1 /* $OpenBSD: auth2-pubkey.c,v 1.19 2008/07/03 21:46:58 otto 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
27 #include <sys/param.h>
28 #include <sys/stat.h>
29
30 #include <fcntl.h>
31 #include <pwd.h>
32 #include <stdio.h>
33 #include <stdarg.h>
34 #include <unistd.h>
35
36 #include "xmalloc.h"
37 #include "ssh.h"
38 #include "ssh2.h"
39 #include "packet.h"
40 #include "buffer.h"
41 #include "log.h"
42 #include "servconf.h"
43 #include "compat.h"
44 #include "key.h"
45 #include "hostfile.h"
46 #include "auth.h"
47 #include "pathnames.h"
48 #include "uidswap.h"
49 #include "auth-options.h"
50 #include "canohost.h"
51 #include "monitor_wrap.h"
52 #include "misc.h"
53
54 __RCSID("$MirOS: src/usr.bin/ssh/auth2-pubkey.c,v 1.8 2008/12/16 22:13:27 tg Exp $");
55
56 /* import */
57 extern ServerOptions options;
58 extern u_char *session_id2;
59 extern u_int session_id2_len;
60
61 static int
userauth_pubkey(Authctxt * authctxt)62 userauth_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 */
93 logit("userauth_pubkey: unsupported public key algorithm: %s",
94 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),
138 buffer_len(&b))) == 1)
139 authenticated = 1;
140 buffer_free(&b);
141 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();
165 done:
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 return authenticated;
172 }
173
174 /* return 1 if user allows given key */
175 static int
user_key_allowed2(struct passwd * pw,Key * key,char * file)176 user_key_allowed2(struct passwd *pw, Key *key, char *file)
177 {
178 char line[SSH_MAX_PUBKEY_BYTES];
179 int found_key = 0;
180 FILE *f;
181 u_long linenum = 0;
182 Key *found;
183 char *fp;
184
185 /* Temporarily use the user's uid. */
186 temporarily_use_uid(pw);
187
188 debug("trying public key file %s", file);
189 f = auth_openkeyfile(file, pw, options.strict_modes);
190
191 if (!f) {
192 restore_uid();
193 return 0;
194 }
195
196 found_key = 0;
197 found = key_new(key->type);
198
199 while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
200 char *cp, *key_options = NULL;
201
202 /* Skip leading whitespace, empty and comment lines. */
203 for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
204 ;
205 if (!*cp || *cp == '\n' || *cp == '#')
206 continue;
207
208 if (key_read(found, &cp) != 1) {
209 /* no key? check if there are options for this key */
210 int quoted = 0;
211 debug2("user_key_allowed: check options: '%s'", cp);
212 key_options = cp;
213 for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
214 if (*cp == '\\' && cp[1] == '"')
215 cp++; /* Skip both */
216 else if (*cp == '"')
217 quoted = !quoted;
218 }
219 /* Skip remaining whitespace. */
220 for (; *cp == ' ' || *cp == '\t'; cp++)
221 ;
222 if (key_read(found, &cp) != 1) {
223 debug2("user_key_allowed: advance: '%s'", cp);
224 /* still no key? advance to next line*/
225 continue;
226 }
227 }
228 if (key_equal(found, key) &&
229 auth_parse_options(pw, key_options, file, linenum) == 1) {
230 found_key = 1;
231 debug("matching key found: file %s, line %lu",
232 file, linenum);
233 fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX);
234 verbose("Found matching %s key: %s",
235 key_type(found), fp);
236 xfree(fp);
237 break;
238 }
239 }
240 restore_uid();
241 fclose(f);
242 key_free(found);
243 if (!found_key)
244 debug2("key not found");
245 return found_key;
246 }
247
248 /* check whether given key is in .etc/ssh/authorised_keys* */
249 int
user_key_allowed(struct passwd * pw,Key * key)250 user_key_allowed(struct passwd *pw, Key *key)
251 {
252 int success;
253 char *file;
254
255 file = authorised_keys_file(pw);
256 success = user_key_allowed2(pw, key, file);
257 xfree(file);
258 if (success)
259 return success;
260
261 /* try suffix "2" for backward compat, too */
262 file = authorised_keys_file2(pw);
263 success = user_key_allowed2(pw, key, file);
264 xfree(file);
265 return success;
266 }
267
268 Authmethod method_pubkey = {
269 "publickey",
270 userauth_pubkey,
271 &options.pubkey_authentication
272 };
273