1 // SPDX-License-Identifier: GPL-2.0-only
2 /* (C) 1999 Jérôme de Vivie <devivie@info.enserb.u-bordeaux.fr>
3 * (C) 1999 Hervé Eychenne <eychenne@info.enserb.u-bordeaux.fr>
4 * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
5 */
6 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
7
8 #include <linux/slab.h>
9 #include <linux/module.h>
10 #include <linux/skbuff.h>
11 #include <linux/interrupt.h>
12
13 #include <linux/netfilter/x_tables.h>
14 #include <linux/netfilter/xt_limit.h>
15
16 struct xt_limit_priv {
17 unsigned long prev;
18 u32 credit;
19 };
20
21 MODULE_LICENSE("GPL");
22 MODULE_AUTHOR("Herve Eychenne <rv@wallfire.org>");
23 MODULE_DESCRIPTION("Xtables: rate-limit match");
24 MODULE_ALIAS("ipt_limit");
25 MODULE_ALIAS("ip6t_limit");
26
27 /* The algorithm used is the Simple Token Bucket Filter (TBF)
28 * see net/sched/sch_tbf.c in the linux source tree
29 */
30
31 /* Rusty: This is my (non-mathematically-inclined) understanding of
32 this algorithm. The `average rate' in jiffies becomes your initial
33 amount of credit `credit' and the most credit you can ever have
34 `credit_cap'. The `peak rate' becomes the cost of passing the
35 test, `cost'.
36
37 `prev' tracks the last packet hit: you gain one credit per jiffy.
38 If you get credit balance more than this, the extra credit is
39 discarded. Every time the match passes, you lose `cost' credits;
40 if you don't have that many, the test fails.
41
42 See Alexey's formal explanation in net/sched/sch_tbf.c.
43
44 To get the maximum range, we multiply by this factor (ie. you get N
45 credits per jiffy). We want to allow a rate as low as 1 per day
46 (slowest userspace tool allows), which means
47 CREDITS_PER_JIFFY*HZ*60*60*24 < 2^32. ie. */
48 #define MAX_CPJ (0xFFFFFFFF / (HZ*60*60*24))
49
50 /* Repeated shift and or gives us all 1s, final shift and add 1 gives
51 * us the power of 2 below the theoretical max, so GCC simply does a
52 * shift. */
53 #define _POW2_BELOW2(x) ((x)|((x)>>1))
54 #define _POW2_BELOW4(x) (_POW2_BELOW2(x)|_POW2_BELOW2((x)>>2))
55 #define _POW2_BELOW8(x) (_POW2_BELOW4(x)|_POW2_BELOW4((x)>>4))
56 #define _POW2_BELOW16(x) (_POW2_BELOW8(x)|_POW2_BELOW8((x)>>8))
57 #define _POW2_BELOW32(x) (_POW2_BELOW16(x)|_POW2_BELOW16((x)>>16))
58 #define POW2_BELOW32(x) ((_POW2_BELOW32(x)>>1) + 1)
59
60 #define CREDITS_PER_JIFFY POW2_BELOW32(MAX_CPJ)
61
62 static bool
63 limit_mt(const struct sk_buff *skb, struct xt_action_param *par)
64 {
65 const struct xt_rateinfo *r = par->matchinfo;
66 struct xt_limit_priv *priv = r->master;
67 unsigned long now;
68 u32 old_credit, new_credit, credit_increase = 0;
69 bool ret;
70
71 /* fastpath if there is nothing to update */
72 if ((READ_ONCE(priv->credit) < r->cost) && (READ_ONCE(priv->prev) == jiffies))
73 return false;
74
75 do {
76 now = jiffies;
77 credit_increase += (now - xchg(&priv->prev, now)) * CREDITS_PER_JIFFY;
78 old_credit = READ_ONCE(priv->credit);
79 new_credit = old_credit;
80 new_credit += credit_increase;
81 if (new_credit > r->credit_cap)
82 new_credit = r->credit_cap;
83 if (new_credit >= r->cost) {
84 ret = true;
85 new_credit -= r->cost;
86 } else {
87 ret = false;
88 }
89 } while (cmpxchg(&priv->credit, old_credit, new_credit) != old_credit);
90
91 return ret;
92 }
93
94 /* Precision saver. */
95 static u32 user2credits(u32 user)
96 {
97 /* If multiplying would overflow... */
98 if (user > 0xFFFFFFFF / (HZ*CREDITS_PER_JIFFY))
99 /* Divide first. */
100 return (user / XT_LIMIT_SCALE) * HZ * CREDITS_PER_JIFFY;
101
102 return (user * HZ * CREDITS_PER_JIFFY) / XT_LIMIT_SCALE;
103 }
104
105 static int limit_mt_check(const struct xt_mtchk_param *par)
106 {
107 struct xt_rateinfo *r = par->matchinfo;
108 struct xt_limit_priv *priv;
109
110 /* Check for overflow. */
111 if (r->burst == 0
112 || user2credits(r->avg * r->burst) < user2credits(r->avg)) {
113 pr_info_ratelimited("Overflow, try lower: %u/%u\n",
114 r->avg, r->burst);
115 return -ERANGE;
116 }
117
118 priv = kmalloc(sizeof(*priv), GFP_KERNEL);
119 if (priv == NULL)
120 return -ENOMEM;
121
122 /* For SMP, we only want to use one set of state. */
123 r->master = priv;
124 /* User avg in seconds * XT_LIMIT_SCALE: convert to jiffies *
125 128. */
126 priv->prev = jiffies;
127 priv->credit = user2credits(r->avg * r->burst); /* Credits full. */
128 if (r->cost == 0) {
129 r->credit_cap = priv->credit; /* Credits full. */
130 r->cost = user2credits(r->avg);
131 }
132
133 return 0;
134 }
135
136 static void limit_mt_destroy(const struct xt_mtdtor_param *par)
137 {
138 const struct xt_rateinfo *info = par->matchinfo;
139
140 kfree(info->master);
141 }
142
143 #ifdef CONFIG_NETFILTER_XTABLES_COMPAT
144 struct compat_xt_rateinfo {
145 u_int32_t avg;
146 u_int32_t burst;
147
148 compat_ulong_t prev;
149 u_int32_t credit;
150 u_int32_t credit_cap, cost;
151
152 u_int32_t master;
153 };
154
155 /* To keep the full "prev" timestamp, the upper 32 bits are stored in the
156 * master pointer, which does not need to be preserved. */
157 static void limit_mt_compat_from_user(void *dst, const void *src)
158 {
159 const struct compat_xt_rateinfo *cm = src;
160 struct xt_rateinfo m = {
161 .avg = cm->avg,
162 .burst = cm->burst,
163 .prev = cm->prev | (unsigned long)cm->master << 32,
164 .credit = cm->credit,
165 .credit_cap = cm->credit_cap,
166 .cost = cm->cost,
167 };
168 memcpy(dst, &m, sizeof(m));
169 }
170
171 static int limit_mt_compat_to_user(void __user *dst, const void *src)
172 {
173 const struct xt_rateinfo *m = src;
174 struct compat_xt_rateinfo cm = {
175 .avg = m->avg,
176 .burst = m->burst,
177 .prev = m->prev,
178 .credit = m->credit,
179 .credit_cap = m->credit_cap,
180 .cost = m->cost,
181 .master = m->prev >> 32,
182 };
183 return copy_to_user(dst, &cm, sizeof(cm)) ? -EFAULT : 0;
184 }
185 #endif /* CONFIG_NETFILTER_XTABLES_COMPAT */
186
187 static struct xt_match limit_mt_reg __read_mostly = {
188 .name = "limit",
189 .revision = 0,
190 .family = NFPROTO_UNSPEC,
191 .match = limit_mt,
192 .checkentry = limit_mt_check,
193 .destroy = limit_mt_destroy,
194 .matchsize = sizeof(struct xt_rateinfo),
195 #ifdef CONFIG_NETFILTER_XTABLES_COMPAT
196 .compatsize = sizeof(struct compat_xt_rateinfo),
197 .compat_from_user = limit_mt_compat_from_user,
198 .compat_to_user = limit_mt_compat_to_user,
199 #endif
200 .usersize = offsetof(struct xt_rateinfo, prev),
201 .me = THIS_MODULE,
202 };
203
204 static int __init limit_mt_init(void)
205 {
206 return xt_register_match(&limit_mt_reg);
207 }
208
209 static void __exit limit_mt_exit(void)
210 {
211 xt_unregister_match(&limit_mt_reg);
212 }
213
214 module_init(limit_mt_init);
215 module_exit(limit_mt_exit);
216
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.