xref: /openbmc/qemu/ui/vnc-auth-sasl.c (revision ba632924) 
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 #include "trace.h"
29 
30 /* Max amount of data we send/recv for SASL steps to prevent DOS */
31 #define SASL_DATA_MAX_LEN (1024 * 1024)
32 
33 
34 void vnc_sasl_client_cleanup(VncState *vs)
35 {
36     if (vs->sasl.conn) {
37         vs->sasl.runSSF = false;
38         vs->sasl.wantSSF = false;
39         vs->sasl.waitWriteSSF = 0;
40         vs->sasl.encodedLength = vs->sasl.encodedOffset = 0;
41         vs->sasl.encoded = NULL;
42         g_free(vs->sasl.username);
43         g_free(vs->sasl.mechlist);
44         vs->sasl.username = vs->sasl.mechlist = NULL;
45         sasl_dispose(&vs->sasl.conn);
46         vs->sasl.conn = NULL;
47     }
48 }
49 
50 
51 size_t vnc_client_write_sasl(VncState *vs)
52 {
53     size_t ret;
54 
55     VNC_DEBUG("Write SASL: Pending output %p size %zd offset %zd "
56               "Encoded: %p size %d offset %d\n",
57               vs->output.buffer, vs->output.capacity, vs->output.offset,
58               vs->sasl.encoded, vs->sasl.encodedLength, vs->sasl.encodedOffset);
59 
60     if (!vs->sasl.encoded) {
61         int err;
62         err = sasl_encode(vs->sasl.conn,
63                           (char *)vs->output.buffer,
64                           vs->output.offset,
65                           (const char **)&vs->sasl.encoded,
66                           &vs->sasl.encodedLength);
67         if (err != SASL_OK)
68             return vnc_client_io_error(vs, -1, NULL);
69 
70         vs->sasl.encodedRawLength = vs->output.offset;
71         vs->sasl.encodedOffset = 0;
72     }
73 
74     ret = vnc_client_write_buf(vs,
75                                vs->sasl.encoded + vs->sasl.encodedOffset,
76                                vs->sasl.encodedLength - vs->sasl.encodedOffset);
77     if (!ret)
78         return 0;
79 
80     vs->sasl.encodedOffset += ret;
81     if (vs->sasl.encodedOffset == vs->sasl.encodedLength) {
82         bool throttled = vs->force_update_offset != 0;
83         size_t offset;
84         if (vs->sasl.encodedRawLength >= vs->force_update_offset) {
85             vs->force_update_offset = 0;
86         } else {
87             vs->force_update_offset -= vs->sasl.encodedRawLength;
88         }
89         if (throttled && vs->force_update_offset == 0) {
90             trace_vnc_client_unthrottle_forced(vs, vs->ioc);
91         }
92         offset = vs->output.offset;
93         buffer_advance(&vs->output, vs->sasl.encodedRawLength);
94         if (offset >= vs->throttle_output_offset &&
95             vs->output.offset < vs->throttle_output_offset) {
96             trace_vnc_client_unthrottle_incremental(vs, vs->ioc,
97                                                     vs->output.offset);
98         }
99         vs->sasl.encoded = NULL;
100         vs->sasl.encodedOffset = vs->sasl.encodedLength = 0;
101     }
102 
103     /* Can't merge this block with one above, because
104      * someone might have written more unencrypted
105      * data in vs->output while we were processing
106      * SASL encoded output
107      */
108     if (vs->output.offset == 0) {
109         if (vs->ioc_tag) {
110             g_source_remove(vs->ioc_tag);
111         }
112         vs->ioc_tag = qio_channel_add_watch(
113             vs->ioc, G_IO_IN, vnc_client_io, vs, NULL);
114     }
115 
116     return ret;
117 }
118 
119 
120 size_t vnc_client_read_sasl(VncState *vs)
121 {
122     size_t ret;
123     uint8_t encoded[4096];
124     const char *decoded;
125     unsigned int decodedLen;
126     int err;
127 
128     ret = vnc_client_read_buf(vs, encoded, sizeof(encoded));
129     if (!ret)
130         return 0;
131 
132     err = sasl_decode(vs->sasl.conn,
133                       (char *)encoded, ret,
134                       &decoded, &decodedLen);
135 
136     if (err != SASL_OK)
137         return vnc_client_io_error(vs, -1, NULL);
138     VNC_DEBUG("Read SASL Encoded %p size %ld Decoded %p size %d\n",
139               encoded, ret, decoded, decodedLen);
140     buffer_reserve(&vs->input, decodedLen);
141     buffer_append(&vs->input, decoded, decodedLen);
142     return decodedLen;
143 }
144 
145 
146 static int vnc_auth_sasl_check_access(VncState *vs)
147 {
148     const void *val;
149     int err;
150     int allow;
151 
152     err = sasl_getprop(vs->sasl.conn, SASL_USERNAME, &val);
153     if (err != SASL_OK) {
154         trace_vnc_auth_fail(vs, vs->auth, "Cannot fetch SASL username",
155                             sasl_errstring(err, NULL, NULL));
156         return -1;
157     }
158     if (val == NULL) {
159         trace_vnc_auth_fail(vs, vs->auth, "No SASL username set", "");
160         return -1;
161     }
162 
163     vs->sasl.username = g_strdup((const char*)val);
164     trace_vnc_auth_sasl_username(vs, vs->sasl.username);
165 
166     if (vs->vd->sasl.acl == NULL) {
167         trace_vnc_auth_sasl_acl(vs, 1);
168         return 0;
169     }
170 
171     allow = qemu_acl_party_is_allowed(vs->vd->sasl.acl, vs->sasl.username);
172 
173     trace_vnc_auth_sasl_acl(vs, allow);
174     return allow ? 0 : -1;
175 }
176 
177 static int vnc_auth_sasl_check_ssf(VncState *vs)
178 {
179     const void *val;
180     int err, ssf;
181 
182     if (!vs->sasl.wantSSF)
183         return 1;
184 
185     err = sasl_getprop(vs->sasl.conn, SASL_SSF, &val);
186     if (err != SASL_OK)
187         return 0;
188 
189     ssf = *(const int *)val;
190 
191     trace_vnc_auth_sasl_ssf(vs, ssf);
192 
193     if (ssf < 56)
194         return 0; /* 56 is good for Kerberos */
195 
196     /* Only setup for read initially, because we're about to send an RPC
197      * reply which must be in plain text. When the next incoming RPC
198      * arrives, we'll switch on writes too
199      *
200      * cf qemudClientReadSASL  in qemud.c
201      */
202     vs->sasl.runSSF = 1;
203 
204     /* We have a SSF that's good enough */
205     return 1;
206 }
207 
208 /*
209  * Step Msg
210  *
211  * Input from client:
212  *
213  * u32 clientin-length
214  * u8-array clientin-string
215  *
216  * Output to client:
217  *
218  * u32 serverout-length
219  * u8-array serverout-strin
220  * u8 continue
221  */
222 
223 static int protocol_client_auth_sasl_step_len(VncState *vs, uint8_t *data, size_t len);
224 
225 static int protocol_client_auth_sasl_step(VncState *vs, uint8_t *data, size_t len)
226 {
227     uint32_t datalen = len;
228     const char *serverout;
229     unsigned int serveroutlen;
230     int err;
231     char *clientdata = NULL;
232 
233     /* NB, distinction of NULL vs "" is *critical* in SASL */
234     if (datalen) {
235         clientdata = (char*)data;
236         clientdata[datalen-1] = '\0'; /* Wire includes '\0', but make sure */
237         datalen--; /* Don't count NULL byte when passing to _start() */
238     }
239 
240     err = sasl_server_step(vs->sasl.conn,
241                            clientdata,
242                            datalen,
243                            &serverout,
244                            &serveroutlen);
245     trace_vnc_auth_sasl_step(vs, data, len, serverout, serveroutlen, err);
246     if (err != SASL_OK &&
247         err != SASL_CONTINUE) {
248         trace_vnc_auth_fail(vs, vs->auth, "Cannot step SASL auth",
249                             sasl_errdetail(vs->sasl.conn));
250         sasl_dispose(&vs->sasl.conn);
251         vs->sasl.conn = NULL;
252         goto authabort;
253     }
254 
255     if (serveroutlen > SASL_DATA_MAX_LEN) {
256         trace_vnc_auth_fail(vs, vs->auth, "SASL data too long", "");
257         sasl_dispose(&vs->sasl.conn);
258         vs->sasl.conn = NULL;
259         goto authabort;
260     }
261 
262     if (serveroutlen) {
263         vnc_write_u32(vs, serveroutlen + 1);
264         vnc_write(vs, serverout, serveroutlen + 1);
265     } else {
266         vnc_write_u32(vs, 0);
267     }
268 
269     /* Whether auth is complete */
270     vnc_write_u8(vs, err == SASL_CONTINUE ? 0 : 1);
271 
272     if (err == SASL_CONTINUE) {
273         /* Wait for step length */
274         vnc_read_when(vs, protocol_client_auth_sasl_step_len, 4);
275     } else {
276         if (!vnc_auth_sasl_check_ssf(vs)) {
277             trace_vnc_auth_fail(vs, vs->auth, "SASL SSF too weak", "");
278             goto authreject;
279         }
280 
281         /* Check username whitelist ACL */
282         if (vnc_auth_sasl_check_access(vs) < 0) {
283             goto authreject;
284         }
285 
286         trace_vnc_auth_pass(vs, vs->auth);
287         vnc_write_u32(vs, 0); /* Accept auth */
288         /*
289          * Delay writing in SSF encoded mode until pending output
290          * buffer is written
291          */
292         if (vs->sasl.runSSF)
293             vs->sasl.waitWriteSSF = vs->output.offset;
294         start_client_init(vs);
295     }
296 
297     return 0;
298 
299  authreject:
300     vnc_write_u32(vs, 1); /* Reject auth */
301     vnc_write_u32(vs, sizeof("Authentication failed"));
302     vnc_write(vs, "Authentication failed", sizeof("Authentication failed"));
303     vnc_flush(vs);
304     vnc_client_error(vs);
305     return -1;
306 
307  authabort:
308     vnc_client_error(vs);
309     return -1;
310 }
311 
312 static int protocol_client_auth_sasl_step_len(VncState *vs, uint8_t *data, size_t len)
313 {
314     uint32_t steplen = read_u32(data, 0);
315 
316     if (steplen > SASL_DATA_MAX_LEN) {
317         trace_vnc_auth_fail(vs, vs->auth, "SASL step len too large", "");
318         vnc_client_error(vs);
319         return -1;
320     }
321 
322     if (steplen == 0)
323         return protocol_client_auth_sasl_step(vs, NULL, 0);
324     else
325         vnc_read_when(vs, protocol_client_auth_sasl_step, steplen);
326     return 0;
327 }
328 
329 /*
330  * Start Msg
331  *
332  * Input from client:
333  *
334  * u32 clientin-length
335  * u8-array clientin-string
336  *
337  * Output to client:
338  *
339  * u32 serverout-length
340  * u8-array serverout-strin
341  * u8 continue
342  */
343 
344 #define SASL_DATA_MAX_LEN (1024 * 1024)
345 
346 static int protocol_client_auth_sasl_start(VncState *vs, uint8_t *data, size_t len)
347 {
348     uint32_t datalen = len;
349     const char *serverout;
350     unsigned int serveroutlen;
351     int err;
352     char *clientdata = NULL;
353 
354     /* NB, distinction of NULL vs "" is *critical* in SASL */
355     if (datalen) {
356         clientdata = (char*)data;
357         clientdata[datalen-1] = '\0'; /* Should be on wire, but make sure */
358         datalen--; /* Don't count NULL byte when passing to _start() */
359     }
360 
361     err = sasl_server_start(vs->sasl.conn,
362                             vs->sasl.mechlist,
363                             clientdata,
364                             datalen,
365                             &serverout,
366                             &serveroutlen);
367     trace_vnc_auth_sasl_start(vs, data, len, serverout, serveroutlen, err);
368     if (err != SASL_OK &&
369         err != SASL_CONTINUE) {
370         trace_vnc_auth_fail(vs, vs->auth, "Cannot start SASL auth",
371                             sasl_errdetail(vs->sasl.conn));
372         sasl_dispose(&vs->sasl.conn);
373         vs->sasl.conn = NULL;
374         goto authabort;
375     }
376     if (serveroutlen > SASL_DATA_MAX_LEN) {
377         trace_vnc_auth_fail(vs, vs->auth, "SASL data too long", "");
378         sasl_dispose(&vs->sasl.conn);
379         vs->sasl.conn = NULL;
380         goto authabort;
381     }
382 
383     if (serveroutlen) {
384         vnc_write_u32(vs, serveroutlen + 1);
385         vnc_write(vs, serverout, serveroutlen + 1);
386     } else {
387         vnc_write_u32(vs, 0);
388     }
389 
390     /* Whether auth is complete */
391     vnc_write_u8(vs, err == SASL_CONTINUE ? 0 : 1);
392 
393     if (err == SASL_CONTINUE) {
394         /* Wait for step length */
395         vnc_read_when(vs, protocol_client_auth_sasl_step_len, 4);
396     } else {
397         if (!vnc_auth_sasl_check_ssf(vs)) {
398             trace_vnc_auth_fail(vs, vs->auth, "SASL SSF too weak", "");
399             goto authreject;
400         }
401 
402         /* Check username whitelist ACL */
403         if (vnc_auth_sasl_check_access(vs) < 0) {
404             goto authreject;
405         }
406 
407         trace_vnc_auth_pass(vs, vs->auth);
408         vnc_write_u32(vs, 0); /* Accept auth */
409         start_client_init(vs);
410     }
411 
412     return 0;
413 
414  authreject:
415     vnc_write_u32(vs, 1); /* Reject auth */
416     vnc_write_u32(vs, sizeof("Authentication failed"));
417     vnc_write(vs, "Authentication failed", sizeof("Authentication failed"));
418     vnc_flush(vs);
419     vnc_client_error(vs);
420     return -1;
421 
422  authabort:
423     vnc_client_error(vs);
424     return -1;
425 }
426 
427 static int protocol_client_auth_sasl_start_len(VncState *vs, uint8_t *data, size_t len)
428 {
429     uint32_t startlen = read_u32(data, 0);
430 
431     if (startlen > SASL_DATA_MAX_LEN) {
432         trace_vnc_auth_fail(vs, vs->auth, "SASL start len too large", "");
433         vnc_client_error(vs);
434         return -1;
435     }
436 
437     if (startlen == 0)
438         return protocol_client_auth_sasl_start(vs, NULL, 0);
439 
440     vnc_read_when(vs, protocol_client_auth_sasl_start, startlen);
441     return 0;
442 }
443 
444 static int protocol_client_auth_sasl_mechname(VncState *vs, uint8_t *data, size_t len)
445 {
446     char *mechname = g_strndup((const char *) data, len);
447     trace_vnc_auth_sasl_mech_choose(vs, mechname);
448 
449     if (strncmp(vs->sasl.mechlist, mechname, len) == 0) {
450         if (vs->sasl.mechlist[len] != '\0' &&
451             vs->sasl.mechlist[len] != ',') {
452             goto fail;
453         }
454     } else {
455         char *offset = strstr(vs->sasl.mechlist, mechname);
456         if (!offset) {
457             goto fail;
458         }
459         if (offset[-1] != ',' ||
460             (offset[len] != '\0'&&
461              offset[len] != ',')) {
462             goto fail;
463         }
464     }
465 
466     g_free(vs->sasl.mechlist);
467     vs->sasl.mechlist = mechname;
468 
469     vnc_read_when(vs, protocol_client_auth_sasl_start_len, 4);
470     return 0;
471 
472  fail:
473     trace_vnc_auth_fail(vs, vs->auth, "Unsupported mechname", mechname);
474     vnc_client_error(vs);
475     g_free(mechname);
476     return -1;
477 }
478 
479 static int protocol_client_auth_sasl_mechname_len(VncState *vs, uint8_t *data, size_t len)
480 {
481     uint32_t mechlen = read_u32(data, 0);
482 
483     if (mechlen > 100) {
484         trace_vnc_auth_fail(vs, vs->auth, "SASL mechname too long", "");
485         vnc_client_error(vs);
486         return -1;
487     }
488     if (mechlen < 1) {
489         trace_vnc_auth_fail(vs, vs->auth, "SASL mechname too short", "");
490         vnc_client_error(vs);
491         return -1;
492     }
493     vnc_read_when(vs, protocol_client_auth_sasl_mechname,mechlen);
494     return 0;
495 }
496 
497 static char *
498 vnc_socket_ip_addr_string(QIOChannelSocket *ioc,
499                           bool local,
500                           Error **errp)
501 {
502     SocketAddress *addr;
503     char *ret;
504 
505     if (local) {
506         addr = qio_channel_socket_get_local_address(ioc, errp);
507     } else {
508         addr = qio_channel_socket_get_remote_address(ioc, errp);
509     }
510     if (!addr) {
511         return NULL;
512     }
513 
514     if (addr->type != SOCKET_ADDRESS_TYPE_INET) {
515         error_setg(errp, "Not an inet socket type");
516         return NULL;
517     }
518     ret = g_strdup_printf("%s;%s", addr->u.inet.host, addr->u.inet.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     Error *local_err = NULL;
529     char *localAddr, *remoteAddr;
530     int mechlistlen;
531 
532     /* Get local & remote client addresses in form  IPADDR;PORT */
533     localAddr = vnc_socket_ip_addr_string(vs->sioc, true, &local_err);
534     if (!localAddr) {
535         trace_vnc_auth_fail(vs, vs->auth, "Cannot format local IP",
536                             error_get_pretty(local_err));
537         goto authabort;
538     }
539 
540     remoteAddr = vnc_socket_ip_addr_string(vs->sioc, false, &local_err);
541     if (!remoteAddr) {
542         trace_vnc_auth_fail(vs, vs->auth, "Cannot format remote IP",
543                             error_get_pretty(local_err));
544         g_free(localAddr);
545         goto authabort;
546     }
547 
548     err = sasl_server_new("vnc",
549                           NULL, /* FQDN - just delegates to gethostname */
550                           NULL, /* User realm */
551                           localAddr,
552                           remoteAddr,
553                           NULL, /* Callbacks, not needed */
554                           SASL_SUCCESS_DATA,
555                           &vs->sasl.conn);
556     g_free(localAddr);
557     g_free(remoteAddr);
558     localAddr = remoteAddr = NULL;
559 
560     if (err != SASL_OK) {
561         trace_vnc_auth_fail(vs, vs->auth,  "SASL context setup failed",
562                             sasl_errstring(err, NULL, NULL));
563         vs->sasl.conn = NULL;
564         goto authabort;
565     }
566 
567     /* Inform SASL that we've got an external SSF layer from TLS/x509 */
568     if (vs->auth == VNC_AUTH_VENCRYPT &&
569         vs->subauth == VNC_AUTH_VENCRYPT_X509SASL) {
570         int keysize;
571         sasl_ssf_t ssf;
572 
573         keysize = qcrypto_tls_session_get_key_size(vs->tls,
574                                                    &local_err);
575         if (keysize < 0) {
576             trace_vnc_auth_fail(vs, vs->auth, "cannot TLS get cipher size",
577                                 error_get_pretty(local_err));
578             sasl_dispose(&vs->sasl.conn);
579             vs->sasl.conn = NULL;
580             goto authabort;
581         }
582         ssf = keysize * CHAR_BIT; /* tls key size is bytes, sasl wants bits */
583 
584         err = sasl_setprop(vs->sasl.conn, SASL_SSF_EXTERNAL, &ssf);
585         if (err != SASL_OK) {
586             trace_vnc_auth_fail(vs, vs->auth, "cannot set SASL external SSF",
587                                 sasl_errstring(err, NULL, NULL));
588             sasl_dispose(&vs->sasl.conn);
589             vs->sasl.conn = NULL;
590             goto authabort;
591         }
592     } else {
593         vs->sasl.wantSSF = 1;
594     }
595 
596     memset (&secprops, 0, sizeof secprops);
597     /* Inform SASL that we've got an external SSF layer from TLS.
598      *
599      * Disable SSF, if using TLS+x509+SASL only. TLS without x509
600      * is not sufficiently strong
601      */
602     if (vs->vd->is_unix ||
603         (vs->auth == VNC_AUTH_VENCRYPT &&
604          vs->subauth == VNC_AUTH_VENCRYPT_X509SASL)) {
605         /* If we've got TLS or UNIX domain sock, we don't care about SSF */
606         secprops.min_ssf = 0;
607         secprops.max_ssf = 0;
608         secprops.maxbufsize = 8192;
609         secprops.security_flags = 0;
610     } else {
611         /* Plain TCP, better get an SSF layer */
612         secprops.min_ssf = 56; /* Good enough to require kerberos */
613         secprops.max_ssf = 100000; /* Arbitrary big number */
614         secprops.maxbufsize = 8192;
615         /* Forbid any anonymous or trivially crackable auth */
616         secprops.security_flags =
617             SASL_SEC_NOANONYMOUS | SASL_SEC_NOPLAINTEXT;
618     }
619 
620     err = sasl_setprop(vs->sasl.conn, SASL_SEC_PROPS, &secprops);
621     if (err != SASL_OK) {
622         trace_vnc_auth_fail(vs, vs->auth, "cannot set SASL security props",
623                             sasl_errstring(err, NULL, NULL));
624         sasl_dispose(&vs->sasl.conn);
625         vs->sasl.conn = NULL;
626         goto authabort;
627     }
628 
629     err = sasl_listmech(vs->sasl.conn,
630                         NULL, /* Don't need to set user */
631                         "", /* Prefix */
632                         ",", /* Separator */
633                         "", /* Suffix */
634                         &mechlist,
635                         NULL,
636                         NULL);
637     if (err != SASL_OK) {
638         trace_vnc_auth_fail(vs, vs->auth, "cannot list SASL mechanisms",
639                             sasl_errdetail(vs->sasl.conn));
640         sasl_dispose(&vs->sasl.conn);
641         vs->sasl.conn = NULL;
642         goto authabort;
643     }
644     trace_vnc_auth_sasl_mech_list(vs, mechlist);
645 
646     vs->sasl.mechlist = g_strdup(mechlist);
647     mechlistlen = strlen(mechlist);
648     vnc_write_u32(vs, mechlistlen);
649     vnc_write(vs, mechlist, mechlistlen);
650     vnc_flush(vs);
651 
652     vnc_read_when(vs, protocol_client_auth_sasl_mechname_len, 4);
653 
654     return;
655 
656  authabort:
657     error_free(local_err);
658     vnc_client_error(vs);
659 }
660 
661 
662