv@wallfire.org>"); 19MODULE_DESCRIPTION("Xtables: rate-limit match"); 20MODULE_ALIAS("ipt_limit"); 21MODULE_ALIAS("ip6t_limit"); 22 23/* The algorithm used is the Simple Token Bucket Filter (TBF) 24 * see net/sched/sch_tbf.c in the linux source tree 25 */ 26 27static DEFINE_SPINLOCK(limit_lock); 28 29/* Rusty: This is my (non-mathematically-inclined) understanding of 30 this algorithm. The `average rate' in jiffies becomes your initial 31 amount of credit `credit' and the most credit you can ever have 32 `credit_cap'. The `peak rate' becomes the cost of passing the 33 test, `cost'. 34 35 `prev' tracks the last packet hit: you gain one credit per jiffy. 36 If you get credit balance more than this, the extra credit is 37 discarded. Every time the match passes, you lose `cost' credits; 38 if you don't have that many, the test fails. 39 40 See Alexey's formal explanation in net/sched/sch_tbf.c. 41 42 To get the maxmum range, we multiply by this factor (ie. you get N 43 credits per jiffy). We want to allow a rate as low as 1 per day 44 (slowest userspace tool allows), which means 45 CREDITS_PER_JIFFY*HZ*60*60*24 < 2^32. ie. */ 46#define MAX_CPJ (0xFFFFFFFF / (HZ*60*60*24)) 47 48/* Repeated shift and or gives us all 1s, final shift and add 1 gives 49 * us the power of 2 below the theoretical max, so GCC simply does a 50 * shift. */ 51#define _POW2_BELOW2(x) ((x)|((x)>>1)) 52#define _POW2_BELOW4(x) (_POW2_BELOW2(x)|_POW2_BELOW2((x)>>2)) 53#define _POW2_BELOW8(x) (_POW2_BELOW4(x)|_POW2_BELOW4((x)>>4)) 54#define _POW2_BELOW16(x) (_POW2_BELOW8(x)|_POW2_BELOW8((x)>>8)) 55#define _POW2_BELOW32(x) (_POW2_BELOW16(x)|_POW2_BELOW16((x)>>16)) 56#define POW2_BELOW32(x) ((_POW2_BELOW32(x)>>1) + 1) 57 58#define CREDITS_PER_JIFFY POW2_BELOW32(MAX_CPJ) 59 60static bool 61limit_mt(const struct sk_buff *skb, const struct net_device *in, 62 const struct net_device *out, const struct xt_match *match, 63 const void *matchinfo, int offset, unsigned int protoff, 64 bool *hotdrop) 65{ 66 struct xt_rateinfo *r = 67 ((const struct xt_rateinfo *)matchinfo)->master; 68 unsigned long now = jiffies; 69 70 spin_lock_bh(&limit_lock); 71 r->credit += (now - xchg(&r->prev, now)) * CREDITS_PER_JIFFY; 72 if (r->credit > r->credit_cap) 73 r->credit = r->credit_cap; 74 75 if (r->credit >= r->cost) { 76 /* We're not limited. */ 77 r->credit -= r->cost; 78 spin_unlock_bh(&limit_lock); 79 return true; 80 } 81 82 spin_unlock_bh(&limit_lock); 83 return false; 84} 85 86/* Precision saver. */ 87static u_int32_t 88user2credits(u_int32_t user) 89{ 90 /* If multiplying would overflow... */ 91 if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY)) 92 /* Divide first. */ 93 return (user / XT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY; 94 95 return (user * HZ * CREDITS_PER_JIFFY) / XT_LIMIT_SCALE; 96} 97 98static bool 99limit_mt_check(const char *tablename, const void *inf, 100 const struct xt_match *match, void *matchinfo, 101 unsigned int hook_mask) 102{ 103 struct xt_rateinfo *r = matchinfo; 104 105 /* Check for overflow. */ 106 if (r->burst == 0 107 || user2credits(r->avg * r->burst) < user2credits(r->avg)) { 108 printk("Overflow in xt_limit, try lower: %u/%u\n", 109 r->avg, r->burst); 110 return false; 111 } 112 113 /* For SMP, we only want to use one set of counters. */ 114 r->master = r; 115 if (r->cost == 0) { 116 /* User avg in seconds * XT_LIMIT_SCALE: convert to jiffies * 117 128. */ 118 r->prev = jiffies; 119 r->credit = user2credits(r->avg * r->burst); /* Credits full. */ 120 r->credit_cap = user2credits(r->avg * r->burst); /* Credits full. */ 121 r->cost = user2credits(r->avg); 122 } 123 return true; 124} 125 126#ifdef CONFIG_COMPAT 127struct compat_xt_rateinfo { 128 u_int32_t avg; 129 u_int32_t burst; 130 131 compat_ulong_t prev; 132 u_int32_t credit; 133 u_int32_t credit_cap, cost; 134 135 u_int32_t master; 136}; 137 138/* To keep the full "prev" timestamp, the upper 32 bits are stored in the 139 * master pointer, which does not need to be preserved. */ 140static void limit_mt_compat_from_user(void *dst, void *src) 141{ 142 const struct compat_xt_rateinfo *cm = src; 143 struct xt_rateinfo m = { 144 .avg = cm->avg, 145 .burst = cm->burst, 146 .prev = cm->prev | (unsigned long)cm->master << 32, 147 .credit = cm->credit, 148 .credit_cap = cm->credit_cap, 149 .cost = cm->cost, 150 }; 151 memcpy(dst, &m, sizeof(m)); 152} 153 154static int limit_mt_compat_to_user(void __user *dst, void *src) 155{ 156 const struct xt_rateinfo *m = src; 157 struct compat_xt_rateinfo cm = { 158 .avg = m->avg, 159 .burst = m->burst, 160 .prev = m->prev, 161 .credit = m->credit, 162 .credit_cap = m->credit_cap, 163 .cost = m->cost, 164 .master = m->prev >> 32, 165 }; 166 return copy_to_user(dst, &cm, sizeof(cm)) ? -EFAULT : 0; 167} 168#endif /* CONFIG_COMPAT */ 169 170static struct xt_match limit_mt_reg __read_mostly = { 171 .name = "limit", 172 .revision = 0, 173 .family = NFPROTO_UNSPEC, 174 .match = limit_mt, 175 .checkentry = limit_mt_check, 176 .matchsize = sizeof(struct xt_rateinfo), 177#ifdef CONFIG_COMPAT 178 .compatsize = sizeof(struct compat_xt_rateinfo), 179 .compat_from_user = limit_mt_compat_from_user, 180 .compat_to_user = limit_mt_compat_to_user, 181#endif 182 .me = THIS_MODULE, 183}; 184 185static int __init limit_mt_init(void) 186{ 187 return xt_register_match(&limit_mt_reg); 188} 189 190static void __exit limit_mt_exit(void) 191{ 192 xt_unregister_match(&limit_mt_reg); 193} 194 195module_init(limit_mt_init); 196module_exit(limit_mt_exit); 197