1/* $OpenBSD: auth2-hostbased.c,v 1.52 2023/03/05 05:34:09 dtucker 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 <stdlib.h>
31#include <pwd.h>
32#include <string.h>
33#include <stdarg.h>
34
35#include "xmalloc.h"
36#include "ssh2.h"
37#include "packet.h"
38#include "kex.h"
39#include "sshbuf.h"
40#include "log.h"
41#include "misc.h"
42#include "servconf.h"
43#include "sshkey.h"
44#include "hostfile.h"
45#include "auth.h"
46#include "canohost.h"
47#ifdef GSSAPI
48#include "ssh-gss.h"
49#endif
50#include "monitor_wrap.h"
51#include "pathnames.h"
52#include "ssherr.h"
53#include "match.h"
54
55/* import */
56extern ServerOptions options;
57
58static int
59userauth_hostbased(struct ssh *ssh, const char *method)
60{
61	Authctxt *authctxt = ssh->authctxt;
62	struct sshbuf *b;
63	struct sshkey *key = NULL;
64	char *pkalg, *cuser, *chost;
65	u_char *pkblob, *sig;
66	size_t alen, blen, slen;
67	int r, pktype, authenticated = 0;
68
69	/* XXX use sshkey_froms() */
70	if ((r = sshpkt_get_cstring(ssh, &pkalg, &alen)) != 0 ||
71	    (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0 ||
72	    (r = sshpkt_get_cstring(ssh, &chost, NULL)) != 0 ||
73	    (r = sshpkt_get_cstring(ssh, &cuser, NULL)) != 0 ||
74	    (r = sshpkt_get_string(ssh, &sig, &slen)) != 0)
75		fatal_fr(r, "parse packet");
76
77	debug_f("cuser %s chost %s pkalg %s slen %zu",
78	    cuser, chost, pkalg, slen);
79#ifdef DEBUG_PK
80	debug("signature:");
81	sshbuf_dump_data(sig, slen, stderr);
82#endif
83	pktype = sshkey_type_from_name(pkalg);
84	if (pktype == KEY_UNSPEC) {
85		/* this is perfectly legal */
86		logit_f("unsupported public key algorithm: %s",
87		    pkalg);
88		goto done;
89	}
90	if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {
91		error_fr(r, "key_from_blob");
92		goto done;
93	}
94	if (key == NULL) {
95		error_f("cannot decode key: %s", pkalg);
96		goto done;
97	}
98	if (key->type != pktype) {
99		error_f("type mismatch for decoded key "
100		    "(received %d, expected %d)", key->type, pktype);
101		goto done;
102	}
103	if (match_pattern_list(pkalg, options.hostbased_accepted_algos, 0) != 1) {
104		logit_f("signature algorithm %s not in "
105		    "HostbasedAcceptedAlgorithms", pkalg);
106		goto done;
107	}
108	if ((r = sshkey_check_cert_sigtype(key,
109	    options.ca_sign_algorithms)) != 0) {
110		logit_fr(r, "certificate signature algorithm %s",
111		    (key->cert == NULL || key->cert->signature_type == NULL) ?
112		    "(null)" : key->cert->signature_type);
113		goto done;
114	}
115	if ((r = sshkey_check_rsa_length(key,
116	    options.required_rsa_size)) != 0) {
117		logit_r(r, "refusing %s key", sshkey_type(key));
118		goto done;
119	}
120
121	if (!authctxt->valid || authctxt->user == NULL) {
122		debug2_f("disabled because of invalid user");
123		goto done;
124	}
125
126	if ((b = sshbuf_new()) == NULL)
127		fatal_f("sshbuf_new failed");
128	/* reconstruct packet */
129	if ((r = sshbuf_put_stringb(b, ssh->kex->session_id)) != 0 ||
130	    (r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 ||
131	    (r = sshbuf_put_cstring(b, authctxt->user)) != 0 ||
132	    (r = sshbuf_put_cstring(b, authctxt->service)) != 0 ||
133	    (r = sshbuf_put_cstring(b, method)) != 0 ||
134	    (r = sshbuf_put_string(b, pkalg, alen)) != 0 ||
135	    (r = sshbuf_put_string(b, pkblob, blen)) != 0 ||
136	    (r = sshbuf_put_cstring(b, chost)) != 0 ||
137	    (r = sshbuf_put_cstring(b, cuser)) != 0)
138		fatal_fr(r, "reconstruct packet");
139#ifdef DEBUG_PK
140	sshbuf_dump(b, stderr);
141#endif
142
143	auth2_record_info(authctxt,
144	    "client user \"%.100s\", client host \"%.100s\"", cuser, chost);
145
146	/* test for allowed key and correct signature */
147	authenticated = 0;
148	if (PRIVSEP(hostbased_key_allowed(ssh, authctxt->pw, cuser,
149	    chost, key)) &&
150	    PRIVSEP(sshkey_verify(key, sig, slen,
151	    sshbuf_ptr(b), sshbuf_len(b), pkalg, ssh->compat, NULL)) == 0)
152		authenticated = 1;
153
154	auth2_record_key(authctxt, authenticated, key);
155	sshbuf_free(b);
156done:
157	debug2_f("authenticated %d", authenticated);
158	sshkey_free(key);
159	free(pkalg);
160	free(pkblob);
161	free(cuser);
162	free(chost);
163	free(sig);
164	return authenticated;
165}
166
167/* return 1 if given hostkey is allowed */
168int
169hostbased_key_allowed(struct ssh *ssh, struct passwd *pw,
170    const char *cuser, char *chost, struct sshkey *key)
171{
172	const char *resolvedname, *ipaddr, *lookup, *reason;
173	HostStatus host_status;
174	int len;
175	char *fp;
176
177	if (auth_key_is_revoked(key))
178		return 0;
179
180	resolvedname = auth_get_canonical_hostname(ssh, options.use_dns);
181	ipaddr = ssh_remote_ipaddr(ssh);
182
183	debug2_f("chost %s resolvedname %s ipaddr %s",
184	    chost, resolvedname, ipaddr);
185
186	if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') {
187		debug2("stripping trailing dot from chost %s", chost);
188		chost[len - 1] = '\0';
189	}
190
191	if (options.hostbased_uses_name_from_packet_only) {
192		if (auth_rhosts2(pw, cuser, chost, chost) == 0) {
193			debug2_f("auth_rhosts2 refused user \"%.100s\" "
194			    "host \"%.100s\" (from packet)", cuser, chost);
195			return 0;
196		}
197		lookup = chost;
198	} else {
199		if (strcasecmp(resolvedname, chost) != 0)
200			logit("userauth_hostbased mismatch: "
201			    "client sends %s, but we resolve %s to %s",
202			    chost, ipaddr, resolvedname);
203		if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0) {
204			debug2_f("auth_rhosts2 refused "
205			    "user \"%.100s\" host \"%.100s\" addr \"%.100s\"",
206			    cuser, resolvedname, ipaddr);
207			return 0;
208		}
209		lookup = resolvedname;
210	}
211	debug2_f("access allowed by auth_rhosts2");
212
213	if (sshkey_is_cert(key) &&
214	    sshkey_cert_check_authority_now(key, 1, 0, 0, lookup, &reason)) {
215		error("%s", reason);
216		auth_debug_add("%s", reason);
217		return 0;
218	}
219
220	host_status = check_key_in_hostfiles(pw, key, lookup,
221	    _PATH_SSH_SYSTEM_HOSTFILE,
222	    options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE);
223
224	/* backward compat if no key has been found. */
225	if (host_status == HOST_NEW) {
226		host_status = check_key_in_hostfiles(pw, key, lookup,
227		    _PATH_SSH_SYSTEM_HOSTFILE2,
228		    options.ignore_user_known_hosts ? NULL :
229		    _PATH_SSH_USER_HOSTFILE2);
230	}
231
232	if (host_status == HOST_OK) {
233		if (sshkey_is_cert(key)) {
234			if ((fp = sshkey_fingerprint(key->cert->signature_key,
235			    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
236				fatal_f("sshkey_fingerprint fail");
237			verbose("Accepted certificate ID \"%s\" signed by "
238			    "%s CA %s from %s@%s", key->cert->key_id,
239			    sshkey_type(key->cert->signature_key), fp,
240			    cuser, lookup);
241		} else {
242			if ((fp = sshkey_fingerprint(key,
243			    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
244				fatal_f("sshkey_fingerprint fail");
245			verbose("Accepted %s public key %s from %s@%s",
246			    sshkey_type(key), fp, cuser, lookup);
247		}
248		free(fp);
249	}
250
251	return (host_status == HOST_OK);
252}
253
254Authmethod method_hostbased = {
255	"hostbased",
256	NULL,
257	userauth_hostbased,
258	&options.hostbased_authentication
259};
260