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Add ``options RANDOM_IP_ID'' which randomizes the ID field of IP packets.

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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 2001-06-01 10:02:28 +00:00
parent 25d1a10fa0
commit 64dddc1872
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=77574
11 changed files with 254 additions and 0 deletions
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7
sys/conf/NOTES
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@ -590,6 +590,13 @@ options IPFILTER_DEFAULT_BLOCK #block all packets by default
options IPSTEALTH #support for stealth forwarding
options TCPDEBUG
# RANDOM_IP_ID causes the ID field in IP packets to be randomized
# instead of incremented by 1 with each packet generated. This
# option closes a minor information leak which allows remote
# observers to determine the rate of packet generation on the
# machine by watching the counter.
options RANDOM_IP_ID
# Statically Link in accept filters
options ACCEPT_FILTER_DATA
options ACCEPT_FILTER_HTTP

1
sys/conf/files
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@ -1037,6 +1037,7 @@ netinet/igmp.c optional inet
netinet/in.c optional inet
netinet/in_gif.c optional gif inet
#netinet/in_hostcache.c optional inet
netinet/ip_id.c optional inet
netinet/in_pcb.c optional inet
netinet/in_proto.c optional inet
netinet/in_rmx.c optional inet

1
sys/conf/options
View File

@ -278,6 +278,7 @@ NETATALK opt_atalk.h
PPP_BSDCOMP opt_ppp.h
PPP_DEFLATE opt_ppp.h
PPP_FILTER opt_ppp.h
RANDOM_IP_ID
SLIP_IFF_OPTS opt_slip.h
TCPDEBUG
TCP_DROP_SYNFIN opt_tcp_input.h

7
sys/i386/conf/NOTES
View File

@ -590,6 +590,13 @@ options IPFILTER_DEFAULT_BLOCK #block all packets by default
options IPSTEALTH #support for stealth forwarding
options TCPDEBUG
# RANDOM_IP_ID causes the ID field in IP packets to be randomized
# instead of incremented by 1 with each packet generated. This
# option closes a minor information leak which allows remote
# observers to determine the rate of packet generation on the
# machine by watching the counter.
options RANDOM_IP_ID
# Statically Link in accept filters
options ACCEPT_FILTER_DATA
options ACCEPT_FILTER_HTTP

210
sys/netinet/ip_id.c Normal file
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@ -0,0 +1,210 @@
/* $OpenBSD: ip_id.c,v 1.2 1999/08/26 13:37:01 provos 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.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by Niels Provos.
* 4. The name of the author may not be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* 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.
*
* $FreeBSD$
*/
/*
* seed = random 15bit
* 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 = 31104 and a maximal period of m-1.
*
* The transaction id is determined by:
* id[n] = seed xor (g^X[n] mod n)
*
* Effectivly the id is restricted to the lower 15 bits, thus
* yielding two different cycles by toggling the msb on and off.
* This avoids reuse issues caused by reseeding.
*/
#include "opt_random_ip_id.h"
#include <sys/param.h>
#include <sys/time.h>
#include <sys/kernel.h>
#include <sys/random.h>
#ifdef RANDOM_IP_ID
#define RU_OUT 180 /* Time after wich will be reseeded */
#define RU_MAX 30000 /* Uniq cycle, avoid blackjack prediction */
#define RU_GEN 2 /* Starting generator */
#define RU_N 32749 /* RU_N-1 = 2*2*3*2729 */
#define RU_AGEN 7 /* determine ru_a as RU_AGEN^(2*rand) */
#define RU_M 31104 /* RU_M = 2^7*3^5 - don't change */
#define PFAC_N 3
const static u_int16_t pfacts[PFAC_N] = {
2,
3,
2729
};
static u_int16_t ru_x;
static u_int16_t ru_seed, ru_seed2;
static u_int16_t ru_a, ru_b;
static u_int16_t ru_g;
static u_int16_t ru_counter = 0;
static u_int16_t ru_msb = 0;
static long ru_reseed;
static u_int32_t tmp; /* Storage for unused random */
static u_int16_t pmod __P((u_int16_t, u_int16_t, u_int16_t));
static void ip_initid __P((void));
u_int16_t ip_randomid __P((void));
/*
* Do a fast modular exponation, returned value will be in the range
* of 0 - (mod-1)
*/
#ifdef __STDC__
static u_int16_t
pmod(u_int16_t gen, u_int16_t exp, u_int16_t mod)
#else
static u_int16_t
pmod(gen, exp, mod)
u_int16_t gen, exp, mod;
#endif
{
u_int16_t s, t, u;
s = 1;
t = gen;
u = exp;
while (u) {
if (u & 1)
s = (s*t) % mod;
u >>= 1;
t = (t*t) % mod;
}
return (s);
}
/*
* Initalizes 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
ip_initid(void)
{
u_int16_t j, i;
int noprime = 1;
struct timeval time;
getmicrotime(&time);
read_random((void *) &tmp, sizeof(tmp));
ru_x = (tmp & 0xFFFF) % RU_M;
/* 15 bits of random seed */
ru_seed = (tmp >> 16) & 0x7FFF;
read_random((void *) &tmp, sizeof(tmp));
ru_seed2 = tmp & 0x7FFF;
read_random((void *) &tmp, sizeof(tmp));
/* Determine the LCG we use */
ru_b = (tmp & 0xfffe) | 1;
ru_a = pmod(RU_AGEN, (tmp >> 16) & 0xfffe, RU_M);
while (ru_b % 3 == 0)
ru_b += 2;
read_random((void *) &tmp, sizeof(tmp));
j = tmp % RU_N;
tmp = tmp >> 16;
/*
* 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; i<PFAC_N; i++)
if (j%pfacts[i] == 0)
break;
if (i>=PFAC_N)
noprime = 0;
else
j = (j+1) % RU_N;
}
ru_g = pmod(RU_GEN,j,RU_N);
ru_counter = 0;
ru_reseed = time.tv_sec + RU_OUT;
ru_msb = ru_msb == 0x8000 ? 0 : 0x8000;
}
u_int16_t
ip_randomid(void)
{
int i, n;
struct timeval time;
getmicrotime(&time);
if (ru_counter >= RU_MAX || time.tv_sec > ru_reseed)
ip_initid();
if (!tmp)
read_random((void *) &tmp, sizeof(tmp));
/* Skip a random number of ids */
n = tmp & 0x3; tmp = tmp >> 2;
if (ru_counter + n >= RU_MAX)
ip_initid();
for (i = 0; i <= n; i++)
/* Linear Congruential Generator */
ru_x = (ru_a*ru_x + ru_b) % RU_M;
ru_counter += i;
return (ru_seed ^ pmod(ru_g,ru_seed2 ^ ru_x,RU_N)) | ru_msb;
}
#endif /* RANDOM_IP_ID */

3
sys/netinet/ip_input.c
View File

@ -44,6 +44,7 @@
#include "opt_ipstealth.h"
#include "opt_ipsec.h"
#include "opt_pfil_hooks.h"
#include "opt_random_ip_id.h"
#include <sys/param.h>
#include <sys/systm.h>
@ -249,7 +250,9 @@ ip_init()
maxnipq = nmbclusters/4;
#ifndef RANDOM_IP_ID
ip_id = time_second & 0xffff;
#endif
ipintrq.ifq_maxlen = ipqmaxlen;
mtx_init(&ipintrq.ifq_mtx, "ip_inq", MTX_DEF);

5
sys/netinet/ip_mroute.c
View File

@ -13,6 +13,7 @@
*/
#include "opt_mrouting.h"
#include "opt_random_ip_id.h"
#include <sys/param.h>
#include <sys/systm.h>
@ -1581,7 +1582,11 @@ encap_send(ip, vifp, m)
*/
ip_copy = mtod(mb_copy, struct ip *);
*ip_copy = multicast_encap_iphdr;
#ifdef RANDOM_IP_ID
ip_copy->ip_id = ip_randomid();
#else
ip_copy->ip_id = htons(ip_id++);
#endif
ip_copy->ip_len += len;
ip_copy->ip_src = vifp->v_lcl_addr;
ip_copy->ip_dst = vifp->v_rmt_addr;

5
sys/netinet/ip_output.c
View File

@ -42,6 +42,7 @@
#include "opt_ipfilter.h"
#include "opt_ipsec.h"
#include "opt_pfil_hooks.h"
#include "opt_random_ip_id.h"
#include <sys/param.h>
#include <sys/systm.h>
@ -208,7 +209,11 @@ ip_output(m0, opt, ro, flags, imo)
if ((flags & (IP_FORWARDING|IP_RAWOUTPUT)) == 0) {
ip->ip_vhl = IP_MAKE_VHL(IPVERSION, hlen >> 2);
ip->ip_off &= IP_DF;
#ifdef RANDOM_IP_ID
ip->ip_id = ip_randomid();
#else
ip->ip_id = htons(ip_id++);
#endif
ipstat.ips_localout++;
} else {
hlen = IP_VHL_HL(ip->ip_vhl) << 2;

6
sys/netinet/ip_var.h
View File

@ -138,7 +138,9 @@ struct route;
struct sockopt;
extern struct ipstat ipstat;
#ifndef RANDOM_IP_ID
extern u_short ip_id; /* ip packet ctr, for ids */
#endif
extern int ip_defttl; /* default IP ttl */
extern int ipforwarding; /* ip forwarding */
extern struct route ipforward_rt; /* ip forwarding cached route */
@ -164,6 +166,10 @@ void ip_slowtimo __P((void));
struct mbuf *
ip_srcroute __P((void));
void ip_stripoptions __P((struct mbuf *, struct mbuf *));
#ifdef RANDOM_IP_ID
u_int16_t
ip_randomid __P((void));
#endif
int rip_ctloutput __P((struct socket *, struct sockopt *));
void rip_ctlinput __P((int, struct sockaddr *, void *));
void rip_init __P((void));

5
sys/netinet/raw_ip.c
View File

@ -36,6 +36,7 @@
#include "opt_inet6.h"
#include "opt_ipsec.h"
#include "opt_random_ip_id.h"
#include <sys/param.h>
#include <sys/systm.h>
@ -220,7 +221,11 @@ rip_output(m, so, dst)
return EINVAL;
}
if (ip->ip_id == 0)
#ifdef RANDOM_IP_ID
ip->ip_id = ip_randomid();
#else
ip->ip_id = htons(ip_id++);
#endif
/* XXX prevent ip_output from overwriting header fields */
flags |= IP_RAWOUTPUT;
ipstat.ips_rawout++;

4
sys/netinet6/ipsec.c
View File

@ -2045,7 +2045,11 @@ ipsec4_encapsulate(m, sav)
ipseclog((LOG_ERR, "IPv4 ipsec: size exceeds limit: "
"leave ip_len as is (invalid packet)\n"));
}
#ifdef RANDOM_IP_ID
ip->ip_id = ip_randomid();
#else
ip->ip_id = htons(ip_id++);
#endif
bcopy(&((struct sockaddr_in *)&sav->sah->saidx.src)->sin_addr,
&ip->ip_src, sizeof(ip->ip_src));
bcopy(&((struct sockaddr_in *)&sav->sah->saidx.dst)->sin_addr,