1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * ebt_limit 4 * 5 * Authors: 6 * Tom Marshall <tommy@home.tig-grr.com> 7 * 8 * Mostly copied from netfilter's ipt_limit.c, see that file for 9 * more explanation 10 * 11 * September, 2003 12 * 13 */ 14 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt 15 #include <linux/module.h> 16 #include <linux/netdevice.h> 17 #include <linux/spinlock.h> 18 #include <linux/netfilter/x_tables.h> 19 #include <linux/netfilter_bridge/ebtables.h> 20 #include <linux/netfilter_bridge/ebt_limit.h> 21 22 static DEFINE_SPINLOCK(limit_lock); 23 24 #define MAX_CPJ (0xFFFFFFFF / (HZ*60*60*24)) 25 26 #define _POW2_BELOW2(x) ((x)|((x)>>1)) 27 #define _POW2_BELOW4(x) (_POW2_BELOW2(x)|_POW2_BELOW2((x)>>2)) 28 #define _POW2_BELOW8(x) (_POW2_BELOW4(x)|_POW2_BELOW4((x)>>4)) 29 #define _POW2_BELOW16(x) (_POW2_BELOW8(x)|_POW2_BELOW8((x)>>8)) 30 #define _POW2_BELOW32(x) (_POW2_BELOW16(x)|_POW2_BELOW16((x)>>16)) 31 #define POW2_BELOW32(x) ((_POW2_BELOW32(x)>>1) + 1) 32 33 #define CREDITS_PER_JIFFY POW2_BELOW32(MAX_CPJ) 34 35 static bool 36 ebt_limit_mt(const struct sk_buff *skb, struct xt_action_param *par) 37 { 38 struct ebt_limit_info *info = (void *)par->matchinfo; 39 unsigned long now = jiffies; 40 41 spin_lock_bh(&limit_lock); 42 info->credit += (now - xchg(&info->prev, now)) * CREDITS_PER_JIFFY; 43 if (info->credit > info->credit_cap) 44 info->credit = info->credit_cap; 45 46 if (info->credit >= info->cost) { 47 /* We're not limited. */ 48 info->credit -= info->cost; 49 spin_unlock_bh(&limit_lock); 50 return true; 51 } 52 53 spin_unlock_bh(&limit_lock); 54 return false; 55 } 56 57 /* Precision saver. */ 58 static u_int32_t 59 user2credits(u_int32_t user) 60 { 61 /* If multiplying would overflow... */ 62 if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY)) 63 /* Divide first. */ 64 return (user / EBT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY; 65 66 return (user * HZ * CREDITS_PER_JIFFY) / EBT_LIMIT_SCALE; 67 } 68 69 static int ebt_limit_mt_check(const struct xt_mtchk_param *par) 70 { 71 struct ebt_limit_info *info = par->matchinfo; 72 73 /* Check for overflow. */ 74 if (info->burst == 0 || 75 user2credits(info->avg * info->burst) < user2credits(info->avg)) { 76 pr_info_ratelimited("overflow, try lower: %u/%u\n", 77 info->avg, info->burst); 78 return -EINVAL; 79 } 80 81 /* User avg in seconds * EBT_LIMIT_SCALE: convert to jiffies * 128. */ 82 info->prev = jiffies; 83 info->credit = user2credits(info->avg * info->burst); 84 info->credit_cap = user2credits(info->avg * info->burst); 85 info->cost = user2credits(info->avg); 86 return 0; 87 } 88 89 90 #ifdef CONFIG_COMPAT 91 /* 92 * no conversion function needed -- 93 * only avg/burst have meaningful values in userspace. 94 */ 95 struct ebt_compat_limit_info { 96 compat_uint_t avg, burst; 97 compat_ulong_t prev; 98 compat_uint_t credit, credit_cap, cost; 99 }; 100 #endif 101 102 static struct xt_match ebt_limit_mt_reg __read_mostly = { 103 .name = "limit", 104 .revision = 0, 105 .family = NFPROTO_BRIDGE, 106 .match = ebt_limit_mt, 107 .checkentry = ebt_limit_mt_check, 108 .matchsize = sizeof(struct ebt_limit_info), 109 .usersize = offsetof(struct ebt_limit_info, prev), 110 #ifdef CONFIG_COMPAT 111 .compatsize = sizeof(struct ebt_compat_limit_info), 112 #endif 113 .me = THIS_MODULE, 114 }; 115 116 static int __init ebt_limit_init(void) 117 { 118 return xt_register_match(&ebt_limit_mt_reg); 119 } 120 121 static void __exit ebt_limit_fini(void) 122 { 123 xt_unregister_match(&ebt_limit_mt_reg); 124 } 125 126 module_init(ebt_limit_init); 127 module_exit(ebt_limit_fini); 128 MODULE_DESCRIPTION("Ebtables: Rate-limit match"); 129 MODULE_LICENSE("GPL"); 130