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/* $OpenBSD: auth2-hostbased.c,v 1.47 2021/07/23 03:37:52 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 <sys/types.h>
#include <stdlib.h>
#include <pwd.h>
#include <string.h>
#include <stdarg.h>
#include "xmalloc.h"
#include "ssh2.h"
#include "packet.h"
#include "kex.h"
#include "sshbuf.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;
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;
/* 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_fr(r, "parse packet");
debug_f("cuser %s chost %s pkalg %s slen %zu",
cuser, chost, pkalg, slen);
#ifdef DEBUG_PK
debug("signature:");
sshbuf_dump_data(sig, slen, stderr);
#endif
pktype = sshkey_type_from_name(pkalg);
if (pktype == KEY_UNSPEC) {
/* this is perfectly legal */
logit_f("unsupported public key algorithm: %s",
pkalg);
goto done;
}
if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {
error_fr(r, "key_from_blob");
goto done;
}
if (key == NULL) {
error_f("cannot decode key: %s", pkalg);
goto done;
}
if (key->type != pktype) {
error_f("type mismatch for decoded key "
"(received %d, expected %d)", 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(pkalg, options.hostbased_accepted_algos, 0) != 1) {
logit_f("key type %s not in HostbasedAcceptedAlgorithms",
sshkey_type(key));
goto done;
}
if ((r = sshkey_check_cert_sigtype(key,
options.ca_sign_algorithms)) != 0) {
logit_fr(r, "certificate signature algorithm %s",
(key->cert == NULL || key->cert->signature_type == NULL) ?
"(null)" : key->cert->signature_type);
goto done;
}
if (!authctxt->valid || authctxt->user == NULL) {
debug2_f("disabled because of invalid user");
goto done;
}
if ((b = sshbuf_new()) == NULL)
fatal_f("sshbuf_new failed");
/* reconstruct packet */
if ((r = sshbuf_put_stringb(b, ssh->kex->session_id)) != 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_fr(r, "reconstruct packet");
#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(ssh, authctxt->pw, cuser,
chost, key)) &&
PRIVSEP(sshkey_verify(key, sig, slen,
sshbuf_ptr(b), sshbuf_len(b), pkalg, ssh->compat, NULL)) == 0)
authenticated = 1;
auth2_record_key(authctxt, authenticated, key);
sshbuf_free(b);
done:
debug2_f("authenticated %d", 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 ssh *ssh, struct passwd *pw,
const char *cuser, char *chost, struct sshkey *key)
{
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_f("chost %s resolvedname %s ipaddr %s",
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_f("auth_rhosts2 refused user \"%.100s\" "
"host \"%.100s\" (from packet)", 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_f("auth_rhosts2 refused "
"user \"%.100s\" host \"%.100s\" addr \"%.100s\"",
cuser, resolvedname, ipaddr);
return 0;
}
lookup = resolvedname;
}
debug2_f("access allowed by auth_rhosts2");
if (sshkey_is_cert(key) &&
sshkey_cert_check_authority_now(key, 1, 0, 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_f("sshkey_fingerprint fail");
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_f("sshkey_fingerprint fail");
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
};
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