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 spinlock_t lock; 22 unsigned long prev; 23 uint32_t credit; 24 }; 25 26 MODULE_LICENSE("GPL"); 27 MODULE_AUTHOR("Herve Eychenne <rv@wallfire.org>"); 28 MODULE_DESCRIPTION("Xtables: rate-limit match"); 29 MODULE_ALIAS("ipt_limit"); 30 MODULE_ALIAS("ip6t_limit"); 31 32 /* The algorithm used is the Simple Token Bucket Filter (TBF) 33 * see net/sched/sch_tbf.c in the linux source tree 34 */ 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 maximum 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 67 static bool 68 limit_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(&priv->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(&priv->lock); 83 return true; 84 } 85 86 spin_unlock_bh(&priv->lock); 87 return false; 88 } 89 90 /* Precision saver. */ 91 static u32 user2credits(u32 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 } 100 101 static int limit_mt_check(const struct xt_mtchk_param *par) 102 { 103 struct xt_rateinfo *r = par->matchinfo; 104 struct xt_limit_priv *priv; 105 106 /* Check for overflow. */ 107 if (r->burst == 0 108 || user2credits(r->avg * r->burst) < user2credits(r->avg)) { 109 pr_info_ratelimited("Overflow, try lower: %u/%u\n", 110 r->avg, r->burst); 111 return -ERANGE; 112 } 113 114 priv = kmalloc(sizeof(*priv), GFP_KERNEL); 115 if (priv == NULL) 116 return -ENOMEM; 117 118 /* For SMP, we only want to use one set of state. */ 119 r->master = priv; 120 /* User avg in seconds * XT_LIMIT_SCALE: convert to jiffies * 121 128. */ 122 priv->prev = jiffies; 123 priv->credit = user2credits(r->avg * r->burst); /* Credits full. */ 124 if (r->cost == 0) { 125 r->credit_cap = priv->credit; /* Credits full. */ 126 r->cost = user2credits(r->avg); 127 } 128 spin_lock_init(&priv->lock); 129 130 return 0; 131 } 132 133 static void limit_mt_destroy(const struct xt_mtdtor_param *par) 134 { 135 const struct xt_rateinfo *info = par->matchinfo; 136 137 kfree(info->master); 138 } 139 140 #ifdef CONFIG_COMPAT 141 struct compat_xt_rateinfo { 142 u_int32_t avg; 143 u_int32_t burst; 144 145 compat_ulong_t prev; 146 u_int32_t credit; 147 u_int32_t credit_cap, cost; 148 149 u_int32_t master; 150 }; 151 152 /* To keep the full "prev" timestamp, the upper 32 bits are stored in the 153 * master pointer, which does not need to be preserved. */ 154 static void limit_mt_compat_from_user(void *dst, const void *src) 155 { 156 const struct compat_xt_rateinfo *cm = src; 157 struct xt_rateinfo m = { 158 .avg = cm->avg, 159 .burst = cm->burst, 160 .prev = cm->prev | (unsigned long)cm->master << 32, 161 .credit = cm->credit, 162 .credit_cap = cm->credit_cap, 163 .cost = cm->cost, 164 }; 165 memcpy(dst, &m, sizeof(m)); 166 } 167 168 static int limit_mt_compat_to_user(void __user *dst, const void *src) 169 { 170 const struct xt_rateinfo *m = src; 171 struct compat_xt_rateinfo cm = { 172 .avg = m->avg, 173 .burst = m->burst, 174 .prev = m->prev, 175 .credit = m->credit, 176 .credit_cap = m->credit_cap, 177 .cost = m->cost, 178 .master = m->prev >> 32, 179 }; 180 return copy_to_user(dst, &cm, sizeof(cm)) ? -EFAULT : 0; 181 } 182 #endif /* CONFIG_COMPAT */ 183 184 static struct xt_match limit_mt_reg __read_mostly = { 185 .name = "limit", 186 .revision = 0, 187 .family = NFPROTO_UNSPEC, 188 .match = limit_mt, 189 .checkentry = limit_mt_check, 190 .destroy = limit_mt_destroy, 191 .matchsize = sizeof(struct xt_rateinfo), 192 #ifdef CONFIG_COMPAT 193 .compatsize = sizeof(struct compat_xt_rateinfo), 194 .compat_from_user = limit_mt_compat_from_user, 195 .compat_to_user = limit_mt_compat_to_user, 196 #endif 197 .usersize = offsetof(struct xt_rateinfo, prev), 198 .me = THIS_MODULE, 199 }; 200 201 static int __init limit_mt_init(void) 202 { 203 return xt_register_match(&limit_mt_reg); 204 } 205 206 static void __exit limit_mt_exit(void) 207 { 208 xt_unregister_match(&limit_mt_reg); 209 } 210 211 module_init(limit_mt_init); 212 module_exit(limit_mt_exit); 213