1 /*
2 * Copyright (c) 2000 Markus Friedl. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution.
12 *
13 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
14 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
15 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
16 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
17 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
18 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
19 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
20 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
21 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
22 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
23 */
24 /*
25 * Copyright 2008 Sun Microsystems, Inc. All rights reserved.
26 * Use is subject to license terms.
27 */
28
29 #include "includes.h"
30 RCSID("$OpenBSD: auth2-pubkey.c,v 1.2 2002/05/31 11:35:15 markus Exp $");
31
32 #include "ssh2.h"
33 #include "xmalloc.h"
34 #include "packet.h"
35 #include "buffer.h"
36 #include "log.h"
37 #include "servconf.h"
38 #include "compat.h"
39 #include "bufaux.h"
40 #include "auth.h"
41 #include "key.h"
42 #include "pathnames.h"
43 #include "uidswap.h"
44 #include "auth-options.h"
45 #include "canohost.h"
46
47 #ifdef USE_PAM
48 #include <security/pam_appl.h>
49 #include "auth-pam.h"
50 #endif /* USE_PAM */
51
52 /* import */
53 extern ServerOptions options;
54 extern u_char *session_id2;
55 extern int session_id2_len;
56
57 static void
userauth_pubkey(Authctxt * authctxt)58 userauth_pubkey(Authctxt *authctxt)
59 {
60 Buffer b;
61 Key *key = NULL;
62 char *pkalg;
63 u_char *pkblob, *sig;
64 u_int alen, blen, slen;
65 int have_sig, pktype;
66 int authenticated = 0;
67
68 if (!authctxt || !authctxt->method)
69 fatal("%s: missing context", __func__);
70
71 have_sig = packet_get_char();
72 if (datafellows & SSH_BUG_PKAUTH) {
73 debug2("userauth_pubkey: SSH_BUG_PKAUTH");
74 /* no explicit pkalg given */
75 pkblob = packet_get_string(&blen);
76 buffer_init(&b);
77 buffer_append(&b, pkblob, blen);
78 /* so we have to extract the pkalg from the pkblob */
79 pkalg = buffer_get_string(&b, &alen);
80 buffer_free(&b);
81 } else {
82 pkalg = packet_get_string(&alen);
83 pkblob = packet_get_string(&blen);
84 }
85 pktype = key_type_from_name(pkalg);
86 if (pktype == KEY_UNSPEC) {
87 /* this is perfectly legal */
88 log("userauth_pubkey: unsupported public key algorithm: %s",
89 pkalg);
90 goto done;
91 }
92 key = key_from_blob(pkblob, blen);
93 if (key == NULL) {
94 error("userauth_pubkey: cannot decode key: %s", pkalg);
95 goto done;
96 }
97 if (key->type != pktype) {
98 error("userauth_pubkey: type mismatch for decoded key "
99 "(received %d, expected %d)", key->type, pktype);
100 goto done;
101 }
102
103 /* Detect and count abandonment */
104 if (authctxt->method->method_data) {
105 Key *prev_key;
106 unsigned char *prev_pkblob;
107 int prev_blen;
108
109 /*
110 * Check for earlier test of a key that was allowed but
111 * not followed up with a pubkey req for the same pubkey
112 * and with a signature.
113 */
114 prev_key = authctxt->method->method_data;
115 if ((prev_blen = key_to_blob(prev_key,
116 &prev_pkblob, NULL))) {
117 if (prev_blen != blen ||
118 memcmp(prev_pkblob, pkblob, blen) != 0) {
119 authctxt->method->abandons++;
120 authctxt->method->attempts++;
121 }
122 }
123 key_free(prev_key);
124 authctxt->method->method_data = NULL;
125 }
126
127 if (have_sig) {
128 sig = packet_get_string(&slen);
129 packet_check_eom();
130 buffer_init(&b);
131 if (datafellows & SSH_OLD_SESSIONID) {
132 buffer_append(&b, session_id2, session_id2_len);
133 } else {
134 buffer_put_string(&b, session_id2, session_id2_len);
135 }
136 /* reconstruct packet */
137 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
138 buffer_put_cstring(&b, authctxt->user);
139 buffer_put_cstring(&b,
140 datafellows & SSH_BUG_PKSERVICE ?
141 "ssh-userauth" :
142 authctxt->service);
143 if (datafellows & SSH_BUG_PKAUTH) {
144 buffer_put_char(&b, have_sig);
145 } else {
146 buffer_put_cstring(&b, "publickey");
147 buffer_put_char(&b, have_sig);
148 buffer_put_cstring(&b, pkalg);
149 }
150 buffer_put_string(&b, pkblob, blen);
151 #ifdef DEBUG_PK
152 buffer_dump(&b);
153 #endif
154 /* test for correct signature */
155 if (user_key_allowed(authctxt->pw, key) &&
156 key_verify(key, sig, slen, buffer_ptr(&b),
157 buffer_len(&b)) == 1) {
158 authenticated = 1;
159 }
160 authctxt->method->postponed = 0;
161 buffer_free(&b);
162 xfree(sig);
163 } else {
164 debug("test whether pkalg/pkblob are acceptable");
165 packet_check_eom();
166
167 /* XXX fake reply and always send PK_OK ? */
168 /*
169 * XXX this allows testing whether a user is allowed
170 * to login: if you happen to have a valid pubkey this
171 * message is sent. the message is NEVER sent at all
172 * if a user is not allowed to login. is this an
173 * issue? -markus
174 */
175 if (user_key_allowed(authctxt->pw, key)) {
176 packet_start(SSH2_MSG_USERAUTH_PK_OK);
177 packet_put_string(pkalg, alen);
178 packet_put_string(pkblob, blen);
179 packet_send();
180 packet_write_wait();
181 authctxt->method->postponed = 1;
182 /*
183 * Remember key that was tried so we can
184 * correctly detect abandonment. See above.
185 */
186 authctxt->method->method_data = (void *) key;
187 key = NULL;
188 }
189 }
190 if (authenticated != 1)
191 auth_clear_options();
192
193 done:
194 /*
195 * XXX TODO: add config options for specifying users for whom
196 * this userauth is insufficient and what userauths may
197 * continue.
198 */
199 #ifdef USE_PAM
200 if (authenticated) {
201 if (!do_pam_non_initial_userauth(authctxt))
202 authenticated = 0;
203 }
204 #endif /* USE_PAM */
205
206 debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg);
207 if (key != NULL)
208 key_free(key);
209 xfree(pkalg);
210 xfree(pkblob);
211 #ifdef HAVE_CYGWIN
212 if (check_nt_auth(0, authctxt->pw) == 0)
213 return;
214 #endif
215 if (authenticated)
216 authctxt->method->authenticated = 1;
217 }
218
219 /* return 1 if user allows given key */
220 static int
user_key_allowed2(struct passwd * pw,Key * key,char * file)221 user_key_allowed2(struct passwd *pw, Key *key, char *file)
222 {
223 char line[8192];
224 int found_key = 0;
225 FILE *f;
226 u_long linenum = 0;
227 struct stat st;
228 Key *found;
229 char *fp;
230
231 if (pw == NULL)
232 return 0;
233
234 /* Temporarily use the user's uid. */
235 temporarily_use_uid(pw);
236
237 debug("trying public key file %s", file);
238
239 /* Fail quietly if file does not exist */
240 if (stat(file, &st) < 0) {
241 /* Restore the privileged uid. */
242 restore_uid();
243 return 0;
244 }
245 /* Open the file containing the authorized keys. */
246 f = fopen(file, "r");
247 if (!f) {
248 /* Restore the privileged uid. */
249 restore_uid();
250 return 0;
251 }
252 if (options.strict_modes &&
253 secure_filename(f, file, pw, line, sizeof(line)) != 0) {
254 (void) fclose(f);
255 log("Authentication refused: %s", line);
256 restore_uid();
257 return 0;
258 }
259
260 found_key = 0;
261 found = key_new(key->type);
262
263 while (fgets(line, sizeof(line), f)) {
264 char *cp, *options = NULL;
265 linenum++;
266 /* Skip leading whitespace, empty and comment lines. */
267 for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
268 ;
269 if (!*cp || *cp == '\n' || *cp == '#')
270 continue;
271
272 if (key_read(found, &cp) != 1) {
273 /* no key? check if there are options for this key */
274 int quoted = 0;
275 debug2("user_key_allowed: check options: '%s'", cp);
276 options = cp;
277 for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
278 if (*cp == '\\' && cp[1] == '"')
279 cp++; /* Skip both */
280 else if (*cp == '"')
281 quoted = !quoted;
282 }
283 /* Skip remaining whitespace. */
284 for (; *cp == ' ' || *cp == '\t'; cp++)
285 ;
286 if (key_read(found, &cp) != 1) {
287 debug2("user_key_allowed: advance: '%s'", cp);
288 /* still no key? advance to next line*/
289 continue;
290 }
291 }
292 if (key_equal(found, key) &&
293 auth_parse_options(pw, options, file, linenum) == 1) {
294 found_key = 1;
295 debug("matching key found: file %s, line %lu",
296 file, linenum);
297 fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX);
298 verbose("Found matching %s key: %s",
299 key_type(found), fp);
300 xfree(fp);
301 break;
302 }
303 }
304 restore_uid();
305 (void) fclose(f);
306 key_free(found);
307 if (!found_key)
308 debug2("key not found");
309 return found_key;
310 }
311
312 /* check whether given key is in .ssh/authorized_keys* */
313 int
user_key_allowed(struct passwd * pw,Key * key)314 user_key_allowed(struct passwd *pw, Key *key)
315 {
316 int success;
317 char *file;
318
319 if (pw == NULL)
320 return 0;
321
322 file = authorized_keys_file(pw);
323 success = user_key_allowed2(pw, key, file);
324 xfree(file);
325 if (success)
326 return success;
327
328 /* try suffix "2" for backward compat, too */
329 file = authorized_keys_file2(pw);
330 success = user_key_allowed2(pw, key, file);
331 xfree(file);
332 return success;
333 }
334
335 static
336 void
userauth_pubkey_abandon(Authctxt * authctxt,Authmethod * method)337 userauth_pubkey_abandon(Authctxt *authctxt, Authmethod *method)
338 {
339 if (!authctxt || !method)
340 return;
341
342 if (method->method_data) {
343 method->abandons++;
344 method->attempts++;
345 key_free((Key *) method->method_data);
346 method->method_data = NULL;
347 }
348 }
349
350 Authmethod method_pubkey = {
351 "publickey",
352 &options.pubkey_authentication,
353 userauth_pubkey,
354 userauth_pubkey_abandon,
355 NULL, NULL, /* method data and hist data */
356 0, /* not initial userauth */
357 0, 0, 0, /* counters */
358 0, 0, 0, 0, 0, 0 /* state */
359 };
360