1/* $OpenBSD: auth2-hostbased.c,v 1.38 2018/09/20 03:28:06 djm Exp $ */
2/*
3 * Copyright (c) 2000 Markus Friedl.  All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
15 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
16 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
17 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
18 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
19 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
20 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
21 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24 */
25
26#include "includes.h"
27
28#include <sys/types.h>
29
30#include <pwd.h>
31#include <string.h>
32#include <stdarg.h>
33
34#include "xmalloc.h"
35#include "ssh2.h"
36#include "packet.h"
37#include "sshbuf.h"
38#include "log.h"
39#include "misc.h"
40#include "servconf.h"
41#include "compat.h"
42#include "sshkey.h"
43#include "hostfile.h"
44#include "auth.h"
45#include "canohost.h"
46#ifdef GSSAPI
47#include "ssh-gss.h"
48#endif
49#include "monitor_wrap.h"
50#include "pathnames.h"
51#include "ssherr.h"
52#include "match.h"
53
54/* import */
55extern ServerOptions options;
56extern u_char *session_id2;
57extern u_int session_id2_len;
58
59static int
60userauth_hostbased(struct ssh *ssh)
61{
62	Authctxt *authctxt = ssh->authctxt;
63	struct sshbuf *b;
64	struct sshkey *key = NULL;
65	char *pkalg, *cuser, *chost;
66	u_char *pkblob, *sig;
67	size_t alen, blen, slen;
68	int r, pktype, authenticated = 0;
69
70	/* XXX use sshkey_froms() */
71	if ((r = sshpkt_get_cstring(ssh, &pkalg, &alen)) != 0 ||
72	    (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0 ||
73	    (r = sshpkt_get_cstring(ssh, &chost, NULL)) != 0 ||
74	    (r = sshpkt_get_cstring(ssh, &cuser, NULL)) != 0 ||
75	    (r = sshpkt_get_string(ssh, &sig, &slen)) != 0)
76		fatal("%s: packet parsing: %s", __func__, ssh_err(r));
77
78	debug("%s: cuser %s chost %s pkalg %s slen %zu", __func__,
79	    cuser, chost, pkalg, slen);
80#ifdef DEBUG_PK
81	debug("signature:");
82	sshbuf_dump_data(sig, slen, stderr);
83#endif
84	pktype = sshkey_type_from_name(pkalg);
85	if (pktype == KEY_UNSPEC) {
86		/* this is perfectly legal */
87		logit("%s: unsupported public key algorithm: %s",
88		    __func__, pkalg);
89		goto done;
90	}
91	if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {
92		error("%s: key_from_blob: %s", __func__, ssh_err(r));
93		goto done;
94	}
95	if (key == NULL) {
96		error("%s: cannot decode key: %s", __func__, pkalg);
97		goto done;
98	}
99	if (key->type != pktype) {
100		error("%s: type mismatch for decoded key "
101		    "(received %d, expected %d)", __func__, key->type, pktype);
102		goto done;
103	}
104	if (sshkey_type_plain(key->type) == KEY_RSA &&
105	    (ssh->compat & SSH_BUG_RSASIGMD5) != 0) {
106		error("Refusing RSA key because peer uses unsafe "
107		    "signature format");
108		goto done;
109	}
110	if (match_pattern_list(pkalg, options.hostbased_key_types, 0) != 1) {
111		logit("%s: key type %s not in HostbasedAcceptedKeyTypes",
112		    __func__, sshkey_type(key));
113		goto done;
114	}
115	if ((r = sshkey_check_cert_sigtype(key,
116	    options.ca_sign_algorithms)) != 0) {
117		logit("%s: certificate signature algorithm %s: %s", __func__,
118		    (key->cert == NULL || key->cert->signature_type == NULL) ?
119		    "(null)" : key->cert->signature_type, ssh_err(r));
120		goto done;
121	}
122
123	if (!authctxt->valid || authctxt->user == NULL) {
124		debug2("%s: disabled because of invalid user", __func__);
125		goto done;
126	}
127
128	if ((b = sshbuf_new()) == NULL)
129		fatal("%s: sshbuf_new failed", __func__);
130	/* reconstruct packet */
131	if ((r = sshbuf_put_string(b, session_id2, session_id2_len)) != 0 ||
132	    (r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 ||
133	    (r = sshbuf_put_cstring(b, authctxt->user)) != 0 ||
134	    (r = sshbuf_put_cstring(b, authctxt->service)) != 0 ||
135	    (r = sshbuf_put_cstring(b, "hostbased")) != 0 ||
136	    (r = sshbuf_put_string(b, pkalg, alen)) != 0 ||
137	    (r = sshbuf_put_string(b, pkblob, blen)) != 0 ||
138	    (r = sshbuf_put_cstring(b, chost)) != 0 ||
139	    (r = sshbuf_put_cstring(b, cuser)) != 0)
140		fatal("%s: buffer error: %s", __func__, ssh_err(r));
141#ifdef DEBUG_PK
142	sshbuf_dump(b, stderr);
143#endif
144
145	auth2_record_info(authctxt,
146	    "client user \"%.100s\", client host \"%.100s\"", cuser, chost);
147
148	/* test for allowed key and correct signature */
149	authenticated = 0;
150	if (PRIVSEP(hostbased_key_allowed(authctxt->pw, cuser, chost, key)) &&
151	    PRIVSEP(sshkey_verify(key, sig, slen,
152	    sshbuf_ptr(b), sshbuf_len(b), pkalg, ssh->compat)) == 0)
153		authenticated = 1;
154
155	auth2_record_key(authctxt, authenticated, key);
156	sshbuf_free(b);
157done:
158	debug2("%s: authenticated %d", __func__, authenticated);
159	sshkey_free(key);
160	free(pkalg);
161	free(pkblob);
162	free(cuser);
163	free(chost);
164	free(sig);
165	return authenticated;
166}
167
168/* return 1 if given hostkey is allowed */
169int
170hostbased_key_allowed(struct passwd *pw, const char *cuser, char *chost,
171    struct sshkey *key)
172{
173	struct ssh *ssh = active_state; /* XXX */
174	const char *resolvedname, *ipaddr, *lookup, *reason;
175	HostStatus host_status;
176	int len;
177	char *fp;
178
179	if (auth_key_is_revoked(key))
180		return 0;
181
182	resolvedname = auth_get_canonical_hostname(ssh, options.use_dns);
183	ipaddr = ssh_remote_ipaddr(ssh);
184
185	debug2("%s: chost %s resolvedname %s ipaddr %s", __func__,
186	    chost, resolvedname, ipaddr);
187
188	if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') {
189		debug2("stripping trailing dot from chost %s", chost);
190		chost[len - 1] = '\0';
191	}
192
193	if (options.hostbased_uses_name_from_packet_only) {
194		if (auth_rhosts2(pw, cuser, chost, chost) == 0) {
195			debug2("%s: auth_rhosts2 refused "
196			    "user \"%.100s\" host \"%.100s\" (from packet)",
197			    __func__, cuser, chost);
198			return 0;
199		}
200		lookup = chost;
201	} else {
202		if (strcasecmp(resolvedname, chost) != 0)
203			logit("userauth_hostbased mismatch: "
204			    "client sends %s, but we resolve %s to %s",
205			    chost, ipaddr, resolvedname);
206		if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0) {
207			debug2("%s: auth_rhosts2 refused "
208			    "user \"%.100s\" host \"%.100s\" addr \"%.100s\"",
209			    __func__, cuser, resolvedname, ipaddr);
210			return 0;
211		}
212		lookup = resolvedname;
213	}
214	debug2("%s: access allowed by auth_rhosts2", __func__);
215
216	if (sshkey_is_cert(key) &&
217	    sshkey_cert_check_authority(key, 1, 0, lookup, &reason)) {
218		error("%s", reason);
219		auth_debug_add("%s", reason);
220		return 0;
221	}
222
223	host_status = check_key_in_hostfiles(pw, key, lookup,
224	    _PATH_SSH_SYSTEM_HOSTFILE,
225	    options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE);
226
227	/* backward compat if no key has been found. */
228	if (host_status == HOST_NEW) {
229		host_status = check_key_in_hostfiles(pw, key, lookup,
230		    _PATH_SSH_SYSTEM_HOSTFILE2,
231		    options.ignore_user_known_hosts ? NULL :
232		    _PATH_SSH_USER_HOSTFILE2);
233	}
234
235	if (host_status == HOST_OK) {
236		if (sshkey_is_cert(key)) {
237			if ((fp = sshkey_fingerprint(key->cert->signature_key,
238			    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
239				fatal("%s: sshkey_fingerprint fail", __func__);
240			verbose("Accepted certificate ID \"%s\" signed by "
241			    "%s CA %s from %s@%s", key->cert->key_id,
242			    sshkey_type(key->cert->signature_key), fp,
243			    cuser, lookup);
244		} else {
245			if ((fp = sshkey_fingerprint(key,
246			    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
247				fatal("%s: sshkey_fingerprint fail", __func__);
248			verbose("Accepted %s public key %s from %s@%s",
249			    sshkey_type(key), fp, cuser, lookup);
250		}
251		free(fp);
252	}
253
254	return (host_status == HOST_OK);
255}
256
257Authmethod method_hostbased = {
258	"hostbased",
259	userauth_hostbased,
260	&options.hostbased_authentication
261};
262