1 /*
2 * ebt_limit
3 *
4 * Authors:
5 * Tom Marshall <tommy@home.tig-grr.com>
6 *
7 * Mostly copied from netfilter's ipt_limit.c, see that file for
8 * more explanation
9 *
10 * September, 2003
11 *
12 */
13
14 #include <linux/netfilter_bridge/ebtables.h>
15 #include <linux/netfilter_bridge/ebt_limit.h>
16 #include <linux/module.h>
17
18 #include <linux/netdevice.h>
19 #include <linux/spinlock.h>
20
21 static DEFINE_SPINLOCK(limit_lock);
22
23 #define MAX_CPJ (0xFFFFFFFF / (HZ*60*60*24))
24
25 #define _POW2_BELOW2(x) ((x)|((x)>>1))
26 #define _POW2_BELOW4(x) (_POW2_BELOW2(x)|_POW2_BELOW2((x)>>2))
27 #define _POW2_BELOW8(x) (_POW2_BELOW4(x)|_POW2_BELOW4((x)>>4))
28 #define _POW2_BELOW16(x) (_POW2_BELOW8(x)|_POW2_BELOW8((x)>>8))
29 #define _POW2_BELOW32(x) (_POW2_BELOW16(x)|_POW2_BELOW16((x)>>16))
30 #define POW2_BELOW32(x) ((_POW2_BELOW32(x)>>1) + 1)
31
32 #define CREDITS_PER_JIFFY POW2_BELOW32(MAX_CPJ)
33
34 static int ebt_limit_match(const struct sk_buff *skb,
35 const struct net_device *in, const struct net_device *out,
36 const void *data, unsigned int datalen)
37 {
38 struct ebt_limit_info *info = (struct ebt_limit_info *)data;
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 EBT_MATCH;
51 }
52
53 spin_unlock_bh(&limit_lock);
54 return EBT_NOMATCH;
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_check(const char *tablename, unsigned int hookmask,
70 const struct ebt_entry *e, void *data, unsigned int datalen)
71 {
72 struct ebt_limit_info *info = data;
73
74 if (datalen != EBT_ALIGN(sizeof(struct ebt_limit_info)))
75 return -EINVAL;
76
77 /* Check for overflow. */
78 if (info->burst == 0 ||
79 user2credits(info->avg * info->burst) < user2credits(info->avg)) {
80 printk("Overflow in ebt_limit, try lower: %u/%u\n",
81 info->avg, info->burst);
82 return -EINVAL;
83 }
84
85 /* User avg in seconds * EBT_LIMIT_SCALE: convert to jiffies * 128. */
86 info->prev = jiffies;
87 info->credit = user2credits(info->avg * info->burst);
88 info->credit_cap = user2credits(info->avg * info->burst);
89 info->cost = user2credits(info->avg);
90 return 0;
91 }
92
93 static struct ebt_match ebt_limit_reg __read_mostly = {
94 .name = EBT_LIMIT_MATCH,
95 .match = ebt_limit_match,
96 .check = ebt_limit_check,
97 .me = THIS_MODULE,
98 };
99
100 static int __init ebt_limit_init(void)
101 {
102 return ebt_register_match(&ebt_limit_reg);
103 }
104
105 static void __exit ebt_limit_fini(void)
106 {
107 ebt_unregister_match(&ebt_limit_reg);
108 }
109
110 module_init(ebt_limit_init);
111 module_exit(ebt_limit_fini);
112 MODULE_DESCRIPTION("Ebtables: Rate-limit match");
113 MODULE_LICENSE("GPL");
114
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