bridge/netfilter/ebt_limit.c

0001 // SPDX-License-Identifier: GPL-2.0-only
0002 /*
0003  *  ebt_limit
0004  *
0005  *  Authors:
0006  *  Tom Marshall <tommy@home.tig-grr.com>
0007  *
0008  *  Mostly copied from netfilter's ipt_limit.c, see that file for
0009  *  more explanation
0010  *
0011  *  September, 2003
0012  *
0013  */
0014 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
0015 #include <linux/module.h>
0016 #include <linux/netdevice.h>
0017 #include <linux/spinlock.h>
0018 #include <linux/netfilter/x_tables.h>
0019 #include <linux/netfilter_bridge/ebtables.h>
0020 #include <linux/netfilter_bridge/ebt_limit.h>
0021
0022 static DEFINE_SPINLOCK(limit_lock);
0023
0024 #define MAX_CPJ (0xFFFFFFFF / (HZ*60*60*24))
0025
0026 #define _POW2_BELOW2(x) ((x)|((x)>>1))
0027 #define _POW2_BELOW4(x) (_POW2_BELOW2(x)|_POW2_BELOW2((x)>>2))
0028 #define _POW2_BELOW8(x) (_POW2_BELOW4(x)|_POW2_BELOW4((x)>>4))
0029 #define _POW2_BELOW16(x) (_POW2_BELOW8(x)|_POW2_BELOW8((x)>>8))
0030 #define _POW2_BELOW32(x) (_POW2_BELOW16(x)|_POW2_BELOW16((x)>>16))
0031 #define POW2_BELOW32(x) ((_POW2_BELOW32(x)>>1) + 1)
0032
0033 #define CREDITS_PER_JIFFY POW2_BELOW32(MAX_CPJ)
0034
0035 static bool
0036 ebt_limit_mt(const struct sk_buff *skb, struct xt_action_param *par)
0037 {
0038     struct ebt_limit_info *info = (void *)par->matchinfo;
0039     unsigned long now = jiffies;
0040
0041     spin_lock_bh(&limit_lock);
0042     info->credit += (now - xchg(&info->prev, now)) * CREDITS_PER_JIFFY;
0043     if (info->credit > info->credit_cap)
0044         info->credit = info->credit_cap;
0045
0046     if (info->credit >= info->cost) {
0047         /* We're not limited. */
0048         info->credit -= info->cost;
0049         spin_unlock_bh(&limit_lock);
0050         return true;
0051     }
0052
0053     spin_unlock_bh(&limit_lock);
0054     return false;
0055 }
0056
0057 /* Precision saver. */
0058 static u_int32_t
0059 user2credits(u_int32_t user)
0060 {
0061     /* If multiplying would overflow... */
0062     if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY))
0063         /* Divide first. */
0064         return (user / EBT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY;
0065
0066     return (user * HZ * CREDITS_PER_JIFFY) / EBT_LIMIT_SCALE;
0067 }
0068
0069 static int ebt_limit_mt_check(const struct xt_mtchk_param *par)
0070 {
0071     struct ebt_limit_info *info = par->matchinfo;
0072
0073     /* Check for overflow. */
0074     if (info->burst == 0 ||
0075         user2credits(info->avg * info->burst) < user2credits(info->avg)) {
0076         pr_info_ratelimited("overflow, try lower: %u/%u\n",
0077                     info->avg, info->burst);
0078         return -EINVAL;
0079     }
0080
0081     /* User avg in seconds * EBT_LIMIT_SCALE: convert to jiffies * 128. */
0082     info->prev = jiffies;
0083     info->credit = user2credits(info->avg * info->burst);
0084     info->credit_cap = user2credits(info->avg * info->burst);
0085     info->cost = user2credits(info->avg);
0086     return 0;
0087 }
0088
0089
0090 #ifdef CONFIG_NETFILTER_XTABLES_COMPAT
0091 /*
0092  * no conversion function needed --
0093  * only avg/burst have meaningful values in userspace.
0094  */
0095 struct ebt_compat_limit_info {
0096     compat_uint_t avg, burst;
0097     compat_ulong_t prev;
0098     compat_uint_t credit, credit_cap, cost;
0099 };
0100 #endif
0101
0102 static struct xt_match ebt_limit_mt_reg __read_mostly = {
0103     .name       = "limit",
0104     .revision   = 0,
0105     .family     = NFPROTO_BRIDGE,
0106     .match      = ebt_limit_mt,
0107     .checkentry = ebt_limit_mt_check,
0108     .matchsize  = sizeof(struct ebt_limit_info),
0109     .usersize   = offsetof(struct ebt_limit_info, prev),
0110 #ifdef CONFIG_NETFILTER_XTABLES_COMPAT
0111     .compatsize = sizeof(struct ebt_compat_limit_info),
0112 #endif
0113     .me     = THIS_MODULE,
0114 };
0115
0116 static int __init ebt_limit_init(void)
0117 {
0118     return xt_register_match(&ebt_limit_mt_reg);
0119 }
0120
0121 static void __exit ebt_limit_fini(void)
0122 {
0123     xt_unregister_match(&ebt_limit_mt_reg);
0124 }
0125
0126 module_init(ebt_limit_init);
0127 module_exit(ebt_limit_fini);
0128 MODULE_DESCRIPTION("Ebtables: Rate-limit match");
0129 MODULE_LICENSE("GPL");