freebsd-dev/sys/netinet/tcp_seq.h
Mike Silbersack 2d610a5028 Temporary feature: Runtime tuneable tcp initial sequence number
generation scheme.  Users may now select between the currently used
OpenBSD algorithm and the older random positive increment method.

While the OpenBSD algorithm is more secure, it also breaks TIME_WAIT
handling; this is causing trouble for an increasing number of folks.

To switch between generation schemes, one sets the sysctl
net.inet.tcp.tcp_seq_genscheme.  0 = random positive increments,
1 = the OpenBSD algorithm.  1 is still the default.

Once a secure _and_ compatible algorithm is implemented, this sysctl
will be removed.

Reviewed by: jlemon
Tested by: numerous subscribers of -net
2001-07-08 02:20:47 +00:00

106 lines
4.0 KiB
C

/*
* Copyright (c) 1982, 1986, 1993, 1995
* The Regents of the University of California. 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. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by the University of
* California, Berkeley and its contributors.
* 4. Neither the name of the University 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 REGENTS 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 REGENTS 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.
*
* @(#)tcp_seq.h 8.3 (Berkeley) 6/21/95
* $FreeBSD$
*/
#ifndef _NETINET_TCP_SEQ_H_
#define _NETINET_TCP_SEQ_H_
/*
* TCP sequence numbers are 32 bit integers operated
* on with modular arithmetic. These macros can be
* used to compare such integers.
*/
#define SEQ_LT(a,b) ((int)((a)-(b)) < 0)
#define SEQ_LEQ(a,b) ((int)((a)-(b)) <= 0)
#define SEQ_GT(a,b) ((int)((a)-(b)) > 0)
#define SEQ_GEQ(a,b) ((int)((a)-(b)) >= 0)
/* for modulo comparisons of timestamps */
#define TSTMP_LT(a,b) ((int)((a)-(b)) < 0)
#define TSTMP_GEQ(a,b) ((int)((a)-(b)) >= 0)
/*
* TCP connection counts are 32 bit integers operated
* on with modular arithmetic. These macros can be
* used to compare such integers.
*/
#define CC_LT(a,b) ((int)((a)-(b)) < 0)
#define CC_LEQ(a,b) ((int)((a)-(b)) <= 0)
#define CC_GT(a,b) ((int)((a)-(b)) > 0)
#define CC_GEQ(a,b) ((int)((a)-(b)) >= 0)
/* Macro to increment a CC: skip 0 which has a special meaning */
#define CC_INC(c) (++(c) == 0 ? ++(c) : (c))
/*
* Macros to initialize tcp sequence numbers for
* send and receive from initial send and receive
* sequence numbers.
*/
#define tcp_rcvseqinit(tp) \
(tp)->rcv_adv = (tp)->rcv_nxt = (tp)->irs + 1
#define tcp_sendseqinit(tp) \
(tp)->snd_una = (tp)->snd_nxt = (tp)->snd_max = (tp)->snd_up = \
(tp)->iss
#define TCP_PAWS_IDLE (24 * 24 * 60 * 60 * hz)
/* timestamp wrap-around time */
#ifdef _KERNEL
extern tcp_cc tcp_ccgen; /* global connection count */
/*
* Increment for tcp_iss each second.
* This is designed to increment at the standard 250 KB/s,
* but with a random component averaging 128 KB.
* We also increment tcp_iss by a quarter of this amount
* each time we use the value for a new connection.
* If defined, the tcp_random18() macro should produce a
* number in the range [0-0x3ffff] that is hard to predict.
*
* The variable tcp_iss and tcp_random18() are only used
* by sequence number generation scheme 0.
*/
#ifndef tcp_random18
#define tcp_random18() (arc4random() & 0x3ffff)
#endif
#define TCP_ISSINCR (122*1024 + tcp_random18())
extern tcp_seq tcp_iss;
#else
#define TCP_ISSINCR (250*1024) /* increment for tcp_iss each second */
#endif /* _KERNEL */
#endif /* _NETINET_TCP_SEQ_H_ */