1/* (C) 1999 J��r��me de Vivie <devivie@info.enserb.u-bordeaux.fr> 2 * (C) 1999 Herv�� 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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt 9 10#include <linux/slab.h> 11#include <linux/module.h> 12#include <linux/skbuff.h> 13#include <linux/spinlock.h> 14#include <linux/interrupt.h> 15 16#include <linux/netfilter/x_tables.h> 17#include <linux/netfilter/xt_limit.h> 18 19struct xt_limit_priv { 20 unsigned long prev; 21 uint32_t credit; 22}; 23 24MODULE_LICENSE("GPL"); 25MODULE_AUTHOR("Herve Eychenne <rv@wallfire.org>"); 26MODULE_DESCRIPTION("Xtables: rate-limit match"); 27MODULE_ALIAS("ipt_limit"); 28MODULE_ALIAS("ip6t_limit"); 29 30/* The algorithm used is the Simple Token Bucket Filter (TBF) 31 * see net/sched/sch_tbf.c in the linux source tree 32 */ 33 34static DEFINE_SPINLOCK(limit_lock); 35 36/* Rusty: This is my (non-mathematically-inclined) understanding of 37 this algorithm. The `average rate' in jiffies becomes your initial 38 amount of credit `credit' and the most credit you can ever have 39 `credit_cap'. The `peak rate' becomes the cost of passing the 40 test, `cost'. 41 42 `prev' tracks the last packet hit: you gain one credit per jiffy. 43 If you get credit balance more than this, the extra credit is 44 discarded. Every time the match passes, you lose `cost' credits; 45 if you don't have that many, the test fails. 46 47 See Alexey's formal explanation in net/sched/sch_tbf.c. 48 49 To get the maxmum range, we multiply by this factor (ie. you get N 50 credits per jiffy). We want to allow a rate as low as 1 per day 51 (slowest userspace tool allows), which means 52 CREDITS_PER_JIFFY*HZ*60*60*24 < 2^32. ie. */ 53#define MAX_CPJ (0xFFFFFFFF / (HZ*60*60*24)) 54 55/* Repeated shift and or gives us all 1s, final shift and add 1 gives 56 * us the power of 2 below the theoretical max, so GCC simply does a 57 * shift. */ 58#define _POW2_BELOW2(x) ((x)|((x)>>1)) 59#define _POW2_BELOW4(x) (_POW2_BELOW2(x)|_POW2_BELOW2((x)>>2)) 60#define _POW2_BELOW8(x) (_POW2_BELOW4(x)|_POW2_BELOW4((x)>>4)) 61#define _POW2_BELOW16(x) (_POW2_BELOW8(x)|_POW2_BELOW8((x)>>8)) 62#define _POW2_BELOW32(x) (_POW2_BELOW16(x)|_POW2_BELOW16((x)>>16)) 63#define POW2_BELOW32(x) ((_POW2_BELOW32(x)>>1) + 1) 64 65#define CREDITS_PER_JIFFY POW2_BELOW32(MAX_CPJ) 66 67static bool 68limit_mt(const struct sk_buff *skb, struct xt_action_param *par) 69{ 70 const struct xt_rateinfo *r = par->matchinfo; 71 struct xt_limit_priv *priv = r->master; 72 unsigned long now = jiffies; 73 74 spin_lock_bh(&limit_lock); 75 priv->credit += (now - xchg(&priv->prev, now)) * CREDITS_PER_JIFFY; 76 if (priv->credit > r->credit_cap) 77 priv->credit = r->credit_cap; 78 79 if (priv->credit >= r->cost) { 80 /* We're not limited. */ 81 priv->credit -= r->cost; 82 spin_unlock_bh(&limit_lock); 83 return true; 84 } 85 86 spin_unlock_bh(&limit_lock); 87 return false; 88} 89 90/* Precision saver. */ 91static u_int32_t 92user2credits(u_int32_t user) 93{ 94 /* If multiplying would overflow... */ 95 if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY)) 96 /* Divide first. */ 97 return (user / XT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY; 98 99 return (user * HZ * CREDITS_PER_JIFFY) / XT_LIMIT_SCALE; 100} 101 102static int limit_mt_check(const struct xt_mtchk_param *par) 103{ 104 struct xt_rateinfo *r = par->matchinfo; 105 struct xt_limit_priv *priv; 106 107 /* Check for overflow. */ 108 if (r->burst == 0 109 || user2credits(r->avg * r->burst) < user2credits(r->avg)) { 110 pr_info("Overflow, try lower: %u/%u\n", 111 r->avg, r->burst); 112 return -ERANGE; 113 } 114 115 priv = kmalloc(sizeof(*priv), GFP_KERNEL); 116 if (priv == NULL) 117 return -ENOMEM; 118 119 /* For SMP, we only want to use one set of state. */ 120 r->master = priv; 121 if (r->cost == 0) { 122 /* User avg in seconds * XT_LIMIT_SCALE: convert to jiffies * 123 128. */ 124 priv->prev = jiffies; 125 priv->credit = user2credits(r->avg * r->burst); /* Credits full. */ 126 r->credit_cap = user2credits(r->avg * r->burst); /* Credits full. */ 127 r->cost = user2credits(r->avg); 128 } 129 return 0; 130} 131 132static void limit_mt_destroy(const struct xt_mtdtor_param *par) 133{ 134 const struct xt_rateinfo *info = par->matchinfo; 135 136 kfree(info->master); 137} 138 139#ifdef CONFIG_COMPAT 140struct compat_xt_rateinfo { 141 u_int32_t avg; 142 u_int32_t burst; 143 144 compat_ulong_t prev; 145 u_int32_t credit; 146 u_int32_t credit_cap, cost; 147 148 u_int32_t master; 149}; 150 151/* To keep the full "prev" timestamp, the upper 32 bits are stored in the 152 * master pointer, which does not need to be preserved. */ 153static void limit_mt_compat_from_user(void *dst, const void *src) 154{ 155 const struct compat_xt_rateinfo *cm = src; 156 struct xt_rateinfo m = { 157 .avg = cm->avg, 158 .burst = cm->burst, 159 .prev = cm->prev | (unsigned long)cm->master << 32, 160 .credit = cm->credit, 161 .credit_cap = cm->credit_cap, 162 .cost = cm->cost, 163 }; 164 memcpy(dst, &m, sizeof(m)); 165} 166 167static int limit_mt_compat_to_user(void __user *dst, const void *src) 168{ 169 const struct xt_rateinfo *m = src; 170 struct compat_xt_rateinfo cm = { 171 .avg = m->avg, 172 .burst = m->burst, 173 .prev = m->prev, 174 .credit = m->credit, 175 .credit_cap = m->credit_cap, 176 .cost = m->cost, 177 .master = m->prev >> 32, 178 }; 179 return copy_to_user(dst, &cm, sizeof(cm)) ? -EFAULT : 0; 180} 181#endif /* CONFIG_COMPAT */ 182 183static struct xt_match limit_mt_reg __read_mostly = { 184 .name = "limit", 185 .revision = 0, 186 .family = NFPROTO_UNSPEC, 187 .match = limit_mt, 188 .checkentry = limit_mt_check, 189 .destroy = limit_mt_destroy, 190 .matchsize = sizeof(struct xt_rateinfo), 191#ifdef CONFIG_COMPAT 192 .compatsize = sizeof(struct compat_xt_rateinfo), 193 .compat_from_user = limit_mt_compat_from_user, 194 .compat_to_user = limit_mt_compat_to_user, 195#endif 196 .me = THIS_MODULE, 197}; 198 199static int __init limit_mt_init(void) 200{ 201 return xt_register_match(&limit_mt_reg); 202} 203 204static void __exit limit_mt_exit(void) 205{ 206 xt_unregister_match(&limit_mt_reg); 207} 208 209module_init(limit_mt_init); 210module_exit(limit_mt_exit); 211