compat.c - platform/external/openssh - Gitiles

 /* $OpenBSD: compat.c,v 1.85 2014/04/20 02:49:32 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 "includes.h"

 #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_6.6.1*",	SSH_NEW_OPENSSH},
 		{ "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;
 }
	/* $OpenBSD: compat.c,v 1.85 2014/04/20 02:49:32 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 "includes.h"

	#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_6.6.1*", SSH_NEW_OPENSSH},
	{ "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;
	}