Linux Audio

Check our new training course

Embedded Linux Audio

Check our new training course
with Creative Commons CC-BY-SA
lecture materials

Bootlin logo

Elixir Cross Referencer

Open Menu /net/bridge/netfilter/ebt_limit.c
Loading...
  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
/*
 *  ebt_limit
 *
 *	Authors:
 *	Tom Marshall <tommy@home.tig-grr.com>
 *
 *	Mostly copied from netfilter's ipt_limit.c, see that file for
 *	more explanation
 *
 *  September, 2003
 *
 */
#include <linux/module.h>
#include <linux/netdevice.h>
#include <linux/spinlock.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter_bridge/ebtables.h>
#include <linux/netfilter_bridge/ebt_limit.h>

static DEFINE_SPINLOCK(limit_lock);

#define MAX_CPJ (0xFFFFFFFF / (HZ*60*60*24))

#define _POW2_BELOW2(x) ((x)|((x)>>1))
#define _POW2_BELOW4(x) (_POW2_BELOW2(x)|_POW2_BELOW2((x)>>2))
#define _POW2_BELOW8(x) (_POW2_BELOW4(x)|_POW2_BELOW4((x)>>4))
#define _POW2_BELOW16(x) (_POW2_BELOW8(x)|_POW2_BELOW8((x)>>8))
#define _POW2_BELOW32(x) (_POW2_BELOW16(x)|_POW2_BELOW16((x)>>16))
#define POW2_BELOW32(x) ((_POW2_BELOW32(x)>>1) + 1)

#define CREDITS_PER_JIFFY POW2_BELOW32(MAX_CPJ)

static bool
ebt_limit_mt(const struct sk_buff *skb, const struct xt_match_param *par)
{
	struct ebt_limit_info *info = (void *)par->matchinfo;
	unsigned long now = jiffies;

	spin_lock_bh(&limit_lock);
	info->credit += (now - xchg(&info->prev, now)) * CREDITS_PER_JIFFY;
	if (info->credit > info->credit_cap)
		info->credit = info->credit_cap;

	if (info->credit >= info->cost) {
		/* We're not limited. */
		info->credit -= info->cost;
		spin_unlock_bh(&limit_lock);
		return true;
	}

	spin_unlock_bh(&limit_lock);
	return false;
}

/* Precision saver. */
static u_int32_t
user2credits(u_int32_t user)
{
	/* If multiplying would overflow... */
	if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY))
		/* Divide first. */
		return (user / EBT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY;

	return (user * HZ * CREDITS_PER_JIFFY) / EBT_LIMIT_SCALE;
}

static bool ebt_limit_mt_check(const struct xt_mtchk_param *par)
{
	struct ebt_limit_info *info = par->matchinfo;

	/* Check for overflow. */
	if (info->burst == 0 ||
	    user2credits(info->avg * info->burst) < user2credits(info->avg)) {
		printk("Overflow in ebt_limit, try lower: %u/%u\n",
			info->avg, info->burst);
		return false;
	}

	/* User avg in seconds * EBT_LIMIT_SCALE: convert to jiffies * 128. */
	info->prev = jiffies;
	info->credit = user2credits(info->avg * info->burst);
	info->credit_cap = user2credits(info->avg * info->burst);
	info->cost = user2credits(info->avg);
	return true;
}

static struct xt_match ebt_limit_mt_reg __read_mostly = {
	.name		= "limit",
	.revision	= 0,
	.family		= NFPROTO_BRIDGE,
	.match		= ebt_limit_mt,
	.checkentry	= ebt_limit_mt_check,
	.matchsize	= XT_ALIGN(sizeof(struct ebt_limit_info)),
	.me		= THIS_MODULE,
};

static int __init ebt_limit_init(void)
{
	return xt_register_match(&ebt_limit_mt_reg);
}

static void __exit ebt_limit_fini(void)
{
	xt_unregister_match(&ebt_limit_mt_reg);
}

module_init(ebt_limit_init);
module_exit(ebt_limit_fini);
MODULE_DESCRIPTION("Ebtables: Rate-limit match");
MODULE_LICENSE("GPL");