1 /* $OpenBSD: auth2-hostbased.c,v 1.47 2021/07/23 03:37:52 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 <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 "compat.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)60 userauth_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_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 (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_accepted_algos, 0) != 1) {
111 logit_f("key type %s not in HostbasedAcceptedAlgorithms",
112 sshkey_type(key));
113 goto done;
114 }
115 if ((r = sshkey_check_cert_sigtype(key,
116 options.ca_sign_algorithms)) != 0) {
117 logit_fr(r, "certificate signature algorithm %s",
118 (key->cert == NULL || key->cert->signature_type == NULL) ?
119 "(null)" : key->cert->signature_type);
120 goto done;
121 }
122
123 if (!authctxt->valid || authctxt->user == NULL) {
124 debug2_f("disabled because of invalid user");
125 goto done;
126 }
127
128 if ((b = sshbuf_new()) == NULL)
129 fatal_f("sshbuf_new failed");
130 /* reconstruct packet */
131 if ((r = sshbuf_put_stringb(b, ssh->kex->session_id)) != 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_fr(r, "reconstruct packet");
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(ssh, authctxt->pw, cuser,
151 chost, key)) &&
152 PRIVSEP(sshkey_verify(key, sig, slen,
153 sshbuf_ptr(b), sshbuf_len(b), pkalg, ssh->compat, NULL)) == 0)
154 authenticated = 1;
155
156 auth2_record_key(authctxt, authenticated, key);
157 sshbuf_free(b);
158 done:
159 debug2_f("authenticated %d", authenticated);
160 sshkey_free(key);
161 free(pkalg);
162 free(pkblob);
163 free(cuser);
164 free(chost);
165 free(sig);
166 return authenticated;
167 }
168
169 /* return 1 if given hostkey is allowed */
170 int
hostbased_key_allowed(struct ssh * ssh,struct passwd * pw,const char * cuser,char * chost,struct sshkey * key)171 hostbased_key_allowed(struct ssh *ssh, struct passwd *pw,
172 const char *cuser, char *chost, struct sshkey *key)
173 {
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_f("chost %s resolvedname %s ipaddr %s",
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_f("auth_rhosts2 refused user \"%.100s\" "
196 "host \"%.100s\" (from packet)", cuser, chost);
197 return 0;
198 }
199 lookup = chost;
200 } else {
201 if (strcasecmp(resolvedname, chost) != 0)
202 logit("userauth_hostbased mismatch: "
203 "client sends %s, but we resolve %s to %s",
204 chost, ipaddr, resolvedname);
205 if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0) {
206 debug2_f("auth_rhosts2 refused "
207 "user \"%.100s\" host \"%.100s\" addr \"%.100s\"",
208 cuser, resolvedname, ipaddr);
209 return 0;
210 }
211 lookup = resolvedname;
212 }
213 debug2_f("access allowed by auth_rhosts2");
214
215 if (sshkey_is_cert(key) &&
216 sshkey_cert_check_authority_now(key, 1, 0, 0, lookup, &reason)) {
217 error("%s", reason);
218 auth_debug_add("%s", reason);
219 return 0;
220 }
221
222 host_status = check_key_in_hostfiles(pw, key, lookup,
223 _PATH_SSH_SYSTEM_HOSTFILE,
224 options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE);
225
226 /* backward compat if no key has been found. */
227 if (host_status == HOST_NEW) {
228 host_status = check_key_in_hostfiles(pw, key, lookup,
229 _PATH_SSH_SYSTEM_HOSTFILE2,
230 options.ignore_user_known_hosts ? NULL :
231 _PATH_SSH_USER_HOSTFILE2);
232 }
233
234 if (host_status == HOST_OK) {
235 if (sshkey_is_cert(key)) {
236 if ((fp = sshkey_fingerprint(key->cert->signature_key,
237 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
238 fatal_f("sshkey_fingerprint fail");
239 verbose("Accepted certificate ID \"%s\" signed by "
240 "%s CA %s from %s@%s", key->cert->key_id,
241 sshkey_type(key->cert->signature_key), fp,
242 cuser, lookup);
243 } else {
244 if ((fp = sshkey_fingerprint(key,
245 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
246 fatal_f("sshkey_fingerprint fail");
247 verbose("Accepted %s public key %s from %s@%s",
248 sshkey_type(key), fp, cuser, lookup);
249 }
250 free(fp);
251 }
252
253 return (host_status == HOST_OK);
254 }
255
256 Authmethod method_hostbased = {
257 "hostbased",
258 userauth_hostbased,
259 &options.hostbased_authentication
260 };
261