xref: /openbmc/qemu/ui/vnc-auth-sasl.c (revision f6476697) 
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 "authz/base.h"
28 #include "vnc.h"
29 #include "trace.h"
30 
31 /*
32  * Apple has deprecated sasl.h functions in OS X 10.11.  Therefore,
33  * files that use SASL API need to disable -Wdeprecated-declarations.
34  */
35 #ifdef CONFIG_DARWIN
36 #pragma GCC diagnostic ignored "-Wdeprecated-declarations"
37 #endif
38 
39 /* Max amount of data we send/recv for SASL steps to prevent DOS */
40 #define SASL_DATA_MAX_LEN (1024 * 1024)
41 
42 
43 bool vnc_sasl_server_init(Error **errp)
44 {
45     int saslErr = sasl_server_init(NULL, "qemu");
46 
47     if (saslErr != SASL_OK) {
48         error_setg(errp, "Failed to initialize SASL auth: %s",
49                    sasl_errstring(saslErr, NULL, NULL));
50         return false;
51     }
52     return true;
53 }
54 
55 void vnc_sasl_client_cleanup(VncState *vs)
56 {
57     if (vs->sasl.conn) {
58         vs->sasl.runSSF = false;
59         vs->sasl.wantSSF = false;
60         vs->sasl.waitWriteSSF = 0;
61         vs->sasl.encodedLength = vs->sasl.encodedOffset = 0;
62         vs->sasl.encoded = NULL;
63         g_free(vs->sasl.username);
64         g_free(vs->sasl.mechlist);
65         vs->sasl.username = vs->sasl.mechlist = NULL;
66         sasl_dispose(&vs->sasl.conn);
67         vs->sasl.conn = NULL;
68     }
69 }
70 
71 
72 size_t vnc_client_write_sasl(VncState *vs)
73 {
74     size_t ret;
75 
76     VNC_DEBUG("Write SASL: Pending output %p size %zd offset %zd "
77               "Encoded: %p size %d offset %d\n",
78               vs->output.buffer, vs->output.capacity, vs->output.offset,
79               vs->sasl.encoded, vs->sasl.encodedLength, vs->sasl.encodedOffset);
80 
81     if (!vs->sasl.encoded) {
82         int err;
83         err = sasl_encode(vs->sasl.conn,
84                           (char *)vs->output.buffer,
85                           vs->output.offset,
86                           (const char **)&vs->sasl.encoded,
87                           &vs->sasl.encodedLength);
88         if (err != SASL_OK)
89             return vnc_client_io_error(vs, -1, NULL);
90 
91         vs->sasl.encodedRawLength = vs->output.offset;
92         vs->sasl.encodedOffset = 0;
93     }
94 
95     ret = vnc_client_write_buf(vs,
96                                vs->sasl.encoded + vs->sasl.encodedOffset,
97                                vs->sasl.encodedLength - vs->sasl.encodedOffset);
98     if (!ret)
99         return 0;
100 
101     vs->sasl.encodedOffset += ret;
102     if (vs->sasl.encodedOffset == vs->sasl.encodedLength) {
103         bool throttled = vs->force_update_offset != 0;
104         size_t offset;
105         if (vs->sasl.encodedRawLength >= vs->force_update_offset) {
106             vs->force_update_offset = 0;
107         } else {
108             vs->force_update_offset -= vs->sasl.encodedRawLength;
109         }
110         if (throttled && vs->force_update_offset == 0) {
111             trace_vnc_client_unthrottle_forced(vs, vs->ioc);
112         }
113         offset = vs->output.offset;
114         buffer_advance(&vs->output, vs->sasl.encodedRawLength);
115         if (offset >= vs->throttle_output_offset &&
116             vs->output.offset < vs->throttle_output_offset) {
117             trace_vnc_client_unthrottle_incremental(vs, vs->ioc,
118                                                     vs->output.offset);
119         }
120         vs->sasl.encoded = NULL;
121         vs->sasl.encodedOffset = vs->sasl.encodedLength = 0;
122     }
123 
124     /* Can't merge this block with one above, because
125      * someone might have written more unencrypted
126      * data in vs->output while we were processing
127      * SASL encoded output
128      */
129     if (vs->output.offset == 0) {
130         if (vs->ioc_tag) {
131             g_source_remove(vs->ioc_tag);
132         }
133         vs->ioc_tag = qio_channel_add_watch(
134             vs->ioc, G_IO_IN | G_IO_HUP | G_IO_ERR,
135             vnc_client_io, vs, NULL);
136     }
137 
138     return ret;
139 }
140 
141 
142 size_t vnc_client_read_sasl(VncState *vs)
143 {
144     size_t ret;
145     uint8_t encoded[4096];
146     const char *decoded;
147     unsigned int decodedLen;
148     int err;
149 
150     ret = vnc_client_read_buf(vs, encoded, sizeof(encoded));
151     if (!ret)
152         return 0;
153 
154     err = sasl_decode(vs->sasl.conn,
155                       (char *)encoded, ret,
156                       &decoded, &decodedLen);
157 
158     if (err != SASL_OK)
159         return vnc_client_io_error(vs, -1, NULL);
160     VNC_DEBUG("Read SASL Encoded %p size %ld Decoded %p size %d\n",
161               encoded, ret, decoded, decodedLen);
162     buffer_reserve(&vs->input, decodedLen);
163     buffer_append(&vs->input, decoded, decodedLen);
164     return decodedLen;
165 }
166 
167 
168 static int vnc_auth_sasl_check_access(VncState *vs)
169 {
170     const void *val;
171     int rv;
172     Error *err = NULL;
173     bool allow;
174 
175     rv = sasl_getprop(vs->sasl.conn, SASL_USERNAME, &val);
176     if (rv != SASL_OK) {
177         trace_vnc_auth_fail(vs, vs->auth, "Cannot fetch SASL username",
178                             sasl_errstring(rv, NULL, NULL));
179         return -1;
180     }
181     if (val == NULL) {
182         trace_vnc_auth_fail(vs, vs->auth, "No SASL username set", "");
183         return -1;
184     }
185 
186     vs->sasl.username = g_strdup((const char*)val);
187     trace_vnc_auth_sasl_username(vs, vs->sasl.username);
188 
189     if (vs->vd->sasl.authzid == NULL) {
190         trace_vnc_auth_sasl_acl(vs, 1);
191         return 0;
192     }
193 
194     allow = qauthz_is_allowed_by_id(vs->vd->sasl.authzid,
195                                     vs->sasl.username, &err);
196     if (err) {
197         trace_vnc_auth_fail(vs, vs->auth, "Error from authz",
198                             error_get_pretty(err));
199         error_free(err);
200         return -1;
201     }
202 
203     trace_vnc_auth_sasl_acl(vs, allow);
204     return allow ? 0 : -1;
205 }
206 
207 static int vnc_auth_sasl_check_ssf(VncState *vs)
208 {
209     const void *val;
210     int err, ssf;
211 
212     if (!vs->sasl.wantSSF)
213         return 1;
214 
215     err = sasl_getprop(vs->sasl.conn, SASL_SSF, &val);
216     if (err != SASL_OK)
217         return 0;
218 
219     ssf = *(const int *)val;
220 
221     trace_vnc_auth_sasl_ssf(vs, ssf);
222 
223     if (ssf < 56)
224         return 0; /* 56 is good for Kerberos */
225 
226     /* Only setup for read initially, because we're about to send an RPC
227      * reply which must be in plain text. When the next incoming RPC
228      * arrives, we'll switch on writes too
229      *
230      * cf qemudClientReadSASL  in qemud.c
231      */
232     vs->sasl.runSSF = 1;
233 
234     /* We have a SSF that's good enough */
235     return 1;
236 }
237 
238 /*
239  * Step Msg
240  *
241  * Input from client:
242  *
243  * u32 clientin-length
244  * u8-array clientin-string
245  *
246  * Output to client:
247  *
248  * u32 serverout-length
249  * u8-array serverout-strin
250  * u8 continue
251  */
252 
253 static int protocol_client_auth_sasl_step_len(VncState *vs, uint8_t *data, size_t len);
254 
255 static int protocol_client_auth_sasl_step(VncState *vs, uint8_t *data, size_t len)
256 {
257     uint32_t datalen = len;
258     const char *serverout;
259     unsigned int serveroutlen;
260     int err;
261     char *clientdata = NULL;
262 
263     /* NB, distinction of NULL vs "" is *critical* in SASL */
264     if (datalen) {
265         clientdata = (char*)data;
266         clientdata[datalen-1] = '\0'; /* Wire includes '\0', but make sure */
267         datalen--; /* Don't count NULL byte when passing to _start() */
268     }
269 
270     err = sasl_server_step(vs->sasl.conn,
271                            clientdata,
272                            datalen,
273                            &serverout,
274                            &serveroutlen);
275     trace_vnc_auth_sasl_step(vs, data, len, serverout, serveroutlen, err);
276     if (err != SASL_OK &&
277         err != SASL_CONTINUE) {
278         trace_vnc_auth_fail(vs, vs->auth, "Cannot step SASL auth",
279                             sasl_errdetail(vs->sasl.conn));
280         sasl_dispose(&vs->sasl.conn);
281         vs->sasl.conn = NULL;
282         goto authabort;
283     }
284 
285     if (serveroutlen > SASL_DATA_MAX_LEN) {
286         trace_vnc_auth_fail(vs, vs->auth, "SASL data too long", "");
287         sasl_dispose(&vs->sasl.conn);
288         vs->sasl.conn = NULL;
289         goto authabort;
290     }
291 
292     if (serveroutlen) {
293         vnc_write_u32(vs, serveroutlen + 1);
294         vnc_write(vs, serverout, serveroutlen + 1);
295     } else {
296         vnc_write_u32(vs, 0);
297     }
298 
299     /* Whether auth is complete */
300     vnc_write_u8(vs, err == SASL_CONTINUE ? 0 : 1);
301 
302     if (err == SASL_CONTINUE) {
303         /* Wait for step length */
304         vnc_read_when(vs, protocol_client_auth_sasl_step_len, 4);
305     } else {
306         if (!vnc_auth_sasl_check_ssf(vs)) {
307             trace_vnc_auth_fail(vs, vs->auth, "SASL SSF too weak", "");
308             goto authreject;
309         }
310 
311         /* Check the username access control list */
312         if (vnc_auth_sasl_check_access(vs) < 0) {
313             goto authreject;
314         }
315 
316         trace_vnc_auth_pass(vs, vs->auth);
317         vnc_write_u32(vs, 0); /* Accept auth */
318         /*
319          * Delay writing in SSF encoded mode until pending output
320          * buffer is written
321          */
322         if (vs->sasl.runSSF)
323             vs->sasl.waitWriteSSF = vs->output.offset;
324         start_client_init(vs);
325     }
326 
327     return 0;
328 
329  authreject:
330     vnc_write_u32(vs, 1); /* Reject auth */
331     vnc_write_u32(vs, sizeof("Authentication failed"));
332     vnc_write(vs, "Authentication failed", sizeof("Authentication failed"));
333     vnc_flush(vs);
334     vnc_client_error(vs);
335     return -1;
336 
337  authabort:
338     vnc_client_error(vs);
339     return -1;
340 }
341 
342 static int protocol_client_auth_sasl_step_len(VncState *vs, uint8_t *data, size_t len)
343 {
344     uint32_t steplen = read_u32(data, 0);
345 
346     if (steplen > SASL_DATA_MAX_LEN) {
347         trace_vnc_auth_fail(vs, vs->auth, "SASL step len too large", "");
348         vnc_client_error(vs);
349         return -1;
350     }
351 
352     if (steplen == 0)
353         return protocol_client_auth_sasl_step(vs, NULL, 0);
354     else
355         vnc_read_when(vs, protocol_client_auth_sasl_step, steplen);
356     return 0;
357 }
358 
359 /*
360  * Start Msg
361  *
362  * Input from client:
363  *
364  * u32 clientin-length
365  * u8-array clientin-string
366  *
367  * Output to client:
368  *
369  * u32 serverout-length
370  * u8-array serverout-strin
371  * u8 continue
372  */
373 
374 #define SASL_DATA_MAX_LEN (1024 * 1024)
375 
376 static int protocol_client_auth_sasl_start(VncState *vs, uint8_t *data, size_t len)
377 {
378     uint32_t datalen = len;
379     const char *serverout;
380     unsigned int serveroutlen;
381     int err;
382     char *clientdata = NULL;
383 
384     /* NB, distinction of NULL vs "" is *critical* in SASL */
385     if (datalen) {
386         clientdata = (char*)data;
387         clientdata[datalen-1] = '\0'; /* Should be on wire, but make sure */
388         datalen--; /* Don't count NULL byte when passing to _start() */
389     }
390 
391     err = sasl_server_start(vs->sasl.conn,
392                             vs->sasl.mechlist,
393                             clientdata,
394                             datalen,
395                             &serverout,
396                             &serveroutlen);
397     trace_vnc_auth_sasl_start(vs, data, len, serverout, serveroutlen, err);
398     if (err != SASL_OK &&
399         err != SASL_CONTINUE) {
400         trace_vnc_auth_fail(vs, vs->auth, "Cannot start SASL auth",
401                             sasl_errdetail(vs->sasl.conn));
402         sasl_dispose(&vs->sasl.conn);
403         vs->sasl.conn = NULL;
404         goto authabort;
405     }
406     if (serveroutlen > SASL_DATA_MAX_LEN) {
407         trace_vnc_auth_fail(vs, vs->auth, "SASL data too long", "");
408         sasl_dispose(&vs->sasl.conn);
409         vs->sasl.conn = NULL;
410         goto authabort;
411     }
412 
413     if (serveroutlen) {
414         vnc_write_u32(vs, serveroutlen + 1);
415         vnc_write(vs, serverout, serveroutlen + 1);
416     } else {
417         vnc_write_u32(vs, 0);
418     }
419 
420     /* Whether auth is complete */
421     vnc_write_u8(vs, err == SASL_CONTINUE ? 0 : 1);
422 
423     if (err == SASL_CONTINUE) {
424         /* Wait for step length */
425         vnc_read_when(vs, protocol_client_auth_sasl_step_len, 4);
426     } else {
427         if (!vnc_auth_sasl_check_ssf(vs)) {
428             trace_vnc_auth_fail(vs, vs->auth, "SASL SSF too weak", "");
429             goto authreject;
430         }
431 
432         /* Check the username access control list */
433         if (vnc_auth_sasl_check_access(vs) < 0) {
434             goto authreject;
435         }
436 
437         trace_vnc_auth_pass(vs, vs->auth);
438         vnc_write_u32(vs, 0); /* Accept auth */
439         start_client_init(vs);
440     }
441 
442     return 0;
443 
444  authreject:
445     vnc_write_u32(vs, 1); /* Reject auth */
446     vnc_write_u32(vs, sizeof("Authentication failed"));
447     vnc_write(vs, "Authentication failed", sizeof("Authentication failed"));
448     vnc_flush(vs);
449     vnc_client_error(vs);
450     return -1;
451 
452  authabort:
453     vnc_client_error(vs);
454     return -1;
455 }
456 
457 static int protocol_client_auth_sasl_start_len(VncState *vs, uint8_t *data, size_t len)
458 {
459     uint32_t startlen = read_u32(data, 0);
460 
461     if (startlen > SASL_DATA_MAX_LEN) {
462         trace_vnc_auth_fail(vs, vs->auth, "SASL start len too large", "");
463         vnc_client_error(vs);
464         return -1;
465     }
466 
467     if (startlen == 0)
468         return protocol_client_auth_sasl_start(vs, NULL, 0);
469 
470     vnc_read_when(vs, protocol_client_auth_sasl_start, startlen);
471     return 0;
472 }
473 
474 static int protocol_client_auth_sasl_mechname(VncState *vs, uint8_t *data, size_t len)
475 {
476     char *mechname = g_strndup((const char *) data, len);
477     trace_vnc_auth_sasl_mech_choose(vs, mechname);
478 
479     if (strncmp(vs->sasl.mechlist, mechname, len) == 0) {
480         if (vs->sasl.mechlist[len] != '\0' &&
481             vs->sasl.mechlist[len] != ',') {
482             goto fail;
483         }
484     } else {
485         char *offset = strstr(vs->sasl.mechlist, mechname);
486         if (!offset) {
487             goto fail;
488         }
489         if (offset[-1] != ',' ||
490             (offset[len] != '\0'&&
491              offset[len] != ',')) {
492             goto fail;
493         }
494     }
495 
496     g_free(vs->sasl.mechlist);
497     vs->sasl.mechlist = mechname;
498 
499     vnc_read_when(vs, protocol_client_auth_sasl_start_len, 4);
500     return 0;
501 
502  fail:
503     trace_vnc_auth_fail(vs, vs->auth, "Unsupported mechname", mechname);
504     vnc_client_error(vs);
505     g_free(mechname);
506     return -1;
507 }
508 
509 static int protocol_client_auth_sasl_mechname_len(VncState *vs, uint8_t *data, size_t len)
510 {
511     uint32_t mechlen = read_u32(data, 0);
512 
513     if (mechlen > 100) {
514         trace_vnc_auth_fail(vs, vs->auth, "SASL mechname too long", "");
515         vnc_client_error(vs);
516         return -1;
517     }
518     if (mechlen < 1) {
519         trace_vnc_auth_fail(vs, vs->auth, "SASL mechname too short", "");
520         vnc_client_error(vs);
521         return -1;
522     }
523     vnc_read_when(vs, protocol_client_auth_sasl_mechname,mechlen);
524     return 0;
525 }
526 
527 static char *
528 vnc_socket_ip_addr_string(QIOChannelSocket *ioc,
529                           bool local,
530                           Error **errp)
531 {
532     SocketAddress *addr;
533     char *ret;
534 
535     if (local) {
536         addr = qio_channel_socket_get_local_address(ioc, errp);
537     } else {
538         addr = qio_channel_socket_get_remote_address(ioc, errp);
539     }
540     if (!addr) {
541         return NULL;
542     }
543 
544     if (addr->type != SOCKET_ADDRESS_TYPE_INET) {
545         error_setg(errp, "Not an inet socket type");
546         qapi_free_SocketAddress(addr);
547         return NULL;
548     }
549     ret = g_strdup_printf("%s;%s", addr->u.inet.host, addr->u.inet.port);
550     qapi_free_SocketAddress(addr);
551     return ret;
552 }
553 
554 void start_auth_sasl(VncState *vs)
555 {
556     const char *mechlist = NULL;
557     sasl_security_properties_t secprops;
558     int err;
559     Error *local_err = NULL;
560     char *localAddr, *remoteAddr;
561     int mechlistlen;
562 
563     /* Get local & remote client addresses in form  IPADDR;PORT */
564     localAddr = vnc_socket_ip_addr_string(vs->sioc, true, &local_err);
565     if (!localAddr) {
566         trace_vnc_auth_fail(vs, vs->auth, "Cannot format local IP",
567                             error_get_pretty(local_err));
568         goto authabort;
569     }
570 
571     remoteAddr = vnc_socket_ip_addr_string(vs->sioc, false, &local_err);
572     if (!remoteAddr) {
573         trace_vnc_auth_fail(vs, vs->auth, "Cannot format remote IP",
574                             error_get_pretty(local_err));
575         g_free(localAddr);
576         goto authabort;
577     }
578 
579     err = sasl_server_new("vnc",
580                           NULL, /* FQDN - just delegates to gethostname */
581                           NULL, /* User realm */
582                           localAddr,
583                           remoteAddr,
584                           NULL, /* Callbacks, not needed */
585                           SASL_SUCCESS_DATA,
586                           &vs->sasl.conn);
587     g_free(localAddr);
588     g_free(remoteAddr);
589     localAddr = remoteAddr = NULL;
590 
591     if (err != SASL_OK) {
592         trace_vnc_auth_fail(vs, vs->auth,  "SASL context setup failed",
593                             sasl_errstring(err, NULL, NULL));
594         vs->sasl.conn = NULL;
595         goto authabort;
596     }
597 
598     /* Inform SASL that we've got an external SSF layer from TLS/x509 */
599     if (vs->auth == VNC_AUTH_VENCRYPT &&
600         vs->subauth == VNC_AUTH_VENCRYPT_X509SASL) {
601         int keysize;
602         sasl_ssf_t ssf;
603 
604         keysize = qcrypto_tls_session_get_key_size(vs->tls,
605                                                    &local_err);
606         if (keysize < 0) {
607             trace_vnc_auth_fail(vs, vs->auth, "cannot TLS get cipher size",
608                                 error_get_pretty(local_err));
609             sasl_dispose(&vs->sasl.conn);
610             vs->sasl.conn = NULL;
611             goto authabort;
612         }
613         ssf = keysize * CHAR_BIT; /* tls key size is bytes, sasl wants bits */
614 
615         err = sasl_setprop(vs->sasl.conn, SASL_SSF_EXTERNAL, &ssf);
616         if (err != SASL_OK) {
617             trace_vnc_auth_fail(vs, vs->auth, "cannot set SASL external SSF",
618                                 sasl_errstring(err, NULL, NULL));
619             sasl_dispose(&vs->sasl.conn);
620             vs->sasl.conn = NULL;
621             goto authabort;
622         }
623     } else {
624         vs->sasl.wantSSF = 1;
625     }
626 
627     memset (&secprops, 0, sizeof secprops);
628     /* Inform SASL that we've got an external SSF layer from TLS.
629      *
630      * Disable SSF, if using TLS+x509+SASL only. TLS without x509
631      * is not sufficiently strong
632      */
633     if (vs->vd->is_unix ||
634         (vs->auth == VNC_AUTH_VENCRYPT &&
635          vs->subauth == VNC_AUTH_VENCRYPT_X509SASL)) {
636         /* If we've got TLS or UNIX domain sock, we don't care about SSF */
637         secprops.min_ssf = 0;
638         secprops.max_ssf = 0;
639         secprops.maxbufsize = 8192;
640         secprops.security_flags = 0;
641     } else {
642         /* Plain TCP, better get an SSF layer */
643         secprops.min_ssf = 56; /* Good enough to require kerberos */
644         secprops.max_ssf = 100000; /* Arbitrary big number */
645         secprops.maxbufsize = 8192;
646         /* Forbid any anonymous or trivially crackable auth */
647         secprops.security_flags =
648             SASL_SEC_NOANONYMOUS | SASL_SEC_NOPLAINTEXT;
649     }
650 
651     err = sasl_setprop(vs->sasl.conn, SASL_SEC_PROPS, &secprops);
652     if (err != SASL_OK) {
653         trace_vnc_auth_fail(vs, vs->auth, "cannot set SASL security props",
654                             sasl_errstring(err, NULL, NULL));
655         sasl_dispose(&vs->sasl.conn);
656         vs->sasl.conn = NULL;
657         goto authabort;
658     }
659 
660     err = sasl_listmech(vs->sasl.conn,
661                         NULL, /* Don't need to set user */
662                         "", /* Prefix */
663                         ",", /* Separator */
664                         "", /* Suffix */
665                         &mechlist,
666                         NULL,
667                         NULL);
668     if (err != SASL_OK) {
669         trace_vnc_auth_fail(vs, vs->auth, "cannot list SASL mechanisms",
670                             sasl_errdetail(vs->sasl.conn));
671         sasl_dispose(&vs->sasl.conn);
672         vs->sasl.conn = NULL;
673         goto authabort;
674     }
675     trace_vnc_auth_sasl_mech_list(vs, mechlist);
676 
677     vs->sasl.mechlist = g_strdup(mechlist);
678     mechlistlen = strlen(mechlist);
679     vnc_write_u32(vs, mechlistlen);
680     vnc_write(vs, mechlist, mechlistlen);
681     vnc_flush(vs);
682 
683     vnc_read_when(vs, protocol_client_auth_sasl_mechname_len, 4);
684 
685     return;
686 
687  authabort:
688     error_free(local_err);
689     vnc_client_error(vs);
690 }
691 
692 
693