1 /* $NetBSD: auth2-hostbased.c,v 1.24 2024/07/08 22:33:43 christos Exp $ */
2 /* $OpenBSD: auth2-hostbased.c,v 1.53 2024/05/17 00:30:23 djm Exp $ */
3
4 /*
5 * Copyright (c) 2000 Markus Friedl. All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
19 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
21 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
25 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26 */
27
28 #include "includes.h"
29 __RCSID("$NetBSD: auth2-hostbased.c,v 1.24 2024/07/08 22:33:43 christos Exp $");
30 #include <sys/types.h>
31
32 #include <stdlib.h>
33 #include <pwd.h>
34 #include <string.h>
35 #include <stdarg.h>
36
37 #include "xmalloc.h"
38 #include "ssh2.h"
39 #include "packet.h"
40 #include "kex.h"
41 #include "sshbuf.h"
42 #include "log.h"
43 #include "misc.h"
44 #include "servconf.h"
45 #include "sshkey.h"
46 #include "hostfile.h"
47 #include "auth.h"
48 #include "canohost.h"
49 #ifdef GSSAPI
50 #include "ssh-gss.h"
51 #endif
52 #include "monitor_wrap.h"
53 #include "pathnames.h"
54 #include "ssherr.h"
55 #include "match.h"
56
57 /* import */
58 extern ServerOptions options;
59 extern struct authmethod_cfg methodcfg_hostbased;
60
61 static int
userauth_hostbased(struct ssh * ssh,const char * method)62 userauth_hostbased(struct ssh *ssh, const char *method)
63 {
64 Authctxt *authctxt = ssh->authctxt;
65 struct sshbuf *b;
66 struct sshkey *key = NULL;
67 char *pkalg, *cuser, *chost;
68 u_char *pkblob, *sig;
69 size_t alen, blen, slen;
70 int r, pktype, authenticated = 0;
71
72 /* XXX use sshkey_froms() */
73 if ((r = sshpkt_get_cstring(ssh, &pkalg, &alen)) != 0 ||
74 (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0 ||
75 (r = sshpkt_get_cstring(ssh, &chost, NULL)) != 0 ||
76 (r = sshpkt_get_cstring(ssh, &cuser, NULL)) != 0 ||
77 (r = sshpkt_get_string(ssh, &sig, &slen)) != 0)
78 fatal_fr(r, "parse packet");
79
80 debug_f("cuser %s chost %s pkalg %s slen %zu",
81 cuser, chost, pkalg, slen);
82 #ifdef DEBUG_PK
83 debug("signature:");
84 sshbuf_dump_data(sig, slen, stderr);
85 #endif
86 pktype = sshkey_type_from_name(pkalg);
87 if (pktype == KEY_UNSPEC) {
88 /* this is perfectly legal */
89 logit_f("unsupported public key algorithm: %s",
90 pkalg);
91 goto done;
92 }
93 if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {
94 error_fr(r, "key_from_blob");
95 goto done;
96 }
97 if (key == NULL) {
98 error_f("cannot decode key: %s", pkalg);
99 goto done;
100 }
101 if (key->type != pktype) {
102 error_f("type mismatch for decoded key "
103 "(received %d, expected %d)", key->type, pktype);
104 goto done;
105 }
106 if (match_pattern_list(pkalg, options.hostbased_accepted_algos, 0) != 1) {
107 logit_f("signature algorithm %s not in "
108 "HostbasedAcceptedAlgorithms", pkalg);
109 goto done;
110 }
111 if ((r = sshkey_check_cert_sigtype(key,
112 options.ca_sign_algorithms)) != 0) {
113 logit_fr(r, "certificate signature algorithm %s",
114 (key->cert == NULL || key->cert->signature_type == NULL) ?
115 "(null)" : key->cert->signature_type);
116 goto done;
117 }
118 if ((r = sshkey_check_rsa_length(key,
119 options.required_rsa_size)) != 0) {
120 logit_r(r, "refusing %s key", sshkey_type(key));
121 goto done;
122 }
123
124 if (!authctxt->valid || authctxt->user == NULL) {
125 debug2_f("disabled because of invalid user");
126 goto done;
127 }
128
129 if ((b = sshbuf_new()) == NULL)
130 fatal_f("sshbuf_new failed");
131 /* reconstruct packet */
132 if ((r = sshbuf_put_stringb(b, ssh->kex->session_id)) != 0 ||
133 (r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 ||
134 (r = sshbuf_put_cstring(b, authctxt->user)) != 0 ||
135 (r = sshbuf_put_cstring(b, authctxt->service)) != 0 ||
136 (r = sshbuf_put_cstring(b, method)) != 0 ||
137 (r = sshbuf_put_string(b, pkalg, alen)) != 0 ||
138 (r = sshbuf_put_string(b, pkblob, blen)) != 0 ||
139 (r = sshbuf_put_cstring(b, chost)) != 0 ||
140 (r = sshbuf_put_cstring(b, cuser)) != 0)
141 fatal_fr(r, "reconstruct packet");
142 #ifdef DEBUG_PK
143 sshbuf_dump(b, stderr);
144 #endif
145
146 auth2_record_info(authctxt,
147 "client user \"%.100s\", client host \"%.100s\"", cuser, chost);
148
149 /* test for allowed key and correct signature */
150 authenticated = 0;
151 if (mm_hostbased_key_allowed(ssh, authctxt->pw, cuser,
152 chost, key) &&
153 mm_sshkey_verify(key, sig, slen,
154 sshbuf_ptr(b), sshbuf_len(b), pkalg, ssh->compat, NULL) == 0)
155 authenticated = 1;
156
157 auth2_record_key(authctxt, authenticated, key);
158 sshbuf_free(b);
159 done:
160 debug2_f("authenticated %d", authenticated);
161 sshkey_free(key);
162 free(pkalg);
163 free(pkblob);
164 free(cuser);
165 free(chost);
166 free(sig);
167 return authenticated;
168 }
169
170 /* return 1 if given hostkey is allowed */
171 int
hostbased_key_allowed(struct ssh * ssh,struct passwd * pw,const char * cuser,char * chost,struct sshkey * key)172 hostbased_key_allowed(struct ssh *ssh, struct passwd *pw,
173 const char *cuser, char *chost, struct sshkey *key)
174 {
175 const char *resolvedname, *ipaddr, *lookup, *reason;
176 HostStatus host_status;
177 int len;
178 char *fp;
179
180 if (auth_key_is_revoked(key))
181 return 0;
182
183 resolvedname = auth_get_canonical_hostname(ssh, options.use_dns);
184 ipaddr = ssh_remote_ipaddr(ssh);
185
186 debug2_f("chost %s resolvedname %s ipaddr %s",
187 chost, resolvedname, ipaddr);
188
189 if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') {
190 debug2("stripping trailing dot from chost %s", chost);
191 chost[len - 1] = '\0';
192 }
193
194 if (options.hostbased_uses_name_from_packet_only) {
195 if (auth_rhosts2(pw, cuser, chost, chost) == 0) {
196 debug2_f("auth_rhosts2 refused user \"%.100s\" "
197 "host \"%.100s\" (from packet)", 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_f("auth_rhosts2 refused "
208 "user \"%.100s\" host \"%.100s\" addr \"%.100s\"",
209 cuser, resolvedname, ipaddr);
210 return 0;
211 }
212 lookup = resolvedname;
213 }
214 debug2_f("access allowed by auth_rhosts2");
215
216 if (sshkey_is_cert(key) &&
217 sshkey_cert_check_authority_now(key, 1, 0, 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_f("sshkey_fingerprint fail");
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_f("sshkey_fingerprint fail");
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
257 Authmethod method_hostbased = {
258 &methodcfg_hostbased,
259 userauth_hostbased,
260 };
261