ip6_id.c revision 120652
1/* $KAME: ip6_id.c,v 1.13 2003/09/16 09:11:19 itojun Exp $ */ 2/* $OpenBSD: ip_id.c,v 1.6 2002/03/15 18:19:52 millert Exp $ */ 3/* $FreeBSD: head/sys/netinet6/ip6_id.c 120652 2003-10-01 21:45:57Z ume $ */ 4 5/* 6 * Copyright (C) 2003 WIDE Project. 7 * All rights reserved. 8 * 9 * Redistribution and use in source and binary forms, with or without 10 * modification, are permitted provided that the following conditions 11 * are met: 12 * 1. Redistributions of source code must retain the above copyright 13 * notice, this list of conditions and the following disclaimer. 14 * 2. Redistributions in binary form must reproduce the above copyright 15 * notice, this list of conditions and the following disclaimer in the 16 * documentation and/or other materials provided with the distribution. 17 * 3. Neither the name of the project nor the names of its contributors 18 * may be used to endorse or promote products derived from this software 19 * without specific prior written permission. 20 * 21 * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND 22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 24 * ARE DISCLAIMED. IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE 25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 31 * SUCH DAMAGE. 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 * 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 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 * Effectivly 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 "opt_random_ip_id.h" 90 91#include <sys/types.h> 92#include <sys/param.h> 93#include <sys/kernel.h> 94#include <sys/socket.h> 95#include <sys/libkern.h> 96 97#include <net/if.h> 98#include <net/route.h> 99#include <netinet/in.h> 100#include <netinet/ip6.h> 101#include <netinet6/ip6_var.h> 102 103#ifdef RANDOM_IP_ID 104 105#ifndef INT32_MAX 106#define INT32_MAX 0x7fffffffU 107#endif 108 109struct randomtab { 110 const int ru_bits; /* resulting bits */ 111 const long ru_out; /* Time after wich will be reseeded */ 112 const u_int32_t ru_max; /* Uniq cycle, avoid blackjack prediction */ 113 const u_int32_t ru_gen; /* Starting generator */ 114 const u_int32_t ru_n; /* ru_n: prime, ru_n - 1: product of pfacts[] */ 115 const u_int32_t ru_agen; /* determine ru_a as ru_agen^(2*rand) */ 116 const u_int32_t ru_m; /* ru_m = 2^x*3^y */ 117 const u_int32_t pfacts[4]; /* factors of ru_n */ 118 119 u_int32_t ru_counter; 120 u_int32_t ru_msb; 121 122 u_int32_t ru_x; 123 u_int32_t ru_seed, ru_seed2; 124 u_int32_t ru_a, ru_b; 125 u_int32_t ru_g; 126 long ru_reseed; 127}; 128 129static struct randomtab randomtab_32 = { 130 32, /* resulting bits */ 131 180, /* Time after wich will be reseeded */ 132 1000000000, /* Uniq cycle, avoid blackjack prediction */ 133 2, /* Starting generator */ 134 2147483629, /* RU_N-1 = 2^2*3^2*59652323 */ 135 7, /* determine ru_a as RU_AGEN^(2*rand) */ 136 1836660096, /* RU_M = 2^7*3^15 - don't change */ 137 { 2, 3, 59652323, 0 }, /* factors of ru_n */ 138}; 139 140static struct randomtab randomtab_20 = { 141 20, /* resulting bits */ 142 180, /* Time after wich will be reseeded */ 143 200000, /* Uniq cycle, avoid blackjack prediction */ 144 2, /* Starting generator */ 145 524269, /* RU_N-1 = 2^2*3^2*14563 */ 146 7, /* determine ru_a as RU_AGEN^(2*rand) */ 147 279936, /* RU_M = 2^7*3^7 - don't change */ 148 { 2, 3, 14563, 0 }, /* factors of ru_n */ 149}; 150 151static u_int32_t pmod(u_int32_t, u_int32_t, u_int32_t); 152static void initid(struct randomtab *); 153static u_int32_t randomid(struct randomtab *); 154 155/* 156 * Do a fast modular exponation, returned value will be in the range 157 * of 0 - (mod-1) 158 */ 159 160static u_int32_t 161pmod(u_int32_t gen, u_int32_t expo, u_int32_t mod) 162{ 163 u_int64_t s, t, u; 164 165 s = 1; 166 t = gen; 167 u = expo; 168 169 while (u) { 170 if (u & 1) 171 s = (s * t) % mod; 172 u >>= 1; 173 t = (t * t) % mod; 174 } 175 return (s); 176} 177 178/* 179 * Initalizes the seed and chooses a suitable generator. Also toggles 180 * the msb flag. The msb flag is used to generate two distinct 181 * cycles of random numbers and thus avoiding reuse of ids. 182 * 183 * This function is called from id_randomid() when needed, an 184 * application does not have to worry about it. 185 */ 186static void 187initid(struct randomtab *p) 188{ 189 u_int32_t j, i; 190 int noprime = 1; 191 192 p->ru_x = arc4random() % p->ru_m; 193 194 /* (bits - 1) bits of random seed */ 195 p->ru_seed = arc4random() & (~0U >> (32 - p->ru_bits + 1)); 196 p->ru_seed2 = arc4random() & (~0U >> (32 - p->ru_bits + 1)); 197 198 /* Determine the LCG we use */ 199 p->ru_b = (arc4random() & (~0U >> (32 - p->ru_bits))) | 1; 200 p->ru_a = pmod(p->ru_agen, 201 (arc4random() & (~0U >> (32 - p->ru_bits))) & (~1U), p->ru_m); 202 while (p->ru_b % 3 == 0) 203 p->ru_b += 2; 204 205 j = arc4random() % p->ru_n; 206 207 /* 208 * Do a fast gcd(j, RU_N - 1), so we can find a j with 209 * gcd(j, RU_N - 1) == 1, giving a new generator for 210 * RU_GEN^j mod RU_N 211 */ 212 while (noprime) { 213 for (i = 0; p->pfacts[i] > 0; i++) 214 if (j % p->pfacts[i] == 0) 215 break; 216 217 if (p->pfacts[i] == 0) 218 noprime = 0; 219 else 220 j = (j + 1) % p->ru_n; 221 } 222 223 p->ru_g = pmod(p->ru_gen, j, p->ru_n); 224 p->ru_counter = 0; 225 226 p->ru_reseed = time_second + p->ru_out; 227 p->ru_msb = p->ru_msb ? 0 : (1U << (p->ru_bits - 1)); 228} 229 230static u_int32_t 231randomid(struct randomtab *p) 232{ 233 int i, n; 234 u_int32_t tmp; 235 236 if (p->ru_counter >= p->ru_max || time_second > p->ru_reseed) 237 initid(p); 238 239 tmp = arc4random(); 240 241 /* Skip a random number of ids */ 242 n = tmp & 0x3; tmp = tmp >> 2; 243 if (p->ru_counter + n >= p->ru_max) 244 initid(p); 245 246 for (i = 0; i <= n; i++) { 247 /* Linear Congruential Generator */ 248 p->ru_x = (u_int32_t)((u_int64_t)p->ru_a * p->ru_x + p->ru_b) % p->ru_m; 249 } 250 251 p->ru_counter += i; 252 253 return (p->ru_seed ^ pmod(p->ru_g, p->ru_seed2 ^ p->ru_x, p->ru_n)) | 254 p->ru_msb; 255} 256 257u_int32_t 258ip6_randomid(void) 259{ 260 261 return randomid(&randomtab_32); 262} 263 264u_int32_t 265ip6_randomflowlabel(void) 266{ 267 268 return randomid(&randomtab_20) & 0xfffff; 269} 270 271#endif /* RANDOM_IP_ID */ 272