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22616013 1/* $OpenBSD: auth2-pubkey.c,v 1.19 2008/07/03 21:46:58 otto Exp $ */
f5799ae1 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"
f5799ae1 27
9108f8d9 28#include <sys/types.h>
29#include <sys/stat.h>
30
22616013 31#include <fcntl.h>
9108f8d9 32#include <pwd.h>
33#include <stdio.h>
34#include <stdarg.h>
22616013 35#include <unistd.h>
9108f8d9 36
37#include "xmalloc.h"
996d5e62 38#include "ssh.h"
f5799ae1 39#include "ssh2.h"
f5799ae1 40#include "packet.h"
41#include "buffer.h"
42#include "log.h"
43#include "servconf.h"
44#include "compat.h"
f5799ae1 45#include "key.h"
9108f8d9 46#include "hostfile.h"
47#include "auth.h"
f5799ae1 48#include "pathnames.h"
49#include "uidswap.h"
50#include "auth-options.h"
51#include "canohost.h"
9108f8d9 52#ifdef GSSAPI
53#include "ssh-gss.h"
54#endif
f5799ae1 55#include "monitor_wrap.h"
996d5e62 56#include "misc.h"
f5799ae1 57
58/* import */
59extern ServerOptions options;
60extern u_char *session_id2;
0fff78ff 61extern u_int session_id2_len;
f5799ae1 62
63static int
64userauth_pubkey(Authctxt *authctxt)
65{
66 Buffer b;
67 Key *key = NULL;
68 char *pkalg;
69 u_char *pkblob, *sig;
70 u_int alen, blen, slen;
71 int have_sig, pktype;
72 int authenticated = 0;
73
74 if (!authctxt->valid) {
75 debug2("userauth_pubkey: disabled because of invalid user");
76 return 0;
77 }
78 have_sig = packet_get_char();
79 if (datafellows & SSH_BUG_PKAUTH) {
80 debug2("userauth_pubkey: SSH_BUG_PKAUTH");
81 /* no explicit pkalg given */
82 pkblob = packet_get_string(&blen);
83 buffer_init(&b);
84 buffer_append(&b, pkblob, blen);
85 /* so we have to extract the pkalg from the pkblob */
86 pkalg = buffer_get_string(&b, &alen);
87 buffer_free(&b);
88 } else {
89 pkalg = packet_get_string(&alen);
90 pkblob = packet_get_string(&blen);
91 }
92 pktype = key_type_from_name(pkalg);
93 if (pktype == KEY_UNSPEC) {
94 /* this is perfectly legal */
0fff78ff 95 logit("userauth_pubkey: unsupported public key algorithm: %s",
f5799ae1 96 pkalg);
97 goto done;
98 }
99 key = key_from_blob(pkblob, blen);
100 if (key == NULL) {
101 error("userauth_pubkey: cannot decode key: %s", pkalg);
102 goto done;
103 }
104 if (key->type != pktype) {
105 error("userauth_pubkey: type mismatch for decoded key "
106 "(received %d, expected %d)", key->type, pktype);
107 goto done;
108 }
109 if (have_sig) {
110 sig = packet_get_string(&slen);
111 packet_check_eom();
112 buffer_init(&b);
113 if (datafellows & SSH_OLD_SESSIONID) {
114 buffer_append(&b, session_id2, session_id2_len);
115 } else {
116 buffer_put_string(&b, session_id2, session_id2_len);
117 }
118 /* reconstruct packet */
119 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
120 buffer_put_cstring(&b, authctxt->user);
121 buffer_put_cstring(&b,
122 datafellows & SSH_BUG_PKSERVICE ?
123 "ssh-userauth" :
124 authctxt->service);
125 if (datafellows & SSH_BUG_PKAUTH) {
126 buffer_put_char(&b, have_sig);
127 } else {
128 buffer_put_cstring(&b, "publickey");
129 buffer_put_char(&b, have_sig);
130 buffer_put_cstring(&b, pkalg);
131 }
132 buffer_put_string(&b, pkblob, blen);
133#ifdef DEBUG_PK
134 buffer_dump(&b);
135#endif
136 /* test for correct signature */
137 authenticated = 0;
138 if (PRIVSEP(user_key_allowed(authctxt->pw, key)) &&
139 PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
cdd66111 140 buffer_len(&b))) == 1)
f5799ae1 141 authenticated = 1;
cdd66111 142 buffer_free(&b);
f5799ae1 143 xfree(sig);
144 } else {
145 debug("test whether pkalg/pkblob are acceptable");
146 packet_check_eom();
147
148 /* XXX fake reply and always send PK_OK ? */
149 /*
150 * XXX this allows testing whether a user is allowed
151 * to login: if you happen to have a valid pubkey this
152 * message is sent. the message is NEVER sent at all
153 * if a user is not allowed to login. is this an
154 * issue? -markus
155 */
156 if (PRIVSEP(user_key_allowed(authctxt->pw, key))) {
157 packet_start(SSH2_MSG_USERAUTH_PK_OK);
158 packet_put_string(pkalg, alen);
159 packet_put_string(pkblob, blen);
160 packet_send();
161 packet_write_wait();
162 authctxt->postponed = 1;
163 }
164 }
165 if (authenticated != 1)
166 auth_clear_options();
167done:
168 debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg);
169 if (key != NULL)
170 key_free(key);
171 xfree(pkalg);
172 xfree(pkblob);
173#ifdef HAVE_CYGWIN
174 if (check_nt_auth(0, authctxt->pw) == 0)
996d5e62 175 authenticated = 0;
f5799ae1 176#endif
177 return authenticated;
178}
179
180/* return 1 if user allows given key */
181static int
182user_key_allowed2(struct passwd *pw, Key *key, char *file)
183{
996d5e62 184 char line[SSH_MAX_PUBKEY_BYTES];
f5799ae1 185 int found_key = 0;
186 FILE *f;
187 u_long linenum = 0;
f5799ae1 188 Key *found;
189 char *fp;
190
f5799ae1 191 /* Temporarily use the user's uid. */
192 temporarily_use_uid(pw);
193
194 debug("trying public key file %s", file);
22616013 195 f = auth_openkeyfile(file, pw, options.strict_modes);
f5799ae1 196
f5799ae1 197 if (!f) {
f5799ae1 198 restore_uid();
199 return 0;
200 }
201
202 found_key = 0;
203 found = key_new(key->type);
204
996d5e62 205 while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
c9f39d2c 206 char *cp, *key_options = NULL;
996d5e62 207
f5799ae1 208 /* Skip leading whitespace, empty and comment lines. */
209 for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
210 ;
211 if (!*cp || *cp == '\n' || *cp == '#')
212 continue;
213
214 if (key_read(found, &cp) != 1) {
215 /* no key? check if there are options for this key */
216 int quoted = 0;
217 debug2("user_key_allowed: check options: '%s'", cp);
c9f39d2c 218 key_options = cp;
f5799ae1 219 for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
220 if (*cp == '\\' && cp[1] == '"')
221 cp++; /* Skip both */
222 else if (*cp == '"')
223 quoted = !quoted;
224 }
225 /* Skip remaining whitespace. */
226 for (; *cp == ' ' || *cp == '\t'; cp++)
227 ;
228 if (key_read(found, &cp) != 1) {
229 debug2("user_key_allowed: advance: '%s'", cp);
230 /* still no key? advance to next line*/
231 continue;
232 }
233 }
234 if (key_equal(found, key) &&
c9f39d2c 235 auth_parse_options(pw, key_options, file, linenum) == 1) {
f5799ae1 236 found_key = 1;
237 debug("matching key found: file %s, line %lu",
238 file, linenum);
239 fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX);
240 verbose("Found matching %s key: %s",
241 key_type(found), fp);
242 xfree(fp);
243 break;
244 }
245 }
246 restore_uid();
247 fclose(f);
248 key_free(found);
249 if (!found_key)
250 debug2("key not found");
251 return found_key;
252}
253
254/* check whether given key is in .ssh/authorized_keys* */
255int
256user_key_allowed(struct passwd *pw, Key *key)
257{
258 int success;
259 char *file;
260
261 file = authorized_keys_file(pw);
262 success = user_key_allowed2(pw, key, file);
263 xfree(file);
264 if (success)
265 return success;
266
267 /* try suffix "2" for backward compat, too */
268 file = authorized_keys_file2(pw);
269 success = user_key_allowed2(pw, key, file);
270 xfree(file);
271 return success;
272}
273
274Authmethod method_pubkey = {
275 "publickey",
276 userauth_pubkey,
277 &options.pubkey_authentication
278};
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