ui/vnc-auth-sasl.c

   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 "qemu/osdep.h"
  26 #include "qapi/error.h"
  27 #include "vnc.h"
  28
  29 /* Max amount of data we send/recv for SASL steps to prevent DOS */
  30 #define SASL_DATA_MAX_LEN (1024 * 1024)
  31
  32
  33 void vnc_sasl_client_cleanup(VncState *vs)
  34 {
  35     if (vs->sasl.conn) {
  36         vs->sasl.runSSF = false;
  37         vs->sasl.wantSSF = false;
  38         vs->sasl.waitWriteSSF = 0;
  39         vs->sasl.encodedLength = vs->sasl.encodedOffset = 0;
  40         vs->sasl.encoded = NULL;
  41         g_free(vs->sasl.username);
  42         g_free(vs->sasl.mechlist);
  43         vs->sasl.username = vs->sasl.mechlist = NULL;
  44         sasl_dispose(&vs->sasl.conn);
  45         vs->sasl.conn = NULL;
  46     }
  47 }
  48
  49
  50 long vnc_client_write_sasl(VncState *vs)
  51 {
  52     long ret;
  53
  54     VNC_DEBUG("Write SASL: Pending output %p size %zd offset %zd "
  55               "Encoded: %p size %d offset %d\n",
  56               vs->output.buffer, vs->output.capacity, vs->output.offset,
  57               vs->sasl.encoded, vs->sasl.encodedLength, vs->sasl.encodedOffset);
  58
  59     if (!vs->sasl.encoded) {
  60         int err;
  61         err = sasl_encode(vs->sasl.conn,
  62                           (char *)vs->output.buffer,
  63                           vs->output.offset,
  64                           (const char **)&vs->sasl.encoded,
  65                           &vs->sasl.encodedLength);
  66         if (err != SASL_OK)
  67             return vnc_client_io_error(vs, -1, NULL);
  68
  69         vs->sasl.encodedOffset = 0;
  70     }
  71
  72     ret = vnc_client_write_buf(vs,
  73                                vs->sasl.encoded + vs->sasl.encodedOffset,
  74                                vs->sasl.encodedLength - vs->sasl.encodedOffset);
  75     if (!ret)
  76         return 0;
  77
  78     vs->sasl.encodedOffset += ret;
  79     if (vs->sasl.encodedOffset == vs->sasl.encodedLength) {
  80         vs->output.offset = 0;
  81         vs->sasl.encoded = NULL;
  82         vs->sasl.encodedOffset = vs->sasl.encodedLength = 0;
  83     }
  84
  85     /* Can't merge this block with one above, because
  86      * someone might have written more unencrypted
  87      * data in vs->output while we were processing
  88      * SASL encoded output
  89      */
  90     if (vs->output.offset == 0) {
  91         if (vs->ioc_tag) {
  92             g_source_remove(vs->ioc_tag);
  93         }
  94         vs->ioc_tag = qio_channel_add_watch(
  95             vs->ioc, G_IO_IN, vnc_client_io, vs, NULL);
  96     }
  97
  98     return ret;
  99 }
 100
 101
 102 long vnc_client_read_sasl(VncState *vs)
 103 {
 104     long ret;
 105     uint8_t encoded[4096];
 106     const char *decoded;
 107     unsigned int decodedLen;
 108     int err;
 109
 110     ret = vnc_client_read_buf(vs, encoded, sizeof(encoded));
 111     if (!ret)
 112         return 0;
 113
 114     err = sasl_decode(vs->sasl.conn,
 115                       (char *)encoded, ret,
 116                       &decoded, &decodedLen);
 117
 118     if (err != SASL_OK)
 119         return vnc_client_io_error(vs, -1, NULL);
 120     VNC_DEBUG("Read SASL Encoded %p size %ld Decoded %p size %d\n",
 121               encoded, ret, decoded, decodedLen);
 122     buffer_reserve(&vs->input, decodedLen);
 123     buffer_append(&vs->input, decoded, decodedLen);
 124     return decodedLen;
 125 }
 126
 127
 128 static int vnc_auth_sasl_check_access(VncState *vs)
 129 {
 130     const void *val;
 131     int err;
 132     int allow;
 133
 134     err = sasl_getprop(vs->sasl.conn, SASL_USERNAME, &val);
 135     if (err != SASL_OK) {
 136         VNC_DEBUG("cannot query SASL username on connection %d (%s), denying access\n",
 137                   err, sasl_errstring(err, NULL, NULL));
 138         return -1;
 139     }
 140     if (val == NULL) {
 141         VNC_DEBUG("no client username was found, denying access\n");
 142         return -1;
 143     }
 144     VNC_DEBUG("SASL client username %s\n", (const char *)val);
 145
 146     vs->sasl.username = g_strdup((const char*)val);
 147
 148     if (vs->vd->sasl.acl == NULL) {
 149         VNC_DEBUG("no ACL activated, allowing access\n");
 150         return 0;
 151     }
 152
 153     allow = qemu_acl_party_is_allowed(vs->vd->sasl.acl, vs->sasl.username);
 154
 155     VNC_DEBUG("SASL client %s %s by ACL\n", vs->sasl.username,
 156               allow ? "allowed" : "denied");
 157     return allow ? 0 : -1;
 158 }
 159
 160 static int vnc_auth_sasl_check_ssf(VncState *vs)
 161 {
 162     const void *val;
 163     int err, ssf;
 164
 165     if (!vs->sasl.wantSSF)
 166         return 1;
 167
 168     err = sasl_getprop(vs->sasl.conn, SASL_SSF, &val);
 169     if (err != SASL_OK)
 170         return 0;
 171
 172     ssf = *(const int *)val;
 173     VNC_DEBUG("negotiated an SSF of %d\n", ssf);
 174     if (ssf < 56)
 175         return 0; /* 56 is good for Kerberos */
 176
 177     /* Only setup for read initially, because we're about to send an RPC
 178      * reply which must be in plain text. When the next incoming RPC
 179      * arrives, we'll switch on writes too
 180      *
 181      * cf qemudClientReadSASL  in qemud.c
 182      */
 183     vs->sasl.runSSF = 1;
 184
 185     /* We have a SSF that's good enough */
 186     return 1;
 187 }
 188
 189 /*
 190  * Step Msg
 191  *
 192  * Input from client:
 193  *
 194  * u32 clientin-length
 195  * u8-array clientin-string
 196  *
 197  * Output to client:
 198  *
 199  * u32 serverout-length
 200  * u8-array serverout-strin
 201  * u8 continue
 202  */
 203
 204 static int protocol_client_auth_sasl_step_len(VncState *vs, uint8_t *data, size_t len);
 205
 206 static int protocol_client_auth_sasl_step(VncState *vs, uint8_t *data, size_t len)
 207 {
 208     uint32_t datalen = len;
 209     const char *serverout;
 210     unsigned int serveroutlen;
 211     int err;
 212     char *clientdata = NULL;
 213
 214     /* NB, distinction of NULL vs "" is *critical* in SASL */
 215     if (datalen) {
 216         clientdata = (char*)data;
 217         clientdata[datalen-1] = '\0'; /* Wire includes '\0', but make sure */
 218         datalen--; /* Don't count NULL byte when passing to _start() */
 219     }
 220
 221     VNC_DEBUG("Step using SASL Data %p (%d bytes)\n",
 222               clientdata, datalen);
 223     err = sasl_server_step(vs->sasl.conn,
 224                            clientdata,
 225                            datalen,
 226                            &serverout,
 227                            &serveroutlen);
 228     if (err != SASL_OK &&
 229         err != SASL_CONTINUE) {
 230         VNC_DEBUG("sasl step failed %d (%s)\n",
 231                   err, sasl_errdetail(vs->sasl.conn));
 232         sasl_dispose(&vs->sasl.conn);
 233         vs->sasl.conn = NULL;
 234         goto authabort;
 235     }
 236
 237     if (serveroutlen > SASL_DATA_MAX_LEN) {
 238         VNC_DEBUG("sasl step reply data too long %d\n",
 239                   serveroutlen);
 240         sasl_dispose(&vs->sasl.conn);
 241         vs->sasl.conn = NULL;
 242         goto authabort;
 243     }
 244
 245     VNC_DEBUG("SASL return data %d bytes, nil; %d\n",
 246               serveroutlen, serverout ? 0 : 1);
 247
 248     if (serveroutlen) {
 249         vnc_write_u32(vs, serveroutlen + 1);
 250         vnc_write(vs, serverout, serveroutlen + 1);
 251     } else {
 252         vnc_write_u32(vs, 0);
 253     }
 254
 255     /* Whether auth is complete */
 256     vnc_write_u8(vs, err == SASL_CONTINUE ? 0 : 1);
 257
 258     if (err == SASL_CONTINUE) {
 259         VNC_DEBUG("%s", "Authentication must continue\n");
 260         /* Wait for step length */
 261         vnc_read_when(vs, protocol_client_auth_sasl_step_len, 4);
 262     } else {
 263         if (!vnc_auth_sasl_check_ssf(vs)) {
 264             VNC_DEBUG("Authentication rejected for weak SSF %p\n", vs->ioc);
 265             goto authreject;
 266         }
 267
 268         /* Check username whitelist ACL */
 269         if (vnc_auth_sasl_check_access(vs) < 0) {
 270             VNC_DEBUG("Authentication rejected for ACL %p\n", vs->ioc);
 271             goto authreject;
 272         }
 273
 274         VNC_DEBUG("Authentication successful %p\n", vs->ioc);
 275         vnc_write_u32(vs, 0); /* Accept auth */
 276         /*
 277          * Delay writing in SSF encoded mode until pending output
 278          * buffer is written
 279          */
 280         if (vs->sasl.runSSF)
 281             vs->sasl.waitWriteSSF = vs->output.offset;
 282         start_client_init(vs);
 283     }
 284
 285     return 0;
 286
 287  authreject:
 288     vnc_write_u32(vs, 1); /* Reject auth */
 289     vnc_write_u32(vs, sizeof("Authentication failed"));
 290     vnc_write(vs, "Authentication failed", sizeof("Authentication failed"));
 291     vnc_flush(vs);
 292     vnc_client_error(vs);
 293     return -1;
 294
 295  authabort:
 296     vnc_client_error(vs);
 297     return -1;
 298 }
 299
 300 static int protocol_client_auth_sasl_step_len(VncState *vs, uint8_t *data, size_t len)
 301 {
 302     uint32_t steplen = read_u32(data, 0);
 303     VNC_DEBUG("Got client step len %d\n", steplen);
 304     if (steplen > SASL_DATA_MAX_LEN) {
 305         VNC_DEBUG("Too much SASL data %d\n", steplen);
 306         vnc_client_error(vs);
 307         return -1;
 308     }
 309
 310     if (steplen == 0)
 311         return protocol_client_auth_sasl_step(vs, NULL, 0);
 312     else
 313         vnc_read_when(vs, protocol_client_auth_sasl_step, steplen);
 314     return 0;
 315 }
 316
 317 /*
 318  * Start Msg
 319  *
 320  * Input from client:
 321  *
 322  * u32 clientin-length
 323  * u8-array clientin-string
 324  *
 325  * Output to client:
 326  *
 327  * u32 serverout-length
 328  * u8-array serverout-strin
 329  * u8 continue
 330  */
 331
 332 #define SASL_DATA_MAX_LEN (1024 * 1024)
 333
 334 static int protocol_client_auth_sasl_start(VncState *vs, uint8_t *data, size_t len)
 335 {
 336     uint32_t datalen = len;
 337     const char *serverout;
 338     unsigned int serveroutlen;
 339     int err;
 340     char *clientdata = NULL;
 341
 342     /* NB, distinction of NULL vs "" is *critical* in SASL */
 343     if (datalen) {
 344         clientdata = (char*)data;
 345         clientdata[datalen-1] = '\0'; /* Should be on wire, but make sure */
 346         datalen--; /* Don't count NULL byte when passing to _start() */
 347     }
 348
 349     VNC_DEBUG("Start SASL auth with mechanism %s. Data %p (%d bytes)\n",
 350               vs->sasl.mechlist, clientdata, datalen);
 351     err = sasl_server_start(vs->sasl.conn,
 352                             vs->sasl.mechlist,
 353                             clientdata,
 354                             datalen,
 355                             &serverout,
 356                             &serveroutlen);
 357     if (err != SASL_OK &&
 358         err != SASL_CONTINUE) {
 359         VNC_DEBUG("sasl start failed %d (%s)\n",
 360                   err, sasl_errdetail(vs->sasl.conn));
 361         sasl_dispose(&vs->sasl.conn);
 362         vs->sasl.conn = NULL;
 363         goto authabort;
 364     }
 365     if (serveroutlen > SASL_DATA_MAX_LEN) {
 366         VNC_DEBUG("sasl start reply data too long %d\n",
 367                   serveroutlen);
 368         sasl_dispose(&vs->sasl.conn);
 369         vs->sasl.conn = NULL;
 370         goto authabort;
 371     }
 372
 373     VNC_DEBUG("SASL return data %d bytes, nil; %d\n",
 374               serveroutlen, serverout ? 0 : 1);
 375
 376     if (serveroutlen) {
 377         vnc_write_u32(vs, serveroutlen + 1);
 378         vnc_write(vs, serverout, serveroutlen + 1);
 379     } else {
 380         vnc_write_u32(vs, 0);
 381     }
 382
 383     /* Whether auth is complete */
 384     vnc_write_u8(vs, err == SASL_CONTINUE ? 0 : 1);
 385
 386     if (err == SASL_CONTINUE) {
 387         VNC_DEBUG("%s", "Authentication must continue\n");
 388         /* Wait for step length */
 389         vnc_read_when(vs, protocol_client_auth_sasl_step_len, 4);
 390     } else {
 391         if (!vnc_auth_sasl_check_ssf(vs)) {
 392             VNC_DEBUG("Authentication rejected for weak SSF %p\n", vs->ioc);
 393             goto authreject;
 394         }
 395
 396         /* Check username whitelist ACL */
 397         if (vnc_auth_sasl_check_access(vs) < 0) {
 398             VNC_DEBUG("Authentication rejected for ACL %p\n", vs->ioc);
 399             goto authreject;
 400         }
 401
 402         VNC_DEBUG("Authentication successful %p\n", vs->ioc);
 403         vnc_write_u32(vs, 0); /* Accept auth */
 404         start_client_init(vs);
 405     }
 406
 407     return 0;
 408
 409  authreject:
 410     vnc_write_u32(vs, 1); /* Reject auth */
 411     vnc_write_u32(vs, sizeof("Authentication failed"));
 412     vnc_write(vs, "Authentication failed", sizeof("Authentication failed"));
 413     vnc_flush(vs);
 414     vnc_client_error(vs);
 415     return -1;
 416
 417  authabort:
 418     vnc_client_error(vs);
 419     return -1;
 420 }
 421
 422 static int protocol_client_auth_sasl_start_len(VncState *vs, uint8_t *data, size_t len)
 423 {
 424     uint32_t startlen = read_u32(data, 0);
 425     VNC_DEBUG("Got client start len %d\n", startlen);
 426     if (startlen > SASL_DATA_MAX_LEN) {
 427         VNC_DEBUG("Too much SASL data %d\n", startlen);
 428         vnc_client_error(vs);
 429         return -1;
 430     }
 431
 432     if (startlen == 0)
 433         return protocol_client_auth_sasl_start(vs, NULL, 0);
 434
 435     vnc_read_when(vs, protocol_client_auth_sasl_start, startlen);
 436     return 0;
 437 }
 438
 439 static int protocol_client_auth_sasl_mechname(VncState *vs, uint8_t *data, size_t len)
 440 {
 441     char *mechname = g_strndup((const char *) data, len);
 442     VNC_DEBUG("Got client mechname '%s' check against '%s'\n",
 443               mechname, vs->sasl.mechlist);
 444
 445     if (strncmp(vs->sasl.mechlist, mechname, len) == 0) {
 446         if (vs->sasl.mechlist[len] != '\0' &&
 447             vs->sasl.mechlist[len] != ',') {
 448             VNC_DEBUG("One %d", vs->sasl.mechlist[len]);
 449             goto fail;
 450         }
 451     } else {
 452         char *offset = strstr(vs->sasl.mechlist, mechname);
 453         VNC_DEBUG("Two %p\n", offset);
 454         if (!offset) {
 455             goto fail;
 456         }
 457         VNC_DEBUG("Two '%s'\n", offset);
 458         if (offset[-1] != ',' ||
 459             (offset[len] != '\0'&&
 460              offset[len] != ',')) {
 461             goto fail;
 462         }
 463     }
 464
 465     g_free(vs->sasl.mechlist);
 466     vs->sasl.mechlist = mechname;
 467
 468     VNC_DEBUG("Validated mechname '%s'\n", mechname);
 469     vnc_read_when(vs, protocol_client_auth_sasl_start_len, 4);
 470     return 0;
 471
 472  fail:
 473     vnc_client_error(vs);
 474     g_free(mechname);
 475     return -1;
 476 }
 477
 478 static int protocol_client_auth_sasl_mechname_len(VncState *vs, uint8_t *data, size_t len)
 479 {
 480     uint32_t mechlen = read_u32(data, 0);
 481     VNC_DEBUG("Got client mechname len %d\n", mechlen);
 482     if (mechlen > 100) {
 483         VNC_DEBUG("Too long SASL mechname data %d\n", mechlen);
 484         vnc_client_error(vs);
 485         return -1;
 486     }
 487     if (mechlen < 1) {
 488         VNC_DEBUG("Too short SASL mechname %d\n", mechlen);
 489         vnc_client_error(vs);
 490         return -1;
 491     }
 492     vnc_read_when(vs, protocol_client_auth_sasl_mechname,mechlen);
 493     return 0;
 494 }
 495
 496 static char *
 497 vnc_socket_ip_addr_string(QIOChannelSocket *ioc,
 498                           bool local,
 499                           Error **errp)
 500 {
 501     SocketAddress *addr;
 502     char *ret;
 503
 504     if (local) {
 505         addr = qio_channel_socket_get_local_address(ioc, errp);
 506     } else {
 507         addr = qio_channel_socket_get_remote_address(ioc, errp);
 508     }
 509     if (!addr) {
 510         return NULL;
 511     }
 512
 513     if (addr->type != SOCKET_ADDRESS_KIND_INET) {
 514         error_setg(errp, "Not an inet socket type");
 515         return NULL;
 516     }
 517     ret = g_strdup_printf("%s;%s", addr->u.inet.data->host,
 518                           addr->u.inet.data->port);
 519     qapi_free_SocketAddress(addr);
 520     return ret;
 521 }
 522
 523 void start_auth_sasl(VncState *vs)
 524 {
 525     const char *mechlist = NULL;
 526     sasl_security_properties_t secprops;
 527     int err;
 528     char *localAddr, *remoteAddr;
 529     int mechlistlen;
 530
 531     VNC_DEBUG("Initialize SASL auth %p\n", vs->ioc);
 532
 533     /* Get local & remote client addresses in form  IPADDR;PORT */
 534     localAddr = vnc_socket_ip_addr_string(vs->sioc, true, NULL);
 535     if (!localAddr) {
 536         goto authabort;
 537     }
 538
 539     remoteAddr = vnc_socket_ip_addr_string(vs->sioc, false, NULL);
 540     if (!remoteAddr) {
 541         g_free(localAddr);
 542         goto authabort;
 543     }
 544
 545     err = sasl_server_new("vnc",
 546                           NULL, /* FQDN - just delegates to gethostname */
 547                           NULL, /* User realm */
 548                           localAddr,
 549                           remoteAddr,
 550                           NULL, /* Callbacks, not needed */
 551                           SASL_SUCCESS_DATA,
 552                           &vs->sasl.conn);
 553     g_free(localAddr);
 554     g_free(remoteAddr);
 555     localAddr = remoteAddr = NULL;
 556
 557     if (err != SASL_OK) {
 558         VNC_DEBUG("sasl context setup failed %d (%s)",
 559                   err, sasl_errstring(err, NULL, NULL));
 560         vs->sasl.conn = NULL;
 561         goto authabort;
 562     }
 563
 564     /* Inform SASL that we've got an external SSF layer from TLS/x509 */
 565     if (vs->auth == VNC_AUTH_VENCRYPT &&
 566         vs->subauth == VNC_AUTH_VENCRYPT_X509SASL) {
 567         Error *local_err = NULL;
 568         int keysize;
 569         sasl_ssf_t ssf;
 570
 571         keysize = qcrypto_tls_session_get_key_size(vs->tls,
 572                                                    &local_err);
 573         if (keysize < 0) {
 574             VNC_DEBUG("cannot TLS get cipher size: %s\n",
 575                       error_get_pretty(local_err));
 576             error_free(local_err);
 577             sasl_dispose(&vs->sasl.conn);
 578             vs->sasl.conn = NULL;
 579             goto authabort;
 580         }
 581         ssf = keysize * CHAR_BIT; /* tls key size is bytes, sasl wants bits */
 582
 583         err = sasl_setprop(vs->sasl.conn, SASL_SSF_EXTERNAL, &ssf);
 584         if (err != SASL_OK) {
 585             VNC_DEBUG("cannot set SASL external SSF %d (%s)\n",
 586                       err, sasl_errstring(err, NULL, NULL));
 587             sasl_dispose(&vs->sasl.conn);
 588             vs->sasl.conn = NULL;
 589             goto authabort;
 590         }
 591     } else {
 592         vs->sasl.wantSSF = 1;
 593     }
 594
 595     memset (&secprops, 0, sizeof secprops);
 596     /* Inform SASL that we've got an external SSF layer from TLS.
 597      *
 598      * Disable SSF, if using TLS+x509+SASL only. TLS without x509
 599      * is not sufficiently strong
 600      */
 601     if (vs->vd->is_unix ||
 602         (vs->auth == VNC_AUTH_VENCRYPT &&
 603          vs->subauth == VNC_AUTH_VENCRYPT_X509SASL)) {
 604         /* If we've got TLS or UNIX domain sock, we don't care about SSF */
 605         secprops.min_ssf = 0;
 606         secprops.max_ssf = 0;
 607         secprops.maxbufsize = 8192;
 608         secprops.security_flags = 0;
 609     } else {
 610         /* Plain TCP, better get an SSF layer */
 611         secprops.min_ssf = 56; /* Good enough to require kerberos */
 612         secprops.max_ssf = 100000; /* Arbitrary big number */
 613         secprops.maxbufsize = 8192;
 614         /* Forbid any anonymous or trivially crackable auth */
 615         secprops.security_flags =
 616             SASL_SEC_NOANONYMOUS | SASL_SEC_NOPLAINTEXT;
 617     }
 618
 619     err = sasl_setprop(vs->sasl.conn, SASL_SEC_PROPS, &secprops);
 620     if (err != SASL_OK) {
 621         VNC_DEBUG("cannot set SASL security props %d (%s)\n",
 622                   err, sasl_errstring(err, NULL, NULL));
 623         sasl_dispose(&vs->sasl.conn);
 624         vs->sasl.conn = NULL;
 625         goto authabort;
 626     }
 627
 628     err = sasl_listmech(vs->sasl.conn,
 629                         NULL, /* Don't need to set user */
 630                         "", /* Prefix */
 631                         ",", /* Separator */
 632                         "", /* Suffix */
 633                         &mechlist,
 634                         NULL,
 635                         NULL);
 636     if (err != SASL_OK) {
 637         VNC_DEBUG("cannot list SASL mechanisms %d (%s)\n",
 638                   err, sasl_errdetail(vs->sasl.conn));
 639         sasl_dispose(&vs->sasl.conn);
 640         vs->sasl.conn = NULL;
 641         goto authabort;
 642     }
 643     VNC_DEBUG("Available mechanisms for client: '%s'\n", mechlist);
 644
 645     vs->sasl.mechlist = g_strdup(mechlist);
 646     mechlistlen = strlen(mechlist);
 647     vnc_write_u32(vs, mechlistlen);
 648     vnc_write(vs, mechlist, mechlistlen);
 649     vnc_flush(vs);
 650
 651     VNC_DEBUG("Wait for client mechname length\n");
 652     vnc_read_when(vs, protocol_client_auth_sasl_mechname_len, 4);
 653
 654     return;
 655
 656  authabort:
 657     vnc_client_error(vs);
 658 }
 659
 660