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 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 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 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 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