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
ebt_limit_mt(const struct sk_buff * skb,struct xt_action_param * par)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
user2credits(u_int32_t user)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
ebt_limit_mt_check(const struct xt_mtchk_param * par)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_NETFILTER_XTABLES_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_NETFILTER_XTABLES_COMPAT
111 .compatsize = sizeof(struct ebt_compat_limit_info),
112 #endif
113 .me = THIS_MODULE,
114 };
115
ebt_limit_init(void)116 static int __init ebt_limit_init(void)
117 {
118 return xt_register_match(&ebt_limit_mt_reg);
119 }
120
ebt_limit_fini(void)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