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https://github.com/opnsense/src.git
synced 2026-06-09 08:43:19 -04:00
Add ``options RANDOM_IP_ID'' which randomizes the ID field of IP packets.
This closes a minor information leak which allows a remote observer to determine the rate at which the machine is generating packets, since the default behaviour is to increment a counter for each packet sent. Reviewed by: -net Obtained from: OpenBSD
This commit is contained in:
Kris Kennaway
parent
25d1a10fa0
commit
64dddc1872
11 changed files with 254 additions and 0 deletions
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@ -590,6 +590,13 @@ options IPFILTER_DEFAULT_BLOCK #block all packets by default
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options IPSTEALTH #support for stealth forwarding
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options TCPDEBUG
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# RANDOM_IP_ID causes the ID field in IP packets to be randomized
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# instead of incremented by 1 with each packet generated. This
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# option closes a minor information leak which allows remote
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# observers to determine the rate of packet generation on the
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# machine by watching the counter.
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options RANDOM_IP_ID
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# Statically Link in accept filters
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options ACCEPT_FILTER_DATA
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options ACCEPT_FILTER_HTTP
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@ -1037,6 +1037,7 @@ netinet/igmp.c optional inet
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netinet/in.c optional inet
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netinet/in_gif.c optional gif inet
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#netinet/in_hostcache.c optional inet
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netinet/ip_id.c optional inet
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netinet/in_pcb.c optional inet
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netinet/in_proto.c optional inet
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netinet/in_rmx.c optional inet
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@ -278,6 +278,7 @@ NETATALK opt_atalk.h
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PPP_BSDCOMP opt_ppp.h
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PPP_DEFLATE opt_ppp.h
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PPP_FILTER opt_ppp.h
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RANDOM_IP_ID
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SLIP_IFF_OPTS opt_slip.h
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TCPDEBUG
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TCP_DROP_SYNFIN opt_tcp_input.h
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@ -590,6 +590,13 @@ options IPFILTER_DEFAULT_BLOCK #block all packets by default
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options IPSTEALTH #support for stealth forwarding
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options TCPDEBUG
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# RANDOM_IP_ID causes the ID field in IP packets to be randomized
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# instead of incremented by 1 with each packet generated. This
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# option closes a minor information leak which allows remote
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# observers to determine the rate of packet generation on the
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# machine by watching the counter.
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options RANDOM_IP_ID
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# Statically Link in accept filters
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options ACCEPT_FILTER_DATA
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options ACCEPT_FILTER_HTTP
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210
sys/netinet/ip_id.c
Normal file
210
sys/netinet/ip_id.c
Normal file
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@ -0,0 +1,210 @@
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/* $OpenBSD: ip_id.c,v 1.2 1999/08/26 13:37:01 provos Exp $ */
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/*
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* Copyright 1998 Niels Provos <provos@citi.umich.edu>
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* All rights reserved.
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*
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* Theo de Raadt <deraadt@openbsd.org> came up with the idea of using
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* such a mathematical system to generate more random (yet non-repeating)
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* ids to solve the resolver/named problem. But Niels designed the
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* actual system based on the constraints.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by Niels Provos.
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* 4. The name of the author may not be used to endorse or promote products
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* derived from this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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* $FreeBSD$
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*/
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/*
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* seed = random 15bit
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* n = prime, g0 = generator to n,
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* j = random so that gcd(j,n-1) == 1
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* g = g0^j mod n will be a generator again.
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*
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* X[0] = random seed.
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* X[n] = a*X[n-1]+b mod m is a Linear Congruential Generator
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* with a = 7^(even random) mod m,
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* b = random with gcd(b,m) == 1
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* m = 31104 and a maximal period of m-1.
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*
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* The transaction id is determined by:
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* id[n] = seed xor (g^X[n] mod n)
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*
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* Effectivly the id is restricted to the lower 15 bits, thus
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* yielding two different cycles by toggling the msb on and off.
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* This avoids reuse issues caused by reseeding.
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*/
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#include "opt_random_ip_id.h"
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#include <sys/param.h>
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#include <sys/time.h>
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#include <sys/kernel.h>
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#include <sys/random.h>
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#ifdef RANDOM_IP_ID
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#define RU_OUT 180 /* Time after wich will be reseeded */
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#define RU_MAX 30000 /* Uniq cycle, avoid blackjack prediction */
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#define RU_GEN 2 /* Starting generator */
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#define RU_N 32749 /* RU_N-1 = 2*2*3*2729 */
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#define RU_AGEN 7 /* determine ru_a as RU_AGEN^(2*rand) */
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#define RU_M 31104 /* RU_M = 2^7*3^5 - don't change */
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#define PFAC_N 3
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const static u_int16_t pfacts[PFAC_N] = {
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2,
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3,
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2729
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};
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static u_int16_t ru_x;
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static u_int16_t ru_seed, ru_seed2;
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static u_int16_t ru_a, ru_b;
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static u_int16_t ru_g;
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static u_int16_t ru_counter = 0;
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static u_int16_t ru_msb = 0;
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static long ru_reseed;
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static u_int32_t tmp; /* Storage for unused random */
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static u_int16_t pmod __P((u_int16_t, u_int16_t, u_int16_t));
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static void ip_initid __P((void));
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u_int16_t ip_randomid __P((void));
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/*
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* Do a fast modular exponation, returned value will be in the range
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* of 0 - (mod-1)
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*/
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#ifdef __STDC__
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static u_int16_t
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pmod(u_int16_t gen, u_int16_t exp, u_int16_t mod)
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#else
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static u_int16_t
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pmod(gen, exp, mod)
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u_int16_t gen, exp, mod;
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#endif
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{
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u_int16_t s, t, u;
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s = 1;
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t = gen;
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u = exp;
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while (u) {
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if (u & 1)
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s = (s*t) % mod;
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u >>= 1;
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t = (t*t) % mod;
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}
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return (s);
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}
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/*
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* Initalizes the seed and chooses a suitable generator. Also toggles
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* the msb flag. The msb flag is used to generate two distinct
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* cycles of random numbers and thus avoiding reuse of ids.
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*
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* This function is called from id_randomid() when needed, an
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* application does not have to worry about it.
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*/
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static void
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ip_initid(void)
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{
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u_int16_t j, i;
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int noprime = 1;
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struct timeval time;
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getmicrotime(&time);
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read_random((void *) &tmp, sizeof(tmp));
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ru_x = (tmp & 0xFFFF) % RU_M;
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/* 15 bits of random seed */
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ru_seed = (tmp >> 16) & 0x7FFF;
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read_random((void *) &tmp, sizeof(tmp));
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ru_seed2 = tmp & 0x7FFF;
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read_random((void *) &tmp, sizeof(tmp));
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/* Determine the LCG we use */
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ru_b = (tmp & 0xfffe) | 1;
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ru_a = pmod(RU_AGEN, (tmp >> 16) & 0xfffe, RU_M);
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while (ru_b % 3 == 0)
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ru_b += 2;
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read_random((void *) &tmp, sizeof(tmp));
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j = tmp % RU_N;
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tmp = tmp >> 16;
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/*
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* Do a fast gcd(j,RU_N-1), so we can find a j with
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* gcd(j, RU_N-1) == 1, giving a new generator for
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* RU_GEN^j mod RU_N
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*/
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while (noprime) {
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for (i=0; i<PFAC_N; i++)
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if (j%pfacts[i] == 0)
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break;
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if (i>=PFAC_N)
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noprime = 0;
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else
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j = (j+1) % RU_N;
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}
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ru_g = pmod(RU_GEN,j,RU_N);
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ru_counter = 0;
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ru_reseed = time.tv_sec + RU_OUT;
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ru_msb = ru_msb == 0x8000 ? 0 : 0x8000;
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}
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u_int16_t
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ip_randomid(void)
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{
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int i, n;
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struct timeval time;
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getmicrotime(&time);
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if (ru_counter >= RU_MAX || time.tv_sec > ru_reseed)
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ip_initid();
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if (!tmp)
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read_random((void *) &tmp, sizeof(tmp));
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/* Skip a random number of ids */
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n = tmp & 0x3; tmp = tmp >> 2;
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if (ru_counter + n >= RU_MAX)
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ip_initid();
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for (i = 0; i <= n; i++)
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/* Linear Congruential Generator */
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ru_x = (ru_a*ru_x + ru_b) % RU_M;
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ru_counter += i;
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return (ru_seed ^ pmod(ru_g,ru_seed2 ^ ru_x,RU_N)) | ru_msb;
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}
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#endif /* RANDOM_IP_ID */
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@ -44,6 +44,7 @@
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#include "opt_ipstealth.h"
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#include "opt_ipsec.h"
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#include "opt_pfil_hooks.h"
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#include "opt_random_ip_id.h"
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#include <sys/param.h>
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#include <sys/systm.h>
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@ -249,7 +250,9 @@ ip_init()
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maxnipq = nmbclusters/4;
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#ifndef RANDOM_IP_ID
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ip_id = time_second & 0xffff;
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#endif
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ipintrq.ifq_maxlen = ipqmaxlen;
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mtx_init(&ipintrq.ifq_mtx, "ip_inq", MTX_DEF);
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@ -13,6 +13,7 @@
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*/
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#include "opt_mrouting.h"
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#include "opt_random_ip_id.h"
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#include <sys/param.h>
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#include <sys/systm.h>
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@ -1581,7 +1582,11 @@ encap_send(ip, vifp, m)
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*/
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ip_copy = mtod(mb_copy, struct ip *);
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*ip_copy = multicast_encap_iphdr;
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#ifdef RANDOM_IP_ID
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ip_copy->ip_id = ip_randomid();
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#else
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ip_copy->ip_id = htons(ip_id++);
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#endif
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ip_copy->ip_len += len;
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ip_copy->ip_src = vifp->v_lcl_addr;
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ip_copy->ip_dst = vifp->v_rmt_addr;
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@ -42,6 +42,7 @@
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#include "opt_ipfilter.h"
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#include "opt_ipsec.h"
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#include "opt_pfil_hooks.h"
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#include "opt_random_ip_id.h"
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#include <sys/param.h>
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#include <sys/systm.h>
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@ -208,7 +209,11 @@ ip_output(m0, opt, ro, flags, imo)
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if ((flags & (IP_FORWARDING|IP_RAWOUTPUT)) == 0) {
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ip->ip_vhl = IP_MAKE_VHL(IPVERSION, hlen >> 2);
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ip->ip_off &= IP_DF;
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#ifdef RANDOM_IP_ID
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ip->ip_id = ip_randomid();
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#else
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ip->ip_id = htons(ip_id++);
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#endif
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ipstat.ips_localout++;
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} else {
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hlen = IP_VHL_HL(ip->ip_vhl) << 2;
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@ -138,7 +138,9 @@ struct route;
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struct sockopt;
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extern struct ipstat ipstat;
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#ifndef RANDOM_IP_ID
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extern u_short ip_id; /* ip packet ctr, for ids */
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#endif
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extern int ip_defttl; /* default IP ttl */
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extern int ipforwarding; /* ip forwarding */
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extern struct route ipforward_rt; /* ip forwarding cached route */
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@ -164,6 +166,10 @@ void ip_slowtimo __P((void));
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struct mbuf *
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ip_srcroute __P((void));
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void ip_stripoptions __P((struct mbuf *, struct mbuf *));
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#ifdef RANDOM_IP_ID
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u_int16_t
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ip_randomid __P((void));
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#endif
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int rip_ctloutput __P((struct socket *, struct sockopt *));
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void rip_ctlinput __P((int, struct sockaddr *, void *));
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void rip_init __P((void));
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@ -36,6 +36,7 @@
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#include "opt_inet6.h"
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#include "opt_ipsec.h"
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#include "opt_random_ip_id.h"
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#include <sys/param.h>
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#include <sys/systm.h>
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@ -220,7 +221,11 @@ rip_output(m, so, dst)
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return EINVAL;
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}
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if (ip->ip_id == 0)
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#ifdef RANDOM_IP_ID
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ip->ip_id = ip_randomid();
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#else
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ip->ip_id = htons(ip_id++);
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#endif
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/* XXX prevent ip_output from overwriting header fields */
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flags |= IP_RAWOUTPUT;
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ipstat.ips_rawout++;
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@ -2045,7 +2045,11 @@ ipsec4_encapsulate(m, sav)
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ipseclog((LOG_ERR, "IPv4 ipsec: size exceeds limit: "
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"leave ip_len as is (invalid packet)\n"));
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}
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#ifdef RANDOM_IP_ID
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ip->ip_id = ip_randomid();
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#else
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ip->ip_id = htons(ip_id++);
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#endif
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bcopy(&((struct sockaddr_in *)&sav->sah->saidx.src)->sin_addr,
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&ip->ip_src, sizeof(ip->ip_src));
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bcopy(&((struct sockaddr_in *)&sav->sah->saidx.dst)->sin_addr,
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