aboutsummaryrefslogtreecommitdiff
path: root/src/pam-freerdp.c
blob: ebc98aff4d0ff9aab2d67208c70206c75590c87f (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
/*
 * Copyright © 2012 Canonical Ltd.
 *
 * This program is free software: you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 3, as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranties of
 * MERCHANTABILITY, SATISFACTORY QUALITY, or FITNESS FOR A PARTICULAR
 * PURPOSE.  See the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 * Author: Ted Gould <ted@canonical.com>
 */

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/wait.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <sys/un.h>
#include <pwd.h>
#include <grp.h>
#include <errno.h>

#include <security/pam_modules.h>
#include <security/pam_modutil.h>
#include <security/pam_appl.h>

#define PAM_TYPE_DOMAIN  1234
#define ALL_GOOD_SIGNAL  "Ar, ready to authenticate cap'n"

static int unpriveleged_kill (struct passwd * pwdent);

static char * global_domain = NULL;
/* FIXME? This is a work around to the fact that PAM seems to be clearing
   the auth token between authorize and open_session.  Which then requires
   us to save it.  Seems like we're the wrong people to do it, but we have
   no choice */
static char * global_password = NULL;

/* Either grab a value or prompt for it */
static char *
get_item (pam_handle_t * pamh, int type)
{
	/* Check to see if we just have the value.  If we do, great
	   let's dup it some we're consitently allocating memory */
	if (type != PAM_TYPE_DOMAIN) {
		/* If it's not a domain we can use the PAM functions because the PAM
		   functions don't support the domain */
		char * value = NULL;
		if (pam_get_item(pamh, type, (const void **)&value) == PAM_SUCCESS && value != NULL) {
			return value;
		}
		if (type == PAM_AUTHTOK && global_password != NULL) {
			/* If we're looking for a password, we didn't get one, before
			   prompting see if we've got a global one. */
			return global_password;
		}
	} else {
		/* Here we only have domains, so we can see if the global domain is
		   useful for us, if we have it */
		if (global_domain != NULL) {
			return global_domain;
		}
	}
	/* Now we need to prompt */

	/* Build up the message we're prompting for */
	struct pam_message message;
	const struct pam_message * pmessage = &message;

	message.msg = NULL;
	message.msg_style = PAM_PROMPT_ECHO_ON;

	switch (type) {
	case PAM_USER:
		message.msg = "login:";
		break;
	case PAM_RUSER:
		message.msg = "remote login:";
		break;
	case PAM_RHOST:
		message.msg = "remote host:";
		break;
	case PAM_AUTHTOK:
		message.msg = "password:";
		message.msg_style = PAM_PROMPT_ECHO_OFF;
		break;
	case PAM_TYPE_DOMAIN:
		message.msg = "domain:";
		break;
	default:
		return NULL;
	}

	struct pam_conv * conv = NULL;
	if (pam_get_item(pamh, PAM_CONV, (const void **)&conv) != PAM_SUCCESS || conv == NULL || conv->conv == NULL) {
		return NULL;
	}

	struct pam_response * responses = NULL;
	if (conv->conv(1, &pmessage, &responses, conv->appdata_ptr) != PAM_SUCCESS || responses == NULL) {
		return NULL;
	}

	char * promptval = responses->resp;
	free(responses);

	/* If we didn't get anything, just move on */
	if (promptval == NULL) {
		return NULL;
	}

	if (type == PAM_AUTHTOK) {
		if (mlock(promptval, strlen(promptval) + 1) != 0) {
			free(promptval);
			return NULL;
		}
	}

	if (type == PAM_RHOST) {
		char * subloc = strstr(promptval, "://");
		if (subloc != NULL) {
			char * original = promptval;
			char * newish = subloc + strlen("://");
			char * endslash = strstr(newish, "/");

			if (endslash != NULL) {
				endslash[0] = '\0';
			}

			promptval = strdup(newish);
			free(original);
		}
	}

	char * retval = NULL;
	if (promptval != NULL) { /* Can't believe it really would be at this point, but let's be sure */
		if (type != PAM_TYPE_DOMAIN) {
			/* We can only use the PAM functions if it's not the domain */
			pam_set_item(pamh, type, (const void *)promptval);
			/* We're returning the value saved by PAM so we can clear promptval */
			pam_get_item(pamh, type, (const void **)&retval);
		}
		if (type == PAM_TYPE_DOMAIN) {
			/* The domain can be saved globally so we can use it for open */
			if (global_domain != NULL) {
				free(global_domain);
			}
			global_domain = strdup(promptval);
			retval = global_domain;
		}
		if (type == PAM_AUTHTOK) {
			/* We also save the password globally if we've got one */
			if (global_password != NULL) {
				memset(global_password, 0, strlen(global_password));
				munlock(global_password, strlen(global_password) + 1);
				free(global_password);
			}
			global_password = strdup(promptval);
			if (mlock(global_password, strlen(global_password) + 1) != 0) {
				/* Woah, can't lock it.  Can't keep it. */
				free(global_password);
				global_password = NULL;
			} else {
				retval = global_password;
			}
		}

		if (type == PAM_AUTHTOK) {
			memset(promptval, 0, strlen(promptval) + 1);
			munlock(promptval, strlen(promptval) + 1);
		}

		free(promptval);
	}

	return retval;
}

#define GET_ITEM(val, type) \
	if ((val = get_item(pamh, type)) == NULL) { \
		retval = PAM_AUTH_ERR; \
		goto done; \
	}

/* Authenticate.  We need to make sure we have a user account, that
   there are remote accounts and then verify them with FreeRDP */
PAM_EXTERN int
pam_sm_authenticate (pam_handle_t *pamh, int flags, int argc, const char **argv)
{
	char * username = NULL;
	char * password = NULL;
	char * ruser = NULL;
	char * rhost = NULL;
	char * rdomain = NULL;
	int retval = PAM_IGNORE;

	/* Get all the values, or prompt for them, or return with
	   an auth error */
	GET_ITEM(username, PAM_USER);
	GET_ITEM(ruser,    PAM_RUSER);
	GET_ITEM(rhost,    PAM_RHOST);
	GET_ITEM(rdomain,  PAM_TYPE_DOMAIN);
	GET_ITEM(password, PAM_AUTHTOK);

	int stdinpipe[2];
	if (pipe(stdinpipe) != 0) {
		retval = PAM_SYSTEM_ERR;
		goto done;
	}

	/* At this point we should have the values, let's check the auth */
	pid_t pid;
	switch (pid = fork()) {
	case 0: { /* child */
		dup2(stdinpipe[0], 0);

		char * args[5];

		args[0] = AUTH_CHECK;
		args[1] = rhost;
		args[2] = ruser;
		args[3] = rdomain;
		args[4] = NULL;

		struct passwd * pwdent = getpwnam(username);
		if (pwdent == NULL) {
			_exit(EXIT_FAILURE);
		}

		/* Setting groups, but allowing EPERM as if we're not 100% root
		   we might not be able to do this */
		if (setgroups(1, &pwdent->pw_gid) != 0 && errno != EPERM) {
			_exit(EXIT_FAILURE);
		}

		if (setgid(pwdent->pw_gid) < 0 || setuid(pwdent->pw_uid) < 0 ||
				setegid(pwdent->pw_gid) < 0 || seteuid(pwdent->pw_uid) < 0) {
			_exit(EXIT_FAILURE);
		}

		if (clearenv() != 0) {
			_exit(EXIT_FAILURE);
		}

		if (chdir(pwdent->pw_dir) != 0) {
			_exit(EXIT_FAILURE);
		}

		setenv("HOME", pwdent->pw_dir, 1);

		execvp(args[0], args);
		_exit(EXIT_FAILURE);
		break;
	}
	case -1: { /* fork'n error! */
		retval = PAM_SYSTEM_ERR;
		break;
	}
	default: {
		int forkret = 0;
		int bytesout = 0;

		bytesout += write(stdinpipe[1], password, strlen(password));
		bytesout += write(stdinpipe[1], "\n", 1);

		close(stdinpipe[1]);

		if (waitpid(pid, &forkret, 0) < 0 || bytesout == 0) {
			retval = PAM_SYSTEM_ERR;
		} else if (forkret == 0) {
			retval = PAM_SUCCESS;
		} else {
			retval = PAM_AUTH_ERR;
		}
	}
	}

	/* Return our status */
done:
	return retval;
}

static int
session_socket_handler (struct passwd * pwdent, int readypipe, const char * ruser, const char * rhost, const char * rdomain, const char * password)
{
	/* Socket stuff */
	int socketfd = 0;
	struct sockaddr_un socket_addr;

	/* Connected user */
	socklen_t connected_addr_size;
	int connectfd = 0;
	struct sockaddr_un connected_addr;

	/* Our buffer */
	char * buffer = NULL;
	int buffer_len = 0;
	int buffer_fill = 0;

	/* Track write out */
	int writedata = 0;

	/* Track ready writing */
	int readywrite = 0;

	/* Setting groups, but allowing EPERM as if we're not 100% root
	   we might not be able to do this */
	if (setgroups(1, &pwdent->pw_gid) != 0 && errno != EPERM) {
		_exit(EXIT_FAILURE);
	}

	if (setgid(pwdent->pw_gid) < 0 || setuid(pwdent->pw_uid) < 0 ||
			setegid(pwdent->pw_gid) < 0 || seteuid(pwdent->pw_uid) < 0) {
		/* Don't need to clean up yet */
		return EXIT_FAILURE;
	}

	if (clearenv() != 0) {
		/* Don't need to clean up yet */
		return EXIT_FAILURE;
	}

	if (chdir(pwdent->pw_dir) != 0) {
		/* Don't need to clean up yet */
		return EXIT_FAILURE;
	}

	if (rdomain[0] == '\0') {
		rdomain = ".";
	}

	/* Build this up as a buffer so we can just write it and see that
	   very, very clearly */
	buffer_len += strlen(ruser) + 1;    /* Add one for the space */
	buffer_len += strlen(rhost) + 1;    /* Add one for the space */
	buffer_len += strlen(rdomain) + 1;  /* Add one for the space */
	buffer_len += strlen(password) + 1; /* Add one for the NULL */

	if (buffer_len < 5) {
		/* Don't need to clean up yet */
		return EXIT_FAILURE;
	}

	buffer = malloc(buffer_len);

	if (buffer == NULL) {
		/* Don't need to clean up yet */
		return EXIT_FAILURE;
	}

	/* Lock the buffer before writing */
	if (mlock(buffer, buffer_len) != 0) {
		/* We can't lock, we go home */
		goto cleanup;
	}

	buffer_fill = snprintf(buffer, buffer_len, "%s %s %s %s", ruser, password, rdomain, rhost);
	if (buffer_fill > buffer_len) {
		/* This really shouldn't happen, but if for some reason we have an
		   difference between they way that the lengths are calculated we want
		   to catch that. */
		goto cleanup;
	}

	/* Make our socket and bind it */
	socketfd = socket(AF_UNIX, SOCK_STREAM, 0);
	if (socketfd < 0) {
		goto cleanup;
	}

	memset(&socket_addr, 0, sizeof(struct sockaddr_un));
	socket_addr.sun_family = AF_UNIX;
	strncpy(socket_addr.sun_path, pwdent->pw_dir, sizeof(socket_addr.sun_path) - 1);
	strncpy(socket_addr.sun_path + strlen(pwdent->pw_dir), "/.freerdp-socket", (sizeof(socket_addr.sun_path) - strlen(pwdent->pw_dir)) - 1);

	/* We bind the socket before forking so that we ensure that
	   there isn't a race condition to get to it.  Things will block
	   otherwise. */
	if (bind(socketfd, (struct sockaddr *)&socket_addr, sizeof(struct sockaddr_un)) < 0) {
		goto cleanup;
	}

	/* Set the socket file permissions to be 600 and the user and group
	   to be the guest user.  NOTE: This won't protect on BSD */
	if (chmod(socket_addr.sun_path, S_IRUSR | S_IWUSR) != 0 ||
			chown(socket_addr.sun_path, pwdent->pw_uid, pwdent->pw_gid) != 0) {
		goto cleanup;
	}

	if (listen(socketfd, 1) < 0) {
		goto cleanup;
	}

	readywrite = write(readypipe, ALL_GOOD_SIGNAL, strlen(ALL_GOOD_SIGNAL) + 1);
	if (readywrite != strlen(ALL_GOOD_SIGNAL) + 1) {
		goto cleanup;
	}

	connected_addr_size = sizeof(struct sockaddr_un);
	connectfd = accept(socketfd, (struct sockaddr *)&connected_addr, &connected_addr_size);
	if (connectfd < 0) {
		goto cleanup;
	}

	writedata = write(connectfd, buffer, buffer_len);

cleanup:
	if (socketfd != 0) {
		close(socketfd);
	}
	if (connectfd != 0) {
		close(connectfd);
	}

	if (buffer != NULL) {
		memset(buffer, 0, buffer_len);
		munlock(buffer, buffer_len);
		free(buffer);
		buffer = NULL;
	}

	/* This should be only true on the write, so we can use this to check
	   out as writedata is init to 0 */
	if (writedata == buffer_len) {
		return 0;
	}

	return EXIT_FAILURE;
}

pid_t session_pid = 0;
/* Open Session.  Here we need to fork a little process so that we can
   give the credentials to the session itself so that it can startup the
   xfreerdp viewer for the login */
PAM_EXTERN int
pam_sm_open_session (pam_handle_t *pamh, int flags, int argc, const char ** argv)
{
	char * username = NULL;
	char * password = NULL;
	char * ruser = NULL;
	char * rhost = NULL;
	char * rdomain = NULL;
	int retval = PAM_SUCCESS;

	/* Get all the values, or prompt for them, or return with
	   an auth error */
	GET_ITEM(username, PAM_USER);
	GET_ITEM(ruser,    PAM_RUSER);
	GET_ITEM(rhost,    PAM_RHOST);
	GET_ITEM(rdomain,  PAM_TYPE_DOMAIN);
	GET_ITEM(password, PAM_AUTHTOK);

	struct passwd * pwdent = getpwnam(username);
	if (pwdent == NULL) {
		retval = PAM_SYSTEM_ERR;
		goto done;
	}

	if (session_pid != 0) {
		unpriveleged_kill(pwdent);
	}

	int sessionready[2];
	if (pipe(sessionready) != 0) {
		retval = PAM_SYSTEM_ERR;
		goto done;
	}

	pid_t pid = fork();
	if (pid == 0) {
		int retval = 0;

		retval = session_socket_handler(pwdent, sessionready[1], ruser, rhost, rdomain, password);

		close(sessionready[1]);
		_exit(retval);
	} else if (pid < 0) {
		close(sessionready[0]);
		close(sessionready[1]);

		retval = PAM_SYSTEM_ERR;
	} else {
		char readbuffer[strlen(ALL_GOOD_SIGNAL) + 1];
		int readlen = 0;

		readlen = read(sessionready[0], readbuffer, strlen(ALL_GOOD_SIGNAL) + 1);

		close(sessionready[0]);

		if (readlen == strlen(ALL_GOOD_SIGNAL) + 1) {
			session_pid = pid;
		} else {
			retval = PAM_SYSTEM_ERR;
		}
	}

done:
    return retval;
}

/* Close Session.  Make sure our little guy has died so he doesn't become
   a zombie and eat things. */
PAM_EXTERN int
pam_sm_close_session (pam_handle_t *pamh, int flags, int argc, const char **argv)
{
	if (session_pid == 0) {
		return PAM_IGNORE;
	}

	char * username = NULL;
	int retval = PAM_SUCCESS;

	GET_ITEM(username, PAM_USER);

	struct passwd * pwdent = getpwnam(username);
	if (pwdent == NULL) {
		retval = PAM_SYSTEM_ERR;
		goto done;
	}

	retval = unpriveleged_kill(pwdent);

done:
	return retval;
}

/* Drop privs and try to kill the process with the PID of session_pid.  
   This ensures that we don't kill something important if there is PID wrap
   around.  */
static int
unpriveleged_kill (struct passwd * pwdent)
{
	int retval = PAM_SUCCESS;

	pid_t pid = fork();
	if (pid == 0) {
		/* Setting groups, but allowing EPERM as if we're not 100% root
		   we might not be able to do this */
		if (setgroups(1, &pwdent->pw_gid) != 0 && errno != EPERM) {
			_exit(EXIT_FAILURE);
		}

		if (setgid(pwdent->pw_gid) < 0 || setuid(pwdent->pw_uid) < 0 ||
				setegid(pwdent->pw_gid) < 0 || seteuid(pwdent->pw_uid) < 0) {
			_exit(EXIT_FAILURE);
		}

		if (clearenv() != 0) {
			_exit(EXIT_FAILURE);
		}

		int killval = kill(session_pid, SIGKILL);
		session_pid = 0;

		if (killval != 0) {
			printf("Unable to kill\n");
		}

		/* NOTE: We're ignoring whether we could kill it or not.  It'd be nice to
		   track that but there are a lot of reason that we could fail there and
		   it's not a bad thing.  Really we're attempting a best effort to clean up
		   we won't be able to gaurantee it. */
		_exit(EXIT_SUCCESS);	
	} else if (pid < 0) {
		retval = PAM_SYSTEM_ERR;
	} else {
		int forkret = 0;

		if (waitpid(pid, &forkret, 0) < 0) {
			retval = PAM_SYSTEM_ERR;
		}
	}

	/* We reset this no matter.  If we error'd trying to do it, we don't
	   want to try again.  We'll just return the error for this time. */
	session_pid = 0;

	return retval;
}

/* LightDM likes to have this function around, but we don't need it as we
   don't have a token hanging around. */
PAM_EXTERN int
pam_sm_setcred (pam_handle_t *pamh, int flags, int argc, const char ** argv)
{
	return PAM_SUCCESS;
}

#ifdef PAM_STATIC

struct pam_module _pam_freerdp_modstruct = {
     "pam_freerdp",
     pam_sm_authenticate,
     pam_sm_setcred,
     NULL,
     pam_sm_open_session,
     pam_sm_close_session,
     NULL,
};

#endif