root/net/bridge/netfilter/ebt_limit.c

DEFINITIONS

1. ebt_limit_mt
2. user2credits
3. ebt_limit_mt_check
4. ebt_limit_init
5. ebt_limit_fini

   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");