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remove the (in)famous SSHv1 CRC compensation attack detector. Despite your cameo in The Matrix movies, you will not be missed. ok markus Upstream-ID: 44261fce51a56d93cdb2af7b6e184be629f667e0
This commit is contained in:
djm@openbsd.org
Damien Miller
parent
e5d3bd36ef
commit
dfa641f758
23
LICENCE
23
LICENCE
@ -75,27 +75,6 @@ OpenSSH contains no GPL code.
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PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
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POSSIBILITY OF SUCH DAMAGES.
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2)
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The 32-bit CRC compensation attack detector in deattack.c was
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contributed by CORE SDI S.A. under a BSD-style license.
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* Cryptographic attack detector for ssh - source code
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*
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* Copyright (c) 1998 CORE SDI S.A., Buenos Aires, Argentina.
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*
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* All rights reserved. Redistribution and use in source and binary
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* forms, with or without modification, are permitted provided that
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* this copyright notice is retained.
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*
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* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
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* WARRANTIES ARE DISCLAIMED. IN NO EVENT SHALL CORE SDI S.A. BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY OR
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* CONSEQUENTIAL DAMAGES RESULTING FROM THE USE OR MISUSE OF THIS
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* SOFTWARE.
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*
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* Ariel Futoransky <futo@core-sdi.com>
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* <http://www.core-sdi.com>
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3)
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ssh-keyscan was contributed by David Mazieres under a BSD-style
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license.
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@ -337,4 +316,4 @@ OpenSSH contains no GPL code.
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------
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$OpenBSD: LICENCE,v 1.19 2004/08/30 09:18:08 markus Exp $
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$OpenBSD: LICENCE,v 1.20 2017/04/30 23:26:16 djm Exp $
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@ -79,7 +79,7 @@ LIBSSH_OBJS=${LIBOPENSSH_OBJS} \
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authfd.o authfile.o bufaux.o bufbn.o bufec.o buffer.o \
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canohost.o channels.o cipher.o cipher-aes.o cipher-aesctr.o \
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cipher-ctr.o cleanup.o \
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compat.o crc32.o deattack.o fatal.o hostfile.o \
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compat.o crc32.o fatal.o hostfile.o \
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log.o match.o moduli.o nchan.o packet.o opacket.o \
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readpass.o rsa.o ttymodes.o xmalloc.o addrmatch.o \
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atomicio.o key.o dispatch.o mac.o uidswap.o uuencode.o misc.o utf8.o \
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165
deattack.c
165
deattack.c
@ -1,165 +0,0 @@
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/* $OpenBSD: deattack.c,v 1.32 2015/01/20 23:14:00 deraadt Exp $ */
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/*
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* Cryptographic attack detector for ssh - source code
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*
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* Copyright (c) 1998 CORE SDI S.A., Buenos Aires, Argentina.
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*
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* All rights reserved. Redistribution and use in source and binary
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* forms, with or without modification, are permitted provided that
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* this copyright notice is retained.
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*
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* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
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* WARRANTIES ARE DISCLAIMED. IN NO EVENT SHALL CORE SDI S.A. BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY OR
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* CONSEQUENTIAL DAMAGES RESULTING FROM THE USE OR MISUSE OF THIS
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* SOFTWARE.
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*
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* Ariel Futoransky <futo@core-sdi.com>
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* <http://www.core-sdi.com>
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*/
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#include "includes.h"
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#include <string.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include "deattack.h"
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#include "crc32.h"
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#include "sshbuf.h"
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#include "misc.h"
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/*
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* CRC attack detection has a worst-case behaviour that is O(N^3) over
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* the number of identical blocks in a packet. This behaviour can be
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* exploited to create a limited denial of service attack.
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*
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* However, because we are dealing with encrypted data, identical
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* blocks should only occur every 2^35 maximally-sized packets or so.
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* Consequently, we can detect this DoS by looking for identical blocks
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* in a packet.
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*
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* The parameter below determines how many identical blocks we will
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* accept in a single packet, trading off between attack detection and
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* likelihood of terminating a legitimate connection. A value of 32
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* corresponds to an average of 2^40 messages before an attack is
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* misdetected
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*/
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#define MAX_IDENTICAL 32
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/* SSH Constants */
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#define SSH_MAXBLOCKS (32 * 1024)
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#define SSH_BLOCKSIZE (8)
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/* Hashing constants */
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#define HASH_MINSIZE (8 * 1024)
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#define HASH_ENTRYSIZE (2)
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#define HASH_FACTOR(x) ((x)*3/2)
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#define HASH_UNUSEDCHAR (0xff)
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#define HASH_UNUSED (0xffff)
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#define HASH_IV (0xfffe)
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#define HASH_MINBLOCKS (7*SSH_BLOCKSIZE)
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/* Hash function (Input keys are cipher results) */
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#define HASH(x) PEEK_U32(x)
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#define CMP(a, b) (memcmp(a, b, SSH_BLOCKSIZE))
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static void
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crc_update(u_int32_t *a, u_int32_t b)
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{
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b ^= *a;
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*a = ssh_crc32((u_char *)&b, sizeof(b));
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}
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/* detect if a block is used in a particular pattern */
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static int
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check_crc(const u_char *S, const u_char *buf, u_int32_t len)
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{
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u_int32_t crc;
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const u_char *c;
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crc = 0;
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for (c = buf; c < buf + len; c += SSH_BLOCKSIZE) {
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if (!CMP(S, c)) {
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crc_update(&crc, 1);
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crc_update(&crc, 0);
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} else {
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crc_update(&crc, 0);
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crc_update(&crc, 0);
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}
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}
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return crc == 0;
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}
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void
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deattack_init(struct deattack_ctx *dctx)
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{
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bzero(dctx, sizeof(*dctx));
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dctx->n = HASH_MINSIZE / HASH_ENTRYSIZE;
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}
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/* Detect a crc32 compensation attack on a packet */
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int
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detect_attack(struct deattack_ctx *dctx, const u_char *buf, u_int32_t len)
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{
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u_int32_t i, j, l, same;
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u_int16_t *tmp;
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const u_char *c, *d;
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if (len > (SSH_MAXBLOCKS * SSH_BLOCKSIZE) ||
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len % SSH_BLOCKSIZE != 0)
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return DEATTACK_ERROR;
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for (l = dctx->n; l < HASH_FACTOR(len / SSH_BLOCKSIZE); l = l << 2)
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;
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if (dctx->h == NULL) {
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if ((dctx->h = calloc(l, HASH_ENTRYSIZE)) == NULL)
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return DEATTACK_ERROR;
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dctx->n = l;
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} else {
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if (l > dctx->n) {
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if ((tmp = reallocarray(dctx->h, l, HASH_ENTRYSIZE))
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== NULL) {
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free(dctx->h);
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dctx->h = NULL;
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return DEATTACK_ERROR;
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}
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dctx->h = tmp;
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dctx->n = l;
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}
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}
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if (len <= HASH_MINBLOCKS) {
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for (c = buf; c < buf + len; c += SSH_BLOCKSIZE) {
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for (d = buf; d < c; d += SSH_BLOCKSIZE) {
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if (!CMP(c, d)) {
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if ((check_crc(c, buf, len)))
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return DEATTACK_DETECTED;
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else
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break;
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}
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}
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}
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return DEATTACK_OK;
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}
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memset(dctx->h, HASH_UNUSEDCHAR, dctx->n * HASH_ENTRYSIZE);
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for (c = buf, same = j = 0; c < (buf + len); c += SSH_BLOCKSIZE, j++) {
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for (i = HASH(c) & (dctx->n - 1); dctx->h[i] != HASH_UNUSED;
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i = (i + 1) & (dctx->n - 1)) {
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if (!CMP(c, buf + dctx->h[i] * SSH_BLOCKSIZE)) {
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if (++same > MAX_IDENTICAL)
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return DEATTACK_DOS_DETECTED;
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if (check_crc(c, buf, len))
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return DEATTACK_DETECTED;
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else
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break;
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}
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}
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dctx->h[i] = j;
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}
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return DEATTACK_OK;
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}
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38
deattack.h
38
deattack.h
@ -1,38 +0,0 @@
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/* $OpenBSD: deattack.h,v 1.11 2015/01/19 19:52:16 markus Exp $ */
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/*
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* Cryptographic attack detector for ssh - Header file
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*
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* Copyright (c) 1998 CORE SDI S.A., Buenos Aires, Argentina.
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*
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* All rights reserved. Redistribution and use in source and binary
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* forms, with or without modification, are permitted provided that
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* this copyright notice is retained.
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*
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* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
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* WARRANTIES ARE DISCLAIMED. IN NO EVENT SHALL CORE SDI S.A. BE
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* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY OR
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* CONSEQUENTIAL DAMAGES RESULTING FROM THE USE OR MISUSE OF THIS
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* SOFTWARE.
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*
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* Ariel Futoransky <futo@core-sdi.com>
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* <http://www.core-sdi.com>
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*/
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#ifndef _DEATTACK_H
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#define _DEATTACK_H
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/* Return codes */
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#define DEATTACK_OK 0
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#define DEATTACK_DETECTED 1
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#define DEATTACK_DOS_DETECTED 2
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#define DEATTACK_ERROR 3
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struct deattack_ctx {
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u_int16_t *h;
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u_int32_t n;
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};
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void deattack_init(struct deattack_ctx *);
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int detect_attack(struct deattack_ctx *, const u_char *, u_int32_t);
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#endif
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7
packet.c
7
packet.c
@ -1,4 +1,4 @@
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/* $OpenBSD: packet.c,v 1.250 2017/04/30 23:23:54 djm Exp $ */
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/* $OpenBSD: packet.c,v 1.251 2017/04/30 23:26:16 djm Exp $ */
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/*
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* Author: Tatu Ylonen <ylo@cs.hut.fi>
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* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
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@ -68,7 +68,6 @@
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#include "xmalloc.h"
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#include "crc32.h"
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#include "deattack.h"
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#include "compat.h"
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#include "ssh1.h"
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#include "ssh2.h"
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@ -216,9 +215,6 @@ struct session_state {
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/* One-off warning about weak ciphers */
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int cipher_warning_done;
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/* SSH1 CRC compensation attack detector */
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struct deattack_ctx deattack;
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/* Hook for fuzzing inbound packets */
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ssh_packet_hook_fn *hook_in;
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void *hook_in_ctx;
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@ -315,7 +311,6 @@ ssh_packet_set_connection(struct ssh *ssh, int fd_in, int fd_out)
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return NULL;
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}
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state->newkeys[MODE_IN] = state->newkeys[MODE_OUT] = NULL;
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deattack_init(&state->deattack);
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/*
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* Cache the IP address of the remote connection for use in error
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* messages that might be generated after the connection has closed.
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