LXR linux/net/bridge/netfilter/ebt

   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
  22static 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
  35static bool
  36ebt_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. */
  58static u_int32_t
  59user2credits(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
  69static 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_NETFILTER_XTABLES_COMPAT
  91/*
  92 * no conversion function needed --
  93 * only avg/burst have meaningful values in userspace.
  94 */
  95struct 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
 102static 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_NETFILTER_XTABLES_COMPAT
 111        .compatsize     = sizeof(struct ebt_compat_limit_info),
 112#endif
 113        .me             = THIS_MODULE,
 114};
 115
 116static int __init ebt_limit_init(void)
 117{
 118        return xt_register_match(&ebt_limit_mt_reg);
 119}
 120
 121static void __exit ebt_limit_fini(void)
 122{
 123        xt_unregister_match(&ebt_limit_mt_reg);
 124}
 125
 126module_init(ebt_limit_init);
 127module_exit(ebt_limit_fini);
 128MODULE_DESCRIPTION("Ebtables: Rate-limit match");
 129MODULE_LICENSE("GPL");
 130