bsd/netinet6/ip6_id.c

   1 /*
   2  * Copyright (c) 2009-2019 Apple Inc. All rights reserved.
   3  *
   4  * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. The rights granted to you under the License
  10  * may not be used to create, or enable the creation or redistribution of,
  11  * unlawful or unlicensed copies of an Apple operating system, or to
  12  * circumvent, violate, or enable the circumvention or violation of, any
  13  * terms of an Apple operating system software license agreement.
  14  *
  15  * Please obtain a copy of the License at
  16  * http://www.opensource.apple.com/apsl/ and read it before using this file.
  17  *
  18  * The Original Code and all software distributed under the License are
  19  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  20  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  21  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  22  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  23  * Please see the License for the specific language governing rights and
  24  * limitations under the License.
  25  *
  26  * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
  27  */
  28
  29 /*-
  30  * Copyright (C) 2003 WIDE Project.
  31  * All rights reserved.
  32  *
  33  * Redistribution and use in source and binary forms, with or without
  34  * modification, are permitted provided that the following conditions
  35  * are met:
  36  * 1. Redistributions of source code must retain the above copyright
  37  *    notice, this list of conditions and the following disclaimer.
  38  * 2. Redistributions in binary form must reproduce the above copyright
  39  *    notice, this list of conditions and the following disclaimer in the
  40  *    documentation and/or other materials provided with the distribution.
  41  * 3. Neither the name of the project nor the names of its contributors
  42  *    may be used to endorse or promote products derived from this software
  43  *    without specific prior written permission.
  44  *
  45  * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
  46  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  47  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  48  * ARE DISCLAIMED.  IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
  49  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  50  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  51  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  52  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  53  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  54  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  55  * SUCH DAMAGE.
  56  */
  57
  58 /*-
  59  * Copyright 1998 Niels Provos <provos@citi.umich.edu>
  60  * All rights reserved.
  61  *
  62  * Theo de Raadt <deraadt@openbsd.org> came up with the idea of using
  63  * such a mathematical system to generate more random (yet non-repeating)
  64  * ids to solve the resolver/named problem.  But Niels designed the
  65  * actual system based on the constraints.
  66  *
  67  * Redistribution and use in source and binary forms, with or without
  68  * modification, are permitted provided that the following conditions
  69  * are met:
  70  * 1. Redistributions of source code must retain the above copyright
  71  *    notice, this list of conditions and the following disclaimer.
  72  * 2. Redistributions in binary form must reproduce the above copyright
  73  *    notice, this list of conditions and the following disclaimer in the
  74  *    documentation and/or other materials provided with the distribution.
  75  * 3. All advertising materials mentioning features or use of this software
  76  *    must display the following acknowledgement:
  77  *      This product includes software developed by Niels Provos.
  78  * 4. The name of the author may not be used to endorse or promote products
  79  *    derived from this software without specific prior written permission.
  80  *
  81  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  82  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  83  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  84  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  85  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  86  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  87  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  88  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  89  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  90  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  91  */
  92
  93 #include <sys/cdefs.h>
  94
  95 /*
  96  * seed = random (bits - 1) bit
  97  * n = prime, g0 = generator to n,
  98  * j = random so that gcd(j,n-1) == 1
  99  * g = g0^j mod n will be a generator again.
 100  *
 101  * X[0] = random seed.
 102  * X[n] = a*X[n-1]+b mod m is a Linear Congruential Generator
 103  * with a = 7^(even random) mod m,
 104  *      b = random with gcd(b,m) == 1
 105  *      m = constant and a maximal period of m-1.
 106  *
 107  * The transaction id is determined by:
 108  * id[n] = seed xor (g^X[n] mod n)
 109  *
 110  * Effectivly the id is restricted to the lower (bits - 1) bits, thus
 111  * yielding two different cycles by toggling the msb on and off.
 112  * This avoids reuse issues caused by reseeding.
 113  */
 114
 115 #include <sys/types.h>
 116 #include <sys/socket.h>
 117 #include <sys/param.h>
 118 #include <sys/time.h>
 119 #include <sys/kernel.h>
 120 #include <sys/random.h>
 121 #include <sys/protosw.h>
 122 #include <libkern/libkern.h>
 123 #include <dev/random/randomdev.h>
 124
 125 #include <net/if.h>
 126 #include <net/route.h>
 127 #include <netinet/in.h>
 128 #include <netinet/ip6.h>
 129 #include <netinet6/ip6_var.h>
 130
 131 struct randomtab {
 132         const int       ru_bits; /* resulting bits */
 133         const long      ru_out; /* Time after wich will be reseeded */
 134         const u_int32_t ru_max; /* Uniq cycle, avoid blackjack prediction */
 135         const u_int32_t ru_gen; /* Starting generator */
 136         const u_int32_t ru_n;   /* ru_n: prime, ru_n - 1: product of pfacts[] */
 137         const u_int32_t ru_agen; /* determine ru_a as ru_agen^(2*rand) */
 138         const u_int32_t ru_m;   /* ru_m = 2^x*3^y */
 139         const u_int32_t pfacts[4];      /* factors of ru_n */
 140
 141         u_int32_t ru_counter;
 142         u_int32_t ru_msb;
 143
 144         u_int32_t ru_x;
 145         u_int32_t ru_seed, ru_seed2;
 146         u_int32_t ru_a, ru_b;
 147         u_int32_t ru_g;
 148         long ru_reseed;
 149 };
 150
 151 static struct randomtab randomtab_32 = {
 152         .ru_bits = 32,          /* resulting bits */
 153         .ru_out = 180,          /* Time after wich will be reseeded */
 154         .ru_max = 1000000000,   /* Uniq cycle, avoid blackjack prediction */
 155         .ru_gen = 2,            /* Starting generator */
 156         .ru_n = 2147483629,     /* RU_N-1 = 2^2*3^2*59652323 */
 157         .ru_agen = 7,           /* determine ru_a as RU_AGEN^(2*rand) */
 158         .ru_m = 1836660096,     /* RU_M = 2^7*3^15 - don't change */
 159         .pfacts = { 2, 3, 59652323, 0 },        /* factors of ru_n */
 160         .ru_counter = 0,
 161         .ru_msb = 0,
 162         .ru_x = 0,
 163         .ru_seed = 0,
 164         .ru_seed2 = 0,
 165         .ru_a = 0,
 166         .ru_b = 0,
 167         .ru_g = 0,
 168         .ru_reseed = 0
 169 };
 170
 171 static u_int32_t pmod(u_int32_t, u_int32_t, u_int32_t);
 172 static void initid(struct randomtab *);
 173 static u_int32_t randomid(struct randomtab *);
 174
 175 /*
 176  * Do a fast modular exponation, returned value will be in the range
 177  * of 0 - (mod-1)
 178  */
 179 static u_int32_t
 180 pmod(u_int32_t gen, u_int32_t expo, u_int32_t mod)
 181 {
 182         u_int64_t s, t, u;
 183
 184         s = 1;
 185         t = gen;
 186         u = expo;
 187
 188         while (u) {
 189                 if (u & 1) {
 190                         s = (s * t) % mod;
 191                 }
 192                 u >>= 1;
 193                 t = (t * t) % mod;
 194         }
 195         return (u_int32_t)s;
 196 }
 197
 198 /*
 199  * Initalizes the seed and chooses a suitable generator. Also toggles
 200  * the msb flag. The msb flag is used to generate two distinct
 201  * cycles of random numbers and thus avoiding reuse of ids.
 202  *
 203  * This function is called from id_randomid() when needed, an
 204  * application does not have to worry about it.
 205  */
 206 static void
 207 initid(struct randomtab *p)
 208 {
 209         time_t curtime = (time_t)net_uptime();
 210         u_int32_t j, i;
 211         int noprime = 1;
 212
 213         p->ru_x = RandomULong() % p->ru_m;
 214
 215         /* (bits - 1) bits of random seed */
 216         p->ru_seed = RandomULong() & (~0U >> (32 - p->ru_bits + 1));
 217         p->ru_seed2 = RandomULong() & (~0U >> (32 - p->ru_bits + 1));
 218
 219         /* Determine the LCG we use */
 220         p->ru_b = (RandomULong() & (~0U >> (32 - p->ru_bits))) | 1;
 221         p->ru_a = pmod(p->ru_agen,
 222             (RandomULong() & (~0U >> (32 - p->ru_bits))) & (~1U), p->ru_m);
 223         while (p->ru_b % 3 == 0) {
 224                 p->ru_b += 2;
 225         }
 226
 227         j = RandomULong() % p->ru_n;
 228
 229         /*
 230          * Do a fast gcd(j, RU_N - 1), so we can find a j with
 231          * gcd(j, RU_N - 1) == 1, giving a new generator for
 232          * RU_GEN^j mod RU_N
 233          */
 234         while (noprime) {
 235                 for (i = 0; p->pfacts[i] > 0; i++) {
 236                         if (j % p->pfacts[i] == 0) {
 237                                 break;
 238                         }
 239                 }
 240
 241                 if (p->pfacts[i] == 0) {
 242                         noprime = 0;
 243                 } else {
 244                         j = (j + 1) % p->ru_n;
 245                 }
 246         }
 247
 248         p->ru_g = pmod(p->ru_gen, j, p->ru_n);
 249         p->ru_counter = 0;
 250
 251         p->ru_reseed = curtime + p->ru_out;
 252         p->ru_msb = p->ru_msb ? 0 : (1U << (p->ru_bits - 1));
 253 }
 254
 255 static u_int32_t
 256 randomid(struct randomtab *p)
 257 {
 258         time_t curtime = (time_t)net_uptime();
 259         int i, n;
 260         u_int32_t tmp;
 261
 262         if (p->ru_counter >= p->ru_max || curtime > p->ru_reseed) {
 263                 initid(p);
 264         }
 265
 266         tmp = RandomULong();
 267
 268         /* Skip a random number of ids */
 269         n = tmp & 0x3; tmp = tmp >> 2;
 270         if (p->ru_counter + n >= p->ru_max) {
 271                 initid(p);
 272         }
 273
 274         for (i = 0; i <= n; i++) {
 275                 /* Linear Congruential Generator */
 276                 p->ru_x = ((u_int64_t)p->ru_a * p->ru_x + p->ru_b) % p->ru_m;
 277         }
 278
 279         p->ru_counter += i;
 280
 281         return (p->ru_seed ^ pmod(p->ru_g, p->ru_seed2 ^ p->ru_x, p->ru_n)) |
 282                p->ru_msb;
 283 }
 284
 285 u_int32_t
 286 ip6_randomid(void)
 287 {
 288         return randomid(&randomtab_32);
 289 }
 290
 291 u_int32_t
 292 ip6_randomflowlabel(void)
 293 {
 294         return RandomULong() & IPV6_FLOWLABEL_MASK;
 295 }