/* $OpenBSD: auth2-hostbased.c,v 1.33 2018/01/23 05:27:21 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 "sshkey.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 "ssherr.h"

#include "match.h"

/* import */

extern ServerOptions options;

extern u_char *session_id2;

extern u_int session_id2_len;

static int

userauth_hostbased(struct ssh *ssh)

{

Authctxt *authctxt = ssh->authctxt;

struct sshbuf *b;

struct sshkey *key = NULL;

char *pkalg, *cuser, *chost;

u_char *pkblob, *sig;

size_t alen, blen, slen;

int r, pktype, authenticated = 0;

if (!authctxt->valid) {

debug2("%s: disabled because of invalid user", __func__);

return 0;

}

/* XXX use sshkey_froms() */

if ((r = sshpkt_get_cstring(ssh, &pkalg, &alen)) != 0 ||

(r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0 ||

(r = sshpkt_get_cstring(ssh, &chost, NULL)) != 0 ||

(r = sshpkt_get_cstring(ssh, &cuser, NULL)) != 0 ||

(r = sshpkt_get_string(ssh, &sig, &slen)) != 0)

fatal("%s: packet parsing: %s", __func__, ssh_err(r));

debug("%s: cuser %s chost %s pkalg %s slen %zu", __func__,

cuser, chost, pkalg, slen);

#ifdef DEBUG_PK

debug("signature:");

sshbuf_dump_data(sig, siglen, stderr);

#endif

pktype = sshkey_type_from_name(pkalg);

if (pktype == KEY_UNSPEC) {

/* this is perfectly legal */

logit("%s: unsupported public key algorithm: %s",

__func__, pkalg);

goto done;

}

if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {

error("%s: key_from_blob: %s", __func__, ssh_err(r));

goto done;

}

if (key == NULL) {

error("%s: cannot decode key: %s", __func__, pkalg);

goto done;

}

if (key->type != pktype) {

error("%s: type mismatch for decoded key "

"(received %d, expected %d)", __func__, key->type, pktype);

goto done;

}

if (sshkey_type_plain(key->type) == KEY_RSA &&

(ssh->compat & 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;

}

if ((b = sshbuf_new()) == NULL)

fatal("%s: sshbuf_new failed", __func__);

/* reconstruct packet */

if ((r = sshbuf_put_string(b, session_id2, session_id2_len)) != 0 ||

(r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 ||

(r = sshbuf_put_cstring(b, authctxt->user)) != 0 ||

(r = sshbuf_put_cstring(b, authctxt->service)) != 0 ||

(r = sshbuf_put_cstring(b, "hostbased")) != 0 ||

(r = sshbuf_put_string(b, pkalg, alen)) != 0 ||

(r = sshbuf_put_string(b, pkblob, blen)) != 0 ||

(r = sshbuf_put_cstring(b, chost)) != 0 ||

(r = sshbuf_put_cstring(b, cuser)) != 0)

fatal("%s: buffer error: %s", __func__, ssh_err(r));

#ifdef DEBUG_PK

sshbuf_dump(b, stderr);

#endif

auth2_record_info(authctxt,

"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(sshkey_verify(key, sig, slen,

sshbuf_ptr(b), sshbuf_len(b), pkalg, ssh->compat)) == 0)

authenticated = 1;

auth2_record_key(authctxt, authenticated, key);

sshbuf_free(b);

done:

debug2("%s: authenticated %d", __func__, authenticated);

sshkey_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,

struct sshkey *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 (sshkey_is_cert(key) &&

sshkey_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 (sshkey_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,

sshkey_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",

sshkey_type(key), fp, cuser, lookup);

}

free(fp);

}

return (host_status == HOST_OK);

}

Authmethod method_hostbased = {

"hostbased",

userauth_hostbased,

&options.hostbased_authentication

};