auth2-hostbased.c - third_party/openssh-portable - Git at Google

 /* $OpenBSD: auth2-hostbased.c,v 1.26 2016/03/07 19:02:43 djm Exp $ */
 /*
  * Copyright (c) 2000 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 <pwd.h>
 #include <string.h>
 #include <stdarg.h>

 #include "xmalloc.h"
 #include "ssh2.h"
 #include "packet.h"
 #include "buffer.h"
 #include "log.h"
 #include "misc.h"
 #include "servconf.h"
 #include "compat.h"
 #include "key.h"
 #include "hostfile.h"
 #include "auth.h"
 #include "canohost.h"
 #ifdef GSSAPI
 #include "ssh-gss.h"
 #endif
 #include "monitor_wrap.h"
 #include "pathnames.h"
 #include "match.h"

 /* import */
 extern ServerOptions options;
 extern u_char *session_id2;
 extern u_int session_id2_len;

 static int
 userauth_hostbased(Authctxt *authctxt)
 {
 	Buffer b;
 	Key *key = NULL;
 	char *pkalg, *cuser, *chost, *service;
 	u_char *pkblob, *sig;
 	u_int alen, blen, slen;
 	int pktype;
 	int authenticated = 0;

 	if (!authctxt->valid) {
 		debug2("userauth_hostbased: disabled because of invalid user");
 		return 0;
 	}
 	pkalg = packet_get_string(&alen);
 	pkblob = packet_get_string(&blen);
 	chost = packet_get_string(NULL);
 	cuser = packet_get_string(NULL);
 	sig = packet_get_string(&slen);

 	debug("userauth_hostbased: cuser %s chost %s pkalg %s slen %d",
 	    cuser, chost, pkalg, slen);
 #ifdef DEBUG_PK
 	debug("signature:");
 	buffer_init(&b);
 	buffer_append(&b, sig, slen);
 	buffer_dump(&b);
 	buffer_free(&b);
 #endif
 	pktype = key_type_from_name(pkalg);
 	if (pktype == KEY_UNSPEC) {
 		/* this is perfectly legal */
 		logit("userauth_hostbased: unsupported "
 		    "public key algorithm: %s", pkalg);
 		goto done;
 	}
 	key = key_from_blob(pkblob, blen);
 	if (key == NULL) {
 		error("userauth_hostbased: cannot decode key: %s", pkalg);
 		goto done;
 	}
 	if (key->type != pktype) {
 		error("userauth_hostbased: type mismatch for decoded key "
 		    "(received %d, expected %d)", key->type, pktype);
 		goto done;
 	}
 	if (key_type_plain(key->type) == KEY_RSA &&
 	    (datafellows & SSH_BUG_RSASIGMD5) != 0) {
 		error("Refusing RSA key because peer uses unsafe "
 		    "signature format");
 		goto done;
 	}
 	if (match_pattern_list(sshkey_ssh_name(key),
 	    options.hostbased_key_types, 0) != 1) {
 		logit("%s: key type %s not in HostbasedAcceptedKeyTypes",
 		    __func__, sshkey_type(key));
 		goto done;
 	}

 	service = datafellows & SSH_BUG_HBSERVICE ? "ssh-userauth" :
 	    authctxt->service;
 	buffer_init(&b);
 	buffer_put_string(&b, session_id2, session_id2_len);
 	/* reconstruct packet */
 	buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
 	buffer_put_cstring(&b, authctxt->user);
 	buffer_put_cstring(&b, service);
 	buffer_put_cstring(&b, "hostbased");
 	buffer_put_string(&b, pkalg, alen);
 	buffer_put_string(&b, pkblob, blen);
 	buffer_put_cstring(&b, chost);
 	buffer_put_cstring(&b, cuser);
 #ifdef DEBUG_PK
 	buffer_dump(&b);
 #endif

 	pubkey_auth_info(authctxt, key,
 	    "client user \"%.100s\", client host \"%.100s\"", cuser, chost);

 	/* test for allowed key and correct signature */
 	authenticated = 0;
 	if (PRIVSEP(hostbased_key_allowed(authctxt->pw, cuser, chost, key)) &&
 	    PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
 			buffer_len(&b))) == 1)
 		authenticated = 1;

 	buffer_free(&b);
 done:
 	debug2("userauth_hostbased: authenticated %d", authenticated);
 	if (key != NULL)
 		key_free(key);
 	free(pkalg);
 	free(pkblob);
 	free(cuser);
 	free(chost);
 	free(sig);
 	return authenticated;
 }

 /* return 1 if given hostkey is allowed */
 int
 hostbased_key_allowed(struct passwd *pw, const char *cuser, char *chost,
     Key *key)
 {
 	struct ssh *ssh = active_state; /* XXX */
 	const char *resolvedname, *ipaddr, *lookup, *reason;
 	HostStatus host_status;
 	int len;
 	char *fp;

 	if (auth_key_is_revoked(key))
 		return 0;

 	resolvedname = auth_get_canonical_hostname(ssh, options.use_dns);
 	ipaddr = ssh_remote_ipaddr(ssh);

 	debug2("%s: chost %s resolvedname %s ipaddr %s", __func__,
 	    chost, resolvedname, ipaddr);

 	if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') {
 		debug2("stripping trailing dot from chost %s", chost);
 		chost[len - 1] = '\0';
 	}

 	if (options.hostbased_uses_name_from_packet_only) {
 		if (auth_rhosts2(pw, cuser, chost, chost) == 0) {
 			debug2("%s: auth_rhosts2 refused "
 			    "user \"%.100s\" host \"%.100s\" (from packet)",
 			    __func__, cuser, chost);
 			return 0;
 		}
 		lookup = chost;
 	} else {
 		if (strcasecmp(resolvedname, chost) != 0)
 			logit("userauth_hostbased mismatch: "
 			    "client sends %s, but we resolve %s to %s",
 			    chost, ipaddr, resolvedname);
 		if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0) {
 			debug2("%s: auth_rhosts2 refused "
 			    "user \"%.100s\" host \"%.100s\" addr \"%.100s\"",
 			    __func__, cuser, resolvedname, ipaddr);
 			return 0;
 		}
 		lookup = resolvedname;
 	}
 	debug2("%s: access allowed by auth_rhosts2", __func__);

 	if (key_is_cert(key) &&
 	    key_cert_check_authority(key, 1, 0, lookup, &reason)) {
 		error("%s", reason);
 		auth_debug_add("%s", reason);
 		return 0;
 	}

 	host_status = check_key_in_hostfiles(pw, key, lookup,
 	    _PATH_SSH_SYSTEM_HOSTFILE,
 	    options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE);

 	/* backward compat if no key has been found. */
 	if (host_status == HOST_NEW) {
 		host_status = check_key_in_hostfiles(pw, key, lookup,
 		    _PATH_SSH_SYSTEM_HOSTFILE2,
 		    options.ignore_user_known_hosts ? NULL :
 		    _PATH_SSH_USER_HOSTFILE2);
 	}

 	if (host_status == HOST_OK) {
 		if (key_is_cert(key)) {
 			if ((fp = sshkey_fingerprint(key->cert->signature_key,
 			    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
 				fatal("%s: sshkey_fingerprint fail", __func__);
 			verbose("Accepted certificate ID \"%s\" signed by "
 			    "%s CA %s from %s@%s", key->cert->key_id,
 			    key_type(key->cert->signature_key), fp,
 			    cuser, lookup);
 		} else {
 			if ((fp = sshkey_fingerprint(key,
 			    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
 				fatal("%s: sshkey_fingerprint fail", __func__);
 			verbose("Accepted %s public key %s from %s@%s",
 			    key_type(key), fp, cuser, lookup);
 		}
 		free(fp);
 	}

 	return (host_status == HOST_OK);
 }

 Authmethod method_hostbased = {
 	"hostbased",
 	userauth_hostbased,
 	&options.hostbased_authentication
 };
	/* $OpenBSD: auth2-hostbased.c,v 1.26 2016/03/07 19:02:43 djm Exp $ */
	/*
	* Copyright (c) 2000 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 <pwd.h>
	#include <string.h>
	#include <stdarg.h>

	#include "xmalloc.h"
	#include "ssh2.h"
	#include "packet.h"
	#include "buffer.h"
	#include "log.h"
	#include "misc.h"
	#include "servconf.h"
	#include "compat.h"
	#include "key.h"
	#include "hostfile.h"
	#include "auth.h"
	#include "canohost.h"
	#ifdef GSSAPI
	#include "ssh-gss.h"
	#endif
	#include "monitor_wrap.h"
	#include "pathnames.h"
	#include "match.h"

	/* import */
	extern ServerOptions options;
	extern u_char *session_id2;
	extern u_int session_id2_len;

	static int
	userauth_hostbased(Authctxt *authctxt)
	{
	Buffer b;
	Key *key = NULL;
	char pkalg, cuser, chost, service;
	u_char pkblob, sig;
	u_int alen, blen, slen;
	int pktype;
	int authenticated = 0;

	if (!authctxt->valid) {
	debug2("userauth_hostbased: disabled because of invalid user");
	return 0;
	}
	pkalg = packet_get_string(&alen);
	pkblob = packet_get_string(&blen);
	chost = packet_get_string(NULL);
	cuser = packet_get_string(NULL);
	sig = packet_get_string(&slen);

	debug("userauth_hostbased: cuser %s chost %s pkalg %s slen %d",
	cuser, chost, pkalg, slen);
	#ifdef DEBUG_PK
	debug("signature:");
	buffer_init(&b);
	buffer_append(&b, sig, slen);
	buffer_dump(&b);
	buffer_free(&b);
	#endif
	pktype = key_type_from_name(pkalg);
	if (pktype == KEY_UNSPEC) {
	/* this is perfectly legal */
	logit("userauth_hostbased: unsupported "
	"public key algorithm: %s", pkalg);
	goto done;
	}
	key = key_from_blob(pkblob, blen);
	if (key == NULL) {
	error("userauth_hostbased: cannot decode key: %s", pkalg);
	goto done;
	}
	if (key->type != pktype) {
	error("userauth_hostbased: type mismatch for decoded key "
	"(received %d, expected %d)", key->type, pktype);
	goto done;
	}
	if (key_type_plain(key->type) == KEY_RSA &&
	(datafellows & SSH_BUG_RSASIGMD5) != 0) {
	error("Refusing RSA key because peer uses unsafe "
	"signature format");
	goto done;
	}
	if (match_pattern_list(sshkey_ssh_name(key),
	options.hostbased_key_types, 0) != 1) {
	logit("%s: key type %s not in HostbasedAcceptedKeyTypes",
	__func__, sshkey_type(key));
	goto done;
	}

	service = datafellows & SSH_BUG_HBSERVICE ? "ssh-userauth" :
	authctxt->service;
	buffer_init(&b);
	buffer_put_string(&b, session_id2, session_id2_len);
	/* reconstruct packet */
	buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
	buffer_put_cstring(&b, authctxt->user);
	buffer_put_cstring(&b, service);
	buffer_put_cstring(&b, "hostbased");
	buffer_put_string(&b, pkalg, alen);
	buffer_put_string(&b, pkblob, blen);
	buffer_put_cstring(&b, chost);
	buffer_put_cstring(&b, cuser);
	#ifdef DEBUG_PK
	buffer_dump(&b);
	#endif

	pubkey_auth_info(authctxt, key,
	"client user \"%.100s\", client host \"%.100s\"", cuser, chost);

	/* test for allowed key and correct signature */
	authenticated = 0;
	if (PRIVSEP(hostbased_key_allowed(authctxt->pw, cuser, chost, key)) &&
	PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
	buffer_len(&b))) == 1)
	authenticated = 1;

	buffer_free(&b);
	done:
	debug2("userauth_hostbased: authenticated %d", authenticated);
	if (key != NULL)
	key_free(key);
	free(pkalg);
	free(pkblob);
	free(cuser);
	free(chost);
	free(sig);
	return authenticated;
	}

	/* return 1 if given hostkey is allowed */
	int
	hostbased_key_allowed(struct passwd pw, const char cuser, char *chost,
	Key *key)
	{
	struct ssh ssh = active_state; / XXX */
	const char resolvedname, ipaddr, lookup, reason;
	HostStatus host_status;
	int len;
	char *fp;

	if (auth_key_is_revoked(key))
	return 0;

	resolvedname = auth_get_canonical_hostname(ssh, options.use_dns);
	ipaddr = ssh_remote_ipaddr(ssh);

	debug2("%s: chost %s resolvedname %s ipaddr %s", __func__,
	chost, resolvedname, ipaddr);

	if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') {
	debug2("stripping trailing dot from chost %s", chost);
	chost[len - 1] = '\0';
	}

	if (options.hostbased_uses_name_from_packet_only) {
	if (auth_rhosts2(pw, cuser, chost, chost) == 0) {
	debug2("%s: auth_rhosts2 refused "
	"user \"%.100s\" host \"%.100s\" (from packet)",
	__func__, cuser, chost);
	return 0;
	}
	lookup = chost;
	} else {
	if (strcasecmp(resolvedname, chost) != 0)
	logit("userauth_hostbased mismatch: "
	"client sends %s, but we resolve %s to %s",
	chost, ipaddr, resolvedname);
	if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0) {
	debug2("%s: auth_rhosts2 refused "
	"user \"%.100s\" host \"%.100s\" addr \"%.100s\"",
	__func__, cuser, resolvedname, ipaddr);
	return 0;
	}
	lookup = resolvedname;
	}
	debug2("%s: access allowed by auth_rhosts2", __func__);

	if (key_is_cert(key) &&
	key_cert_check_authority(key, 1, 0, lookup, &reason)) {
	error("%s", reason);
	auth_debug_add("%s", reason);
	return 0;
	}

	host_status = check_key_in_hostfiles(pw, key, lookup,
	_PATH_SSH_SYSTEM_HOSTFILE,
	options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE);

	/* backward compat if no key has been found. */
	if (host_status == HOST_NEW) {
	host_status = check_key_in_hostfiles(pw, key, lookup,
	_PATH_SSH_SYSTEM_HOSTFILE2,
	options.ignore_user_known_hosts ? NULL :
	_PATH_SSH_USER_HOSTFILE2);
	}

	if (host_status == HOST_OK) {
	if (key_is_cert(key)) {
	if ((fp = sshkey_fingerprint(key->cert->signature_key,
	options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
	fatal("%s: sshkey_fingerprint fail", __func__);
	verbose("Accepted certificate ID \"%s\" signed by "
	"%s CA %s from %s@%s", key->cert->key_id,
	key_type(key->cert->signature_key), fp,
	cuser, lookup);
	} else {
	if ((fp = sshkey_fingerprint(key,
	options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
	fatal("%s: sshkey_fingerprint fail", __func__);
	verbose("Accepted %s public key %s from %s@%s",
	key_type(key), fp, cuser, lookup);
	}
	free(fp);
	}

	return (host_status == HOST_OK);
	}

	Authmethod method_hostbased = {
	"hostbased",
	userauth_hostbased,
	&options.hostbased_authentication
	};