ip6_id.c

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/*-
 * SPDX-License-Identifier: (BSD-3-Clause AND BSD-2-Clause)
 *
 * Copyright (C) 2003 WIDE Project.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the project nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      $KAME: ip6_id.c,v 1.13 2003/09/16 09:11:19 itojun Exp $
 */
 
/*-
 * Copyright 1998 Niels Provos <provos@citi.umich.edu>
 * All rights reserved.
 *
 * Theo de Raadt <deraadt@openbsd.org> came up with the idea of using
 * such a mathematical system to generate more random (yet non-repeating)
 * ids to solve the resolver/named problem.  But Niels designed the
 * actual system based on the constraints.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * $OpenBSD: ip6_id.c,v 1.3 2003/12/12 06:57:12 itojun Exp $
 */
 
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
 
/*
 * seed = random (bits - 1) bit
 * n = prime, g0 = generator to n,
 * j = random so that gcd(j,n-1) == 1
 * g = g0^j mod n will be a generator again.
 *
 * X[0] = random seed.
 * X[n] = a*X[n-1]+b mod m is a Linear Congruential Generator
 * with a = 7^(even random) mod m,
 *      b = random with gcd(b,m) == 1
 *      m = constant and a maximal period of m-1.
 *
 * The transaction id is determined by:
 * id[n] = seed xor (g^X[n] mod n)
 *
 * Effectively the id is restricted to the lower (bits - 1) bits, thus
 * yielding two different cycles by toggling the msb on and off.
 * This avoids reuse issues caused by reseeding.
 */
 
#include <sys/types.h>
#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/random.h>
#include <sys/socket.h>
#include <sys/libkern.h>
 
#include <net/if.h>
#include <net/route.h>
#include <net/vnet.h>
#include <netinet/in.h>
#include <netinet/ip6.h>
#include <netinet6/ip6_var.h>
 
#ifndef INT32_MAX
#define INT32_MAX       0x7fffffffU
#endif
 
struct randomtab {
        const int       ru_bits; /* resulting bits */
        const long      ru_out; /* Time after which will be reseeded */
        const u_int32_t ru_max; /* Uniq cycle, avoid blackjack prediction */
        const u_int32_t ru_gen; /* Starting generator */
        const u_int32_t ru_n;   /* ru_n: prime, ru_n - 1: product of pfacts[] */
        const u_int32_t ru_agen; /* determine ru_a as ru_agen^(2*rand) */
        const u_int32_t ru_m;   /* ru_m = 2^x*3^y */
        const u_int32_t pfacts[4];      /* factors of ru_n */
 
        u_int32_t ru_counter;
        u_int32_t ru_msb;
 
        u_int32_t ru_x;
        u_int32_t ru_seed, ru_seed2;
        u_int32_t ru_a, ru_b;
        u_int32_t ru_g;
        long ru_reseed;
};
 
static struct randomtab randomtab_32 = {
        32,                     /* resulting bits */
        180,                    /* Time after which will be reseeded */
        1000000000,             /* Uniq cycle, avoid blackjack prediction */
        2,                      /* Starting generator */
        2147483629,             /* RU_N-1 = 2^2*3^2*59652323 */
        7,                      /* determine ru_a as RU_AGEN^(2*rand) */
        1836660096,             /* RU_M = 2^7*3^15 - don't change */
        { 2, 3, 59652323, 0 },  /* factors of ru_n */
};
 
static struct randomtab randomtab_20 = {
        20,                     /* resulting bits */
        180,                    /* Time after which will be reseeded */
        200000,                 /* Uniq cycle, avoid blackjack prediction */
        2,                      /* Starting generator */
        524269,                 /* RU_N-1 = 2^2*3^2*14563 */
        7,                      /* determine ru_a as RU_AGEN^(2*rand) */
        279936,                 /* RU_M = 2^7*3^7 - don't change */
        { 2, 3, 14563, 0 },     /* factors of ru_n */
};
 
static u_int32_t pmod(u_int32_t, u_int32_t, u_int32_t);
static void initid(struct randomtab *);
static u_int32_t randomid(struct randomtab *);
 
/*
 * Do a fast modular exponation, returned value will be in the range
 * of 0 - (mod-1)
 */
static u_int32_t
pmod(u_int32_t gen, u_int32_t expo, u_int32_t mod)
{
        u_int64_t s, t, u;
 
        s = 1;
        t = gen;
        u = expo;
 
        while (u) {
                if (u & 1)
                        s = (s * t) % mod;
                u >>= 1;
                t = (t * t) % mod;
        }
        return (s);
}
 
/*
 * Initializes the seed and chooses a suitable generator. Also toggles
 * the msb flag. The msb flag is used to generate two distinct
 * cycles of random numbers and thus avoiding reuse of ids.
 *
 * This function is called from id_randomid() when needed, an
 * application does not have to worry about it.
 */
static void
initid(struct randomtab *p)
{
        u_int32_t j, i;
        int noprime = 1;
 
        p->ru_x = arc4random() % p->ru_m;
 
        /* (bits - 1) bits of random seed */
        p->ru_seed = arc4random() & (~0U >> (32 - p->ru_bits + 1));
        p->ru_seed2 = arc4random() & (~0U >> (32 - p->ru_bits + 1));
 
        /* Determine the LCG we use */
        p->ru_b = (arc4random() & (~0U >> (32 - p->ru_bits))) | 1;
        p->ru_a = pmod(p->ru_agen,
            (arc4random() & (~0U >> (32 - p->ru_bits))) & (~1U), p->ru_m);
        while (p->ru_b % 3 == 0)
                p->ru_b += 2;
 
        j = arc4random() % p->ru_n;
 
        /*
         * Do a fast gcd(j, RU_N - 1), so we can find a j with
         * gcd(j, RU_N - 1) == 1, giving a new generator for
         * RU_GEN^j mod RU_N
         */
        while (noprime) {
                for (i = 0; p->pfacts[i] > 0; i++)
                        if (j % p->pfacts[i] == 0)
                                break;
 
                if (p->pfacts[i] == 0)
                        noprime = 0;
                else
                        j = (j + 1) % p->ru_n;
        }
 
        p->ru_g = pmod(p->ru_gen, j, p->ru_n);
        p->ru_counter = 0;
 
        p->ru_reseed = time_uptime + p->ru_out;
        p->ru_msb = p->ru_msb ? 0 : (1U << (p->ru_bits - 1));
}
 
static u_int32_t
randomid(struct randomtab *p)
{
        int i, n;
 
        if (p->ru_counter >= p->ru_max || time_uptime > p->ru_reseed)
                initid(p);
 
        /* Skip a random number of ids */
        n = arc4random() & 0x3;
        if (p->ru_counter + n >= p->ru_max)
                initid(p);
 
        for (i = 0; i <= n; i++) {
                /* Linear Congruential Generator */
                p->ru_x = (u_int32_t)((u_int64_t)p->ru_a * p->ru_x + p->ru_b) % p->ru_m;
        }
 
        p->ru_counter += i;
 
        return (p->ru_seed ^ pmod(p->ru_g, p->ru_seed2 + p->ru_x, p->ru_n)) |
            p->ru_msb;
}
 
u_int32_t
ip6_randomid(void)
{
 
        return randomid(&randomtab_32);
}
 
u_int32_t
ip6_randomflowlabel(void)
{
 
        /*
         * It's ok to emit zero flow labels early, before random is available
         * (seeded).  RFC 6437:
         *
         * "A Flow Label of zero is used to indicate packets that have not been
         * labeled."
         */
        if (__predict_false(!is_random_seeded()))
                return (0);
 
        return randomid(&randomtab_20) & 0xfffff;
}