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Damien Millerd7834352006-08-05 12:39:39 +10001/* $OpenBSD: auth2-pubkey.c,v 1.15 2006/08/03 03:34:41 deraadt Exp $ */
Ben Lindstrom855bf3a2002-06-06 20:27:55 +00002/*
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"
Damien Millerf17883e2006-03-15 11:45:54 +110027
28#include <sys/types.h>
29#include <sys/stat.h>
Ben Lindstrom855bf3a2002-06-06 20:27:55 +000030
Damien Miller9f2abc42006-07-10 20:53:08 +100031#include <pwd.h>
Damien Millera7a73ee2006-08-05 11:37:59 +100032#include <stdio.h>
Damien Millerd7834352006-08-05 12:39:39 +100033#include <stdarg.h>
Damien Miller9f2abc42006-07-10 20:53:08 +100034
Damien Millerd7834352006-08-05 12:39:39 +100035#include "xmalloc.h"
Darren Tucker22cc7412004-12-06 22:47:41 +110036#include "ssh.h"
Ben Lindstrom855bf3a2002-06-06 20:27:55 +000037#include "ssh2.h"
Ben Lindstrom855bf3a2002-06-06 20:27:55 +000038#include "packet.h"
39#include "buffer.h"
40#include "log.h"
41#include "servconf.h"
42#include "compat.h"
Ben Lindstrom855bf3a2002-06-06 20:27:55 +000043#include "key.h"
Damien Millerd7834352006-08-05 12:39:39 +100044#include "hostfile.h"
45#include "auth.h"
Ben Lindstrom855bf3a2002-06-06 20:27:55 +000046#include "pathnames.h"
47#include "uidswap.h"
48#include "auth-options.h"
49#include "canohost.h"
Damien Millerd7834352006-08-05 12:39:39 +100050#ifdef GSSAPI
51#include "ssh-gss.h"
52#endif
Ben Lindstrom855bf3a2002-06-06 20:27:55 +000053#include "monitor_wrap.h"
Darren Tuckerf0f90982004-12-11 13:39:50 +110054#include "misc.h"
Ben Lindstrom855bf3a2002-06-06 20:27:55 +000055
56/* import */
57extern ServerOptions options;
58extern u_char *session_id2;
Darren Tucker502d3842003-06-28 12:38:01 +100059extern u_int session_id2_len;
Ben Lindstrom855bf3a2002-06-06 20:27:55 +000060
61static int
62userauth_pubkey(Authctxt *authctxt)
63{
64 Buffer b;
65 Key *key = NULL;
66 char *pkalg;
67 u_char *pkblob, *sig;
68 u_int alen, blen, slen;
69 int have_sig, pktype;
70 int authenticated = 0;
71
72 if (!authctxt->valid) {
73 debug2("userauth_pubkey: disabled because of invalid user");
74 return 0;
75 }
76 have_sig = packet_get_char();
77 if (datafellows & SSH_BUG_PKAUTH) {
78 debug2("userauth_pubkey: SSH_BUG_PKAUTH");
79 /* no explicit pkalg given */
80 pkblob = packet_get_string(&blen);
81 buffer_init(&b);
82 buffer_append(&b, pkblob, blen);
83 /* so we have to extract the pkalg from the pkblob */
84 pkalg = buffer_get_string(&b, &alen);
85 buffer_free(&b);
86 } else {
87 pkalg = packet_get_string(&alen);
88 pkblob = packet_get_string(&blen);
89 }
90 pktype = key_type_from_name(pkalg);
91 if (pktype == KEY_UNSPEC) {
92 /* this is perfectly legal */
Damien Miller996acd22003-04-09 20:59:48 +100093 logit("userauth_pubkey: unsupported public key algorithm: %s",
Ben Lindstrom855bf3a2002-06-06 20:27:55 +000094 pkalg);
95 goto done;
96 }
97 key = key_from_blob(pkblob, blen);
98 if (key == NULL) {
99 error("userauth_pubkey: cannot decode key: %s", pkalg);
100 goto done;
101 }
102 if (key->type != pktype) {
103 error("userauth_pubkey: type mismatch for decoded key "
104 "(received %d, expected %d)", key->type, pktype);
105 goto done;
106 }
107 if (have_sig) {
108 sig = packet_get_string(&slen);
109 packet_check_eom();
110 buffer_init(&b);
111 if (datafellows & SSH_OLD_SESSIONID) {
112 buffer_append(&b, session_id2, session_id2_len);
113 } else {
114 buffer_put_string(&b, session_id2, session_id2_len);
115 }
116 /* reconstruct packet */
117 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
118 buffer_put_cstring(&b, authctxt->user);
119 buffer_put_cstring(&b,
120 datafellows & SSH_BUG_PKSERVICE ?
121 "ssh-userauth" :
122 authctxt->service);
123 if (datafellows & SSH_BUG_PKAUTH) {
124 buffer_put_char(&b, have_sig);
125 } else {
126 buffer_put_cstring(&b, "publickey");
127 buffer_put_char(&b, have_sig);
128 buffer_put_cstring(&b, pkalg);
129 }
130 buffer_put_string(&b, pkblob, blen);
131#ifdef DEBUG_PK
132 buffer_dump(&b);
133#endif
134 /* test for correct signature */
135 authenticated = 0;
136 if (PRIVSEP(user_key_allowed(authctxt->pw, key)) &&
137 PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
Damien Millerfb1310e2004-01-21 11:02:50 +1100138 buffer_len(&b))) == 1)
Ben Lindstrom855bf3a2002-06-06 20:27:55 +0000139 authenticated = 1;
Damien Millerfb1310e2004-01-21 11:02:50 +1100140 buffer_free(&b);
Ben Lindstrom855bf3a2002-06-06 20:27:55 +0000141 xfree(sig);
142 } else {
143 debug("test whether pkalg/pkblob are acceptable");
144 packet_check_eom();
145
146 /* XXX fake reply and always send PK_OK ? */
147 /*
148 * XXX this allows testing whether a user is allowed
149 * to login: if you happen to have a valid pubkey this
150 * message is sent. the message is NEVER sent at all
151 * if a user is not allowed to login. is this an
152 * issue? -markus
153 */
154 if (PRIVSEP(user_key_allowed(authctxt->pw, key))) {
155 packet_start(SSH2_MSG_USERAUTH_PK_OK);
156 packet_put_string(pkalg, alen);
157 packet_put_string(pkblob, blen);
158 packet_send();
159 packet_write_wait();
160 authctxt->postponed = 1;
161 }
162 }
163 if (authenticated != 1)
164 auth_clear_options();
165done:
166 debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg);
167 if (key != NULL)
168 key_free(key);
169 xfree(pkalg);
170 xfree(pkblob);
171#ifdef HAVE_CYGWIN
172 if (check_nt_auth(0, authctxt->pw) == 0)
Damien Miller47656792004-09-11 22:42:09 +1000173 authenticated = 0;
Ben Lindstrom855bf3a2002-06-06 20:27:55 +0000174#endif
175 return authenticated;
176}
177
178/* return 1 if user allows given key */
179static int
180user_key_allowed2(struct passwd *pw, Key *key, char *file)
181{
Darren Tucker22cc7412004-12-06 22:47:41 +1100182 char line[SSH_MAX_PUBKEY_BYTES];
Ben Lindstrom855bf3a2002-06-06 20:27:55 +0000183 int found_key = 0;
184 FILE *f;
185 u_long linenum = 0;
186 struct stat st;
187 Key *found;
188 char *fp;
189
Ben Lindstrom855bf3a2002-06-06 20:27:55 +0000190 /* Temporarily use the user's uid. */
191 temporarily_use_uid(pw);
192
193 debug("trying public key file %s", file);
194
195 /* Fail quietly if file does not exist */
196 if (stat(file, &st) < 0) {
197 /* Restore the privileged uid. */
198 restore_uid();
199 return 0;
200 }
201 /* Open the file containing the authorized keys. */
202 f = fopen(file, "r");
203 if (!f) {
204 /* Restore the privileged uid. */
205 restore_uid();
206 return 0;
207 }
208 if (options.strict_modes &&
209 secure_filename(f, file, pw, line, sizeof(line)) != 0) {
210 fclose(f);
Damien Miller996acd22003-04-09 20:59:48 +1000211 logit("Authentication refused: %s", line);
Ben Lindstrom855bf3a2002-06-06 20:27:55 +0000212 restore_uid();
213 return 0;
214 }
215
216 found_key = 0;
217 found = key_new(key->type);
218
Darren Tucker22cc7412004-12-06 22:47:41 +1100219 while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
Darren Tucker3f9fdc72004-06-22 12:56:01 +1000220 char *cp, *key_options = NULL;
Darren Tucker22cc7412004-12-06 22:47:41 +1100221
Ben Lindstrom855bf3a2002-06-06 20:27:55 +0000222 /* Skip leading whitespace, empty and comment lines. */
223 for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
224 ;
225 if (!*cp || *cp == '\n' || *cp == '#')
226 continue;
227
228 if (key_read(found, &cp) != 1) {
229 /* no key? check if there are options for this key */
230 int quoted = 0;
231 debug2("user_key_allowed: check options: '%s'", cp);
Darren Tucker3f9fdc72004-06-22 12:56:01 +1000232 key_options = cp;
Ben Lindstrom855bf3a2002-06-06 20:27:55 +0000233 for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
234 if (*cp == '\\' && cp[1] == '"')
235 cp++; /* Skip both */
236 else if (*cp == '"')
237 quoted = !quoted;
238 }
239 /* Skip remaining whitespace. */
240 for (; *cp == ' ' || *cp == '\t'; cp++)
241 ;
242 if (key_read(found, &cp) != 1) {
243 debug2("user_key_allowed: advance: '%s'", cp);
244 /* still no key? advance to next line*/
245 continue;
246 }
247 }
248 if (key_equal(found, key) &&
Darren Tucker3f9fdc72004-06-22 12:56:01 +1000249 auth_parse_options(pw, key_options, file, linenum) == 1) {
Ben Lindstrom855bf3a2002-06-06 20:27:55 +0000250 found_key = 1;
251 debug("matching key found: file %s, line %lu",
252 file, linenum);
253 fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX);
254 verbose("Found matching %s key: %s",
255 key_type(found), fp);
256 xfree(fp);
257 break;
258 }
259 }
260 restore_uid();
261 fclose(f);
262 key_free(found);
263 if (!found_key)
264 debug2("key not found");
265 return found_key;
266}
267
268/* check whether given key is in .ssh/authorized_keys* */
269int
270user_key_allowed(struct passwd *pw, Key *key)
271{
272 int success;
273 char *file;
274
275 file = authorized_keys_file(pw);
276 success = user_key_allowed2(pw, key, file);
277 xfree(file);
278 if (success)
279 return success;
280
281 /* try suffix "2" for backward compat, too */
282 file = authorized_keys_file2(pw);
283 success = user_key_allowed2(pw, key, file);
284 xfree(file);
285 return success;
286}
287
288Authmethod method_pubkey = {
289 "publickey",
290 userauth_pubkey,
291 &options.pubkey_authentication
292};