1 /* $NetBSD: auth2-hostbased.c,v 1.23 2023/07/26 17:58:15 christos Exp $ */
2 /* $OpenBSD: auth2-hostbased.c,v 1.52 2023/03/05 05:34:09 dtucker Exp $ */
3 /*
4 * Copyright (c) 2000 Markus Friedl. All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
16 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
17 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
18 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
19 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
20 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
21 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
22 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
23 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
24 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
25 */
26
27 #include "includes.h"
28 __RCSID("$NetBSD: auth2-hostbased.c,v 1.23 2023/07/26 17:58:15 christos Exp $");
29 #include <sys/types.h>
30
31 #include <stdlib.h>
32 #include <pwd.h>
33 #include <string.h>
34 #include <stdarg.h>
35
36 #include "xmalloc.h"
37 #include "ssh2.h"
38 #include "packet.h"
39 #include "kex.h"
40 #include "sshbuf.h"
41 #include "log.h"
42 #include "misc.h"
43 #include "servconf.h"
44 #include "sshkey.h"
45 #include "hostfile.h"
46 #include "auth.h"
47 #include "canohost.h"
48 #ifdef GSSAPI
49 #include "ssh-gss.h"
50 #endif
51 #include "monitor_wrap.h"
52 #include "pathnames.h"
53 #include "ssherr.h"
54 #include "match.h"
55
56 /* import */
57 extern ServerOptions options;
58
59 static int
userauth_hostbased(struct ssh * ssh,const char * method)60 userauth_hostbased(struct ssh *ssh, const char *method)
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_fr(r, "parse packet");
77
78 debug_f("cuser %s chost %s pkalg %s slen %zu",
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_f("unsupported public key algorithm: %s",
88 pkalg);
89 goto done;
90 }
91 if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {
92 error_fr(r, "key_from_blob");
93 goto done;
94 }
95 if (key == NULL) {
96 error_f("cannot decode key: %s", pkalg);
97 goto done;
98 }
99 if (key->type != pktype) {
100 error_f("type mismatch for decoded key "
101 "(received %d, expected %d)", key->type, pktype);
102 goto done;
103 }
104 if (match_pattern_list(pkalg, options.hostbased_accepted_algos, 0) != 1) {
105 logit_f("signature algorithm %s not in "
106 "HostbasedAcceptedAlgorithms", pkalg);
107 goto done;
108 }
109 if ((r = sshkey_check_cert_sigtype(key,
110 options.ca_sign_algorithms)) != 0) {
111 logit_fr(r, "certificate signature algorithm %s",
112 (key->cert == NULL || key->cert->signature_type == NULL) ?
113 "(null)" : key->cert->signature_type);
114 goto done;
115 }
116 if ((r = sshkey_check_rsa_length(key,
117 options.required_rsa_size)) != 0) {
118 logit_r(r, "refusing %s key", sshkey_type(key));
119 goto done;
120 }
121
122 if (!authctxt->valid || authctxt->user == NULL) {
123 debug2_f("disabled because of invalid user");
124 goto done;
125 }
126
127 if ((b = sshbuf_new()) == NULL)
128 fatal_f("sshbuf_new failed");
129 /* reconstruct packet */
130 if ((r = sshbuf_put_stringb(b, ssh->kex->session_id)) != 0 ||
131 (r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 ||
132 (r = sshbuf_put_cstring(b, authctxt->user)) != 0 ||
133 (r = sshbuf_put_cstring(b, authctxt->service)) != 0 ||
134 (r = sshbuf_put_cstring(b, method)) != 0 ||
135 (r = sshbuf_put_string(b, pkalg, alen)) != 0 ||
136 (r = sshbuf_put_string(b, pkblob, blen)) != 0 ||
137 (r = sshbuf_put_cstring(b, chost)) != 0 ||
138 (r = sshbuf_put_cstring(b, cuser)) != 0)
139 fatal_fr(r, "reconstruct packet");
140 #ifdef DEBUG_PK
141 sshbuf_dump(b, stderr);
142 #endif
143
144 auth2_record_info(authctxt,
145 "client user \"%.100s\", client host \"%.100s\"", cuser, chost);
146
147 /* test for allowed key and correct signature */
148 authenticated = 0;
149 if (PRIVSEP(hostbased_key_allowed(ssh, authctxt->pw, cuser,
150 chost, key)) &&
151 PRIVSEP(sshkey_verify(key, sig, slen,
152 sshbuf_ptr(b), sshbuf_len(b), pkalg, ssh->compat, NULL)) == 0)
153 authenticated = 1;
154
155 auth2_record_key(authctxt, authenticated, key);
156 sshbuf_free(b);
157 done:
158 debug2_f("authenticated %d", 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 */
169 int
hostbased_key_allowed(struct ssh * ssh,struct passwd * pw,const char * cuser,char * chost,struct sshkey * key)170 hostbased_key_allowed(struct ssh *ssh, struct passwd *pw,
171 const char *cuser, char *chost, struct sshkey *key)
172 {
173 const char *resolvedname, *ipaddr, *lookup, *reason;
174 HostStatus host_status;
175 int len;
176 char *fp;
177
178 if (auth_key_is_revoked(key))
179 return 0;
180
181 resolvedname = auth_get_canonical_hostname(ssh, options.use_dns);
182 ipaddr = ssh_remote_ipaddr(ssh);
183
184 debug2_f("chost %s resolvedname %s ipaddr %s",
185 chost, resolvedname, ipaddr);
186
187 if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') {
188 debug2("stripping trailing dot from chost %s", chost);
189 chost[len - 1] = '\0';
190 }
191
192 if (options.hostbased_uses_name_from_packet_only) {
193 if (auth_rhosts2(pw, cuser, chost, chost) == 0) {
194 debug2_f("auth_rhosts2 refused user \"%.100s\" "
195 "host \"%.100s\" (from packet)", cuser, chost);
196 return 0;
197 }
198 lookup = chost;
199 } else {
200 if (strcasecmp(resolvedname, chost) != 0)
201 logit("userauth_hostbased mismatch: "
202 "client sends %s, but we resolve %s to %s",
203 chost, ipaddr, resolvedname);
204 if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0) {
205 debug2_f("auth_rhosts2 refused "
206 "user \"%.100s\" host \"%.100s\" addr \"%.100s\"",
207 cuser, resolvedname, ipaddr);
208 return 0;
209 }
210 lookup = resolvedname;
211 }
212 debug2_f("access allowed by auth_rhosts2");
213
214 if (sshkey_is_cert(key) &&
215 sshkey_cert_check_authority_now(key, 1, 0, 0, lookup, &reason)) {
216 error("%s", reason);
217 auth_debug_add("%s", reason);
218 return 0;
219 }
220
221 host_status = check_key_in_hostfiles(pw, key, lookup,
222 _PATH_SSH_SYSTEM_HOSTFILE,
223 options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE);
224
225 /* backward compat if no key has been found. */
226 if (host_status == HOST_NEW) {
227 host_status = check_key_in_hostfiles(pw, key, lookup,
228 _PATH_SSH_SYSTEM_HOSTFILE2,
229 options.ignore_user_known_hosts ? NULL :
230 _PATH_SSH_USER_HOSTFILE2);
231 }
232
233 if (host_status == HOST_OK) {
234 if (sshkey_is_cert(key)) {
235 if ((fp = sshkey_fingerprint(key->cert->signature_key,
236 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
237 fatal_f("sshkey_fingerprint fail");
238 verbose("Accepted certificate ID \"%s\" signed by "
239 "%s CA %s from %s@%s", key->cert->key_id,
240 sshkey_type(key->cert->signature_key), fp,
241 cuser, lookup);
242 } else {
243 if ((fp = sshkey_fingerprint(key,
244 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
245 fatal_f("sshkey_fingerprint fail");
246 verbose("Accepted %s public key %s from %s@%s",
247 sshkey_type(key), fp, cuser, lookup);
248 }
249 free(fp);
250 }
251
252 return (host_status == HOST_OK);
253 }
254
255 Authmethod method_hostbased = {
256 "hostbased",
257 NULL,
258 userauth_hostbased,
259 &options.hostbased_authentication
260 };
261