Date: Fri, 25 May 2001 23:38:12 -0700 From: Kris Kennaway <kris@obsecurity.org> To: net@FreeBSD.org Subject: Randomized IP ID patch Message-ID: <20010525233811.A44455@xor.obsecurity.org>
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A while back I posted a version of this which was activated by sysctl,
but people didn't like the per-packet performance overhead, so here's
an updated version which uses a compile-time option. Please review;
I'd like to commit this soon.
Kris
Index: conf/files
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
RCS file: /home/ncvs/src/sys/conf/files,v
retrieving revision 1.517
diff -u -r1.517 files
--- conf/files 2001/05/16 07:31:56 1.517
+++ conf/files 2001/05/26 05:09:59
@@ -1010,6 +1010,7 @@
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
Index: conf/options
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
RCS file: /home/ncvs/src/sys/conf/options,v
retrieving revision 1.271
diff -u -r1.271 options
--- conf/options 2001/05/13 20:52:36 1.271
+++ conf/options 2001/05/26 05:10:39
@@ -283,6 +283,7 @@
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
Index: netinet/ip_input.c
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
RCS file: /home/ncvs/src/sys/netinet/ip_input.c,v
retrieving revision 1.165
diff -u -r1.165 ip_input.c
--- netinet/ip_input.c 2001/03/19 09:16:16 1.165
+++ netinet/ip_input.c 2001/05/26 06:15:51
@@ -44,6 +44,7 @@
#include "opt_ipstealth.h"
#include "opt_ipsec.h"
#include "opt_pfil_hooks.h"
+#include "opt_random_ip_id.h"
=20
#include <sys/param.h>
#include <sys/systm.h>
@@ -249,7 +250,9 @@
=20
maxnipq =3D nmbclusters/4;
=20
+#ifndef RANDOM_IP_ID
ip_id =3D time_second & 0xffff;
+#endif
ipintrq.ifq_maxlen =3D ipqmaxlen;
mtx_init(&ipintrq.ifq_mtx, "ip_inq", MTX_DEF);
=20
Index: netinet/ip_mroute.c
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
RCS file: /home/ncvs/src/sys/netinet/ip_mroute.c,v
retrieving revision 1.62
diff -u -r1.62 ip_mroute.c
--- netinet/ip_mroute.c 2001/02/06 11:20:42 1.62
+++ netinet/ip_mroute.c 2001/05/26 06:16:07
@@ -13,6 +13,7 @@
*/
=20
#include "opt_mrouting.h"
+#include "opt_random_ip_id.h"
=20
#include <sys/param.h>
#include <sys/systm.h>
@@ -1581,7 +1582,11 @@
*/
ip_copy =3D mtod(mb_copy, struct ip *);
*ip_copy =3D multicast_encap_iphdr;
+#ifdef RANDOM_IP_ID
+ ip_copy->ip_id =3D ip_randomid();
+#else
ip_copy->ip_id =3D htons(ip_id++);
+#endif
ip_copy->ip_len +=3D len;
ip_copy->ip_src =3D vifp->v_lcl_addr;
ip_copy->ip_dst =3D vifp->v_rmt_addr;
Index: netinet/ip_output.c
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
RCS file: /home/ncvs/src/sys/netinet/ip_output.c,v
retrieving revision 1.124
diff -u -r1.124 ip_output.c
--- netinet/ip_output.c 2001/03/13 17:07:06 1.124
+++ netinet/ip_output.c 2001/05/26 06:16:24
@@ -42,6 +42,7 @@
#include "opt_ipfilter.h"
#include "opt_ipsec.h"
#include "opt_pfil_hooks.h"
+#include "opt_random_ip_id.h"
=20
#include <sys/param.h>
#include <sys/systm.h>
@@ -208,7 +209,11 @@
if ((flags & (IP_FORWARDING|IP_RAWOUTPUT)) =3D=3D 0) {
ip->ip_vhl =3D IP_MAKE_VHL(IPVERSION, hlen >> 2);
ip->ip_off &=3D IP_DF;
+#ifdef RANDOM_IP_ID
+ ip->ip_id =3D ip_randomid();
+#else
ip->ip_id =3D htons(ip_id++);
+#endif
ipstat.ips_localout++;
} else {
hlen =3D IP_VHL_HL(ip->ip_vhl) << 2;
Index: netinet/ip_var.h
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
RCS file: /home/ncvs/src/sys/netinet/ip_var.h,v
retrieving revision 1.54
diff -u -r1.54 ip_var.h
--- netinet/ip_var.h 2001/03/19 09:16:16 1.54
+++ netinet/ip_var.h 2001/05/26 03:15:06
@@ -138,7 +138,9 @@
struct sockopt;
=20
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 @@
struct mbuf *
ip_srcroute __P((void));
void ip_stripoptions __P((struct mbuf *, struct mbuf *));
+#ifdef RANDOM_IP_ID
+u_int16_t=09
+ 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));
Index: netinet/raw_ip.c
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
RCS file: /home/ncvs/src/sys/netinet/raw_ip.c,v
retrieving revision 1.76
diff -u -r1.76 raw_ip.c
--- netinet/raw_ip.c 2001/05/11 14:37:34 1.76
+++ netinet/raw_ip.c 2001/05/26 06:16:51
@@ -36,6 +36,7 @@
=20
#include "opt_inet6.h"
#include "opt_ipsec.h"
+#include "opt_random_ip_id.h"
=20
#include <sys/param.h>
#include <sys/systm.h>
@@ -220,7 +221,11 @@
return EINVAL;
}
if (ip->ip_id =3D=3D 0)
+#ifdef RANDOM_IP_ID
+ ip->ip_id =3D ip_randomid();
+#else
ip->ip_id =3D htons(ip_id++);
+#endif
/* XXX prevent ip_output from overwriting header fields */
flags |=3D IP_RAWOUTPUT;
ipstat.ips_rawout++;
Index: netinet6/ipsec.c
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
RCS file: /home/ncvs/src/sys/netinet6/ipsec.c,v
retrieving revision 1.10
diff -u -r1.10 ipsec.c
--- netinet6/ipsec.c 2001/03/16 17:52:48 1.10
+++ netinet6/ipsec.c 2001/05/26 03:12:20
@@ -2045,7 +2045,11 @@
ipseclog((LOG_ERR, "IPv4 ipsec: size exceeds limit: "
"leave ip_len as is (invalid packet)\n"));
}
+#ifdef RANDOM_IP_ID
+ ip->ip_id =3D ip_randomid();
+#else
ip->ip_id =3D 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,
Index: i386/conf/NOTES
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
RCS file: /mnt/ncvs/src/sys/i386/conf/NOTES,v
retrieving revision 1.914
diff -u -r1.914 NOTES
--- i386/conf/NOTES 2001/05/13 20:52:39 1.914
+++ i386/conf/NOTES 2001/05/26 06:34:01
@@ -590,6 +590,12 @@
options IPSTEALTH #support for stealth forwarding
options TCPDEBUG
=20
+# RANDOM_IP_ID causes the ID field in IP packets to be randomized
+# instead of incremented by 1. This option prevents remote observers
+# from determining the traffic load on the machine by watching the
+# counter.
+options RANDOM_IP_ID
+
# Statically Link in accept filters
options ACCEPT_FILTER_DATA
options ACCEPT_FILTER_HTTP
--- /dev/null Fri May 25 23:33:00 2001
+++ netinet/ip_id.c Fri May 25 23:26:26 2001
@@ -0,0 +1,214 @@
+/* $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 WARRANTI=
ES
+ * 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 US=
E,
+ * 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.
+ *
+ * $FreeBSD$
+ */
+
+/*=20
+ * seed =3D random 15bit
+ * n =3D prime, g0 =3D generator to n,
+ * j =3D random so that gcd(j,n-1) =3D=3D 1
+ * g =3D g0^j mod n will be a generator again.
+ *
+ * X[0] =3D random seed.
+ * X[n] =3D a*X[n-1]+b mod m is a Linear Congruential Generator
+ * with a =3D 7^(even random) mod m,=20
+ * b =3D random with gcd(b,m) =3D=3D 1
+ * m =3D 31104 and a maximal period of m-1.
+ *
+ * The transaction id is determined by:
+ * id[n] =3D 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 =3D 2*2*3*2729 */
+#define RU_AGEN 7 /* determine ru_a as RU_AGEN^(2*rand) */
+#define RU_M 31104 /* RU_M =3D 2^7*3^5 - don't change */
+
+#define PFAC_N 3
+const static u_int16_t pfacts[PFAC_N] =3D {
+ 2,=20
+ 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 =3D 0;
+static u_int16_t ru_msb =3D 0;
+static long ru_reseed;
+static u_int32_t tmp; /* Storage for unused random */
+static int randomize =3D 0;
+
+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 =3D 1;
+ t =3D gen;
+ u =3D exp;
+
+ while (u) {
+ if (u & 1)
+ s =3D (s*t) % mod;
+ u >>=3D 1;
+ t =3D (t*t) % mod;
+ }
+ return (s);
+}
+
+/*=20
+ * Initalizes the seed and chooses a suitable generator. Also toggles=20
+ * 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=20
+ * application does not have to worry about it.
+ */
+static void=20
+ip_initid(void)
+{
+ u_int16_t j, i;
+ int noprime =3D 1;
+ struct timeval time;
+
+ getmicrotime(&time);
+ read_random((void *) &tmp, sizeof(tmp));
+ ru_x =3D (tmp & 0xFFFF) % RU_M;
+
+ /* 15 bits of random seed */
+ ru_seed =3D (tmp >> 16) & 0x7FFF;
+ read_random((void *) &tmp, sizeof(tmp));
+ ru_seed2 =3D tmp & 0x7FFF;
+
+ read_random((void *) &tmp, sizeof(tmp));
+
+ /* Determine the LCG we use */
+ ru_b =3D (tmp & 0xfffe) | 1;
+ ru_a =3D pmod(RU_AGEN, (tmp >> 16) & 0xfffe, RU_M);
+ while (ru_b % 3 =3D=3D 0)
+ ru_b +=3D 2;
+=09
+ read_random((void *) &tmp, sizeof(tmp));
+ j =3D tmp % RU_N;
+ tmp =3D tmp >> 16;
+
+ /*=20
+ * Do a fast gcd(j,RU_N-1), so we can find a j with
+ * gcd(j, RU_N-1) =3D=3D 1, giving a new generator for
+ * RU_GEN^j mod RU_N
+ */
+
+ while (noprime) {
+ for (i=3D0; i<PFAC_N; i++)
+ if (j%pfacts[i] =3D=3D 0)
+ break;
+
+ if (i>=3DPFAC_N)
+ noprime =3D 0;
+ else=20
+ j =3D (j+1) % RU_N;
+ }
+
+ ru_g =3D pmod(RU_GEN,j,RU_N);
+ ru_counter =3D 0;
+
+ ru_reseed =3D time.tv_sec + RU_OUT;
+ ru_msb =3D ru_msb =3D=3D 0x8000 ? 0 : 0x8000;=20
+}
+
+u_int16_t
+ip_randomid(void)
+{
+ int i, n;
+ static u_short ip_id =3D 0; /* ip packet ctr, for ids */
+ static int ip_id_init =3D 0;
+ struct timeval time;
+
+ getmicrotime(&time);
+ if (ru_counter >=3D RU_MAX || time.tv_sec > ru_reseed)
+ ip_initid();
+
+ if (!tmp)
+ read_random((void *) &tmp, sizeof(tmp));
+
+ /* Skip a random number of ids */
+ n =3D tmp & 0x3; tmp =3D tmp >> 2;
+ if (ru_counter + n >=3D RU_MAX)
+ ip_initid();
+
+ for (i =3D 0; i <=3D n; i++)
+ /* Linear Congruential Generator */
+ ru_x =3D (ru_a*ru_x + ru_b) % RU_M;
+
+ ru_counter +=3D i;
+
+ return (ru_seed ^ pmod(ru_g,ru_seed2 ^ ru_x,RU_N)) | ru_msb;
+ }
+}
+
+#endif /* RANDOM_IP_ID */
--n8g4imXOkfNTN/H1
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