1 /*- 2 * Copyright (C) 2003 WIDE Project. 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 3. Neither the name of the project nor the names of its contributors 14 * may be used to endorse or promote products derived from this software 15 * without specific prior written permission. 16 * 17 * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND 18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 20 * ARE DISCLAIMED. IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE 21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 27 * SUCH DAMAGE. 28 * 29 * $KAME: ip6_id.c,v 1.13 2003/09/16 09:11:19 itojun Exp $ 30 */ 31 32 /*- 33 * SPDX-License-Identifier: BSD-4-Clause AND BSD-3-Clause 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 * 3. All advertising materials mentioning features or use of this software 52 * must display the following acknowledgement: 53 * This product includes software developed by Niels Provos. 54 * 4. The name of the author may not be used to endorse or promote products 55 * derived from this software without specific prior written permission. 56 * 57 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 58 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 59 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 60 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 61 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 62 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 63 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 64 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 65 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 66 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 67 * 68 * $OpenBSD: ip_id.c,v 1.6 2002/03/15 18:19:52 millert Exp $ 69 */ 70 71 #include <sys/cdefs.h> 72 __FBSDID("$FreeBSD$"); 73 74 /* 75 * seed = random (bits - 1) bit 76 * n = prime, g0 = generator to n, 77 * j = random so that gcd(j,n-1) == 1 78 * g = g0^j mod n will be a generator again. 79 * 80 * X[0] = random seed. 81 * X[n] = a*X[n-1]+b mod m is a Linear Congruential Generator 82 * with a = 7^(even random) mod m, 83 * b = random with gcd(b,m) == 1 84 * m = constant and a maximal period of m-1. 85 * 86 * The transaction id is determined by: 87 * id[n] = seed xor (g^X[n] mod n) 88 * 89 * Effectivly the id is restricted to the lower (bits - 1) bits, thus 90 * yielding two different cycles by toggling the msb on and off. 91 * This avoids reuse issues caused by reseeding. 92 */ 93 94 #include <sys/types.h> 95 #include <sys/param.h> 96 #include <sys/kernel.h> 97 #include <sys/socket.h> 98 #include <sys/libkern.h> 99 100 #include <net/if.h> 101 #include <net/route.h> 102 #include <net/vnet.h> 103 #include <netinet/in.h> 104 #include <netinet/ip6.h> 105 #include <netinet6/ip6_var.h> 106 107 #ifndef INT32_MAX 108 #define INT32_MAX 0x7fffffffU 109 #endif 110 111 struct randomtab { 112 const int ru_bits; /* resulting bits */ 113 const long ru_out; /* Time after which will be reseeded */ 114 const u_int32_t ru_max; /* Uniq cycle, avoid blackjack prediction */ 115 const u_int32_t ru_gen; /* Starting generator */ 116 const u_int32_t ru_n; /* ru_n: prime, ru_n - 1: product of pfacts[] */ 117 const u_int32_t ru_agen; /* determine ru_a as ru_agen^(2*rand) */ 118 const u_int32_t ru_m; /* ru_m = 2^x*3^y */ 119 const u_int32_t pfacts[4]; /* factors of ru_n */ 120 121 u_int32_t ru_counter; 122 u_int32_t ru_msb; 123 124 u_int32_t ru_x; 125 u_int32_t ru_seed, ru_seed2; 126 u_int32_t ru_a, ru_b; 127 u_int32_t ru_g; 128 long ru_reseed; 129 }; 130 131 static struct randomtab randomtab_32 = { 132 32, /* resulting bits */ 133 180, /* Time after which will be reseeded */ 134 1000000000, /* Uniq cycle, avoid blackjack prediction */ 135 2, /* Starting generator */ 136 2147483629, /* RU_N-1 = 2^2*3^2*59652323 */ 137 7, /* determine ru_a as RU_AGEN^(2*rand) */ 138 1836660096, /* RU_M = 2^7*3^15 - don't change */ 139 { 2, 3, 59652323, 0 }, /* factors of ru_n */ 140 }; 141 142 static struct randomtab randomtab_20 = { 143 20, /* resulting bits */ 144 180, /* Time after which will be reseeded */ 145 200000, /* Uniq cycle, avoid blackjack prediction */ 146 2, /* Starting generator */ 147 524269, /* RU_N-1 = 2^2*3^2*14563 */ 148 7, /* determine ru_a as RU_AGEN^(2*rand) */ 149 279936, /* RU_M = 2^7*3^7 - don't change */ 150 { 2, 3, 14563, 0 }, /* factors of ru_n */ 151 }; 152 153 static u_int32_t pmod(u_int32_t, u_int32_t, u_int32_t); 154 static void initid(struct randomtab *); 155 static u_int32_t randomid(struct randomtab *); 156 157 /* 158 * Do a fast modular exponation, returned value will be in the range 159 * of 0 - (mod-1) 160 */ 161 static u_int32_t 162 pmod(u_int32_t gen, u_int32_t expo, u_int32_t mod) 163 { 164 u_int64_t s, t, u; 165 166 s = 1; 167 t = gen; 168 u = expo; 169 170 while (u) { 171 if (u & 1) 172 s = (s * t) % mod; 173 u >>= 1; 174 t = (t * t) % mod; 175 } 176 return (s); 177 } 178 179 /* 180 * Initalizes the seed and chooses a suitable generator. Also toggles 181 * the msb flag. The msb flag is used to generate two distinct 182 * cycles of random numbers and thus avoiding reuse of ids. 183 * 184 * This function is called from id_randomid() when needed, an 185 * application does not have to worry about it. 186 */ 187 static void 188 initid(struct randomtab *p) 189 { 190 u_int32_t j, i; 191 int noprime = 1; 192 193 p->ru_x = arc4random() % p->ru_m; 194 195 /* (bits - 1) bits of random seed */ 196 p->ru_seed = arc4random() & (~0U >> (32 - p->ru_bits + 1)); 197 p->ru_seed2 = arc4random() & (~0U >> (32 - p->ru_bits + 1)); 198 199 /* Determine the LCG we use */ 200 p->ru_b = (arc4random() & (~0U >> (32 - p->ru_bits))) | 1; 201 p->ru_a = pmod(p->ru_agen, 202 (arc4random() & (~0U >> (32 - p->ru_bits))) & (~1U), p->ru_m); 203 while (p->ru_b % 3 == 0) 204 p->ru_b += 2; 205 206 j = arc4random() % p->ru_n; 207 208 /* 209 * Do a fast gcd(j, RU_N - 1), so we can find a j with 210 * gcd(j, RU_N - 1) == 1, giving a new generator for 211 * RU_GEN^j mod RU_N 212 */ 213 while (noprime) { 214 for (i = 0; p->pfacts[i] > 0; i++) 215 if (j % p->pfacts[i] == 0) 216 break; 217 218 if (p->pfacts[i] == 0) 219 noprime = 0; 220 else 221 j = (j + 1) % p->ru_n; 222 } 223 224 p->ru_g = pmod(p->ru_gen, j, p->ru_n); 225 p->ru_counter = 0; 226 227 p->ru_reseed = time_uptime + p->ru_out; 228 p->ru_msb = p->ru_msb ? 0 : (1U << (p->ru_bits - 1)); 229 } 230 231 static u_int32_t 232 randomid(struct randomtab *p) 233 { 234 int i, n; 235 u_int32_t tmp; 236 237 if (p->ru_counter >= p->ru_max || time_uptime > p->ru_reseed) 238 initid(p); 239 240 tmp = arc4random(); 241 242 /* Skip a random number of ids */ 243 n = tmp & 0x3; tmp = tmp >> 2; 244 if (p->ru_counter + n >= p->ru_max) 245 initid(p); 246 247 for (i = 0; i <= n; i++) { 248 /* Linear Congruential Generator */ 249 p->ru_x = (u_int32_t)((u_int64_t)p->ru_a * p->ru_x + p->ru_b) % p->ru_m; 250 } 251 252 p->ru_counter += i; 253 254 return (p->ru_seed ^ pmod(p->ru_g, p->ru_seed2 ^ p->ru_x, p->ru_n)) | 255 p->ru_msb; 256 } 257 258 u_int32_t 259 ip6_randomid(void) 260 { 261 262 return randomid(&randomtab_32); 263 } 264 265 u_int32_t 266 ip6_randomflowlabel(void) 267 { 268 269 return randomid(&randomtab_20) & 0xfffff; 270 } 271