1 /* $OpenBSD: auth2-pubkey.c,v 1.29 2011/05/23 03:30:07 djm 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 #include "includes.h" 27 28 #include <sys/types.h> 29 #include <sys/stat.h> 30 31 #include <fcntl.h> 32 #include <pwd.h> 33 #include <stdio.h> 34 #include <stdarg.h> 35 #include <string.h> 36 #include <time.h> 37 #include <unistd.h> 38 39 #include "xmalloc.h" 40 #include "ssh.h" 41 #include "ssh2.h" 42 #include "packet.h" 43 #include "buffer.h" 44 #include "log.h" 45 #include "servconf.h" 46 #include "compat.h" 47 #include "key.h" 48 #include "hostfile.h" 49 #include "auth.h" 50 #include "pathnames.h" 51 #include "uidswap.h" 52 #include "auth-options.h" 53 #include "canohost.h" 54 #ifdef GSSAPI 55 #include "ssh-gss.h" 56 #endif 57 #include "monitor_wrap.h" 58 #include "misc.h" 59 #include "authfile.h" 60 #include "match.h" 61 62 /* import */ 63 extern ServerOptions options; 64 extern u_char *session_id2; 65 extern u_int session_id2_len; 66 67 static int 68 userauth_pubkey(Authctxt *authctxt) 69 { 70 Buffer b; 71 Key *key = NULL; 72 char *pkalg; 73 u_char *pkblob, *sig; 74 u_int alen, blen, slen; 75 int have_sig, pktype; 76 int authenticated = 0; 77 78 if (!authctxt->valid) { 79 debug2("userauth_pubkey: disabled because of invalid user"); 80 return 0; 81 } 82 have_sig = packet_get_char(); 83 if (datafellows & SSH_BUG_PKAUTH) { 84 debug2("userauth_pubkey: SSH_BUG_PKAUTH"); 85 /* no explicit pkalg given */ 86 pkblob = packet_get_string(&blen); 87 buffer_init(&b); 88 buffer_append(&b, pkblob, blen); 89 /* so we have to extract the pkalg from the pkblob */ 90 pkalg = buffer_get_string(&b, &alen); 91 buffer_free(&b); 92 } else { 93 pkalg = packet_get_string(&alen); 94 pkblob = packet_get_string(&blen); 95 } 96 pktype = key_type_from_name(pkalg); 97 if (pktype == KEY_UNSPEC) { 98 /* this is perfectly legal */ 99 logit("userauth_pubkey: unsupported public key algorithm: %s", 100 pkalg); 101 goto done; 102 } 103 key = key_from_blob(pkblob, blen); 104 if (key == NULL) { 105 error("userauth_pubkey: cannot decode key: %s", pkalg); 106 goto done; 107 } 108 if (key->type != pktype) { 109 error("userauth_pubkey: type mismatch for decoded key " 110 "(received %d, expected %d)", key->type, pktype); 111 goto done; 112 } 113 if (have_sig) { 114 sig = packet_get_string(&slen); 115 packet_check_eom(); 116 buffer_init(&b); 117 if (datafellows & SSH_OLD_SESSIONID) { 118 buffer_append(&b, session_id2, session_id2_len); 119 } else { 120 buffer_put_string(&b, session_id2, session_id2_len); 121 } 122 /* reconstruct packet */ 123 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST); 124 buffer_put_cstring(&b, authctxt->user); 125 buffer_put_cstring(&b, 126 datafellows & SSH_BUG_PKSERVICE ? 127 "ssh-userauth" : 128 authctxt->service); 129 if (datafellows & SSH_BUG_PKAUTH) { 130 buffer_put_char(&b, have_sig); 131 } else { 132 buffer_put_cstring(&b, "publickey"); 133 buffer_put_char(&b, have_sig); 134 buffer_put_cstring(&b, pkalg); 135 } 136 buffer_put_string(&b, pkblob, blen); 137 #ifdef DEBUG_PK 138 buffer_dump(&b); 139 #endif 140 /* test for correct signature */ 141 authenticated = 0; 142 if (PRIVSEP(user_key_allowed(authctxt->pw, key)) && 143 PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b), 144 buffer_len(&b))) == 1) 145 authenticated = 1; 146 buffer_free(&b); 147 xfree(sig); 148 } else { 149 debug("test whether pkalg/pkblob are acceptable"); 150 packet_check_eom(); 151 152 /* XXX fake reply and always send PK_OK ? */ 153 /* 154 * XXX this allows testing whether a user is allowed 155 * to login: if you happen to have a valid pubkey this 156 * message is sent. the message is NEVER sent at all 157 * if a user is not allowed to login. is this an 158 * issue? -markus 159 */ 160 if (PRIVSEP(user_key_allowed(authctxt->pw, key))) { 161 packet_start(SSH2_MSG_USERAUTH_PK_OK); 162 packet_put_string(pkalg, alen); 163 packet_put_string(pkblob, blen); 164 packet_send(); 165 packet_write_wait(); 166 authctxt->postponed = 1; 167 } 168 } 169 if (authenticated != 1) 170 auth_clear_options(); 171 done: 172 debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg); 173 if (key != NULL) 174 key_free(key); 175 xfree(pkalg); 176 xfree(pkblob); 177 return authenticated; 178 } 179 180 static int 181 match_principals_option(const char *principal_list, struct KeyCert *cert) 182 { 183 char *result; 184 u_int i; 185 186 /* XXX percent_expand() sequences for authorized_principals? */ 187 188 for (i = 0; i < cert->nprincipals; i++) { 189 if ((result = match_list(cert->principals[i], 190 principal_list, NULL)) != NULL) { 191 debug3("matched principal from key options \"%.100s\"", 192 result); 193 xfree(result); 194 return 1; 195 } 196 } 197 return 0; 198 } 199 200 static int 201 match_principals_file(char *file, struct passwd *pw, struct KeyCert *cert) 202 { 203 FILE *f; 204 char line[SSH_MAX_PUBKEY_BYTES], *cp, *ep, *line_opts; 205 u_long linenum = 0; 206 u_int i; 207 208 temporarily_use_uid(pw); 209 debug("trying authorized principals file %s", file); 210 if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) { 211 restore_uid(); 212 return 0; 213 } 214 while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) { 215 /* Skip leading whitespace. */ 216 for (cp = line; *cp == ' ' || *cp == '\t'; cp++) 217 ; 218 /* Skip blank and comment lines. */ 219 if ((ep = strchr(cp, '#')) != NULL) 220 *ep = '\0'; 221 if (!*cp || *cp == '\n') 222 continue; 223 /* Trim trailing whitespace. */ 224 ep = cp + strlen(cp) - 1; 225 while (ep > cp && (*ep == '\n' || *ep == ' ' || *ep == '\t')) 226 *ep-- = '\0'; 227 /* 228 * If the line has internal whitespace then assume it has 229 * key options. 230 */ 231 line_opts = NULL; 232 if ((ep = strrchr(cp, ' ')) != NULL || 233 (ep = strrchr(cp, '\t')) != NULL) { 234 for (; *ep == ' ' || *ep == '\t'; ep++) 235 ; 236 line_opts = cp; 237 cp = ep; 238 } 239 for (i = 0; i < cert->nprincipals; i++) { 240 if (strcmp(cp, cert->principals[i]) == 0) { 241 debug3("matched principal from file \"%.100s\"", 242 cert->principals[i]); 243 if (auth_parse_options(pw, line_opts, 244 file, linenum) != 1) 245 continue; 246 fclose(f); 247 restore_uid(); 248 return 1; 249 } 250 } 251 } 252 fclose(f); 253 restore_uid(); 254 return 0; 255 } 256 257 /* return 1 if user allows given key */ 258 static int 259 user_key_allowed2(struct passwd *pw, Key *key, char *file) 260 { 261 char line[SSH_MAX_PUBKEY_BYTES]; 262 const char *reason; 263 int found_key = 0; 264 FILE *f; 265 u_long linenum = 0; 266 Key *found; 267 char *fp; 268 269 /* Temporarily use the user's uid. */ 270 temporarily_use_uid(pw); 271 272 debug("trying public key file %s", file); 273 f = auth_openkeyfile(file, pw, options.strict_modes); 274 275 if (!f) { 276 restore_uid(); 277 return 0; 278 } 279 280 found_key = 0; 281 found = key_new(key_is_cert(key) ? KEY_UNSPEC : key->type); 282 283 while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) { 284 char *cp, *key_options = NULL; 285 286 auth_clear_options(); 287 288 /* Skip leading whitespace, empty and comment lines. */ 289 for (cp = line; *cp == ' ' || *cp == '\t'; cp++) 290 ; 291 if (!*cp || *cp == '\n' || *cp == '#') 292 continue; 293 294 if (key_read(found, &cp) != 1) { 295 /* no key? check if there are options for this key */ 296 int quoted = 0; 297 debug2("user_key_allowed: check options: '%s'", cp); 298 key_options = cp; 299 for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) { 300 if (*cp == '\\' && cp[1] == '"') 301 cp++; /* Skip both */ 302 else if (*cp == '"') 303 quoted = !quoted; 304 } 305 /* Skip remaining whitespace. */ 306 for (; *cp == ' ' || *cp == '\t'; cp++) 307 ; 308 if (key_read(found, &cp) != 1) { 309 debug2("user_key_allowed: advance: '%s'", cp); 310 /* still no key? advance to next line*/ 311 continue; 312 } 313 } 314 if (key_is_cert(key)) { 315 if (!key_equal(found, key->cert->signature_key)) 316 continue; 317 if (auth_parse_options(pw, key_options, file, 318 linenum) != 1) 319 continue; 320 if (!key_is_cert_authority) 321 continue; 322 fp = key_fingerprint(found, SSH_FP_MD5, 323 SSH_FP_HEX); 324 debug("matching CA found: file %s, line %lu, %s %s", 325 file, linenum, key_type(found), fp); 326 /* 327 * If the user has specified a list of principals as 328 * a key option, then prefer that list to matching 329 * their username in the certificate principals list. 330 */ 331 if (authorized_principals != NULL && 332 !match_principals_option(authorized_principals, 333 key->cert)) { 334 reason = "Certificate does not contain an " 335 "authorized principal"; 336 fail_reason: 337 xfree(fp); 338 error("%s", reason); 339 auth_debug_add("%s", reason); 340 continue; 341 } 342 if (key_cert_check_authority(key, 0, 0, 343 authorized_principals == NULL ? pw->pw_name : NULL, 344 &reason) != 0) 345 goto fail_reason; 346 if (auth_cert_options(key, pw) != 0) { 347 xfree(fp); 348 continue; 349 } 350 verbose("Accepted certificate ID \"%s\" " 351 "signed by %s CA %s via %s", key->cert->key_id, 352 key_type(found), fp, file); 353 xfree(fp); 354 found_key = 1; 355 break; 356 } else if (key_equal(found, key)) { 357 if (auth_parse_options(pw, key_options, file, 358 linenum) != 1) 359 continue; 360 if (key_is_cert_authority) 361 continue; 362 found_key = 1; 363 debug("matching key found: file %s, line %lu", 364 file, linenum); 365 fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX); 366 verbose("Found matching %s key: %s", 367 key_type(found), fp); 368 xfree(fp); 369 break; 370 } 371 } 372 restore_uid(); 373 fclose(f); 374 key_free(found); 375 if (!found_key) 376 debug2("key not found"); 377 return found_key; 378 } 379 380 /* Authenticate a certificate key against TrustedUserCAKeys */ 381 static int 382 user_cert_trusted_ca(struct passwd *pw, Key *key) 383 { 384 char *ca_fp, *principals_file = NULL; 385 const char *reason; 386 int ret = 0; 387 388 if (!key_is_cert(key) || options.trusted_user_ca_keys == NULL) 389 return 0; 390 391 ca_fp = key_fingerprint(key->cert->signature_key, 392 SSH_FP_MD5, SSH_FP_HEX); 393 394 if (key_in_file(key->cert->signature_key, 395 options.trusted_user_ca_keys, 1) != 1) { 396 debug2("%s: CA %s %s is not listed in %s", __func__, 397 key_type(key->cert->signature_key), ca_fp, 398 options.trusted_user_ca_keys); 399 goto out; 400 } 401 /* 402 * If AuthorizedPrincipals is in use, then compare the certificate 403 * principals against the names in that file rather than matching 404 * against the username. 405 */ 406 if ((principals_file = authorized_principals_file(pw)) != NULL) { 407 if (!match_principals_file(principals_file, pw, key->cert)) { 408 reason = "Certificate does not contain an " 409 "authorized principal"; 410 fail_reason: 411 error("%s", reason); 412 auth_debug_add("%s", reason); 413 goto out; 414 } 415 } 416 if (key_cert_check_authority(key, 0, 1, 417 principals_file == NULL ? pw->pw_name : NULL, &reason) != 0) 418 goto fail_reason; 419 if (auth_cert_options(key, pw) != 0) 420 goto out; 421 422 verbose("Accepted certificate ID \"%s\" signed by %s CA %s via %s", 423 key->cert->key_id, key_type(key->cert->signature_key), ca_fp, 424 options.trusted_user_ca_keys); 425 ret = 1; 426 427 out: 428 if (principals_file != NULL) 429 xfree(principals_file); 430 if (ca_fp != NULL) 431 xfree(ca_fp); 432 return ret; 433 } 434 435 /* check whether given key is in .ssh/authorized_keys* */ 436 int 437 user_key_allowed(struct passwd *pw, Key *key) 438 { 439 u_int success, i; 440 char *file; 441 442 if (auth_key_is_revoked(key)) 443 return 0; 444 if (key_is_cert(key) && auth_key_is_revoked(key->cert->signature_key)) 445 return 0; 446 447 success = user_cert_trusted_ca(pw, key); 448 if (success) 449 return success; 450 451 for (i = 0; !success && i < options.num_authkeys_files; i++) { 452 file = expand_authorized_keys( 453 options.authorized_keys_files[i], pw); 454 success = user_key_allowed2(pw, key, file); 455 xfree(file); 456 } 457 458 return success; 459 } 460 461 Authmethod method_pubkey = { 462 "publickey", 463 userauth_pubkey, 464 &options.pubkey_authentication 465 }; 466
