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 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("iptables 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 int 61ipt_limit_match(const struct sk_buff *skb, 62 const struct net_device *in, 63 const struct net_device *out, 64 const struct xt_match *match, 65 const void *matchinfo, 66 int offset, 67 unsigned int protoff, 68 int *hotdrop) 69{ 70 struct xt_rateinfo *r = ((struct xt_rateinfo *)matchinfo)->master; 71 unsigned long now = jiffies; 72 73 spin_lock_bh(&limit_lock); 74 r->credit += (now - xchg(&r->prev, now)) * CREDITS_PER_JIFFY; 75 if (r->credit > r->credit_cap) 76 r->credit = r->credit_cap; 77 78 if (r->credit >= r->cost) { 79 /* We're not limited. */ 80 r->credit -= r->cost; 81 spin_unlock_bh(&limit_lock); 82 return 1; 83 } 84 85 spin_unlock_bh(&limit_lock); 86 return 0; 87} 88 89/* Precision saver. */ 90static u_int32_t 91user2credits(u_int32_t user) 92{ 93 /* If multiplying would overflow... */ 94 if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY)) 95 /* Divide first. */ 96 return (user / XT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY; 97 98 return (user * HZ * CREDITS_PER_JIFFY) / XT_LIMIT_SCALE; 99} 100 101static int 102ipt_limit_checkentry(const char *tablename, 103 const void *inf, 104 const struct xt_match *match, 105 void *matchinfo, 106 unsigned int hook_mask) 107{ 108 struct xt_rateinfo *r = matchinfo; 109 110 /* Check for overflow. */ 111 if (r->burst == 0 112 || user2credits(r->avg * r->burst) < user2credits(r->avg)) { 113 printk("Overflow in xt_limit, try lower: %u/%u\n", 114 r->avg, r->burst); 115 return 0; 116 } 117 118 /* For SMP, we only want to use one set of counters. */ 119 r->master = r; 120 if (r->cost == 0) { 121 /* User avg in seconds * XT_LIMIT_SCALE: convert to jiffies * 122 128. */ 123 r->prev = jiffies; 124 r->credit = user2credits(r->avg * r->burst); /* Credits full. */ 125 r->credit_cap = user2credits(r->avg * r->burst); /* Credits full. */ 126 r->cost = user2credits(r->avg); 127 } 128 return 1; 129} 130 131#ifdef CONFIG_COMPAT 132struct compat_xt_rateinfo { 133 u_int32_t avg; 134 u_int32_t burst; 135 136 compat_ulong_t prev; 137 u_int32_t credit; 138 u_int32_t credit_cap, cost; 139 140 u_int32_t master; 141}; 142 143/* To keep the full "prev" timestamp, the upper 32 bits are stored in the 144 * master pointer, which does not need to be preserved. */ 145static void compat_from_user(void *dst, void *src) 146{ 147 struct compat_xt_rateinfo *cm = src; 148 struct xt_rateinfo m = { 149 .avg = cm->avg, 150 .burst = cm->burst, 151 .prev = cm->prev | (unsigned long)cm->master << 32, 152 .credit = cm->credit, 153 .credit_cap = cm->credit_cap, 154 .cost = cm->cost, 155 }; 156 memcpy(dst, &m, sizeof(m)); 157} 158 159static int compat_to_user(void __user *dst, void *src) 160{ 161 struct xt_rateinfo *m = src; 162 struct compat_xt_rateinfo cm = { 163 .avg = m->avg, 164 .burst = m->burst, 165 .prev = m->prev, 166 .credit = m->credit, 167 .credit_cap = m->credit_cap, 168 .cost = m->cost, 169 .master = m->prev >> 32, 170 }; 171 return copy_to_user(dst, &cm, sizeof(cm)) ? -EFAULT : 0; 172} 173#endif /* CONFIG_COMPAT */ 174 175static struct xt_match xt_limit_match[] = { 176 { 177 .name = "limit", 178 .family = AF_INET, 179 .checkentry = ipt_limit_checkentry, 180 .match = ipt_limit_match, 181 .matchsize = sizeof(struct xt_rateinfo), 182#ifdef CONFIG_COMPAT 183 .compatsize = sizeof(struct compat_xt_rateinfo), 184 .compat_from_user = compat_from_user, 185 .compat_to_user = compat_to_user, 186#endif 187 .me = THIS_MODULE, 188 }, 189 { 190 .name = "limit", 191 .family = AF_INET6, 192 .checkentry = ipt_limit_checkentry, 193 .match = ipt_limit_match, 194 .matchsize = sizeof(struct xt_rateinfo), 195 .me = THIS_MODULE, 196 }, 197}; 198 199static int __init xt_limit_init(void) 200{ 201 return xt_register_matches(xt_limit_match, ARRAY_SIZE(xt_limit_match)); 202} 203 204static void __exit xt_limit_fini(void) 205{ 206 xt_unregister_matches(xt_limit_match, ARRAY_SIZE(xt_limit_match)); 207} 208 209module_init(xt_limit_init); 210module_exit(xt_limit_fini); 211