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
21static 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
34static 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. */
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_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 = (struct ebt_limit_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
93static struct ebt_match ebt_limit_reg =
94{
95	.name		= EBT_LIMIT_MATCH,
96	.match		= ebt_limit_match,
97	.check		= ebt_limit_check,
98	.me		= THIS_MODULE,
99};
100
101static int __init ebt_limit_init(void)
102{
103	return ebt_register_match(&ebt_limit_reg);
104}
105
106static void __exit ebt_limit_fini(void)
107{
108	ebt_unregister_match(&ebt_limit_reg);
109}
110
111module_init(ebt_limit_init);
112module_exit(ebt_limit_fini);
113MODULE_LICENSE("GPL");
114