summaryrefslogtreecommitdiffstats
path: root/auth-options.c
blob: 57b49f7fd7518c5865f7e7b27be87f7cae882bb3 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
/* $OpenBSD: auth-options.c,v 1.72 2016/11/30 02:57:40 djm Exp $ */
/*
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 * As far as I am concerned, the code I have written for this software
 * can be used freely for any purpose.  Any derived versions of this
 * software must be clearly marked as such, and if the derived work is
 * incompatible with the protocol description in the RFC file, it must be
 * called by a name other than "ssh" or "Secure Shell".
 */

#include "includes.h"

#include <sys/types.h>

#include <netdb.h>
#include <pwd.h>
#include <string.h>
#include <stdio.h>
#include <stdarg.h>

#include "openbsd-compat/sys-queue.h"

#include "key.h"	/* XXX for typedef */
#include "buffer.h"	/* XXX for typedef */
#include "xmalloc.h"
#include "match.h"
#include "ssherr.h"
#include "log.h"
#include "canohost.h"
#include "packet.h"
#include "sshbuf.h"
#include "misc.h"
#include "channels.h"
#include "servconf.h"
#include "sshkey.h"
#include "auth-options.h"
#include "hostfile.h"
#include "auth.h"

/* Flags set authorized_keys flags */
int no_port_forwarding_flag = 0;
int no_agent_forwarding_flag = 0;
int no_x11_forwarding_flag = 0;
int no_pty_flag = 0;
int no_user_rc = 0;
int key_is_cert_authority = 0;

/* "command=" option. */
char *forced_command = NULL;

/* "environment=" options. */
struct envstring *custom_environment = NULL;

/* "tunnel=" option. */
int forced_tun_device = -1;

/* "principals=" option. */
char *authorized_principals = NULL;

extern ServerOptions options;

void
auth_clear_options(void)
{
	no_agent_forwarding_flag = 0;
	no_port_forwarding_flag = 0;
	no_pty_flag = 0;
	no_x11_forwarding_flag = 0;
	no_user_rc = 0;
	key_is_cert_authority = 0;
	while (custom_environment) {
		struct envstring *ce = custom_environment;
		custom_environment = ce->next;
		free(ce->s);
		free(ce);
	}
	free(forced_command);
	forced_command = NULL;
	free(authorized_principals);
	authorized_principals = NULL;
	forced_tun_device = -1;
	channel_clear_permitted_opens();
}

/*
 * Match flag 'opt' in *optsp, and if allow_negate is set then also match
 * 'no-opt'. Returns -1 if option not matched, 1 if option matches or 0
 * if negated option matches. 
 * If the option or negated option matches, then *optsp is updated to
 * point to the first character after the option and, if 'msg' is not NULL
 * then a message based on it added via auth_debug_add().
 */
static int
match_flag(const char *opt, int allow_negate, char **optsp, const char *msg)
{
	size_t opt_len = strlen(opt);
	char *opts = *optsp;
	int negate = 0;

	if (allow_negate && strncasecmp(opts, "no-", 3) == 0) {
		opts += 3;
		negate = 1;
	}
	if (strncasecmp(opts, opt, opt_len) == 0) {
		*optsp = opts + opt_len;
		if (msg != NULL) {
			auth_debug_add("%s %s.", msg,
			    negate ? "disabled" : "enabled");
		}
		return negate ? 0 : 1;
	}
	return -1;
}

/*
 * return 1 if access is granted, 0 if not.
 * side effect: sets key option flags
 */
int
auth_parse_options(struct passwd *pw, char *opts, char *file, u_long linenum)
{
	struct ssh *ssh = active_state;		/* XXX */
	const char *cp;
	int i, r;

	/* reset options */
	auth_clear_options();

	if (!opts)
		return 1;

	while (*opts && *opts != ' ' && *opts != '\t') {
		if ((r = match_flag("cert-authority", 0, &opts, NULL)) != -1) {
			key_is_cert_authority = r;
			goto next_option;
		}
		if ((r = match_flag("restrict", 0, &opts, NULL)) != -1) {
			auth_debug_add("Key is restricted.");
			no_port_forwarding_flag = 1;
			no_agent_forwarding_flag = 1;
			no_x11_forwarding_flag = 1;
			no_pty_flag = 1;
			no_user_rc = 1;
			goto next_option;
		}
		if ((r = match_flag("port-forwarding", 1, &opts,
		    "Port forwarding")) != -1) {
			no_port_forwarding_flag = r != 1;
			goto next_option;
		}
		if ((r = match_flag("agent-forwarding", 1, &opts,
		    "Agent forwarding")) != -1) {
			no_agent_forwarding_flag = r != 1;
			goto next_option;
		}
		if ((r = match_flag("x11-forwarding", 1, &opts,
		    "X11 forwarding")) != -1) {
			no_x11_forwarding_flag = r != 1;
			goto next_option;
		}
		if ((r = match_flag("pty", 1, &opts,
		    "PTY allocation")) != -1) {
			no_pty_flag = r != 1;
			goto next_option;
		}
		if ((r = match_flag("user-rc", 1, &opts,
		    "User rc execution")) != -1) {
			no_user_rc = r != 1;
			goto next_option;
		}
		cp = "command=\"";
		if (strncasecmp(opts, cp, strlen(cp)) == 0) {
			opts += strlen(cp);
			free(forced_command);
			forced_command = xmalloc(strlen(opts) + 1);
			i = 0;
			while (*opts) {
				if (*opts == '"')
					break;
				if (*opts == '\\' && opts[1] == '"') {
					opts += 2;
					forced_command[i++] = '"';
					continue;
				}
				forced_command[i++] = *opts++;
			}
			if (!*opts) {
				debug("%.100s, line %lu: missing end quote",
				    file, linenum);
				auth_debug_add("%.100s, line %lu: missing end quote",
				    file, linenum);
				free(forced_command);
				forced_command = NULL;
				goto bad_option;
			}
			forced_command[i] = '\0';
			auth_debug_add("Forced command.");
			opts++;
			goto next_option;
		}
		cp = "principals=\"";
		if (strncasecmp(opts, cp, strlen(cp)) == 0) {
			opts += strlen(cp);
			free(authorized_principals);
			authorized_principals = xmalloc(strlen(opts) + 1);
			i = 0;
			while (*opts) {
				if (*opts == '"')
					break;
				if (*opts == '\\' && opts[1] == '"') {
					opts += 2;
					authorized_principals[i++] = '"';
					continue;
				}
				authorized_principals[i++] = *opts++;
			}
			if (!*opts) {
				debug("%.100s, line %lu: missing end quote",
				    file, linenum);
				auth_debug_add("%.100s, line %lu: missing end quote",
				    file, linenum);
				free(authorized_principals);
				authorized_principals = NULL;
				goto bad_option;
			}
			authorized_principals[i] = '\0';
			auth_debug_add("principals: %.900s",
			    authorized_principals);
			opts++;
			goto next_option;
		}
		cp = "environment=\"";
		if (strncasecmp(opts, cp, strlen(cp)) == 0) {
			char *s;
			struct envstring *new_envstring;

			opts += strlen(cp);
			s = xmalloc(strlen(opts) + 1);
			i = 0;
			while (*opts) {
				if (*opts == '"')
					break;
				if (*opts == '\\' && opts[1] == '"') {
					opts += 2;
					s[i++] = '"';
					continue;
				}
				s[i++] = *opts++;
			}
			if (!*opts) {
				debug("%.100s, line %lu: missing end quote",
				    file, linenum);
				auth_debug_add("%.100s, line %lu: missing end quote",
				    file, linenum);
				free(s);
				goto bad_option;
			}
			s[i] = '\0';
			opts++;
			if (options.permit_user_env) {
				auth_debug_add("Adding to environment: "
				    "%.900s", s);
				debug("Adding to environment: %.900s", s);
				new_envstring = xcalloc(1,
				    sizeof(*new_envstring));
				new_envstring->s = s;
				new_envstring->next = custom_environment;
				custom_environment = new_envstring;
				s = NULL;
			}
			free(s);
			goto next_option;
		}
		cp = "from=\"";
		if (strncasecmp(opts, cp, strlen(cp)) == 0) {
			const char *remote_ip = ssh_remote_ipaddr(ssh);
			const char *remote_host = auth_get_canonical_hostname(
			    ssh, options.use_dns);
			char *patterns = xmalloc(strlen(opts) + 1);

			opts += strlen(cp);
			i = 0;
			while (*opts) {
				if (*opts == '"')
					break;
				if (*opts == '\\' && opts[1] == '"') {
					opts += 2;
					patterns[i++] = '"';
					continue;
				}
				patterns[i++] = *opts++;
			}
			if (!*opts) {
				debug("%.100s, line %lu: missing end quote",
				    file, linenum);
				auth_debug_add("%.100s, line %lu: missing end quote",
				    file, linenum);
				free(patterns);
				goto bad_option;
			}
			patterns[i] = '\0';
			opts++;
			switch (match_host_and_ip(remote_host, remote_ip,
			    patterns)) {
			case 1:
				free(patterns);
				/* Host name matches. */
				goto next_option;
			case -1:
				debug("%.100s, line %lu: invalid criteria",
				    file, linenum);
				auth_debug_add("%.100s, line %lu: "
				    "invalid criteria", file, linenum);
				/* FALLTHROUGH */
			case 0:
				free(patterns);
				logit("Authentication tried for %.100s with "
				    "correct key but not from a permitted "
				    "host (host=%.200s, ip=%.200s).",
				    pw->pw_name, remote_host, remote_ip);
				auth_debug_add("Your host '%.200s' is not "
				    "permitted to use this key for login.",
				    remote_host);
				break;
			}
			/* deny access */
			return 0;
		}
		cp = "permitopen=\"";
		if (strncasecmp(opts, cp, strlen(cp)) == 0) {
			char *host, *p;
			int port;
			char *patterns = xmalloc(strlen(opts) + 1);

			opts += strlen(cp);
			i = 0;
			while (*opts) {
				if (*opts == '"')
					break;
				if (*opts == '\\' && opts[1] == '"') {
					opts += 2;
					patterns[i++] = '"';
					continue;
				}
				patterns[i++] = *opts++;
			}
			if (!*opts) {
				debug("%.100s, line %lu: missing end quote",
				    file, linenum);
				auth_debug_add("%.100s, line %lu: missing "
				    "end quote", file, linenum);
				free(patterns);
				goto bad_option;
			}
			patterns[i] = '\0';
			opts++;
			p = patterns;
			/* XXX - add streamlocal support */
			host = hpdelim(&p);
			if (host == NULL || strlen(host) >= NI_MAXHOST) {
				debug("%.100s, line %lu: Bad permitopen "
				    "specification <%.100s>", file, linenum,
				    patterns);
				auth_debug_add("%.100s, line %lu: "
				    "Bad permitopen specification", file,
				    linenum);
				free(patterns);
				goto bad_option;
			}
			host = cleanhostname(host);
			if (p == NULL || (port = permitopen_port(p)) < 0) {
				debug("%.100s, line %lu: Bad permitopen port "
				    "<%.100s>", file, linenum, p ? p : "");
				auth_debug_add("%.100s, line %lu: "
				    "Bad permitopen port", file, linenum);
				free(patterns);
				goto bad_option;
			}
			if ((options.allow_tcp_forwarding & FORWARD_LOCAL) != 0)
				channel_add_permitted_opens(host, port);
			free(patterns);
			goto next_option;
		}
		cp = "tunnel=\"";
		if (strncasecmp(opts, cp, strlen(cp)) == 0) {
			char *tun = NULL;
			opts += strlen(cp);
			tun = xmalloc(strlen(opts) + 1);
			i = 0;
			while (*opts) {
				if (*opts == '"')
					break;
				tun[i++] = *opts++;
			}
			if (!*opts) {
				debug("%.100s, line %lu: missing end quote",
				    file, linenum);
				auth_debug_add("%.100s, line %lu: missing end quote",
				    file, linenum);
				free(tun);
				forced_tun_device = -1;
				goto bad_option;
			}
			tun[i] = '\0';
			forced_tun_device = a2tun(tun, NULL);
			free(tun);
			if (forced_tun_device == SSH_TUNID_ERR) {
				debug("%.100s, line %lu: invalid tun device",
				    file, linenum);
				auth_debug_add("%.100s, line %lu: invalid tun device",
				    file, linenum);
				forced_tun_device = -1;
				goto bad_option;
			}
			auth_debug_add("Forced tun device: %d", forced_tun_device);
			opts++;
			goto next_option;
		}
next_option:
		/*
		 * Skip the comma, and move to the next option
		 * (or break out if there are no more).
		 */
		if (!*opts)
			fatal("Bugs in auth-options.c option processing.");
		if (*opts == ' ' || *opts == '\t')
			break;		/* End of options. */
		if (*opts != ',')
			goto bad_option;
		opts++;
		/* Process the next option. */
	}

	/* grant access */
	return 1;

bad_option:
	logit("Bad options in %.100s file, line %lu: %.50s",
	    file, linenum, opts);
	auth_debug_add("Bad options in %.100s file, line %lu: %.50s",
	    file, linenum, opts);

	/* deny access */
	return 0;
}

#define OPTIONS_CRITICAL	1
#define OPTIONS_EXTENSIONS	2
static int
parse_option_list(struct sshbuf *oblob, struct passwd *pw,
    u_int which, int crit,
    int *cert_no_port_forwarding_flag,
    int *cert_no_agent_forwarding_flag,
    int *cert_no_x11_forwarding_flag,
    int *cert_no_pty_flag,
    int *cert_no_user_rc,
    char **cert_forced_command,
    int *cert_source_address_done)
{
	struct ssh *ssh = active_state;		/* XXX */
	char *command, *allowed;
	const char *remote_ip;
	char *name = NULL;
	struct sshbuf *c = NULL, *data = NULL;
	int r, ret = -1, result, found;

	if ((c = sshbuf_fromb(oblob)) == NULL) {
		error("%s: sshbuf_fromb failed", __func__);
		goto out;
	}

	while (sshbuf_len(c) > 0) {
		sshbuf_free(data);
		data = NULL;
		if ((r = sshbuf_get_cstring(c, &name, NULL)) != 0 ||
		    (r = sshbuf_froms(c, &data)) != 0) {
			error("Unable to parse certificate options: %s",
			    ssh_err(r));
			goto out;
		}
		debug3("found certificate option \"%.100s\" len %zu",
		    name, sshbuf_len(data));
		found = 0;
		if ((which & OPTIONS_EXTENSIONS) != 0) {
			if (strcmp(name, "permit-X11-forwarding") == 0) {
				*cert_no_x11_forwarding_flag = 0;
				found = 1;
			} else if (strcmp(name,
			    "permit-agent-forwarding") == 0) {
				*cert_no_agent_forwarding_flag = 0;
				found = 1;
			} else if (strcmp(name,
			    "permit-port-forwarding") == 0) {
				*cert_no_port_forwarding_flag = 0;
				found = 1;
			} else if (strcmp(name, "permit-pty") == 0) {
				*cert_no_pty_flag = 0;
				found = 1;
			} else if (strcmp(name, "permit-user-rc") == 0) {
				*cert_no_user_rc = 0;
				found = 1;
			}
		}
		if (!found && (which & OPTIONS_CRITICAL) != 0) {
			if (strcmp(name, "force-command") == 0) {
				if ((r = sshbuf_get_cstring(data, &command,
				    NULL)) != 0) {
					error("Unable to parse \"%s\" "
					    "section: %s", name, ssh_err(r));
					goto out;
				}
				if (*cert_forced_command != NULL) {
					error("Certificate has multiple "
					    "force-command options");
					free(command);
					goto out;
				}
				*cert_forced_command = command;
				found = 1;
			}
			if (strcmp(name, "source-address") == 0) {
				if ((r = sshbuf_get_cstring(data, &allowed,
				    NULL)) != 0) {
					error("Unable to parse \"%s\" "
					    "section: %s", name, ssh_err(r));
					goto out;
				}
				if ((*cert_source_address_done)++) {
					error("Certificate has multiple "
					    "source-address options");
					free(allowed);
					goto out;
				}
				remote_ip = ssh_remote_ipaddr(ssh);
				result = addr_match_cidr_list(remote_ip,
				    allowed);
				free(allowed);
				switch (result) {
				case 1:
					/* accepted */
					break;
				case 0:
					/* no match */
					logit("Authentication tried for %.100s "
					    "with valid certificate but not "
					    "from a permitted host "
					    "(ip=%.200s).", pw->pw_name,
					    remote_ip);
					auth_debug_add("Your address '%.200s' "
					    "is not permitted to use this "
					    "certificate for login.",
					    remote_ip);
					goto out;
				case -1:
				default:
					error("Certificate source-address "
					    "contents invalid");
					goto out;
				}
				found = 1;
			}
		}

		if (!found) {
			if (crit) {
				error("Certificate critical option \"%s\" "
				    "is not supported", name);
				goto out;
			} else {
				logit("Certificate extension \"%s\" "
				    "is not supported", name);
			}
		} else if (sshbuf_len(data) != 0) {
			error("Certificate option \"%s\" corrupt "
			    "(extra data)", name);
			goto out;
		}
		free(name);
		name = NULL;
	}
	/* successfully parsed all options */
	ret = 0;

 out:
	if (ret != 0 &&
	    cert_forced_command != NULL &&
	    *cert_forced_command != NULL) {
		free(*cert_forced_command);
		*cert_forced_command = NULL;
	}
	free(name);
	sshbuf_free(data);
	sshbuf_free(c);
	return ret;
}

/*
 * Set options from critical certificate options. These supersede user key
 * options so this must be called after auth_parse_options().
 */
int
auth_cert_options(struct sshkey *k, struct passwd *pw, const char **reason)
{
	int cert_no_port_forwarding_flag = 1;
	int cert_no_agent_forwarding_flag = 1;
	int cert_no_x11_forwarding_flag = 1;
	int cert_no_pty_flag = 1;
	int cert_no_user_rc = 1;
	char *cert_forced_command = NULL;
	int cert_source_address_done = 0;

	*reason = "invalid certificate options";

	/* Separate options and extensions for v01 certs */
	if (parse_option_list(k->cert->critical, pw,
	    OPTIONS_CRITICAL, 1, NULL, NULL, NULL, NULL, NULL,
	    &cert_forced_command,
	    &cert_source_address_done) == -1)
		return -1;
	if (parse_option_list(k->cert->extensions, pw,
	    OPTIONS_EXTENSIONS, 0,
	    &cert_no_port_forwarding_flag,
	    &cert_no_agent_forwarding_flag,
	    &cert_no_x11_forwarding_flag,
	    &cert_no_pty_flag,
	    &cert_no_user_rc,
	    NULL, NULL) == -1)
		return -1;

	no_port_forwarding_flag |= cert_no_port_forwarding_flag;
	no_agent_forwarding_flag |= cert_no_agent_forwarding_flag;
	no_x11_forwarding_flag |= cert_no_x11_forwarding_flag;
	no_pty_flag |= cert_no_pty_flag;
	no_user_rc |= cert_no_user_rc;
	/*
	 * Only permit both CA and key option forced-command if they match.
	 * Otherwise refuse the certificate.
	 */
	if (cert_forced_command != NULL && forced_command != NULL) {
		if (strcmp(forced_command, cert_forced_command) == 0) {
			free(forced_command);
			forced_command = cert_forced_command;
		} else {
			*reason = "certificate and key options forced command "
			    "do not match";
			free(cert_forced_command);
			return -1;
		}
	} else if (cert_forced_command != NULL)
		forced_command = cert_forced_command;
	/* success */
	*reason = NULL;
	return 0;
}