// SPDX-License-Identifier: GPL-2.0-only
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/*
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* ebt_limit
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*
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* Authors:
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* Tom Marshall <tommy@home.tig-grr.com>
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*
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* Mostly copied from netfilter's ipt_limit.c, see that file for
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* more explanation
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*
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* September, 2003
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*
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/module.h>
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#include <linux/netdevice.h>
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#include <linux/spinlock.h>
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#include <linux/netfilter/x_tables.h>
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#include <linux/netfilter_bridge/ebtables.h>
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#include <linux/netfilter_bridge/ebt_limit.h>
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static DEFINE_SPINLOCK(limit_lock);
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#define MAX_CPJ (0xFFFFFFFF / (HZ*60*60*24))
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#define _POW2_BELOW2(x) ((x)|((x)>>1))
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#define _POW2_BELOW4(x) (_POW2_BELOW2(x)|_POW2_BELOW2((x)>>2))
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#define _POW2_BELOW8(x) (_POW2_BELOW4(x)|_POW2_BELOW4((x)>>4))
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#define _POW2_BELOW16(x) (_POW2_BELOW8(x)|_POW2_BELOW8((x)>>8))
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#define _POW2_BELOW32(x) (_POW2_BELOW16(x)|_POW2_BELOW16((x)>>16))
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#define POW2_BELOW32(x) ((_POW2_BELOW32(x)>>1) + 1)
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#define CREDITS_PER_JIFFY POW2_BELOW32(MAX_CPJ)
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static bool
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ebt_limit_mt(const struct sk_buff *skb, struct xt_action_param *par)
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{
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struct ebt_limit_info *info = (void *)par->matchinfo;
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unsigned long now = jiffies;
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spin_lock_bh(&limit_lock);
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info->credit += (now - xchg(&info->prev, now)) * CREDITS_PER_JIFFY;
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if (info->credit > info->credit_cap)
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info->credit = info->credit_cap;
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if (info->credit >= info->cost) {
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/* We're not limited. */
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info->credit -= info->cost;
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spin_unlock_bh(&limit_lock);
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return true;
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}
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spin_unlock_bh(&limit_lock);
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return false;
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}
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/* Precision saver. */
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static u_int32_t
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user2credits(u_int32_t user)
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{
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/* If multiplying would overflow... */
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if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY))
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/* Divide first. */
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return (user / EBT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY;
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return (user * HZ * CREDITS_PER_JIFFY) / EBT_LIMIT_SCALE;
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}
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static int ebt_limit_mt_check(const struct xt_mtchk_param *par)
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{
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struct ebt_limit_info *info = par->matchinfo;
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/* Check for overflow. */
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if (info->burst == 0 ||
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user2credits(info->avg * info->burst) < user2credits(info->avg)) {
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pr_info_ratelimited("overflow, try lower: %u/%u\n",
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info->avg, info->burst);
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return -EINVAL;
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}
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/* User avg in seconds * EBT_LIMIT_SCALE: convert to jiffies * 128. */
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info->prev = jiffies;
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info->credit = user2credits(info->avg * info->burst);
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info->credit_cap = user2credits(info->avg * info->burst);
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info->cost = user2credits(info->avg);
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return 0;
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}
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#ifdef CONFIG_COMPAT
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/*
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* no conversion function needed --
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* only avg/burst have meaningful values in userspace.
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*/
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struct ebt_compat_limit_info {
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compat_uint_t avg, burst;
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compat_ulong_t prev;
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compat_uint_t credit, credit_cap, cost;
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};
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#endif
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static struct xt_match ebt_limit_mt_reg __read_mostly = {
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.name = "limit",
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.revision = 0,
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.family = NFPROTO_BRIDGE,
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.match = ebt_limit_mt,
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.checkentry = ebt_limit_mt_check,
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.matchsize = sizeof(struct ebt_limit_info),
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.usersize = offsetof(struct ebt_limit_info, prev),
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#ifdef CONFIG_COMPAT
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.compatsize = sizeof(struct ebt_compat_limit_info),
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#endif
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.me = THIS_MODULE,
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};
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static int __init ebt_limit_init(void)
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{
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return xt_register_match(&ebt_limit_mt_reg);
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}
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static void __exit ebt_limit_fini(void)
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{
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xt_unregister_match(&ebt_limit_mt_reg);
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}
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module_init(ebt_limit_init);
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module_exit(ebt_limit_fini);
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MODULE_DESCRIPTION("Ebtables: Rate-limit match");
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MODULE_LICENSE("GPL");
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