1 /* $OpenBSD: auth2-hostbased.c,v 1.17 2013/12/30 23:52:27 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 "servconf.h"
40 #include "compat.h"
41 #include "key.h"
42 #include "hostfile.h"
43 #include "auth.h"
44 #include "canohost.h"
45 #ifdef GSSAPI
46 #include "ssh-gss.h"
47 #endif
48 #include "monitor_wrap.h"
49 #include "pathnames.h"
50
51 /* import */
52 extern ServerOptions options;
53 extern u_char *session_id2;
54 extern u_int session_id2_len;
55
56 static int
userauth_hostbased(Authctxt * authctxt)57 userauth_hostbased(Authctxt *authctxt)
58 {
59 Buffer b;
60 Key *key = NULL;
61 char *pkalg, *cuser, *chost, *service;
62 u_char *pkblob, *sig;
63 u_int alen, blen, slen;
64 int pktype;
65 int authenticated = 0;
66
67 if (!authctxt->valid) {
68 debug2("userauth_hostbased: disabled because of invalid user");
69 return 0;
70 }
71 pkalg = packet_get_string(&alen);
72 pkblob = packet_get_string(&blen);
73 chost = packet_get_string(NULL);
74 cuser = packet_get_string(NULL);
75 sig = packet_get_string(&slen);
76
77 debug("userauth_hostbased: cuser %s chost %s pkalg %s slen %d",
78 cuser, chost, pkalg, slen);
79 #ifdef DEBUG_PK
80 debug("signature:");
81 buffer_init(&b);
82 buffer_append(&b, sig, slen);
83 buffer_dump(&b);
84 buffer_free(&b);
85 #endif
86 pktype = key_type_from_name(pkalg);
87 if (pktype == KEY_UNSPEC) {
88 /* this is perfectly legal */
89 logit("userauth_hostbased: unsupported "
90 "public key algorithm: %s", pkalg);
91 goto done;
92 }
93 key = key_from_blob(pkblob, blen);
94 if (key == NULL) {
95 error("userauth_hostbased: cannot decode key: %s", pkalg);
96 goto done;
97 }
98 if (key->type != pktype) {
99 error("userauth_hostbased: type mismatch for decoded key "
100 "(received %d, expected %d)", key->type, pktype);
101 goto done;
102 }
103 if (key_type_plain(key->type) == KEY_RSA &&
104 (datafellows & SSH_BUG_RSASIGMD5) != 0) {
105 error("Refusing RSA key because peer uses unsafe "
106 "signature format");
107 goto done;
108 }
109 service = datafellows & SSH_BUG_HBSERVICE ? "ssh-userauth" :
110 authctxt->service;
111 buffer_init(&b);
112 buffer_put_string(&b, session_id2, session_id2_len);
113 /* reconstruct packet */
114 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
115 buffer_put_cstring(&b, authctxt->user);
116 buffer_put_cstring(&b, service);
117 buffer_put_cstring(&b, "hostbased");
118 buffer_put_string(&b, pkalg, alen);
119 buffer_put_string(&b, pkblob, blen);
120 buffer_put_cstring(&b, chost);
121 buffer_put_cstring(&b, cuser);
122 #ifdef DEBUG_PK
123 buffer_dump(&b);
124 #endif
125
126 pubkey_auth_info(authctxt, key,
127 "client user \"%.100s\", client host \"%.100s\"", cuser, chost);
128
129 /* test for allowed key and correct signature */
130 authenticated = 0;
131 if (PRIVSEP(hostbased_key_allowed(authctxt->pw, cuser, chost, key)) &&
132 PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
133 buffer_len(&b))) == 1)
134 authenticated = 1;
135
136 buffer_free(&b);
137 done:
138 debug2("userauth_hostbased: authenticated %d", authenticated);
139 if (key != NULL)
140 key_free(key);
141 free(pkalg);
142 free(pkblob);
143 free(cuser);
144 free(chost);
145 free(sig);
146 return authenticated;
147 }
148
149 /* return 1 if given hostkey is allowed */
150 int
hostbased_key_allowed(struct passwd * pw,const char * cuser,char * chost,Key * key)151 hostbased_key_allowed(struct passwd *pw, const char *cuser, char *chost,
152 Key *key)
153 {
154 const char *resolvedname, *ipaddr, *lookup, *reason;
155 HostStatus host_status;
156 int len;
157 char *fp;
158
159 if (auth_key_is_revoked(key))
160 return 0;
161
162 resolvedname = get_canonical_hostname(options.use_dns);
163 ipaddr = get_remote_ipaddr();
164
165 debug2("userauth_hostbased: chost %s resolvedname %s ipaddr %s",
166 chost, resolvedname, ipaddr);
167
168 if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') {
169 debug2("stripping trailing dot from chost %s", chost);
170 chost[len - 1] = '\0';
171 }
172
173 if (options.hostbased_uses_name_from_packet_only) {
174 if (auth_rhosts2(pw, cuser, chost, chost) == 0)
175 return 0;
176 lookup = chost;
177 } else {
178 if (strcasecmp(resolvedname, chost) != 0)
179 logit("userauth_hostbased mismatch: "
180 "client sends %s, but we resolve %s to %s",
181 chost, ipaddr, resolvedname);
182 if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0)
183 return 0;
184 lookup = resolvedname;
185 }
186 debug2("userauth_hostbased: access allowed by auth_rhosts2");
187
188 if (key_is_cert(key) &&
189 key_cert_check_authority(key, 1, 0, lookup, &reason)) {
190 error("%s", reason);
191 auth_debug_add("%s", reason);
192 return 0;
193 }
194
195 host_status = check_key_in_hostfiles(pw, key, lookup,
196 _PATH_SSH_SYSTEM_HOSTFILE,
197 options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE);
198
199 /* backward compat if no key has been found. */
200 if (host_status == HOST_NEW) {
201 host_status = check_key_in_hostfiles(pw, key, lookup,
202 _PATH_SSH_SYSTEM_HOSTFILE2,
203 options.ignore_user_known_hosts ? NULL :
204 _PATH_SSH_USER_HOSTFILE2);
205 }
206
207 if (host_status == HOST_OK) {
208 if (key_is_cert(key)) {
209 fp = key_fingerprint(key->cert->signature_key,
210 SSH_FP_MD5, SSH_FP_HEX);
211 verbose("Accepted certificate ID \"%s\" signed by "
212 "%s CA %s from %s@%s", key->cert->key_id,
213 key_type(key->cert->signature_key), fp,
214 cuser, lookup);
215 } else {
216 fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX);
217 verbose("Accepted %s public key %s from %s@%s",
218 key_type(key), fp, cuser, lookup);
219 }
220 free(fp);
221 }
222
223 return (host_status == HOST_OK);
224 }
225
226 Authmethod method_hostbased = {
227 "hostbased",
228 userauth_hostbased,
229 &options.hostbased_authentication
230 };
231