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 } 263