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