1 /* 2 * QEMU VNC display driver: SASL auth protocol 3 * 4 * Copyright (C) 2009 Red Hat, Inc 5 * 6 * Permission is hereby granted, free of charge, to any person obtaining a copy 7 * of this software and associated documentation files (the "Software"), to deal 8 * in the Software without restriction, including without limitation the rights 9 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell 10 * copies of the Software, and to permit persons to whom the Software is 11 * furnished to do so, subject to the following conditions: 12 * 13 * The above copyright notice and this permission notice shall be included in 14 * all copies or substantial portions of the Software. 15 * 16 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 17 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 18 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL 19 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 20 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 21 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN 22 * THE SOFTWARE. 23 */ 24 25 #include "vnc.h" 26 27 /* Max amount of data we send/recv for SASL steps to prevent DOS */ 28 #define SASL_DATA_MAX_LEN (1024 * 1024) 29 30 31 void vnc_sasl_client_cleanup(VncState *vs) 32 { 33 if (vs->sasl.conn) { 34 vs->sasl.runSSF = vs->sasl.waitWriteSSF = vs->sasl.wantSSF = 0; 35 vs->sasl.encodedLength = vs->sasl.encodedOffset = 0; 36 vs->sasl.encoded = NULL; 37 free(vs->sasl.username); 38 free(vs->sasl.mechlist); 39 vs->sasl.username = vs->sasl.mechlist = NULL; 40 sasl_dispose(&vs->sasl.conn); 41 vs->sasl.conn = NULL; 42 } 43 } 44 45 46 long vnc_client_write_sasl(VncState *vs) 47 { 48 long ret; 49 50 VNC_DEBUG("Write SASL: Pending output %p size %zd offset %zd " 51 "Encoded: %p size %d offset %d\n", 52 vs->output.buffer, vs->output.capacity, vs->output.offset, 53 vs->sasl.encoded, vs->sasl.encodedLength, vs->sasl.encodedOffset); 54 55 if (!vs->sasl.encoded) { 56 int err; 57 err = sasl_encode(vs->sasl.conn, 58 (char *)vs->output.buffer, 59 vs->output.offset, 60 (const char **)&vs->sasl.encoded, 61 &vs->sasl.encodedLength); 62 if (err != SASL_OK) 63 return vnc_client_io_error(vs, -1, EIO); 64 65 vs->sasl.encodedOffset = 0; 66 } 67 68 ret = vnc_client_write_buf(vs, 69 vs->sasl.encoded + vs->sasl.encodedOffset, 70 vs->sasl.encodedLength - vs->sasl.encodedOffset); 71 if (!ret) 72 return 0; 73 74 vs->sasl.encodedOffset += ret; 75 if (vs->sasl.encodedOffset == vs->sasl.encodedLength) { 76 vs->output.offset = 0; 77 vs->sasl.encoded = NULL; 78 vs->sasl.encodedOffset = vs->sasl.encodedLength = 0; 79 } 80 81 /* Can't merge this block with one above, because 82 * someone might have written more unencrypted 83 * data in vs->output while we were processing 84 * SASL encoded output 85 */ 86 if (vs->output.offset == 0) { 87 qemu_set_fd_handler2(vs->csock, NULL, vnc_client_read, NULL, vs); 88 } 89 90 return ret; 91 } 92 93 94 long vnc_client_read_sasl(VncState *vs) 95 { 96 long ret; 97 uint8_t encoded[4096]; 98 const char *decoded; 99 unsigned int decodedLen; 100 int err; 101 102 ret = vnc_client_read_buf(vs, encoded, sizeof(encoded)); 103 if (!ret) 104 return 0; 105 106 err = sasl_decode(vs->sasl.conn, 107 (char *)encoded, ret, 108 &decoded, &decodedLen); 109 110 if (err != SASL_OK) 111 return vnc_client_io_error(vs, -1, -EIO); 112 VNC_DEBUG("Read SASL Encoded %p size %ld Decoded %p size %d\n", 113 encoded, ret, decoded, decodedLen); 114 buffer_reserve(&vs->input, decodedLen); 115 buffer_append(&vs->input, decoded, decodedLen); 116 return decodedLen; 117 } 118 119 120 static int vnc_auth_sasl_check_access(VncState *vs) 121 { 122 const void *val; 123 int err; 124 int allow; 125 126 err = sasl_getprop(vs->sasl.conn, SASL_USERNAME, &val); 127 if (err != SASL_OK) { 128 VNC_DEBUG("cannot query SASL username on connection %d (%s), denying access\n", 129 err, sasl_errstring(err, NULL, NULL)); 130 return -1; 131 } 132 if (val == NULL) { 133 VNC_DEBUG("no client username was found, denying access\n"); 134 return -1; 135 } 136 VNC_DEBUG("SASL client username %s\n", (const char *)val); 137 138 vs->sasl.username = g_strdup((const char*)val); 139 140 if (vs->vd->sasl.acl == NULL) { 141 VNC_DEBUG("no ACL activated, allowing access\n"); 142 return 0; 143 } 144 145 allow = qemu_acl_party_is_allowed(vs->vd->sasl.acl, vs->sasl.username); 146 147 VNC_DEBUG("SASL client %s %s by ACL\n", vs->sasl.username, 148 allow ? "allowed" : "denied"); 149 return allow ? 0 : -1; 150 } 151 152 static int vnc_auth_sasl_check_ssf(VncState *vs) 153 { 154 const void *val; 155 int err, ssf; 156 157 if (!vs->sasl.wantSSF) 158 return 1; 159 160 err = sasl_getprop(vs->sasl.conn, SASL_SSF, &val); 161 if (err != SASL_OK) 162 return 0; 163 164 ssf = *(const int *)val; 165 VNC_DEBUG("negotiated an SSF of %d\n", ssf); 166 if (ssf < 56) 167 return 0; /* 56 is good for Kerberos */ 168 169 /* Only setup for read initially, because we're about to send an RPC 170 * reply which must be in plain text. When the next incoming RPC 171 * arrives, we'll switch on writes too 172 * 173 * cf qemudClientReadSASL in qemud.c 174 */ 175 vs->sasl.runSSF = 1; 176 177 /* We have a SSF that's good enough */ 178 return 1; 179 } 180 181 /* 182 * Step Msg 183 * 184 * Input from client: 185 * 186 * u32 clientin-length 187 * u8-array clientin-string 188 * 189 * Output to client: 190 * 191 * u32 serverout-length 192 * u8-array serverout-strin 193 * u8 continue 194 */ 195 196 static int protocol_client_auth_sasl_step_len(VncState *vs, uint8_t *data, size_t len); 197 198 static int protocol_client_auth_sasl_step(VncState *vs, uint8_t *data, size_t len) 199 { 200 uint32_t datalen = len; 201 const char *serverout; 202 unsigned int serveroutlen; 203 int err; 204 char *clientdata = NULL; 205 206 /* NB, distinction of NULL vs "" is *critical* in SASL */ 207 if (datalen) { 208 clientdata = (char*)data; 209 clientdata[datalen-1] = '\0'; /* Wire includes '\0', but make sure */ 210 datalen--; /* Don't count NULL byte when passing to _start() */ 211 } 212 213 VNC_DEBUG("Step using SASL Data %p (%d bytes)\n", 214 clientdata, datalen); 215 err = sasl_server_step(vs->sasl.conn, 216 clientdata, 217 datalen, 218 &serverout, 219 &serveroutlen); 220 if (err != SASL_OK && 221 err != SASL_CONTINUE) { 222 VNC_DEBUG("sasl step failed %d (%s)\n", 223 err, sasl_errdetail(vs->sasl.conn)); 224 sasl_dispose(&vs->sasl.conn); 225 vs->sasl.conn = NULL; 226 goto authabort; 227 } 228 229 if (serveroutlen > SASL_DATA_MAX_LEN) { 230 VNC_DEBUG("sasl step reply data too long %d\n", 231 serveroutlen); 232 sasl_dispose(&vs->sasl.conn); 233 vs->sasl.conn = NULL; 234 goto authabort; 235 } 236 237 VNC_DEBUG("SASL return data %d bytes, nil; %d\n", 238 serveroutlen, serverout ? 0 : 1); 239 240 if (serveroutlen) { 241 vnc_write_u32(vs, serveroutlen + 1); 242 vnc_write(vs, serverout, serveroutlen + 1); 243 } else { 244 vnc_write_u32(vs, 0); 245 } 246 247 /* Whether auth is complete */ 248 vnc_write_u8(vs, err == SASL_CONTINUE ? 0 : 1); 249 250 if (err == SASL_CONTINUE) { 251 VNC_DEBUG("%s", "Authentication must continue\n"); 252 /* Wait for step length */ 253 vnc_read_when(vs, protocol_client_auth_sasl_step_len, 4); 254 } else { 255 if (!vnc_auth_sasl_check_ssf(vs)) { 256 VNC_DEBUG("Authentication rejected for weak SSF %d\n", vs->csock); 257 goto authreject; 258 } 259 260 /* Check username whitelist ACL */ 261 if (vnc_auth_sasl_check_access(vs) < 0) { 262 VNC_DEBUG("Authentication rejected for ACL %d\n", vs->csock); 263 goto authreject; 264 } 265 266 VNC_DEBUG("Authentication successful %d\n", vs->csock); 267 vnc_write_u32(vs, 0); /* Accept auth */ 268 /* 269 * Delay writing in SSF encoded mode until pending output 270 * buffer is written 271 */ 272 if (vs->sasl.runSSF) 273 vs->sasl.waitWriteSSF = vs->output.offset; 274 start_client_init(vs); 275 } 276 277 return 0; 278 279 authreject: 280 vnc_write_u32(vs, 1); /* Reject auth */ 281 vnc_write_u32(vs, sizeof("Authentication failed")); 282 vnc_write(vs, "Authentication failed", sizeof("Authentication failed")); 283 vnc_flush(vs); 284 vnc_client_error(vs); 285 return -1; 286 287 authabort: 288 vnc_client_error(vs); 289 return -1; 290 } 291 292 static int protocol_client_auth_sasl_step_len(VncState *vs, uint8_t *data, size_t len) 293 { 294 uint32_t steplen = read_u32(data, 0); 295 VNC_DEBUG("Got client step len %d\n", steplen); 296 if (steplen > SASL_DATA_MAX_LEN) { 297 VNC_DEBUG("Too much SASL data %d\n", steplen); 298 vnc_client_error(vs); 299 return -1; 300 } 301 302 if (steplen == 0) 303 return protocol_client_auth_sasl_step(vs, NULL, 0); 304 else 305 vnc_read_when(vs, protocol_client_auth_sasl_step, steplen); 306 return 0; 307 } 308 309 /* 310 * Start Msg 311 * 312 * Input from client: 313 * 314 * u32 clientin-length 315 * u8-array clientin-string 316 * 317 * Output to client: 318 * 319 * u32 serverout-length 320 * u8-array serverout-strin 321 * u8 continue 322 */ 323 324 #define SASL_DATA_MAX_LEN (1024 * 1024) 325 326 static int protocol_client_auth_sasl_start(VncState *vs, uint8_t *data, size_t len) 327 { 328 uint32_t datalen = len; 329 const char *serverout; 330 unsigned int serveroutlen; 331 int err; 332 char *clientdata = NULL; 333 334 /* NB, distinction of NULL vs "" is *critical* in SASL */ 335 if (datalen) { 336 clientdata = (char*)data; 337 clientdata[datalen-1] = '\0'; /* Should be on wire, but make sure */ 338 datalen--; /* Don't count NULL byte when passing to _start() */ 339 } 340 341 VNC_DEBUG("Start SASL auth with mechanism %s. Data %p (%d bytes)\n", 342 vs->sasl.mechlist, clientdata, datalen); 343 err = sasl_server_start(vs->sasl.conn, 344 vs->sasl.mechlist, 345 clientdata, 346 datalen, 347 &serverout, 348 &serveroutlen); 349 if (err != SASL_OK && 350 err != SASL_CONTINUE) { 351 VNC_DEBUG("sasl start failed %d (%s)\n", 352 err, sasl_errdetail(vs->sasl.conn)); 353 sasl_dispose(&vs->sasl.conn); 354 vs->sasl.conn = NULL; 355 goto authabort; 356 } 357 if (serveroutlen > SASL_DATA_MAX_LEN) { 358 VNC_DEBUG("sasl start reply data too long %d\n", 359 serveroutlen); 360 sasl_dispose(&vs->sasl.conn); 361 vs->sasl.conn = NULL; 362 goto authabort; 363 } 364 365 VNC_DEBUG("SASL return data %d bytes, nil; %d\n", 366 serveroutlen, serverout ? 0 : 1); 367 368 if (serveroutlen) { 369 vnc_write_u32(vs, serveroutlen + 1); 370 vnc_write(vs, serverout, serveroutlen + 1); 371 } else { 372 vnc_write_u32(vs, 0); 373 } 374 375 /* Whether auth is complete */ 376 vnc_write_u8(vs, err == SASL_CONTINUE ? 0 : 1); 377 378 if (err == SASL_CONTINUE) { 379 VNC_DEBUG("%s", "Authentication must continue\n"); 380 /* Wait for step length */ 381 vnc_read_when(vs, protocol_client_auth_sasl_step_len, 4); 382 } else { 383 if (!vnc_auth_sasl_check_ssf(vs)) { 384 VNC_DEBUG("Authentication rejected for weak SSF %d\n", vs->csock); 385 goto authreject; 386 } 387 388 /* Check username whitelist ACL */ 389 if (vnc_auth_sasl_check_access(vs) < 0) { 390 VNC_DEBUG("Authentication rejected for ACL %d\n", vs->csock); 391 goto authreject; 392 } 393 394 VNC_DEBUG("Authentication successful %d\n", vs->csock); 395 vnc_write_u32(vs, 0); /* Accept auth */ 396 start_client_init(vs); 397 } 398 399 return 0; 400 401 authreject: 402 vnc_write_u32(vs, 1); /* Reject auth */ 403 vnc_write_u32(vs, sizeof("Authentication failed")); 404 vnc_write(vs, "Authentication failed", sizeof("Authentication failed")); 405 vnc_flush(vs); 406 vnc_client_error(vs); 407 return -1; 408 409 authabort: 410 vnc_client_error(vs); 411 return -1; 412 } 413 414 static int protocol_client_auth_sasl_start_len(VncState *vs, uint8_t *data, size_t len) 415 { 416 uint32_t startlen = read_u32(data, 0); 417 VNC_DEBUG("Got client start len %d\n", startlen); 418 if (startlen > SASL_DATA_MAX_LEN) { 419 VNC_DEBUG("Too much SASL data %d\n", startlen); 420 vnc_client_error(vs); 421 return -1; 422 } 423 424 if (startlen == 0) 425 return protocol_client_auth_sasl_start(vs, NULL, 0); 426 427 vnc_read_when(vs, protocol_client_auth_sasl_start, startlen); 428 return 0; 429 } 430 431 static int protocol_client_auth_sasl_mechname(VncState *vs, uint8_t *data, size_t len) 432 { 433 char *mechname = malloc(len + 1); 434 if (!mechname) { 435 VNC_DEBUG("Out of memory reading mechname\n"); 436 vnc_client_error(vs); 437 } 438 strncpy(mechname, (char*)data, len); 439 mechname[len] = '\0'; 440 VNC_DEBUG("Got client mechname '%s' check against '%s'\n", 441 mechname, vs->sasl.mechlist); 442 443 if (strncmp(vs->sasl.mechlist, mechname, len) == 0) { 444 if (vs->sasl.mechlist[len] != '\0' && 445 vs->sasl.mechlist[len] != ',') { 446 VNC_DEBUG("One %d", vs->sasl.mechlist[len]); 447 goto fail; 448 } 449 } else { 450 char *offset = strstr(vs->sasl.mechlist, mechname); 451 VNC_DEBUG("Two %p\n", offset); 452 if (!offset) { 453 goto fail; 454 } 455 VNC_DEBUG("Two '%s'\n", offset); 456 if (offset[-1] != ',' || 457 (offset[len] != '\0'&& 458 offset[len] != ',')) { 459 goto fail; 460 } 461 } 462 463 free(vs->sasl.mechlist); 464 vs->sasl.mechlist = mechname; 465 466 VNC_DEBUG("Validated mechname '%s'\n", mechname); 467 vnc_read_when(vs, protocol_client_auth_sasl_start_len, 4); 468 return 0; 469 470 fail: 471 vnc_client_error(vs); 472 free(mechname); 473 return -1; 474 } 475 476 static int protocol_client_auth_sasl_mechname_len(VncState *vs, uint8_t *data, size_t len) 477 { 478 uint32_t mechlen = read_u32(data, 0); 479 VNC_DEBUG("Got client mechname len %d\n", mechlen); 480 if (mechlen > 100) { 481 VNC_DEBUG("Too long SASL mechname data %d\n", mechlen); 482 vnc_client_error(vs); 483 return -1; 484 } 485 if (mechlen < 1) { 486 VNC_DEBUG("Too short SASL mechname %d\n", mechlen); 487 vnc_client_error(vs); 488 return -1; 489 } 490 vnc_read_when(vs, protocol_client_auth_sasl_mechname,mechlen); 491 return 0; 492 } 493 494 void start_auth_sasl(VncState *vs) 495 { 496 const char *mechlist = NULL; 497 sasl_security_properties_t secprops; 498 int err; 499 char *localAddr, *remoteAddr; 500 int mechlistlen; 501 502 VNC_DEBUG("Initialize SASL auth %d\n", vs->csock); 503 504 /* Get local & remote client addresses in form IPADDR;PORT */ 505 if (!(localAddr = vnc_socket_local_addr("%s;%s", vs->csock))) 506 goto authabort; 507 508 if (!(remoteAddr = vnc_socket_remote_addr("%s;%s", vs->csock))) { 509 free(localAddr); 510 goto authabort; 511 } 512 513 err = sasl_server_new("vnc", 514 NULL, /* FQDN - just delegates to gethostname */ 515 NULL, /* User realm */ 516 localAddr, 517 remoteAddr, 518 NULL, /* Callbacks, not needed */ 519 SASL_SUCCESS_DATA, 520 &vs->sasl.conn); 521 free(localAddr); 522 free(remoteAddr); 523 localAddr = remoteAddr = NULL; 524 525 if (err != SASL_OK) { 526 VNC_DEBUG("sasl context setup failed %d (%s)", 527 err, sasl_errstring(err, NULL, NULL)); 528 vs->sasl.conn = NULL; 529 goto authabort; 530 } 531 532 #ifdef CONFIG_VNC_TLS 533 /* Inform SASL that we've got an external SSF layer from TLS/x509 */ 534 if (vs->auth == VNC_AUTH_VENCRYPT && 535 vs->subauth == VNC_AUTH_VENCRYPT_X509SASL) { 536 gnutls_cipher_algorithm_t cipher; 537 sasl_ssf_t ssf; 538 539 cipher = gnutls_cipher_get(vs->tls.session); 540 if (!(ssf = (sasl_ssf_t)gnutls_cipher_get_key_size(cipher))) { 541 VNC_DEBUG("%s", "cannot TLS get cipher size\n"); 542 sasl_dispose(&vs->sasl.conn); 543 vs->sasl.conn = NULL; 544 goto authabort; 545 } 546 ssf *= 8; /* tls key size is bytes, sasl wants bits */ 547 548 err = sasl_setprop(vs->sasl.conn, SASL_SSF_EXTERNAL, &ssf); 549 if (err != SASL_OK) { 550 VNC_DEBUG("cannot set SASL external SSF %d (%s)\n", 551 err, sasl_errstring(err, NULL, NULL)); 552 sasl_dispose(&vs->sasl.conn); 553 vs->sasl.conn = NULL; 554 goto authabort; 555 } 556 } else 557 #endif /* CONFIG_VNC_TLS */ 558 vs->sasl.wantSSF = 1; 559 560 memset (&secprops, 0, sizeof secprops); 561 /* Inform SASL that we've got an external SSF layer from TLS */ 562 if (strncmp(vs->vd->display, "unix:", 5) == 0 563 #ifdef CONFIG_VNC_TLS 564 /* Disable SSF, if using TLS+x509+SASL only. TLS without x509 565 is not sufficiently strong */ 566 || (vs->auth == VNC_AUTH_VENCRYPT && 567 vs->subauth == VNC_AUTH_VENCRYPT_X509SASL) 568 #endif /* CONFIG_VNC_TLS */ 569 ) { 570 /* If we've got TLS or UNIX domain sock, we don't care about SSF */ 571 secprops.min_ssf = 0; 572 secprops.max_ssf = 0; 573 secprops.maxbufsize = 8192; 574 secprops.security_flags = 0; 575 } else { 576 /* Plain TCP, better get an SSF layer */ 577 secprops.min_ssf = 56; /* Good enough to require kerberos */ 578 secprops.max_ssf = 100000; /* Arbitrary big number */ 579 secprops.maxbufsize = 8192; 580 /* Forbid any anonymous or trivially crackable auth */ 581 secprops.security_flags = 582 SASL_SEC_NOANONYMOUS | SASL_SEC_NOPLAINTEXT; 583 } 584 585 err = sasl_setprop(vs->sasl.conn, SASL_SEC_PROPS, &secprops); 586 if (err != SASL_OK) { 587 VNC_DEBUG("cannot set SASL security props %d (%s)\n", 588 err, sasl_errstring(err, NULL, NULL)); 589 sasl_dispose(&vs->sasl.conn); 590 vs->sasl.conn = NULL; 591 goto authabort; 592 } 593 594 err = sasl_listmech(vs->sasl.conn, 595 NULL, /* Don't need to set user */ 596 "", /* Prefix */ 597 ",", /* Separator */ 598 "", /* Suffix */ 599 &mechlist, 600 NULL, 601 NULL); 602 if (err != SASL_OK) { 603 VNC_DEBUG("cannot list SASL mechanisms %d (%s)\n", 604 err, sasl_errdetail(vs->sasl.conn)); 605 sasl_dispose(&vs->sasl.conn); 606 vs->sasl.conn = NULL; 607 goto authabort; 608 } 609 VNC_DEBUG("Available mechanisms for client: '%s'\n", mechlist); 610 611 if (!(vs->sasl.mechlist = strdup(mechlist))) { 612 VNC_DEBUG("Out of memory"); 613 sasl_dispose(&vs->sasl.conn); 614 vs->sasl.conn = NULL; 615 goto authabort; 616 } 617 mechlistlen = strlen(mechlist); 618 vnc_write_u32(vs, mechlistlen); 619 vnc_write(vs, mechlist, mechlistlen); 620 vnc_flush(vs); 621 622 VNC_DEBUG("Wait for client mechname length\n"); 623 vnc_read_when(vs, protocol_client_auth_sasl_mechname_len, 4); 624 625 return; 626 627 authabort: 628 vnc_client_error(vs); 629 return; 630 } 631 632 633