1 /* (C) 1999 Jérôme de Vivie <devivie@info.enserb.u-bordeaux.fr> 2 * (C) 1999 Hervé Eychenne <eychenne@info.enserb.u-bordeaux.fr> 3 * (C) 2006-2012 Patrick McHardy <kaber@trash.net> 4 * 5 * This program is free software; you can redistribute it and/or modify 6 * it under the terms of the GNU General Public License version 2 as 7 * published by the Free Software Foundation. 8 */ 9 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt 10 11 #include <linux/slab.h> 12 #include <linux/module.h> 13 #include <linux/skbuff.h> 14 #include <linux/spinlock.h> 15 #include <linux/interrupt.h> 16 17 #include <linux/netfilter/x_tables.h> 18 #include <linux/netfilter/xt_limit.h> 19 20 struct xt_limit_priv { 21 unsigned long prev; 22 uint32_t credit; 23 }; 24 25 MODULE_LICENSE("GPL"); 26 MODULE_AUTHOR("Herve Eychenne <rv@wallfire.org>"); 27 MODULE_DESCRIPTION("Xtables: rate-limit match"); 28 MODULE_ALIAS("ipt_limit"); 29 MODULE_ALIAS("ip6t_limit"); 30 31 /* The algorithm used is the Simple Token Bucket Filter (TBF) 32 * see net/sched/sch_tbf.c in the linux source tree 33 */ 34 35 static DEFINE_SPINLOCK(limit_lock); 36 37 /* Rusty: This is my (non-mathematically-inclined) understanding of 38 this algorithm. The `average rate' in jiffies becomes your initial 39 amount of credit `credit' and the most credit you can ever have 40 `credit_cap'. The `peak rate' becomes the cost of passing the 41 test, `cost'. 42 43 `prev' tracks the last packet hit: you gain one credit per jiffy. 44 If you get credit balance more than this, the extra credit is 45 discarded. Every time the match passes, you lose `cost' credits; 46 if you don't have that many, the test fails. 47 48 See Alexey's formal explanation in net/sched/sch_tbf.c. 49 50 To get the maxmum range, we multiply by this factor (ie. you get N 51 credits per jiffy). We want to allow a rate as low as 1 per day 52 (slowest userspace tool allows), which means 53 CREDITS_PER_JIFFY*HZ*60*60*24 < 2^32. ie. */ 54 #define MAX_CPJ (0xFFFFFFFF / (HZ*60*60*24)) 55 56 /* Repeated shift and or gives us all 1s, final shift and add 1 gives 57 * us the power of 2 below the theoretical max, so GCC simply does a 58 * shift. */ 59 #define _POW2_BELOW2(x) ((x)|((x)>>1)) 60 #define _POW2_BELOW4(x) (_POW2_BELOW2(x)|_POW2_BELOW2((x)>>2)) 61 #define _POW2_BELOW8(x) (_POW2_BELOW4(x)|_POW2_BELOW4((x)>>4)) 62 #define _POW2_BELOW16(x) (_POW2_BELOW8(x)|_POW2_BELOW8((x)>>8)) 63 #define _POW2_BELOW32(x) (_POW2_BELOW16(x)|_POW2_BELOW16((x)>>16)) 64 #define POW2_BELOW32(x) ((_POW2_BELOW32(x)>>1) + 1) 65 66 #define CREDITS_PER_JIFFY POW2_BELOW32(MAX_CPJ) 67 68 static bool 69 limit_mt(const struct sk_buff *skb, struct xt_action_param *par) 70 { 71 const struct xt_rateinfo *r = par->matchinfo; 72 struct xt_limit_priv *priv = r->master; 73 unsigned long now = jiffies; 74 75 spin_lock_bh(&limit_lock); 76 priv->credit += (now - xchg(&priv->prev, now)) * CREDITS_PER_JIFFY; 77 if (priv->credit > r->credit_cap) 78 priv->credit = r->credit_cap; 79 80 if (priv->credit >= r->cost) { 81 /* We're not limited. */ 82 priv->credit -= r->cost; 83 spin_unlock_bh(&limit_lock); 84 return true; 85 } 86 87 spin_unlock_bh(&limit_lock); 88 return false; 89 } 90 91 /* Precision saver. */ 92 static u32 user2credits(u32 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 } 101 102 static 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 /* User avg in seconds * XT_LIMIT_SCALE: convert to jiffies * 122 128. */ 123 priv->prev = jiffies; 124 priv->credit = user2credits(r->avg * r->burst); /* Credits full. */ 125 if (r->cost == 0) { 126 r->credit_cap = priv->credit; /* Credits full. */ 127 r->cost = user2credits(r->avg); 128 } 129 return 0; 130 } 131 132 static 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 140 struct 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. */ 153 static 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 } 166 167 static 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 */ 182 183 static 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 }; 198 199 static int __init limit_mt_init(void) 200 { 201 return xt_register_match(&limit_mt_reg); 202 } 203 204 static void __exit limit_mt_exit(void) 205 { 206 xt_unregister_match(&limit_mt_reg); 207 } 208 209 module_init(limit_mt_init); 210 module_exit(limit_mt_exit); 211