The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/netinet6/ip6_id.c

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    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: releng/5.2/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 
  109 struct 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 
  129 static 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 
  140 static 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 
  151 static u_int32_t pmod(u_int32_t, u_int32_t, u_int32_t);
  152 static void initid(struct randomtab *);
  153 static 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 
  160 static u_int32_t
  161 pmod(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  */
  186 static void
  187 initid(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 
  230 static u_int32_t
  231 randomid(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 
  257 u_int32_t
  258 ip6_randomid(void)
  259 {
  260 
  261         return randomid(&randomtab_32);
  262 }
  263 
  264 u_int32_t
  265 ip6_randomflowlabel(void)
  266 {
  267 
  268         return randomid(&randomtab_20) & 0xfffff;
  269 }
  270 
  271 #endif /* RANDOM_IP_ID */

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