1 // SPDX-License-Identifier: GPL-2.0-only 2 /* (C) 1999 Jérôme de Vivie <devivie@info.enserb.u-bordeaux.fr> 3 * (C) 1999 Hervé Eychenne <eychenne@info.enserb.u-bordeaux.fr> 4 * (C) 2006-2012 Patrick McHardy <kaber@trash.net> 5 */ 6 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt 7 8 #include <linux/slab.h> 9 #include <linux/module.h> 10 #include <linux/skbuff.h> 11 #include <linux/interrupt.h> 12 13 #include <linux/netfilter/x_tables.h> 14 #include <linux/netfilter/xt_limit.h> 15 16 struct xt_limit_priv { 17 unsigned long prev; 18 u32 credit; 19 }; 20 21 MODULE_LICENSE("GPL"); 22 MODULE_AUTHOR("Herve Eychenne <rv@wallfire.org>"); 23 MODULE_DESCRIPTION("Xtables: rate-limit match"); 24 MODULE_ALIAS("ipt_limit"); 25 MODULE_ALIAS("ip6t_limit"); 26 27 /* The algorithm used is the Simple Token Bucket Filter (TBF) 28 * see net/sched/sch_tbf.c in the linux source tree 29 */ 30 31 /* Rusty: This is my (non-mathematically-inclined) understanding of 32 this algorithm. The `average rate' in jiffies becomes your initial 33 amount of credit `credit' and the most credit you can ever have 34 `credit_cap'. The `peak rate' becomes the cost of passing the 35 test, `cost'. 36 37 `prev' tracks the last packet hit: you gain one credit per jiffy. 38 If you get credit balance more than this, the extra credit is 39 discarded. Every time the match passes, you lose `cost' credits; 40 if you don't have that many, the test fails. 41 42 See Alexey's formal explanation in net/sched/sch_tbf.c. 43 44 To get the maximum range, we multiply by this factor (ie. you get N 45 credits per jiffy). We want to allow a rate as low as 1 per day 46 (slowest userspace tool allows), which means 47 CREDITS_PER_JIFFY*HZ*60*60*24 < 2^32. ie. */ 48 #define MAX_CPJ (0xFFFFFFFF / (HZ*60*60*24)) 49 50 /* Repeated shift and or gives us all 1s, final shift and add 1 gives 51 * us the power of 2 below the theoretical max, so GCC simply does a 52 * shift. */ 53 #define _POW2_BELOW2(x) ((x)|((x)>>1)) 54 #define _POW2_BELOW4(x) (_POW2_BELOW2(x)|_POW2_BELOW2((x)>>2)) 55 #define _POW2_BELOW8(x) (_POW2_BELOW4(x)|_POW2_BELOW4((x)>>4)) 56 #define _POW2_BELOW16(x) (_POW2_BELOW8(x)|_POW2_BELOW8((x)>>8)) 57 #define _POW2_BELOW32(x) (_POW2_BELOW16(x)|_POW2_BELOW16((x)>>16)) 58 #define POW2_BELOW32(x) ((_POW2_BELOW32(x)>>1) + 1) 59 60 #define CREDITS_PER_JIFFY POW2_BELOW32(MAX_CPJ) 61 62 static bool 63 limit_mt(const struct sk_buff *skb, struct xt_action_param *par) 64 { 65 const struct xt_rateinfo *r = par->matchinfo; 66 struct xt_limit_priv *priv = r->master; 67 unsigned long now; 68 u32 old_credit, new_credit, credit_increase = 0; 69 bool ret; 70 71 /* fastpath if there is nothing to update */ 72 if ((READ_ONCE(priv->credit) < r->cost) && (READ_ONCE(priv->prev) == jiffies)) 73 return false; 74 75 do { 76 now = jiffies; 77 credit_increase += (now - xchg(&priv->prev, now)) * CREDITS_PER_JIFFY; 78 old_credit = READ_ONCE(priv->credit); 79 new_credit = old_credit; 80 new_credit += credit_increase; 81 if (new_credit > r->credit_cap) 82 new_credit = r->credit_cap; 83 if (new_credit >= r->cost) { 84 ret = true; 85 new_credit -= r->cost; 86 } else { 87 ret = false; 88 } 89 } while (cmpxchg(&priv->credit, old_credit, new_credit) != old_credit); 90 91 return ret; 92 } 93 94 /* Precision saver. */ 95 static u32 user2credits(u32 user) 96 { 97 /* If multiplying would overflow... */ 98 if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY)) 99 /* Divide first. */ 100 return (user / XT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY; 101 102 return (user * HZ * CREDITS_PER_JIFFY) / XT_LIMIT_SCALE; 103 } 104 105 static int limit_mt_check(const struct xt_mtchk_param *par) 106 { 107 struct xt_rateinfo *r = par->matchinfo; 108 struct xt_limit_priv *priv; 109 110 /* Check for overflow. */ 111 if (r->burst == 0 112 || user2credits(r->avg * r->burst) < user2credits(r->avg)) { 113 pr_info_ratelimited("Overflow, try lower: %u/%u\n", 114 r->avg, r->burst); 115 return -ERANGE; 116 } 117 118 priv = kmalloc(sizeof(*priv), GFP_KERNEL); 119 if (priv == NULL) 120 return -ENOMEM; 121 122 /* For SMP, we only want to use one set of state. */ 123 r->master = priv; 124 /* User avg in seconds * XT_LIMIT_SCALE: convert to jiffies * 125 128. */ 126 priv->prev = jiffies; 127 priv->credit = user2credits(r->avg * r->burst); /* Credits full. */ 128 if (r->cost == 0) { 129 r->credit_cap = priv->credit; /* Credits full. */ 130 r->cost = user2credits(r->avg); 131 } 132 133 return 0; 134 } 135 136 static void limit_mt_destroy(const struct xt_mtdtor_param *par) 137 { 138 const struct xt_rateinfo *info = par->matchinfo; 139 140 kfree(info->master); 141 } 142 143 #ifdef CONFIG_NETFILTER_XTABLES_COMPAT 144 struct compat_xt_rateinfo { 145 u_int32_t avg; 146 u_int32_t burst; 147 148 compat_ulong_t prev; 149 u_int32_t credit; 150 u_int32_t credit_cap, cost; 151 152 u_int32_t master; 153 }; 154 155 /* To keep the full "prev" timestamp, the upper 32 bits are stored in the 156 * master pointer, which does not need to be preserved. */ 157 static void limit_mt_compat_from_user(void *dst, const void *src) 158 { 159 const struct compat_xt_rateinfo *cm = src; 160 struct xt_rateinfo m = { 161 .avg = cm->avg, 162 .burst = cm->burst, 163 .prev = cm->prev | (unsigned long)cm->master << 32, 164 .credit = cm->credit, 165 .credit_cap = cm->credit_cap, 166 .cost = cm->cost, 167 }; 168 memcpy(dst, &m, sizeof(m)); 169 } 170 171 static int limit_mt_compat_to_user(void __user *dst, const void *src) 172 { 173 const struct xt_rateinfo *m = src; 174 struct compat_xt_rateinfo cm = { 175 .avg = m->avg, 176 .burst = m->burst, 177 .prev = m->prev, 178 .credit = m->credit, 179 .credit_cap = m->credit_cap, 180 .cost = m->cost, 181 .master = m->prev >> 32, 182 }; 183 return copy_to_user(dst, &cm, sizeof(cm)) ? -EFAULT : 0; 184 } 185 #endif /* CONFIG_NETFILTER_XTABLES_COMPAT */ 186 187 static struct xt_match limit_mt_reg __read_mostly = { 188 .name = "limit", 189 .revision = 0, 190 .family = NFPROTO_UNSPEC, 191 .match = limit_mt, 192 .checkentry = limit_mt_check, 193 .destroy = limit_mt_destroy, 194 .matchsize = sizeof(struct xt_rateinfo), 195 #ifdef CONFIG_NETFILTER_XTABLES_COMPAT 196 .compatsize = sizeof(struct compat_xt_rateinfo), 197 .compat_from_user = limit_mt_compat_from_user, 198 .compat_to_user = limit_mt_compat_to_user, 199 #endif 200 .usersize = offsetof(struct xt_rateinfo, prev), 201 .me = THIS_MODULE, 202 }; 203 204 static int __init limit_mt_init(void) 205 { 206 return xt_register_match(&limit_mt_reg); 207 } 208 209 static void __exit limit_mt_exit(void) 210 { 211 xt_unregister_match(&limit_mt_reg); 212 } 213 214 module_init(limit_mt_init); 215 module_exit(limit_mt_exit); 216