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/random.h> 93 #include <sys/socket.h> 94 #include <sys/libkern.h> 95 96 #include <net/if.h> 97 #include <net/route.h> 98 #include <net/vnet.h> 99 #include <netinet/in.h> 100 #include <netinet/ip6.h> 101 #include <netinet6/ip6_var.h> 102 103 #ifndef INT32_MAX 104 #define INT32_MAX 0x7fffffffU 105 #endif 106 107 struct randomtab { 108 const int ru_bits; /* resulting bits */ 109 const long ru_out; /* Time after which will be reseeded */ 110 const u_int32_t ru_max; /* Uniq cycle, avoid blackjack prediction */ 111 const u_int32_t ru_gen; /* Starting generator */ 112 const u_int32_t ru_n; /* ru_n: prime, ru_n - 1: product of pfacts[] */ 113 const u_int32_t ru_agen; /* determine ru_a as ru_agen^(2*rand) */ 114 const u_int32_t ru_m; /* ru_m = 2^x*3^y */ 115 const u_int32_t pfacts[4]; /* factors of ru_n */ 116 117 u_int32_t ru_counter; 118 u_int32_t ru_msb; 119 120 u_int32_t ru_x; 121 u_int32_t ru_seed, ru_seed2; 122 u_int32_t ru_a, ru_b; 123 u_int32_t ru_g; 124 long ru_reseed; 125 }; 126 127 static struct randomtab randomtab_32 = { 128 32, /* resulting bits */ 129 180, /* Time after which will be reseeded */ 130 1000000000, /* Uniq cycle, avoid blackjack prediction */ 131 2, /* Starting generator */ 132 2147483629, /* RU_N-1 = 2^2*3^2*59652323 */ 133 7, /* determine ru_a as RU_AGEN^(2*rand) */ 134 1836660096, /* RU_M = 2^7*3^15 - don't change */ 135 { 2, 3, 59652323, 0 }, /* factors of ru_n */ 136 }; 137 138 static struct randomtab randomtab_20 = { 139 20, /* resulting bits */ 140 180, /* Time after which will be reseeded */ 141 200000, /* Uniq cycle, avoid blackjack prediction */ 142 2, /* Starting generator */ 143 524269, /* RU_N-1 = 2^2*3^2*14563 */ 144 7, /* determine ru_a as RU_AGEN^(2*rand) */ 145 279936, /* RU_M = 2^7*3^7 - don't change */ 146 { 2, 3, 14563, 0 }, /* factors of ru_n */ 147 }; 148 149 static u_int32_t pmod(u_int32_t, u_int32_t, u_int32_t); 150 static void initid(struct randomtab *); 151 static u_int32_t randomid(struct randomtab *); 152 153 /* 154 * Do a fast modular exponation, returned value will be in the range 155 * of 0 - (mod-1) 156 */ 157 static u_int32_t 158 pmod(u_int32_t gen, u_int32_t expo, u_int32_t mod) 159 { 160 u_int64_t s, t, u; 161 162 s = 1; 163 t = gen; 164 u = expo; 165 166 while (u) { 167 if (u & 1) 168 s = (s * t) % mod; 169 u >>= 1; 170 t = (t * t) % mod; 171 } 172 return (s); 173 } 174 175 /* 176 * Initializes the seed and chooses a suitable generator. Also toggles 177 * the msb flag. The msb flag is used to generate two distinct 178 * cycles of random numbers and thus avoiding reuse of ids. 179 * 180 * This function is called from id_randomid() when needed, an 181 * application does not have to worry about it. 182 */ 183 static void 184 initid(struct randomtab *p) 185 { 186 u_int32_t j, i; 187 int noprime = 1; 188 189 p->ru_x = arc4random() % p->ru_m; 190 191 /* (bits - 1) bits of random seed */ 192 p->ru_seed = arc4random() & (~0U >> (32 - p->ru_bits + 1)); 193 p->ru_seed2 = arc4random() & (~0U >> (32 - p->ru_bits + 1)); 194 195 /* Determine the LCG we use */ 196 p->ru_b = (arc4random() & (~0U >> (32 - p->ru_bits))) | 1; 197 p->ru_a = pmod(p->ru_agen, 198 (arc4random() & (~0U >> (32 - p->ru_bits))) & (~1U), p->ru_m); 199 while (p->ru_b % 3 == 0) 200 p->ru_b += 2; 201 202 j = arc4random() % p->ru_n; 203 204 /* 205 * Do a fast gcd(j, RU_N - 1), so we can find a j with 206 * gcd(j, RU_N - 1) == 1, giving a new generator for 207 * RU_GEN^j mod RU_N 208 */ 209 while (noprime) { 210 for (i = 0; p->pfacts[i] > 0; i++) 211 if (j % p->pfacts[i] == 0) 212 break; 213 214 if (p->pfacts[i] == 0) 215 noprime = 0; 216 else 217 j = (j + 1) % p->ru_n; 218 } 219 220 p->ru_g = pmod(p->ru_gen, j, p->ru_n); 221 p->ru_counter = 0; 222 223 p->ru_reseed = time_uptime + p->ru_out; 224 p->ru_msb = p->ru_msb ? 0 : (1U << (p->ru_bits - 1)); 225 } 226 227 static u_int32_t 228 randomid(struct randomtab *p) 229 { 230 int i, n; 231 232 if (p->ru_counter >= p->ru_max || time_uptime > p->ru_reseed) 233 initid(p); 234 235 /* Skip a random number of ids */ 236 n = arc4random() & 0x3; 237 if (p->ru_counter + n >= p->ru_max) 238 initid(p); 239 240 for (i = 0; i <= n; i++) { 241 /* Linear Congruential Generator */ 242 p->ru_x = (u_int32_t)((u_int64_t)p->ru_a * p->ru_x + p->ru_b) % p->ru_m; 243 } 244 245 p->ru_counter += i; 246 247 return (p->ru_seed ^ pmod(p->ru_g, p->ru_seed2 + p->ru_x, p->ru_n)) | 248 p->ru_msb; 249 } 250 251 u_int32_t 252 ip6_randomid(void) 253 { 254 255 return randomid(&randomtab_32); 256 } 257 258 u_int32_t 259 ip6_randomflowlabel(void) 260 { 261 262 /* 263 * It's ok to emit zero flow labels early, before random is available 264 * (seeded). RFC 6437: 265 * 266 * "A Flow Label of zero is used to indicate packets that have not been 267 * labeled." 268 */ 269 if (__predict_false(!is_random_seeded())) 270 return (0); 271 272 return randomid(&randomtab_20) & 0xfffff; 273 } 274