1 /* $OpenBSD: auth2-hostbased.c,v 1.26 2016/03/07 19:02:43 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 "buffer.h"
38 #include "log.h"
39 #include "misc.h"
40 #include "servconf.h"
41 #include "compat.h"
42 #include "key.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 "match.h"
52
53 /* import */
54 extern ServerOptions options;
55 extern u_char *session_id2;
56 extern u_int session_id2_len;
57
58 static int
userauth_hostbased(Authctxt * authctxt)59 userauth_hostbased(Authctxt *authctxt)
60 {
61 Buffer b;
62 Key *key = NULL;
63 char *pkalg, *cuser, *chost, *service;
64 u_char *pkblob, *sig;
65 u_int alen, blen, slen;
66 int pktype;
67 int authenticated = 0;
68
69 if (!authctxt->valid) {
70 debug2("userauth_hostbased: disabled because of invalid user");
71 return 0;
72 }
73 pkalg = packet_get_string(&alen);
74 pkblob = packet_get_string(&blen);
75 chost = packet_get_string(NULL);
76 cuser = packet_get_string(NULL);
77 sig = packet_get_string(&slen);
78
79 debug("userauth_hostbased: cuser %s chost %s pkalg %s slen %d",
80 cuser, chost, pkalg, slen);
81 #ifdef DEBUG_PK
82 debug("signature:");
83 buffer_init(&b);
84 buffer_append(&b, sig, slen);
85 buffer_dump(&b);
86 buffer_free(&b);
87 #endif
88 pktype = key_type_from_name(pkalg);
89 if (pktype == KEY_UNSPEC) {
90 /* this is perfectly legal */
91 logit("userauth_hostbased: unsupported "
92 "public key algorithm: %s", pkalg);
93 goto done;
94 }
95 key = key_from_blob(pkblob, blen);
96 if (key == NULL) {
97 error("userauth_hostbased: cannot decode key: %s", pkalg);
98 goto done;
99 }
100 if (key->type != pktype) {
101 error("userauth_hostbased: type mismatch for decoded key "
102 "(received %d, expected %d)", key->type, pktype);
103 goto done;
104 }
105 if (key_type_plain(key->type) == KEY_RSA &&
106 (datafellows & SSH_BUG_RSASIGMD5) != 0) {
107 error("Refusing RSA key because peer uses unsafe "
108 "signature format");
109 goto done;
110 }
111 if (match_pattern_list(sshkey_ssh_name(key),
112 options.hostbased_key_types, 0) != 1) {
113 logit("%s: key type %s not in HostbasedAcceptedKeyTypes",
114 __func__, sshkey_type(key));
115 goto done;
116 }
117
118 service = datafellows & SSH_BUG_HBSERVICE ? "ssh-userauth" :
119 authctxt->service;
120 buffer_init(&b);
121 buffer_put_string(&b, session_id2, session_id2_len);
122 /* reconstruct packet */
123 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
124 buffer_put_cstring(&b, authctxt->user);
125 buffer_put_cstring(&b, service);
126 buffer_put_cstring(&b, "hostbased");
127 buffer_put_string(&b, pkalg, alen);
128 buffer_put_string(&b, pkblob, blen);
129 buffer_put_cstring(&b, chost);
130 buffer_put_cstring(&b, cuser);
131 #ifdef DEBUG_PK
132 buffer_dump(&b);
133 #endif
134
135 pubkey_auth_info(authctxt, key,
136 "client user \"%.100s\", client host \"%.100s\"", cuser, chost);
137
138 /* test for allowed key and correct signature */
139 authenticated = 0;
140 if (PRIVSEP(hostbased_key_allowed(authctxt->pw, cuser, chost, key)) &&
141 PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
142 buffer_len(&b))) == 1)
143 authenticated = 1;
144
145 buffer_free(&b);
146 done:
147 debug2("userauth_hostbased: authenticated %d", authenticated);
148 if (key != NULL)
149 key_free(key);
150 free(pkalg);
151 free(pkblob);
152 free(cuser);
153 free(chost);
154 free(sig);
155 return authenticated;
156 }
157
158 /* return 1 if given hostkey is allowed */
159 int
hostbased_key_allowed(struct passwd * pw,const char * cuser,char * chost,Key * key)160 hostbased_key_allowed(struct passwd *pw, const char *cuser, char *chost,
161 Key *key)
162 {
163 struct ssh *ssh = active_state; /* XXX */
164 const char *resolvedname, *ipaddr, *lookup, *reason;
165 HostStatus host_status;
166 int len;
167 char *fp;
168
169 if (auth_key_is_revoked(key))
170 return 0;
171
172 resolvedname = auth_get_canonical_hostname(ssh, options.use_dns);
173 ipaddr = ssh_remote_ipaddr(ssh);
174
175 debug2("%s: chost %s resolvedname %s ipaddr %s", __func__,
176 chost, resolvedname, ipaddr);
177
178 if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') {
179 debug2("stripping trailing dot from chost %s", chost);
180 chost[len - 1] = '\0';
181 }
182
183 if (options.hostbased_uses_name_from_packet_only) {
184 if (auth_rhosts2(pw, cuser, chost, chost) == 0) {
185 debug2("%s: auth_rhosts2 refused "
186 "user \"%.100s\" host \"%.100s\" (from packet)",
187 __func__, cuser, chost);
188 return 0;
189 }
190 lookup = chost;
191 } else {
192 if (strcasecmp(resolvedname, chost) != 0)
193 logit("userauth_hostbased mismatch: "
194 "client sends %s, but we resolve %s to %s",
195 chost, ipaddr, resolvedname);
196 if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0) {
197 debug2("%s: auth_rhosts2 refused "
198 "user \"%.100s\" host \"%.100s\" addr \"%.100s\"",
199 __func__, cuser, resolvedname, ipaddr);
200 return 0;
201 }
202 lookup = resolvedname;
203 }
204 debug2("%s: access allowed by auth_rhosts2", __func__);
205
206 if (key_is_cert(key) &&
207 key_cert_check_authority(key, 1, 0, lookup, &reason)) {
208 error("%s", reason);
209 auth_debug_add("%s", reason);
210 return 0;
211 }
212
213 host_status = check_key_in_hostfiles(pw, key, lookup,
214 _PATH_SSH_SYSTEM_HOSTFILE,
215 options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE);
216
217 /* backward compat if no key has been found. */
218 if (host_status == HOST_NEW) {
219 host_status = check_key_in_hostfiles(pw, key, lookup,
220 _PATH_SSH_SYSTEM_HOSTFILE2,
221 options.ignore_user_known_hosts ? NULL :
222 _PATH_SSH_USER_HOSTFILE2);
223 }
224
225 if (host_status == HOST_OK) {
226 if (key_is_cert(key)) {
227 if ((fp = sshkey_fingerprint(key->cert->signature_key,
228 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
229 fatal("%s: sshkey_fingerprint fail", __func__);
230 verbose("Accepted certificate ID \"%s\" signed by "
231 "%s CA %s from %s@%s", key->cert->key_id,
232 key_type(key->cert->signature_key), fp,
233 cuser, lookup);
234 } else {
235 if ((fp = sshkey_fingerprint(key,
236 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
237 fatal("%s: sshkey_fingerprint fail", __func__);
238 verbose("Accepted %s public key %s from %s@%s",
239 key_type(key), fp, cuser, lookup);
240 }
241 free(fp);
242 }
243
244 return (host_status == HOST_OK);
245 }
246
247 Authmethod method_hostbased = {
248 "hostbased",
249 userauth_hostbased,
250 &options.hostbased_authentication
251 };
252