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OpenSSH 6.5 and 6.6 have a bug that causes ~0.2% of connections
using the curve25519-sha256@libssh.org KEX exchange method to fail
when connecting with something that implements the spec properly.

Disable this KEX method when speaking to one of the affected
versions.

reported by Aris Adamantiadis; ok markus@

/* $OpenBSD: compat.c,v 1.83 2014/04/18 23:52:25 djm Exp $ */
/*
 * Copyright (c) 1999, 2000, 2001, 2002 Markus Friedl.  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.
 *
 * 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.
 */

#include <sys/types.h>

#include <stdlib.h>
#include <string.h>
#include <stdarg.h>

#include "xmalloc.h"
#include "buffer.h"
#include "packet.h"
#include "compat.h"
#include "log.h"
#include "match.h"

int compat13 = 0;
int compat20 = 0;
int datafellows = 0;

void
enable_compat20(void)
{
	if (compat20)
		return;
	debug("Enabling compatibility mode for protocol 2.0");
	compat20 = 1;
}
void
enable_compat13(void)
{
	debug("Enabling compatibility mode for protocol 1.3");
	compat13 = 1;
}
/* datafellows bug compatibility */
void
compat_datafellows(const char *version)
{
	int i;
	static struct {
		char	*pat;
		int	bugs;
	} check[] = {
		{ "OpenSSH-2.0*,"
		  "OpenSSH-2.1*,"
		  "OpenSSH_2.1*,"
		  "OpenSSH_2.2*",	SSH_OLD_SESSIONID|SSH_BUG_BANNER|
					SSH_OLD_DHGEX|SSH_BUG_NOREKEY|
					SSH_BUG_EXTEOF|SSH_OLD_FORWARD_ADDR},
		{ "OpenSSH_2.3.0*",	SSH_BUG_BANNER|SSH_BUG_BIGENDIANAES|
					SSH_OLD_DHGEX|SSH_BUG_NOREKEY|
					SSH_BUG_EXTEOF|SSH_OLD_FORWARD_ADDR},
		{ "OpenSSH_2.3.*",	SSH_BUG_BIGENDIANAES|SSH_OLD_DHGEX|
					SSH_BUG_NOREKEY|SSH_BUG_EXTEOF|
					SSH_OLD_FORWARD_ADDR},
		{ "OpenSSH_2.5.0p1*,"
		  "OpenSSH_2.5.1p1*",
					SSH_BUG_BIGENDIANAES|SSH_OLD_DHGEX|
					SSH_BUG_NOREKEY|SSH_BUG_EXTEOF|
					SSH_OLD_FORWARD_ADDR},
		{ "OpenSSH_2.5.0*,"
		  "OpenSSH_2.5.1*,"
		  "OpenSSH_2.5.2*",	SSH_OLD_DHGEX|SSH_BUG_NOREKEY|
					SSH_BUG_EXTEOF|SSH_OLD_FORWARD_ADDR},
		{ "OpenSSH_2.5.3*",	SSH_BUG_NOREKEY|SSH_BUG_EXTEOF|
					SSH_OLD_FORWARD_ADDR},
		{ "OpenSSH_2.*,"
		  "OpenSSH_3.0*,"
		  "OpenSSH_3.1*",	SSH_BUG_EXTEOF|SSH_OLD_FORWARD_ADDR},
		{ "OpenSSH_3.*",	SSH_OLD_FORWARD_ADDR },
		{ "Sun_SSH_1.0*",	SSH_BUG_NOREKEY|SSH_BUG_EXTEOF},
		{ "OpenSSH_4*",		0 },
		{ "OpenSSH_5*",		SSH_NEW_OPENSSH|SSH_BUG_DYNAMIC_RPORT},
		{ "OpenSSH_6.5*,"
		  "OpenSSH_6.6",	SSH_NEW_OPENSSH|SSH_BUG_CURVE25519PAD},
		{ "OpenSSH*",		SSH_NEW_OPENSSH },
		{ "*MindTerm*",		0 },
		{ "2.1.0*",		SSH_BUG_SIGBLOB|SSH_BUG_HMAC|
					SSH_OLD_SESSIONID|SSH_BUG_DEBUG|
					SSH_BUG_RSASIGMD5|SSH_BUG_HBSERVICE|
					SSH_BUG_FIRSTKEX },
		{ "2.1 *",		SSH_BUG_SIGBLOB|SSH_BUG_HMAC|
					SSH_OLD_SESSIONID|SSH_BUG_DEBUG|
					SSH_BUG_RSASIGMD5|SSH_BUG_HBSERVICE|
					SSH_BUG_FIRSTKEX },
		{ "2.0.13*,"
		  "2.0.14*,"
		  "2.0.15*,"
		  "2.0.16*,"
		  "2.0.17*,"
		  "2.0.18*,"
		  "2.0.19*",		SSH_BUG_SIGBLOB|SSH_BUG_HMAC|
					SSH_OLD_SESSIONID|SSH_BUG_DEBUG|
					SSH_BUG_PKSERVICE|SSH_BUG_X11FWD|
					SSH_BUG_PKOK|SSH_BUG_RSASIGMD5|
					SSH_BUG_HBSERVICE|SSH_BUG_OPENFAILURE|
					SSH_BUG_DUMMYCHAN|SSH_BUG_FIRSTKEX },
		{ "2.0.11*,"
		  "2.0.12*",		SSH_BUG_SIGBLOB|SSH_BUG_HMAC|
					SSH_OLD_SESSIONID|SSH_BUG_DEBUG|
					SSH_BUG_PKSERVICE|SSH_BUG_X11FWD|
					SSH_BUG_PKAUTH|SSH_BUG_PKOK|
					SSH_BUG_RSASIGMD5|SSH_BUG_OPENFAILURE|
					SSH_BUG_DUMMYCHAN|SSH_BUG_FIRSTKEX },
		{ "2.0.*",		SSH_BUG_SIGBLOB|SSH_BUG_HMAC|
					SSH_OLD_SESSIONID|SSH_BUG_DEBUG|
					SSH_BUG_PKSERVICE|SSH_BUG_X11FWD|
					SSH_BUG_PKAUTH|SSH_BUG_PKOK|
					SSH_BUG_RSASIGMD5|SSH_BUG_OPENFAILURE|
					SSH_BUG_DERIVEKEY|SSH_BUG_DUMMYCHAN|
					SSH_BUG_FIRSTKEX },
		{ "2.2.0*,"
		  "2.3.0*",		SSH_BUG_HMAC|SSH_BUG_DEBUG|
					SSH_BUG_RSASIGMD5|SSH_BUG_FIRSTKEX },
		{ "2.3.*",		SSH_BUG_DEBUG|SSH_BUG_RSASIGMD5|
					SSH_BUG_FIRSTKEX },
		{ "2.4",		SSH_OLD_SESSIONID },	/* Van Dyke */
		{ "2.*",		SSH_BUG_DEBUG|SSH_BUG_FIRSTKEX|
					SSH_BUG_RFWD_ADDR },
		{ "3.0.*",		SSH_BUG_DEBUG },
		{ "3.0 SecureCRT*",	SSH_OLD_SESSIONID },
		{ "1.7 SecureFX*",	SSH_OLD_SESSIONID },
		{ "1.2.18*,"
		  "1.2.19*,"
		  "1.2.20*,"
		  "1.2.21*,"
		  "1.2.22*",		SSH_BUG_IGNOREMSG },
		{ "1.3.2*",		/* F-Secure */
					SSH_BUG_IGNOREMSG },
		{ "*SSH Compatible Server*",			/* Netscreen */
					SSH_BUG_PASSWORDPAD },
		{ "*OSU_0*,"
		  "OSU_1.0*,"
		  "OSU_1.1*,"
		  "OSU_1.2*,"
		  "OSU_1.3*,"
		  "OSU_1.4*,"
		  "OSU_1.5alpha1*,"
		  "OSU_1.5alpha2*,"
		  "OSU_1.5alpha3*",	SSH_BUG_PASSWORDPAD },
		{ "*SSH_Version_Mapper*",
					SSH_BUG_SCANNER },
		{ "Probe-*",
					SSH_BUG_PROBE },
		{ NULL,			0 }
	};

	/* process table, return first match */
	for (i = 0; check[i].pat; i++) {
		if (match_pattern_list(version, check[i].pat,
		    strlen(check[i].pat), 0) == 1) {
			datafellows = check[i].bugs;
			debug("match: %s pat %s compat 0x%08x",
			    version, check[i].pat, datafellows);
			return;
		}
	}
	debug("no match: %s", version);
}

#define	SEP	","
int
proto_spec(const char *spec)
{
	char *s, *p, *q;
	int ret = SSH_PROTO_UNKNOWN;

	if (spec == NULL)
		return ret;
	q = s = xstrdup(spec);
	for ((p = strsep(&q, SEP)); p && *p != '\0'; (p = strsep(&q, SEP))) {
		switch (atoi(p)) {
		case 1:
			if (ret == SSH_PROTO_UNKNOWN)
				ret |= SSH_PROTO_1_PREFERRED;
			ret |= SSH_PROTO_1;
			break;
		case 2:
			ret |= SSH_PROTO_2;
			break;
		default:
			logit("ignoring bad proto spec: '%s'.", p);
			break;
		}
	}
	free(s);
	return ret;
}

/*
 * Filters a proposal string, excluding any algorithm matching the 'filter'
 * pattern list.
 */
static char *
filter_proposal(char *proposal, const char *filter)
{
	Buffer b;
	char *orig_prop, *fix_prop;
	char *cp, *tmp;

	buffer_init(&b);
	tmp = orig_prop = xstrdup(proposal);
	while ((cp = strsep(&tmp, ",")) != NULL) {
		if (match_pattern_list(cp, filter, strlen(cp), 0) != 1) {
			if (buffer_len(&b) > 0)
				buffer_append(&b, ",", 1);
			buffer_append(&b, cp, strlen(cp));
		} else
			debug2("Compat: skipping algorithm \"%s\"", cp);
	}
	buffer_append(&b, "\0", 1);
	fix_prop = xstrdup(buffer_ptr(&b));
	buffer_free(&b);
	free(orig_prop);

	return fix_prop;
}

char *
compat_cipher_proposal(char *cipher_prop)
{
	if (!(datafellows & SSH_BUG_BIGENDIANAES))
		return cipher_prop;
	debug2("%s: original cipher proposal: %s", __func__, cipher_prop);
	cipher_prop = filter_proposal(cipher_prop, "aes*");
	debug2("%s: compat cipher proposal: %s", __func__, cipher_prop);
	if (*cipher_prop == '\0')
		fatal("No supported ciphers found");
	return cipher_prop;
}

char *
compat_pkalg_proposal(char *pkalg_prop)
{
	if (!(datafellows & SSH_BUG_RSASIGMD5))
		return pkalg_prop;
	debug2("%s: original public key proposal: %s", __func__, pkalg_prop);
	pkalg_prop = filter_proposal(pkalg_prop, "ssh-rsa");
	debug2("%s: compat public key proposal: %s", __func__, pkalg_prop);
	if (*pkalg_prop == '\0')
		fatal("No supported PK algorithms found");
	return pkalg_prop;
}

char *
compat_kex_proposal(char *kex_prop)
{
	if (!(datafellows & SSH_BUG_CURVE25519PAD))
		return kex_prop;
	debug2("%s: original KEX proposal: %s", __func__, kex_prop);
	kex_prop = filter_proposal(kex_prop, "curve25519-sha256@libssh.org");
	debug2("%s: compat KEX proposal: %s", __func__, kex_prop);
	if (*kex_prop == '\0')
		fatal("No supported key exchange algorithms found");
	return kex_prop;
}