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 /*
67 * seed = random (bits - 1) bit
68 * n = prime, g0 = generator to n,
69 * j = random so that gcd(j,n-1) == 1
70 * g = g0^j mod n will be a generator again.
71 *
72 * X[0] = random seed.
73 * X[n] = a*X[n-1]+b mod m is a Linear Congruential Generator
74 * with a = 7^(even random) mod m,
75 * b = random with gcd(b,m) == 1
76 * m = constant and a maximal period of m-1.
77 *
78 * The transaction id is determined by:
79 * id[n] = seed xor (g^X[n] mod n)
80 *
81 * Effectively the id is restricted to the lower (bits - 1) bits, thus
82 * yielding two different cycles by toggling the msb on and off.
83 * This avoids reuse issues caused by reseeding.
84 */
85
86 #include <sys/types.h>
87 #include <sys/param.h>
88 #include <sys/kernel.h>
89 #include <sys/random.h>
90 #include <sys/socket.h>
91 #include <sys/libkern.h>
92
93 #include <net/if.h>
94 #include <net/route.h>
95 #include <net/vnet.h>
96 #include <netinet/in.h>
97 #include <netinet/ip6.h>
98 #include <netinet6/ip6_var.h>
99
100 #ifndef INT32_MAX
101 #define INT32_MAX 0x7fffffffU
102 #endif
103
104 struct randomtab {
105 const int ru_bits; /* resulting bits */
106 const long ru_out; /* Time after which will be reseeded */
107 const u_int32_t ru_max; /* Uniq cycle, avoid blackjack prediction */
108 const u_int32_t ru_gen; /* Starting generator */
109 const u_int32_t ru_n; /* ru_n: prime, ru_n - 1: product of pfacts[] */
110 const u_int32_t ru_agen; /* determine ru_a as ru_agen^(2*rand) */
111 const u_int32_t ru_m; /* ru_m = 2^x*3^y */
112 const u_int32_t pfacts[4]; /* factors of ru_n */
113
114 u_int32_t ru_counter;
115 u_int32_t ru_msb;
116
117 u_int32_t ru_x;
118 u_int32_t ru_seed, ru_seed2;
119 u_int32_t ru_a, ru_b;
120 u_int32_t ru_g;
121 long ru_reseed;
122 };
123
124 static struct randomtab randomtab_32 = {
125 32, /* resulting bits */
126 180, /* Time after which will be reseeded */
127 1000000000, /* Uniq cycle, avoid blackjack prediction */
128 2, /* Starting generator */
129 2147483629, /* RU_N-1 = 2^2*3^2*59652323 */
130 7, /* determine ru_a as RU_AGEN^(2*rand) */
131 1836660096, /* RU_M = 2^7*3^15 - don't change */
132 { 2, 3, 59652323, 0 }, /* factors of ru_n */
133 };
134
135 static struct randomtab randomtab_20 = {
136 20, /* resulting bits */
137 180, /* Time after which will be reseeded */
138 200000, /* Uniq cycle, avoid blackjack prediction */
139 2, /* Starting generator */
140 524269, /* RU_N-1 = 2^2*3^2*14563 */
141 7, /* determine ru_a as RU_AGEN^(2*rand) */
142 279936, /* RU_M = 2^7*3^7 - don't change */
143 { 2, 3, 14563, 0 }, /* factors of ru_n */
144 };
145
146 static u_int32_t pmod(u_int32_t, u_int32_t, u_int32_t);
147 static void initid(struct randomtab *);
148 static u_int32_t randomid(struct randomtab *);
149
150 /*
151 * Do a fast modular exponation, returned value will be in the range
152 * of 0 - (mod-1)
153 */
154 static u_int32_t
pmod(u_int32_t gen,u_int32_t expo,u_int32_t mod)155 pmod(u_int32_t gen, u_int32_t expo, u_int32_t mod)
156 {
157 u_int64_t s, t, u;
158
159 s = 1;
160 t = gen;
161 u = expo;
162
163 while (u) {
164 if (u & 1)
165 s = (s * t) % mod;
166 u >>= 1;
167 t = (t * t) % mod;
168 }
169 return (s);
170 }
171
172 /*
173 * Initializes the seed and chooses a suitable generator. Also toggles
174 * the msb flag. The msb flag is used to generate two distinct
175 * cycles of random numbers and thus avoiding reuse of ids.
176 *
177 * This function is called from id_randomid() when needed, an
178 * application does not have to worry about it.
179 */
180 static void
initid(struct randomtab * p)181 initid(struct randomtab *p)
182 {
183 u_int32_t j, i;
184 int noprime = 1;
185
186 p->ru_x = arc4random() % p->ru_m;
187
188 /* (bits - 1) bits of random seed */
189 p->ru_seed = arc4random() & (~0U >> (32 - p->ru_bits + 1));
190 p->ru_seed2 = arc4random() & (~0U >> (32 - p->ru_bits + 1));
191
192 /* Determine the LCG we use */
193 p->ru_b = (arc4random() & (~0U >> (32 - p->ru_bits))) | 1;
194 p->ru_a = pmod(p->ru_agen,
195 (arc4random() & (~0U >> (32 - p->ru_bits))) & (~1U), p->ru_m);
196 while (p->ru_b % 3 == 0)
197 p->ru_b += 2;
198
199 j = arc4random() % p->ru_n;
200
201 /*
202 * Do a fast gcd(j, RU_N - 1), so we can find a j with
203 * gcd(j, RU_N - 1) == 1, giving a new generator for
204 * RU_GEN^j mod RU_N
205 */
206 while (noprime) {
207 for (i = 0; p->pfacts[i] > 0; i++)
208 if (j % p->pfacts[i] == 0)
209 break;
210
211 if (p->pfacts[i] == 0)
212 noprime = 0;
213 else
214 j = (j + 1) % p->ru_n;
215 }
216
217 p->ru_g = pmod(p->ru_gen, j, p->ru_n);
218 p->ru_counter = 0;
219
220 p->ru_reseed = time_uptime + p->ru_out;
221 p->ru_msb = p->ru_msb ? 0 : (1U << (p->ru_bits - 1));
222 }
223
224 static u_int32_t
randomid(struct randomtab * p)225 randomid(struct randomtab *p)
226 {
227 int i, n;
228
229 if (p->ru_counter >= p->ru_max || time_uptime > p->ru_reseed)
230 initid(p);
231
232 /* Skip a random number of ids */
233 n = arc4random() & 0x3;
234 if (p->ru_counter + n >= p->ru_max)
235 initid(p);
236
237 for (i = 0; i <= n; i++) {
238 /* Linear Congruential Generator */
239 p->ru_x = (u_int32_t)((u_int64_t)p->ru_a * p->ru_x + p->ru_b) % p->ru_m;
240 }
241
242 p->ru_counter += i;
243
244 return (p->ru_seed ^ pmod(p->ru_g, p->ru_seed2 + p->ru_x, p->ru_n)) |
245 p->ru_msb;
246 }
247
248 u_int32_t
ip6_randomid(void)249 ip6_randomid(void)
250 {
251
252 return randomid(&randomtab_32);
253 }
254
255 u_int32_t
ip6_randomflowlabel(void)256 ip6_randomflowlabel(void)
257 {
258
259 /*
260 * It's ok to emit zero flow labels early, before random is available
261 * (seeded). RFC 6437:
262 *
263 * "A Flow Label of zero is used to indicate packets that have not been
264 * labeled."
265 */
266 if (__predict_false(!is_random_seeded()))
267 return (0);
268
269 return randomid(&randomtab_20) & 0xfffff;
270 }
271