1/* (C) 1999 Jérôme de Vivie <devivie@info.enserb.u-bordeaux.fr>
2 * (C) 1999 Hervé Eychenne <eychenne@info.enserb.u-bordeaux.fr>
3 * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
4 *
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License version 2 as
7 * published by the Free Software Foundation.
8 */
9#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
10
11#include <linux/slab.h>
12#include <linux/module.h>
13#include <linux/skbuff.h>
14#include <linux/spinlock.h>
15#include <linux/interrupt.h>
16
17#include <linux/netfilter/x_tables.h>
18#include <linux/netfilter/xt_limit.h>
19
20struct xt_limit_priv {
21	unsigned long prev;
22	uint32_t credit;
23};
24
25MODULE_LICENSE("GPL");
26MODULE_AUTHOR("Herve Eychenne <rv@wallfire.org>");
27MODULE_DESCRIPTION("Xtables: rate-limit match");
28MODULE_ALIAS("ipt_limit");
29MODULE_ALIAS("ip6t_limit");
30
31/* The algorithm used is the Simple Token Bucket Filter (TBF)
32 * see net/sched/sch_tbf.c in the linux source tree
33 */
34
35static DEFINE_SPINLOCK(limit_lock);
36
37/* Rusty: This is my (non-mathematically-inclined) understanding of
38   this algorithm.  The `average rate' in jiffies becomes your initial
39   amount of credit `credit' and the most credit you can ever have
40   `credit_cap'.  The `peak rate' becomes the cost of passing the
41   test, `cost'.
42
43   `prev' tracks the last packet hit: you gain one credit per jiffy.
44   If you get credit balance more than this, the extra credit is
45   discarded.  Every time the match passes, you lose `cost' credits;
46   if you don't have that many, the test fails.
47
48   See Alexey's formal explanation in net/sched/sch_tbf.c.
49
50   To get the maxmum range, we multiply by this factor (ie. you get N
51   credits per jiffy).  We want to allow a rate as low as 1 per day
52   (slowest userspace tool allows), which means
53   CREDITS_PER_JIFFY*HZ*60*60*24 < 2^32. ie. */
54#define MAX_CPJ (0xFFFFFFFF / (HZ*60*60*24))
55
56/* Repeated shift and or gives us all 1s, final shift and add 1 gives
57 * us the power of 2 below the theoretical max, so GCC simply does a
58 * shift. */
59#define _POW2_BELOW2(x) ((x)|((x)>>1))
60#define _POW2_BELOW4(x) (_POW2_BELOW2(x)|_POW2_BELOW2((x)>>2))
61#define _POW2_BELOW8(x) (_POW2_BELOW4(x)|_POW2_BELOW4((x)>>4))
62#define _POW2_BELOW16(x) (_POW2_BELOW8(x)|_POW2_BELOW8((x)>>8))
63#define _POW2_BELOW32(x) (_POW2_BELOW16(x)|_POW2_BELOW16((x)>>16))
64#define POW2_BELOW32(x) ((_POW2_BELOW32(x)>>1) + 1)
65
66#define CREDITS_PER_JIFFY POW2_BELOW32(MAX_CPJ)
67
68static bool
69limit_mt(const struct sk_buff *skb, struct xt_action_param *par)
70{
71	const struct xt_rateinfo *r = par->matchinfo;
72	struct xt_limit_priv *priv = r->master;
73	unsigned long now = jiffies;
74
75	spin_lock_bh(&limit_lock);
76	priv->credit += (now - xchg(&priv->prev, now)) * CREDITS_PER_JIFFY;
77	if (priv->credit > r->credit_cap)
78		priv->credit = r->credit_cap;
79
80	if (priv->credit >= r->cost) {
81		/* We're not limited. */
82		priv->credit -= r->cost;
83		spin_unlock_bh(&limit_lock);
84		return true;
85	}
86
87	spin_unlock_bh(&limit_lock);
88	return false;
89}
90
91/* Precision saver. */
92static u32 user2credits(u32 user)
93{
94	/* If multiplying would overflow... */
95	if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY))
96		/* Divide first. */
97		return (user / XT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY;
98
99	return (user * HZ * CREDITS_PER_JIFFY) / XT_LIMIT_SCALE;
100}
101
102static int limit_mt_check(const struct xt_mtchk_param *par)
103{
104	struct xt_rateinfo *r = par->matchinfo;
105	struct xt_limit_priv *priv;
106
107	/* Check for overflow. */
108	if (r->burst == 0
109	    || user2credits(r->avg * r->burst) < user2credits(r->avg)) {
110		pr_info("Overflow, try lower: %u/%u\n",
111			r->avg, r->burst);
112		return -ERANGE;
113	}
114
115	priv = kmalloc(sizeof(*priv), GFP_KERNEL);
116	if (priv == NULL)
117		return -ENOMEM;
118
119	/* For SMP, we only want to use one set of state. */
120	r->master = priv;
121	/* User avg in seconds * XT_LIMIT_SCALE: convert to jiffies *
122	   128. */
123	priv->prev = jiffies;
124	priv->credit = user2credits(r->avg * r->burst); /* Credits full. */
125	if (r->cost == 0) {
126		r->credit_cap = priv->credit; /* Credits full. */
127		r->cost = user2credits(r->avg);
128	}
129	return 0;
130}
131
132static void limit_mt_destroy(const struct xt_mtdtor_param *par)
133{
134	const struct xt_rateinfo *info = par->matchinfo;
135
136	kfree(info->master);
137}
138
139#ifdef CONFIG_COMPAT
140struct compat_xt_rateinfo {
141	u_int32_t avg;
142	u_int32_t burst;
143
144	compat_ulong_t prev;
145	u_int32_t credit;
146	u_int32_t credit_cap, cost;
147
148	u_int32_t master;
149};
150
151/* To keep the full "prev" timestamp, the upper 32 bits are stored in the
152 * master pointer, which does not need to be preserved. */
153static void limit_mt_compat_from_user(void *dst, const void *src)
154{
155	const struct compat_xt_rateinfo *cm = src;
156	struct xt_rateinfo m = {
157		.avg		= cm->avg,
158		.burst		= cm->burst,
159		.prev		= cm->prev | (unsigned long)cm->master << 32,
160		.credit		= cm->credit,
161		.credit_cap	= cm->credit_cap,
162		.cost		= cm->cost,
163	};
164	memcpy(dst, &m, sizeof(m));
165}
166
167static int limit_mt_compat_to_user(void __user *dst, const void *src)
168{
169	const struct xt_rateinfo *m = src;
170	struct compat_xt_rateinfo cm = {
171		.avg		= m->avg,
172		.burst		= m->burst,
173		.prev		= m->prev,
174		.credit		= m->credit,
175		.credit_cap	= m->credit_cap,
176		.cost		= m->cost,
177		.master		= m->prev >> 32,
178	};
179	return copy_to_user(dst, &cm, sizeof(cm)) ? -EFAULT : 0;
180}
181#endif /* CONFIG_COMPAT */
182
183static struct xt_match limit_mt_reg __read_mostly = {
184	.name             = "limit",
185	.revision         = 0,
186	.family           = NFPROTO_UNSPEC,
187	.match            = limit_mt,
188	.checkentry       = limit_mt_check,
189	.destroy          = limit_mt_destroy,
190	.matchsize        = sizeof(struct xt_rateinfo),
191#ifdef CONFIG_COMPAT
192	.compatsize       = sizeof(struct compat_xt_rateinfo),
193	.compat_from_user = limit_mt_compat_from_user,
194	.compat_to_user   = limit_mt_compat_to_user,
195#endif
196	.me               = THIS_MODULE,
197};
198
199static int __init limit_mt_init(void)
200{
201	return xt_register_match(&limit_mt_reg);
202}
203
204static void __exit limit_mt_exit(void)
205{
206	xt_unregister_match(&limit_mt_reg);
207}
208
209module_init(limit_mt_init);
210module_exit(limit_mt_exit);
211