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Refactor creation of KEX proposal.

This adds kex_proposal_populate_entries (and corresponding free) which
populates the KEX proposal array with dynamically allocated strings.
This replaces the previous mix of static and dynamic that has been the
source of previous leaks and bugs.  Remove unused compat functions.
With & ok djm@.

/* $OpenBSD: compat.c,v 1.126 2023/03/06 12:14:48 dtucker 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 "packet.h"
#include "compat.h"
#include "log.h"
#include "match.h"

/* determine bug flags from SSH protocol banner */
void
compat_banner(struct ssh *ssh, const char *version)
{
	int i;
	static struct {
		char	*pat;
		int	bugs;
	} check[] = {
		{ "OpenSSH_2.*,"
		  "OpenSSH_3.0*,"
		  "OpenSSH_3.1*",	SSH_BUG_EXTEOF|SSH_OLD_FORWARD_ADDR|
					SSH_BUG_SIGTYPE},
		{ "OpenSSH_3.*",	SSH_OLD_FORWARD_ADDR|SSH_BUG_SIGTYPE },
		{ "Sun_SSH_1.0*",	SSH_BUG_NOREKEY|SSH_BUG_EXTEOF|
					SSH_BUG_SIGTYPE},
		{ "OpenSSH_2*,"
		  "OpenSSH_3*,"
		  "OpenSSH_4*",		SSH_BUG_SIGTYPE },
		{ "OpenSSH_5*",		SSH_NEW_OPENSSH|SSH_BUG_DYNAMIC_RPORT|
					SSH_BUG_SIGTYPE},
		{ "OpenSSH_6.6.1*",	SSH_NEW_OPENSSH|SSH_BUG_SIGTYPE},
		{ "OpenSSH_6.5*,"
		  "OpenSSH_6.6*",	SSH_NEW_OPENSSH|SSH_BUG_CURVE25519PAD|
					SSH_BUG_SIGTYPE},
		{ "OpenSSH_7.4*",	SSH_NEW_OPENSSH|SSH_BUG_SIGTYPE|
					SSH_BUG_SIGTYPE74},
		{ "OpenSSH_7.0*,"
		  "OpenSSH_7.1*,"
		  "OpenSSH_7.2*,"
		  "OpenSSH_7.3*,"
		  "OpenSSH_7.5*,"
		  "OpenSSH_7.6*,"
		  "OpenSSH_7.7*",	SSH_NEW_OPENSSH|SSH_BUG_SIGTYPE},
		{ "OpenSSH*",		SSH_NEW_OPENSSH },
		{ "*MindTerm*",		0 },
		{ "3.0.*",		SSH_BUG_DEBUG },
		{ "3.0 SecureCRT*",	SSH_OLD_SESSIONID },
		{ "1.7 SecureFX*",	SSH_OLD_SESSIONID },
		{ "Cisco-1.*",		SSH_BUG_DHGEX_LARGE|
					SSH_BUG_HOSTKEYS },
		{ "*SSH_Version_Mapper*",
					SSH_BUG_SCANNER },
		{ "PuTTY_Local:*,"	/* dev versions < Sep 2014 */
		  "PuTTY-Release-0.5*," /* 0.50-0.57, DH-GEX in >=0.52 */
		  "PuTTY_Release_0.5*,"	/* 0.58-0.59 */
		  "PuTTY_Release_0.60*,"
		  "PuTTY_Release_0.61*,"
		  "PuTTY_Release_0.62*,"
		  "PuTTY_Release_0.63*,"
		  "PuTTY_Release_0.64*",
					SSH_OLD_DHGEX },
		{ "FuTTY*",		SSH_OLD_DHGEX }, /* Putty Fork */
		{ "Probe-*",
					SSH_BUG_PROBE },
		{ "TeraTerm SSH*,"
		  "TTSSH/1.5.*,"
		  "TTSSH/2.1*,"
		  "TTSSH/2.2*,"
		  "TTSSH/2.3*,"
		  "TTSSH/2.4*,"
		  "TTSSH/2.5*,"
		  "TTSSH/2.6*,"
		  "TTSSH/2.70*,"
		  "TTSSH/2.71*,"
		  "TTSSH/2.72*",	SSH_BUG_HOSTKEYS },
		{ "WinSCP_release_4*,"
		  "WinSCP_release_5.0*,"
		  "WinSCP_release_5.1,"
		  "WinSCP_release_5.1.*,"
		  "WinSCP_release_5.5,"
		  "WinSCP_release_5.5.*,"
		  "WinSCP_release_5.6,"
		  "WinSCP_release_5.6.*,"
		  "WinSCP_release_5.7,"
		  "WinSCP_release_5.7.1,"
		  "WinSCP_release_5.7.2,"
		  "WinSCP_release_5.7.3,"
		  "WinSCP_release_5.7.4",
					SSH_OLD_DHGEX },
		{ "ConfD-*",
					SSH_BUG_UTF8TTYMODE },
		{ "Twisted_*",		0 },
		{ "Twisted*",		SSH_BUG_DEBUG },
		{ NULL,			0 }
	};

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

/* Always returns pointer to allocated memory, caller must free. */
char *
compat_kex_proposal(struct ssh *ssh, const char *p)
{
	char *cp = NULL, *cp2 = NULL;

	if ((ssh->compat & (SSH_BUG_CURVE25519PAD|SSH_OLD_DHGEX)) == 0)
		return xstrdup(p);
	debug2_f("original KEX proposal: %s", p);
	if ((ssh->compat & SSH_BUG_CURVE25519PAD) != 0)
		if ((cp = match_filter_denylist(p,
		    "curve25519-sha256@libssh.org")) == NULL)
			fatal("match_filter_denylist failed");
	if ((ssh->compat & SSH_OLD_DHGEX) != 0) {
		if ((cp2 = match_filter_denylist(cp ? cp : p,
		    "diffie-hellman-group-exchange-sha256,"
		    "diffie-hellman-group-exchange-sha1")) == NULL)
			fatal("match_filter_denylist failed");
		free(cp);
		cp = cp2;
	}
	if (cp == NULL || *cp == '\0')
		fatal("No supported key exchange algorithms found");
	debug2_f("compat KEX proposal: %s", cp);
	return cp;
}