FreeBSD/Linux Kernel Cross Reference
sys/netinet6/ip6_id.c
1 /*-
2 * SPDX-License-Identifier: (BSD-3-Clause AND BSD-2-Clause)
3 *
4 * Copyright (C) 2003 WIDE Project.
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 * 3. Neither the name of the project nor the names of its contributors
16 * may be used to endorse or promote products derived from this software
17 * without specific prior written permission.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
20 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
22 * ARE DISCLAIMED. IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
23 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
24 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
25 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
26 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
27 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
28 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
29 * SUCH DAMAGE.
30 *
31 * $KAME: ip6_id.c,v 1.13 2003/09/16 09:11:19 itojun Exp $
32 */
33
34 /*-
35 * Copyright 1998 Niels Provos <provos@citi.umich.edu>
36 * All rights reserved.
37 *
38 * Theo de Raadt <deraadt@openbsd.org> came up with the idea of using
39 * such a mathematical system to generate more random (yet non-repeating)
40 * ids to solve the resolver/named problem. But Niels designed the
41 * actual system based on the constraints.
42 *
43 * Redistribution and use in source and binary forms, with or without
44 * modification, are permitted provided that the following conditions
45 * are met:
46 * 1. Redistributions of source code must retain the above copyright
47 * notice, this list of conditions and the following disclaimer.
48 * 2. Redistributions in binary form must reproduce the above copyright
49 * notice, this list of conditions and the following disclaimer in the
50 * documentation and/or other materials provided with the distribution.
51 *
52 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
53 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
54 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
55 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
56 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
57 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
58 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
59 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
60 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
61 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
62 *
63 * $OpenBSD: ip6_id.c,v 1.3 2003/12/12 06:57:12 itojun Exp $
64 */
65
66 #include <sys/cdefs.h>
67 __FBSDID("$FreeBSD$");
68
69 /*
70 * seed = random (bits - 1) bit
71 * n = prime, g0 = generator to n,
72 * j = random so that gcd(j,n-1) == 1
73 * g = g0^j mod n will be a generator again.
74 *
75 * X[0] = random seed.
76 * X[n] = a*X[n-1]+b mod m is a Linear Congruential Generator
77 * with a = 7^(even random) mod m,
78 * b = random with gcd(b,m) == 1
79 * m = constant and a maximal period of m-1.
80 *
81 * The transaction id is determined by:
82 * id[n] = seed xor (g^X[n] mod n)
83 *
84 * Effectively the id is restricted to the lower (bits - 1) bits, thus
85 * yielding two different cycles by toggling the msb on and off.
86 * This avoids reuse issues caused by reseeding.
87 */
88
89 #include <sys/types.h>
90 #include <sys/param.h>
91 #include <sys/kernel.h>
92 #include <sys/socket.h>
93 #include <sys/libkern.h>
94
95 #include <net/if.h>
96 #include <net/route.h>
97 #include <net/vnet.h>
98 #include <netinet/in.h>
99 #include <netinet/ip6.h>
100 #include <netinet6/ip6_var.h>
101
102 #ifndef INT32_MAX
103 #define INT32_MAX 0x7fffffffU
104 #endif
105
106 struct randomtab {
107 const int ru_bits; /* resulting bits */
108 const long ru_out; /* Time after which will be reseeded */
109 const u_int32_t ru_max; /* Uniq cycle, avoid blackjack prediction */
110 const u_int32_t ru_gen; /* Starting generator */
111 const u_int32_t ru_n; /* ru_n: prime, ru_n - 1: product of pfacts[] */
112 const u_int32_t ru_agen; /* determine ru_a as ru_agen^(2*rand) */
113 const u_int32_t ru_m; /* ru_m = 2^x*3^y */
114 const u_int32_t pfacts[4]; /* factors of ru_n */
115
116 u_int32_t ru_counter;
117 u_int32_t ru_msb;
118
119 u_int32_t ru_x;
120 u_int32_t ru_seed, ru_seed2;
121 u_int32_t ru_a, ru_b;
122 u_int32_t ru_g;
123 long ru_reseed;
124 };
125
126 static struct randomtab randomtab_32 = {
127 32, /* resulting bits */
128 180, /* Time after which will be reseeded */
129 1000000000, /* Uniq cycle, avoid blackjack prediction */
130 2, /* Starting generator */
131 2147483629, /* RU_N-1 = 2^2*3^2*59652323 */
132 7, /* determine ru_a as RU_AGEN^(2*rand) */
133 1836660096, /* RU_M = 2^7*3^15 - don't change */
134 { 2, 3, 59652323, 0 }, /* factors of ru_n */
135 };
136
137 static struct randomtab randomtab_20 = {
138 20, /* resulting bits */
139 180, /* Time after which will be reseeded */
140 200000, /* Uniq cycle, avoid blackjack prediction */
141 2, /* Starting generator */
142 524269, /* RU_N-1 = 2^2*3^2*14563 */
143 7, /* determine ru_a as RU_AGEN^(2*rand) */
144 279936, /* RU_M = 2^7*3^7 - don't change */
145 { 2, 3, 14563, 0 }, /* factors of ru_n */
146 };
147
148 static u_int32_t pmod(u_int32_t, u_int32_t, u_int32_t);
149 static void initid(struct randomtab *);
150 static u_int32_t randomid(struct randomtab *);
151
152 /*
153 * Do a fast modular exponation, returned value will be in the range
154 * of 0 - (mod-1)
155 */
156 static u_int32_t
157 pmod(u_int32_t gen, u_int32_t expo, u_int32_t mod)
158 {
159 u_int64_t s, t, u;
160
161 s = 1;
162 t = gen;
163 u = expo;
164
165 while (u) {
166 if (u & 1)
167 s = (s * t) % mod;
168 u >>= 1;
169 t = (t * t) % mod;
170 }
171 return (s);
172 }
173
174 /*
175 * Initializes the seed and chooses a suitable generator. Also toggles
176 * the msb flag. The msb flag is used to generate two distinct
177 * cycles of random numbers and thus avoiding reuse of ids.
178 *
179 * This function is called from id_randomid() when needed, an
180 * application does not have to worry about it.
181 */
182 static void
183 initid(struct randomtab *p)
184 {
185 u_int32_t j, i;
186 int noprime = 1;
187
188 p->ru_x = arc4random() % p->ru_m;
189
190 /* (bits - 1) bits of random seed */
191 p->ru_seed = arc4random() & (~0U >> (32 - p->ru_bits + 1));
192 p->ru_seed2 = arc4random() & (~0U >> (32 - p->ru_bits + 1));
193
194 /* Determine the LCG we use */
195 p->ru_b = (arc4random() & (~0U >> (32 - p->ru_bits))) | 1;
196 p->ru_a = pmod(p->ru_agen,
197 (arc4random() & (~0U >> (32 - p->ru_bits))) & (~1U), p->ru_m);
198 while (p->ru_b % 3 == 0)
199 p->ru_b += 2;
200
201 j = arc4random() % p->ru_n;
202
203 /*
204 * Do a fast gcd(j, RU_N - 1), so we can find a j with
205 * gcd(j, RU_N - 1) == 1, giving a new generator for
206 * RU_GEN^j mod RU_N
207 */
208 while (noprime) {
209 for (i = 0; p->pfacts[i] > 0; i++)
210 if (j % p->pfacts[i] == 0)
211 break;
212
213 if (p->pfacts[i] == 0)
214 noprime = 0;
215 else
216 j = (j + 1) % p->ru_n;
217 }
218
219 p->ru_g = pmod(p->ru_gen, j, p->ru_n);
220 p->ru_counter = 0;
221
222 p->ru_reseed = time_uptime + p->ru_out;
223 p->ru_msb = p->ru_msb ? 0 : (1U << (p->ru_bits - 1));
224 }
225
226 static u_int32_t
227 randomid(struct randomtab *p)
228 {
229 int i, n;
230
231 if (p->ru_counter >= p->ru_max || time_uptime > p->ru_reseed)
232 initid(p);
233
234 /* Skip a random number of ids */
235 n = arc4random() & 0x3;
236 if (p->ru_counter + n >= p->ru_max)
237 initid(p);
238
239 for (i = 0; i <= n; i++) {
240 /* Linear Congruential Generator */
241 p->ru_x = (u_int32_t)((u_int64_t)p->ru_a * p->ru_x + p->ru_b) % p->ru_m;
242 }
243
244 p->ru_counter += i;
245
246 return (p->ru_seed ^ pmod(p->ru_g, p->ru_seed2 + p->ru_x, p->ru_n)) |
247 p->ru_msb;
248 }
249
250 u_int32_t
251 ip6_randomid(void)
252 {
253
254 return randomid(&randomtab_32);
255 }
256
257 u_int32_t
258 ip6_randomflowlabel(void)
259 {
260
261 return randomid(&randomtab_20) & 0xfffff;
262 }
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