File: session-child.c

package info (click to toggle)
lightdm 1.18.3-1
  • links: PTS, VCS
  • area: main
  • in suites: stretch
  • size: 8,028 kB
  • ctags: 3,701
  • sloc: ansic: 26,653; sh: 4,811; makefile: 1,266; cpp: 1,162; python: 258; xml: 19
file content (835 lines) | stat: -rw-r--r-- 26,303 bytes parent folder | download
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
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
#include <config.h>

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <pwd.h>
#include <grp.h>
#include <glib.h>
#include <security/pam_appl.h>
#include <utmp.h>
#include <utmpx.h>
#include <sys/mman.h>

#if HAVE_LIBAUDIT
#include <libaudit.h>
#endif

#include "configuration.h"
#include "session-child.h"
#include "session.h"
#include "console-kit.h"
#include "login1.h"
#include "log-file.h"
#include "privileges.h"
#include "x-authority.h"
#include "configuration.h"

/* Child process being run */
static GPid child_pid = 0;

/* Pipe to communicate with daemon */
static int from_daemon_output = 0;
static int to_daemon_input = 0;

static gboolean is_interactive;
static gboolean do_authenticate;
static gboolean authentication_complete = FALSE;
static pam_handle_t *pam_handle;

/* Maximum length of a string to pass between daemon and session */
#define MAX_STRING_LENGTH 65535

static void
write_data (const void *buf, size_t count)
{
    if (write (to_daemon_input, buf, count) != count)
        g_printerr ("Error writing to daemon: %s\n", strerror (errno));
}

static void
write_string (const char *value)
{
    int length;

    length = value ? strlen (value) : -1;
    write_data (&length, sizeof (length));
    if (value)
        write_data (value, sizeof (char) * length);
}

static ssize_t
read_data (void *buf, size_t count)
{
    ssize_t n_read;

    n_read = read (from_daemon_output, buf, count);
    if (n_read < 0)
        g_printerr ("Error reading from daemon: %s\n", strerror (errno));

    return n_read;
}

static gchar *
read_string_full (void* (*alloc_fn)(size_t n))
{
    int length;
    char *value;

    if (read_data (&length, sizeof (length)) <= 0)
        return NULL;
    if (length < 0)
        return NULL;
    if (length > MAX_STRING_LENGTH)
    {
        g_printerr ("Invalid string length %d from daemon\n", length);
        return NULL;
    }

    value = (*alloc_fn) (sizeof (char) * (length + 1));
    read_data (value, length);
    value[length] = '\0';

    return value;
}

static gchar *
read_string (void)
{
    return read_string_full (g_malloc);
}

static int
pam_conv_cb (int msg_length, const struct pam_message **msg, struct pam_response **resp, void *app_data)
{
    int i, error;
    gboolean auth_complete = FALSE;
    struct pam_response *response;
    gchar *username = NULL;

    /* FIXME: We don't support communication after pam_authenticate completes */
    if (authentication_complete)
        return PAM_SUCCESS;

    /* Cancel authentication if requiring input */
    if (!is_interactive)
    {
        for (i = 0; i < msg_length; i++)
        {
            if (msg[i]->msg_style == PAM_PROMPT_ECHO_ON || msg[i]->msg_style == PAM_PROMPT_ECHO_OFF)
            {
                g_printerr ("Stopping PAM conversation, interaction requested but not supported\n");
                return PAM_CONV_ERR;
            }
        }

        /* Ignore informational messages */
        return PAM_SUCCESS;
    }

    /* Check if we changed user */
    pam_get_item (pam_handle, PAM_USER, (const void **) &username);

    /* Notify the daemon */
    write_string (username);
    write_data (&auth_complete, sizeof (auth_complete));
    write_data (&msg_length, sizeof (msg_length));
    for (i = 0; i < msg_length; i++)
    {
        const struct pam_message *m = msg[i];
        write_data (&m->msg_style, sizeof (m->msg_style));
        write_string (m->msg);
    }

    /* Get response */
    read_data (&error, sizeof (error));
    if (error != PAM_SUCCESS)
        return error;
    response = calloc (msg_length, sizeof (struct pam_response));
    for (i = 0; i < msg_length; i++)
    {
        struct pam_response *r = &response[i];
        // callers of this function inside pam will expect to be able to call
        // free() on the strings we give back.  So alloc with malloc.
        r->resp = read_string_full (malloc);
        read_data (&r->resp_retcode, sizeof (r->resp_retcode));
    }

    *resp = response;
    return PAM_SUCCESS;
}

static void
signal_cb (int signum)
{
    /* Pass on signal to child, otherwise just quit */
    if (child_pid > 0)
        kill (child_pid, signum);
    else
        exit (EXIT_SUCCESS);
}

static XAuthority *
read_xauth (void)
{
    gchar *x_authority_name;
    guint16 x_authority_family;
    guint8 *x_authority_address;
    gsize x_authority_address_length;
    gchar *x_authority_number;
    guint8 *x_authority_data;
    gsize x_authority_data_length;

    x_authority_name = read_string ();
    if (!x_authority_name)
        return NULL;

    read_data (&x_authority_family, sizeof (x_authority_family));
    read_data (&x_authority_address_length, sizeof (x_authority_address_length));
    x_authority_address = g_malloc (x_authority_address_length);
    read_data (x_authority_address, x_authority_address_length);
    x_authority_number = read_string ();
    read_data (&x_authority_data_length, sizeof (x_authority_data_length));
    x_authority_data = g_malloc (x_authority_data_length);
    read_data (x_authority_data, x_authority_data_length);

    return x_authority_new (x_authority_family, x_authority_address, x_authority_address_length, x_authority_number, x_authority_name, x_authority_data, x_authority_data_length);
}

/* GNU provides this but we can't rely on that so let's make our own version */
static void
updwtmpx (const gchar *wtmp_file, struct utmpx *ut)
{
    struct utmp u;

    memset (&u, 0, sizeof (u));
    u.ut_type = ut->ut_type;
    u.ut_pid = ut->ut_pid;
    if (ut->ut_line)
        strncpy (u.ut_line, ut->ut_line, sizeof (u.ut_line));
    if (ut->ut_id)
        strncpy (u.ut_id, ut->ut_id, sizeof (u.ut_id));
    if (ut->ut_user)
        strncpy (u.ut_user, ut->ut_user, sizeof (u.ut_user));
    if (ut->ut_host)
        strncpy (u.ut_host, ut->ut_host, sizeof (u.ut_host));
    u.ut_tv.tv_sec = ut->ut_tv.tv_sec;
    u.ut_tv.tv_usec = ut->ut_tv.tv_usec;

    updwtmp (wtmp_file, &u);
}

#if HAVE_LIBAUDIT
static void
audit_event (int type, const gchar *username, uid_t uid, const gchar *remote_host_name, const gchar *tty, gboolean success)
{
    int auditfd, result;
    const char *op = NULL;

    auditfd = audit_open ();
    if (auditfd < 0) {
        g_printerr ("Error opening audit socket: %s\n", strerror (errno));
        return;
    }

    if (type == AUDIT_USER_LOGIN)
        op = "login";
    else if (type == AUDIT_USER_LOGOUT)
        op = "logout";
    result = success == TRUE ? 1 : 0;

    if (audit_log_acct_message (auditfd, type, NULL, op, username, uid, remote_host_name, NULL, tty, result) <= 0)
        g_printerr ("Error writing audit message: %s\n", strerror (errno));

    close (auditfd);
}
#endif

int
session_child_run (int argc, char **argv)
{
    struct pam_conv conversation = { pam_conv_cb, NULL };
    int i, version, fd, result;
    gboolean auth_complete = TRUE;
    User *user = NULL;
    gchar *log_filename;
    LogMode log_mode = LOG_MODE_BACKUP_AND_TRUNCATE;
    gsize env_length;
    gsize command_argc;
    gchar **command_argv;
    GVariantBuilder ck_parameters;
    int return_code;
    int authentication_result;
    gchar *authentication_result_string;
    gchar *service;
    gchar *username;
    gchar *tty;
    gchar *remote_host_name;
    gchar *xdisplay;
    XAuthority *x_authority = NULL;
    gchar *x_authority_filename;
    GDBusConnection *bus;
    const gchar *login1_session_id = NULL;
    gchar *console_kit_cookie = NULL;
    const gchar *locale_value;
    gchar *locale_var;
    static const gchar * const locale_var_names[] = {
        "LC_PAPER",
        "LC_NAME",
        "LC_ADDRESS",
        "LC_TELEPHONE",
        "LC_MEASUREMENT",
        "LC_IDENTIFICATION",
        "LC_COLLATE",
        "LC_CTYPE",
        "LC_MONETARY",
        "LC_NUMERIC",
        "LC_TIME",
        "LC_MESSAGES",
        "LC_ALL",
        "LANG",
        NULL
    };
    gid_t gid;
    uid_t uid;
    const gchar *home_directory;
    GError *error = NULL;

#if !defined(GLIB_VERSION_2_36)
    g_type_init ();
#endif

    if (config_get_boolean (config_get_instance (), "LightDM", "lock-memory"))
    {
        /* Protect memory from being paged to disk, as we deal with passwords */
        mlockall (MCL_CURRENT | MCL_FUTURE);
    }

    /* Make input non-blocking */
    fd = open ("/dev/null", O_RDONLY);
    dup2 (fd, STDIN_FILENO);
    close (fd);

    /* Close stdout */
    fd = open ("/dev/null", O_WRONLY);
    dup2 (fd, STDOUT_FILENO);
    close (fd);

    /* Get the pipe from the daemon */
    if (argc != 4)
    {
        g_printerr ("Usage: lightdm --session-child INPUTFD OUTPUTFD\n");
        return EXIT_FAILURE;
    }
    from_daemon_output = atoi (argv[2]);
    to_daemon_input = atoi (argv[3]);
    if (from_daemon_output == 0 || to_daemon_input == 0)
    {
        g_printerr ("Invalid file descriptors %s %s\n", argv[2], argv[3]);
        return EXIT_FAILURE;
    }

    /* Don't let these pipes leak to the command we will run */
    fcntl (from_daemon_output, F_SETFD, FD_CLOEXEC);
    fcntl (to_daemon_input, F_SETFD, FD_CLOEXEC);

    /* Read a version number so we can handle upgrades (i.e. a newer version of session child is run for an old daemon */
    read_data (&version, sizeof (version));

    service = read_string ();
    username = read_string ();
    read_data (&do_authenticate, sizeof (do_authenticate));
    read_data (&is_interactive, sizeof (is_interactive));
    read_string (); /* Used to be class, now we just use the environment variable */
    tty = read_string ();
    remote_host_name = read_string ();
    xdisplay = read_string ();
    x_authority = read_xauth ();

    /* Setup PAM */
    result = pam_start (service, username, &conversation, &pam_handle);
    if (result != PAM_SUCCESS)
    {
        g_printerr ("Failed to start PAM: %s", pam_strerror (NULL, result));
        return EXIT_FAILURE;
    }
    if (xdisplay)
    {
#ifdef PAM_XDISPLAY
        pam_set_item (pam_handle, PAM_XDISPLAY, xdisplay);
#endif
        pam_set_item (pam_handle, PAM_TTY, xdisplay);
    }
    else if (tty)
        pam_set_item (pam_handle, PAM_TTY, tty);

#ifdef PAM_XAUTHDATA
    if (x_authority)
    {
        struct pam_xauth_data value;

        value.name = (char *) x_authority_get_authorization_name (x_authority);
        value.namelen = strlen (x_authority_get_authorization_name (x_authority));
        value.data = (char *) x_authority_get_authorization_data (x_authority);
        value.datalen = x_authority_get_authorization_data_length (x_authority);
        pam_set_item (pam_handle, PAM_XAUTHDATA, &value);
    }
#endif

    /* Authenticate */
    if (do_authenticate)
    {
        const gchar *new_username;

        authentication_result = pam_authenticate (pam_handle, 0);

        /* See what user we ended up as */
        if (pam_get_item (pam_handle, PAM_USER, (const void **) &new_username) != PAM_SUCCESS)
        {
            pam_end (pam_handle, 0);
            return EXIT_FAILURE;
        }
        g_free (username);
        username = g_strdup (new_username);

        /* Write record to btmp database */
        if (authentication_result == PAM_AUTH_ERR)
        {
            struct utmpx ut;
            struct timeval tv;

            memset (&ut, 0, sizeof (ut));
            ut.ut_type = USER_PROCESS;
            ut.ut_pid = getpid ();
            if (xdisplay)
                strncpy (ut.ut_id, xdisplay, sizeof (ut.ut_id));
            if (tty && g_str_has_prefix (tty, "/dev/"))
                strncpy (ut.ut_line, tty + strlen ("/dev/"), sizeof (ut.ut_line));
            strncpy (ut.ut_user, username, sizeof (ut.ut_user));
            if (xdisplay)
                strncpy (ut.ut_host, xdisplay, sizeof (ut.ut_host));
            else if (remote_host_name)
                strncpy (ut.ut_host, remote_host_name, sizeof (ut.ut_host));
            gettimeofday (&tv, NULL);
            ut.ut_tv.tv_sec = tv.tv_sec;
            ut.ut_tv.tv_usec = tv.tv_usec;

            updwtmpx ("/var/log/btmp", &ut);

#if HAVE_LIBAUDIT
            audit_event (AUDIT_USER_LOGIN, username, -1, remote_host_name, tty, FALSE);
#endif
        }

        /* Check account is valid */
        if (authentication_result == PAM_SUCCESS)
            authentication_result = pam_acct_mgmt (pam_handle, 0);
        if (authentication_result == PAM_NEW_AUTHTOK_REQD)
            authentication_result = pam_chauthtok (pam_handle, PAM_CHANGE_EXPIRED_AUTHTOK);
    }
    else
        authentication_result = PAM_SUCCESS;
    authentication_complete = TRUE;

    if (authentication_result == PAM_SUCCESS)
    {
        /* Fail authentication if user doesn't actually exist */
        user = accounts_get_user_by_name (username);
        if (!user)
        {
            g_printerr ("Failed to get information on user %s: %s\n", username, strerror (errno));
            authentication_result = PAM_USER_UNKNOWN;
        }
        else
        {
            /* Set POSIX variables */
            if (user_get_uid (user) == 0)
              pam_putenv (pam_handle, "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin");
            else
              pam_putenv (pam_handle, "PATH=/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games");
            pam_putenv (pam_handle, g_strdup_printf ("USER=%s", username));
            pam_putenv (pam_handle, g_strdup_printf ("LOGNAME=%s", username));
            pam_putenv (pam_handle, g_strdup_printf ("HOME=%s", user_get_home_directory (user)));
            pam_putenv (pam_handle, g_strdup_printf ("SHELL=%s", user_get_shell (user)));

            /* Let the greeter and user session inherit the system default locale */
            for (i = 0; locale_var_names[i] != NULL; i++)
            {
                if ((locale_value = g_getenv (locale_var_names[i])) != NULL)
                {
                    locale_var = g_strdup_printf ("%s=%s", locale_var_names[i], locale_value);
                    pam_putenv (pam_handle, locale_var);
                    g_free (locale_var);
                }
            }
        }
    }

    authentication_result_string = g_strdup (pam_strerror (pam_handle, authentication_result));

    /* Report authentication result */
    write_string (username);
    write_data (&auth_complete, sizeof (auth_complete));
    write_data (&authentication_result, sizeof (authentication_result));
    write_string (authentication_result_string);

    /* Check we got a valid user */
    if (!username)
    {
        g_printerr ("No user selected during authentication\n");
        pam_end (pam_handle, 0);
        return EXIT_FAILURE;
    }

    /* Stop if we didn't authenticated */
    if (authentication_result != PAM_SUCCESS)
    {
        pam_end (pam_handle, 0);
        return EXIT_FAILURE;
    }

    /* Get the command to run (blocks) */
    log_filename = read_string ();
    if (version >= 3)
        read_data (&log_mode, sizeof (log_mode));
    if (version >= 1)
    {
        g_free (tty);
        tty = read_string ();
    }
    x_authority_filename = read_string ();
    if (version >= 1)
    {
        g_free (xdisplay);
        xdisplay = read_string ();
        if (x_authority)
            g_object_unref (x_authority);
        x_authority = read_xauth ();
    }
    read_data (&env_length, sizeof (env_length));
    for (i = 0; i < env_length; i++)
        pam_putenv (pam_handle, read_string ());
    read_data (&command_argc, sizeof (command_argc));
    command_argv = g_malloc (sizeof (gchar *) * (command_argc + 1));
    for (i = 0; i < command_argc; i++)
        command_argv[i] = read_string ();
    command_argv[i] = NULL;

    /* If nothing to run just refresh credentials because we successfully authenticated */
    if (command_argc == 0)
    {
        pam_setcred (pam_handle, PAM_REINITIALIZE_CRED);
        pam_end (pam_handle, 0);
        return EXIT_SUCCESS;
    }

    /* Redirect stderr to a log file */
    if (log_filename)
    {
        if (g_path_is_absolute (log_filename))
        {
            fd = log_file_open (log_filename, log_mode);
            dup2 (fd, STDERR_FILENO);
            close (fd);
            g_free (log_filename);
            log_filename = NULL;
        }
    }
    else
    {
        fd = open ("/dev/null", O_WRONLY);
        dup2 (fd, STDERR_FILENO);
        close (fd);
    }

    /* Set group membership - these can be overriden in pam_setcred */
    if (getuid () == 0)
    {
        if (initgroups (username, user_get_gid (user)) < 0)
        {
            g_printerr ("Failed to initialize supplementary groups for %s: %s\n", username, strerror (errno));
            _exit (EXIT_FAILURE);
        }
    }

    /* Set credentials */
    result = pam_setcred (pam_handle, PAM_ESTABLISH_CRED);
    if (result != PAM_SUCCESS)
    {
        g_printerr ("Failed to establish PAM credentials: %s\n", pam_strerror (pam_handle, result));
        pam_end (pam_handle, 0);
        return EXIT_FAILURE;
    }

    /* Open the session */
    result = pam_open_session (pam_handle, 0);
    if (result != PAM_SUCCESS)
    {
        g_printerr ("Failed to open PAM session: %s\n", pam_strerror (pam_handle, result));
        pam_end (pam_handle, 0);
        return EXIT_FAILURE;
    }

    /* Open a connection to the system bus for ConsoleKit - we must keep it open or CK will close the session */
    bus = g_bus_get_sync (G_BUS_TYPE_SYSTEM, NULL, &error);
    if (error)
        g_printerr ("Unable to contact system bus: %s", error->message);
    if (!bus)
    {
        pam_end (pam_handle, 0);
        return EXIT_FAILURE;
    }

    /* Check what logind session we are, or fallback to ConsoleKit */
    login1_session_id = pam_getenv (pam_handle, "XDG_SESSION_ID");
    if (login1_session_id)
    {
        write_string (login1_session_id);
        if (version >= 2)
            write_string (NULL);
    }
    else
    {
        g_variant_builder_init (&ck_parameters, G_VARIANT_TYPE ("(a(sv))"));
        g_variant_builder_open (&ck_parameters, G_VARIANT_TYPE ("a(sv)"));
        g_variant_builder_add (&ck_parameters, "(sv)", "unix-user", g_variant_new_int32 (user_get_uid (user)));
        if (g_strcmp0 (pam_getenv (pam_handle, "XDG_SESSION_CLASS"), "greeter") == 0)
            g_variant_builder_add (&ck_parameters, "(sv)", "session-type", g_variant_new_string ("LoginWindow"));
        if (xdisplay)
        {
            g_variant_builder_add (&ck_parameters, "(sv)", "x11-display", g_variant_new_string (xdisplay));
            if (tty)
                g_variant_builder_add (&ck_parameters, "(sv)", "x11-display-device", g_variant_new_string (tty));
        }
        if (remote_host_name)
        {
            g_variant_builder_add (&ck_parameters, "(sv)", "is-local", g_variant_new_boolean (FALSE));
            g_variant_builder_add (&ck_parameters, "(sv)", "remote-host-name", g_variant_new_string (remote_host_name));
        }
        else
            g_variant_builder_add (&ck_parameters, "(sv)", "is-local", g_variant_new_boolean (TRUE));
        console_kit_cookie = ck_open_session (&ck_parameters);
        if (version >= 2)
            write_string (NULL);
        write_string (console_kit_cookie);
        if (console_kit_cookie)
        {
            gchar *value;
            gchar *runtime_dir;
            value = g_strdup_printf ("XDG_SESSION_COOKIE=%s", console_kit_cookie);
            pam_putenv (pam_handle, value);
            g_free (value);

            runtime_dir = ck_get_xdg_runtime_dir (console_kit_cookie);
            if (runtime_dir)
            {
                gchar *value;
                value = g_strdup_printf ("XDG_RUNTIME_DIR=%s", runtime_dir);
                pam_putenv (pam_handle, value);
                g_free (value);
                g_free (runtime_dir);
            }
        }
    }

    /* Write X authority */
    if (x_authority)
    {
        gboolean drop_privileges, result;
        gchar *value;
        GError *error = NULL;

        drop_privileges = geteuid () == 0;
        if (drop_privileges)
            privileges_drop (user_get_uid (user), user_get_gid (user));
        result = x_authority_write (x_authority, XAUTH_WRITE_MODE_REPLACE, x_authority_filename, &error);
        if (drop_privileges)
            privileges_reclaim ();

        if (error)
            g_printerr ("Error writing X authority: %s\n", error->message);
        g_clear_error (&error);
        if (!result)
        {
            pam_end (pam_handle, 0);
            return EXIT_FAILURE;
        }

        value = g_strdup_printf ("XAUTHORITY=%s", x_authority_filename);
        pam_putenv (pam_handle, value);
        g_free (value);
    }

    /* Catch terminate signal and pass it to the child */
    signal (SIGTERM, signal_cb);

    /* Run the command as the authenticated user */
    uid = user_get_uid (user);
    gid = user_get_gid (user);
    home_directory = user_get_home_directory (user);
    child_pid = fork ();
    if (child_pid == 0)
    {
        /* Make this process its own session */
        if (setsid () < 0)
            _exit (errno);

        /* Change to this user */
        if (getuid () == 0)
        {
            if (setgid (gid) != 0)
                _exit (errno);

            if (setuid (uid) != 0)
                _exit (errno);
        }

        /* Change working directory */
        /* NOTE: This must be done after the permissions are changed because NFS filesystems can
         * be setup so the local root user accesses the NFS files as 'nobody'.  If the home directories
         * are not system readable then the chdir can fail */
        if (chdir (home_directory) != 0)
            _exit (errno);

        if (log_filename)
        {
            fd = log_file_open (log_filename, log_mode);
            if (fd >= 0)
            {
                dup2 (fd, STDERR_FILENO);
                close (fd);
            }
        }

        /* Reset SIGPIPE handler so the child has default behaviour (we disabled it at LightDM start) */
        signal (SIGPIPE, SIG_DFL);

        /* Run the command */
        execve (command_argv[0], command_argv, pam_getenvlist (pam_handle));
        _exit (EXIT_FAILURE);
    }

    /* Bail out if failed to fork */
    if (child_pid < 0)
    {
        g_printerr ("Failed to fork session child process: %s\n", strerror (errno));
        return_code = EXIT_FAILURE;
    }

    /* Wait for the command to complete (blocks) */
    if (child_pid > 0)
    {
        /* Log to utmp */
        if (g_strcmp0 (pam_getenv (pam_handle, "XDG_SESSION_CLASS"), "greeter") != 0)
        {
            struct utmpx ut;
            struct timeval tv;

            memset (&ut, 0, sizeof (ut));
            ut.ut_type = USER_PROCESS;
            ut.ut_pid = child_pid;
            if (xdisplay)
                strncpy (ut.ut_id, xdisplay, sizeof (ut.ut_id));
            if (tty && g_str_has_prefix (tty, "/dev/"))
                strncpy (ut.ut_line, tty + strlen ("/dev/"), sizeof (ut.ut_line));
            strncpy (ut.ut_user, username, sizeof (ut.ut_user));
            if (xdisplay)
                strncpy (ut.ut_host, xdisplay, sizeof (ut.ut_host));
            else if (remote_host_name)
                strncpy (ut.ut_host, remote_host_name, sizeof (ut.ut_host));
            gettimeofday (&tv, NULL);
            ut.ut_tv.tv_sec = tv.tv_sec;
            ut.ut_tv.tv_usec = tv.tv_usec;

            /* Write records to utmp/wtmp databases */
            setutxent ();
            if (!pututxline (&ut))
                g_printerr ("Failed to write utmpx: %s\n", strerror (errno));
            endutxent ();
            updwtmpx ("/var/log/wtmp", &ut);

#if HAVE_LIBAUDIT          
            audit_event (AUDIT_USER_LOGIN, username, uid, remote_host_name, tty, TRUE);
#endif
        }

        waitpid (child_pid, &return_code, 0);
        child_pid = 0;

        /* Log to utmp */
        if (g_strcmp0 (pam_getenv (pam_handle, "XDG_SESSION_CLASS"), "greeter") != 0)
        {
            struct utmpx ut;
            struct timeval tv;

            memset (&ut, 0, sizeof (ut));
            ut.ut_type = DEAD_PROCESS;
            ut.ut_pid = child_pid;
            if (xdisplay)
                strncpy (ut.ut_id, xdisplay, sizeof (ut.ut_id));
            if (tty && g_str_has_prefix (tty, "/dev/"))
                strncpy (ut.ut_line, tty + strlen ("/dev/"), sizeof (ut.ut_line));
            strncpy (ut.ut_user, username, sizeof (ut.ut_user));
            if (xdisplay)
                strncpy (ut.ut_host, xdisplay, sizeof (ut.ut_host));
            else if (remote_host_name)
                strncpy (ut.ut_host, remote_host_name, sizeof (ut.ut_host));
            gettimeofday (&tv, NULL);
            ut.ut_tv.tv_sec = tv.tv_sec;
            ut.ut_tv.tv_usec = tv.tv_usec;

            /* Write records to utmp/wtmp databases */
            setutxent ();
            if (!pututxline (&ut))
                g_printerr ("Failed to write utmpx: %s\n", strerror (errno));
            endutxent ();
            updwtmpx ("/var/log/wtmp", &ut);

#if HAVE_LIBAUDIT
            audit_event (AUDIT_USER_LOGOUT, username, uid, remote_host_name, tty, TRUE);
#endif
        }
    }

    /* Remove X authority */
    if (x_authority)
    {
        gboolean drop_privileges, result;
        GError *error = NULL;

        drop_privileges = geteuid () == 0;
        if (drop_privileges)
            privileges_drop (user_get_uid (user), user_get_gid (user));
        result = x_authority_write (x_authority, XAUTH_WRITE_MODE_REMOVE, x_authority_filename, &error);
        if (drop_privileges)
            privileges_reclaim ();

        if (error)
            g_printerr ("Error removing X authority: %s\n", error->message);
        g_clear_error (&error);
        if (!result)
            _exit (EXIT_FAILURE);
    }

    /* Close the Console Kit session */
    if (console_kit_cookie)
        ck_close_session (console_kit_cookie);

    /* Close the session */
    pam_close_session (pam_handle, 0);

    /* Remove credentials */
    pam_setcred (pam_handle, PAM_DELETE_CRED);

    pam_end (pam_handle, 0);
    pam_handle = NULL;

    /* Return result of session process to the daemon */
    return return_code;
}