summaryrefslogtreecommitdiff
path: root/login/utmp_file.c
blob: 392a39b5e80093efd5d161edc624b0b35592f394 (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
/* Copyright (C) 1996-2013 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Ulrich Drepper <drepper@cygnus.com>
   and Paul Janzen <pcj@primenet.com>, 1996.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */

#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdbool.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <utmp.h>
#include <not-cancel.h>
#include <kernel-features.h>

#include "utmp-private.h"
#include "utmp-equal.h"


/* Descriptor for the file and position.  */
static int file_fd = -1;
static bool file_writable;
static off64_t file_offset;

/* Cache for the last read entry.  */
static struct utmp last_entry;


/* Locking timeout.  */
#ifndef TIMEOUT
# define TIMEOUT 10
#endif

/* Do-nothing handler for locking timeout.  */
static void timeout_handler (int signum) {};

/* LOCK_FILE(fd, type) failure_statement
     attempts to get a lock on the utmp file referenced by FD.  If it fails,
     the failure_statement is executed, otherwise it is skipped.
   LOCKING_FAILED()
     jumps into the UNLOCK_FILE macro and ensures cleanup of LOCK_FILE.
   UNLOCK_FILE(fd)
     unlocks the utmp file referenced by FD and performs the cleanup of
     LOCK_FILE.
 */
#define LOCK_FILE(fd, type) \
{									      \
  struct flock fl;							      \
  struct sigaction action, old_action;					      \
  unsigned int old_timeout;						      \
									      \
  /* Cancel any existing alarm.  */					      \
  old_timeout = alarm (0);						      \
									      \
  /* Establish signal handler.  */					      \
  action.sa_handler = timeout_handler;					      \
  __sigemptyset (&action.sa_mask);					      \
  action.sa_flags = 0;							      \
  __sigaction (SIGALRM, &action, &old_action);				      \
									      \
  alarm (TIMEOUT);							      \
									      \
  /* Try to get the lock.  */						      \
  memset (&fl, '\0', sizeof (struct flock));				      \
  fl.l_type = (type);							      \
  fl.l_whence = SEEK_SET;						      \
  if (fcntl_not_cancel ((fd), F_SETLKW, &fl) < 0)

#define LOCKING_FAILED() \
  goto unalarm_return

#define UNLOCK_FILE(fd) \
  /* Unlock the file.  */						      \
  fl.l_type = F_UNLCK;							      \
  fcntl_not_cancel ((fd), F_SETLKW, &fl);				      \
									      \
 unalarm_return:							      \
  /* Reset the signal handler and alarm.  We must reset the alarm	      \
     before resetting the handler so our alarm does not generate a	      \
     spurious SIGALRM seen by the user.  However, we cannot just set	      \
     the user's old alarm before restoring the handler, because then	      \
     it's possible our handler could catch the user alarm's SIGARLM	      \
     and then the user would never see the signal he expected.  */	      \
  alarm (0);								      \
  __sigaction (SIGALRM, &old_action, NULL);				      \
  if (old_timeout != 0)							      \
    alarm (old_timeout);						      \
} while (0)


/* Functions defined here.  */
static int setutent_file (void);
static int getutent_r_file (struct utmp *buffer, struct utmp **result);
static int getutid_r_file (const struct utmp *key, struct utmp *buffer,
			   struct utmp **result);
static int getutline_r_file (const struct utmp *key, struct utmp *buffer,
			     struct utmp **result);
static struct utmp *pututline_file (const struct utmp *data);
static void endutent_file (void);
static int updwtmp_file (const char *file, const struct utmp *utmp);

/* Jump table for file functions.  */
const struct utfuncs __libc_utmp_file_functions =
{
  setutent_file,
  getutent_r_file,
  getutid_r_file,
  getutline_r_file,
  pututline_file,
  endutent_file,
  updwtmp_file
};


#ifndef TRANSFORM_UTMP_FILE_NAME
# define TRANSFORM_UTMP_FILE_NAME(file_name) (file_name)
#endif

static int
setutent_file (void)
{
  if (file_fd < 0)
    {
      const char *file_name;

      file_name = TRANSFORM_UTMP_FILE_NAME (__libc_utmp_file_name);

#ifdef O_CLOEXEC
# define O_flags O_LARGEFILE | O_CLOEXEC
#else
# define O_flags O_LARGEFILE
#endif
      file_writable = false;
      file_fd = open_not_cancel_2 (file_name, O_RDONLY | O_flags);
      if (file_fd == -1)
	return 0;

#ifndef __ASSUME_O_CLOEXEC
# ifdef O_CLOEXEC
      if (__have_o_cloexec <= 0)
# endif
	{
	  /* We have to make sure the file is `closed on exec'.  */
	  int result = fcntl_not_cancel (file_fd, F_GETFD, 0);
	  if (result >= 0)
	    {
# ifdef O_CLOEXEC
	      if (__have_o_cloexec == 0)
		__have_o_cloexec = (result & FD_CLOEXEC) ? 1 : -1;

	      if (__have_o_cloexec < 0)
# endif
		result = fcntl_not_cancel (file_fd, F_SETFD,
					   result | FD_CLOEXEC);
	    }

	  if (result == -1)
	    {
	      close_not_cancel_no_status (file_fd);
	      return 0;
	    }
	}
#endif
    }

  __lseek64 (file_fd, 0, SEEK_SET);
  file_offset = 0;

  /* Make sure the entry won't match.  */
#if _HAVE_UT_TYPE - 0
  last_entry.ut_type = -1;
#else
  last_entry.ut_line[0] = '\177';
# if _HAVE_UT_ID - 0
  last_entry.ut_id[0] = '\0';
# endif
#endif

  return 1;
}


static int
getutent_r_file (struct utmp *buffer, struct utmp **result)
{
  ssize_t nbytes;

  assert (file_fd >= 0);

  if (file_offset == -1l)
    {
      /* Not available.  */
      *result = NULL;
      return -1;
    }

  LOCK_FILE (file_fd, F_RDLCK)
    {
      nbytes = 0;
      LOCKING_FAILED ();
    }

  /* Read the next entry.  */
  nbytes = read_not_cancel (file_fd, &last_entry, sizeof (struct utmp));

  UNLOCK_FILE (file_fd);

  if (nbytes != sizeof (struct utmp))
    {
      if (nbytes != 0)
	file_offset = -1l;
      *result = NULL;
      return -1;
    }

  /* Update position pointer.  */
  file_offset += sizeof (struct utmp);

  memcpy (buffer, &last_entry, sizeof (struct utmp));
  *result = buffer;

  return 0;
}


static int
internal_getut_r (const struct utmp *id, struct utmp *buffer,
		  bool *lock_failed)
{
  int result = -1;

  LOCK_FILE (file_fd, F_RDLCK)
    {
      *lock_failed = true;
      LOCKING_FAILED ();
    }

#if _HAVE_UT_TYPE - 0
  if (id->ut_type == RUN_LVL || id->ut_type == BOOT_TIME
      || id->ut_type == OLD_TIME || id->ut_type == NEW_TIME)
    {
      /* Search for next entry with type RUN_LVL, BOOT_TIME,
	 OLD_TIME, or NEW_TIME.  */

      while (1)
	{
	  /* Read the next entry.  */
	  if (read_not_cancel (file_fd, buffer, sizeof (struct utmp))
	      != sizeof (struct utmp))
	    {
	      __set_errno (ESRCH);
	      file_offset = -1l;
	      goto unlock_return;
	    }
	  file_offset += sizeof (struct utmp);

	  if (id->ut_type == buffer->ut_type)
	    break;
	}
    }
  else
#endif /* _HAVE_UT_TYPE */
    {
      /* Search for the next entry with the specified ID and with type
	 INIT_PROCESS, LOGIN_PROCESS, USER_PROCESS, or DEAD_PROCESS.  */

      while (1)
	{
	  /* Read the next entry.  */
	  if (read_not_cancel (file_fd, buffer, sizeof (struct utmp))
	      != sizeof (struct utmp))
	    {
	      __set_errno (ESRCH);
	      file_offset = -1l;
	      goto unlock_return;
	    }
	  file_offset += sizeof (struct utmp);

	  if (__utmp_equal (buffer, id))
	    break;
	}
    }

  result = 0;

unlock_return:
  UNLOCK_FILE (file_fd);

  return result;
}


/* For implementing this function we don't use the getutent_r function
   because we can avoid the reposition on every new entry this way.  */
static int
getutid_r_file (const struct utmp *id, struct utmp *buffer,
		struct utmp **result)
{
  assert (file_fd >= 0);

  if (file_offset == -1l)
    {
      *result = NULL;
      return -1;
    }

  /* We don't have to distinguish whether we can lock the file or
     whether there is no entry.  */
  bool lock_failed = false;
  if (internal_getut_r (id, &last_entry, &lock_failed) < 0)
    {
      *result = NULL;
      return -1;
    }

  memcpy (buffer, &last_entry, sizeof (struct utmp));
  *result = buffer;

  return 0;
}


/* For implementing this function we don't use the getutent_r function
   because we can avoid the reposition on every new entry this way.  */
static int
getutline_r_file (const struct utmp *line, struct utmp *buffer,
		  struct utmp **result)
{
  assert (file_fd >= 0);

  if (file_offset == -1l)
    {
      *result = NULL;
      return -1;
    }

  LOCK_FILE (file_fd, F_RDLCK)
    {
      *result = NULL;
      LOCKING_FAILED ();
    }

  while (1)
    {
      /* Read the next entry.  */
      if (read_not_cancel (file_fd, &last_entry, sizeof (struct utmp))
	  != sizeof (struct utmp))
	{
	  __set_errno (ESRCH);
	  file_offset = -1l;
	  *result = NULL;
	  goto unlock_return;
	}
      file_offset += sizeof (struct utmp);

      /* Stop if we found a user or login entry.  */
      if (
#if _HAVE_UT_TYPE - 0
	  (last_entry.ut_type == USER_PROCESS
	   || last_entry.ut_type == LOGIN_PROCESS)
	  &&
#endif
	  !strncmp (line->ut_line, last_entry.ut_line, sizeof line->ut_line))
	break;
    }

  memcpy (buffer, &last_entry, sizeof (struct utmp));
  *result = buffer;

unlock_return:
  UNLOCK_FILE (file_fd);

  return ((*result == NULL) ? -1 : 0);
}


static struct utmp *
pututline_file (const struct utmp *data)
{
  struct utmp buffer;
  struct utmp *pbuf;
  int found;

  assert (file_fd >= 0);

  if (! file_writable)
    {
      /* We must make the file descriptor writable before going on.  */
      const char *file_name = TRANSFORM_UTMP_FILE_NAME (__libc_utmp_file_name);

      int new_fd = open_not_cancel_2 (file_name, O_RDWR | O_flags);
      if (new_fd == -1)
	return NULL;

#ifndef __ASSUME_O_CLOEXEC
# ifdef O_CLOEXEC
      if (__have_o_cloexec <= 0)
# endif
	{
	  /* We have to make sure the file is `closed on exec'.  */
	  int result = fcntl_not_cancel (file_fd, F_GETFD, 0);
	  if (result >= 0)
	    {
# ifdef O_CLOEXEC
	      if (__have_o_cloexec == 0)
		__have_o_cloexec = (result & FD_CLOEXEC) ? 1 : -1;

	      if (__have_o_cloexec < 0)
# endif
		result = fcntl_not_cancel (file_fd, F_SETFD,
					   result | FD_CLOEXEC);
	    }

	  if (result == -1)
	    {
	      close_not_cancel_no_status (file_fd);
	      return NULL;
	    }
	}
#endif

      if (__lseek64 (new_fd, __lseek64 (file_fd, 0, SEEK_CUR), SEEK_SET) == -1
	  || __dup2 (new_fd, file_fd) < 0)
	{
	  close_not_cancel_no_status (new_fd);
	  return NULL;
	}
      close_not_cancel_no_status (new_fd);
      file_writable = true;
    }

  /* Find the correct place to insert the data.  */
  if (file_offset > 0
      && (
#if _HAVE_UT_TYPE - 0
	  (last_entry.ut_type == data->ut_type
	   && (last_entry.ut_type == RUN_LVL
	       || last_entry.ut_type == BOOT_TIME
	       || last_entry.ut_type == OLD_TIME
	       || last_entry.ut_type == NEW_TIME))
	  ||
#endif
	  __utmp_equal (&last_entry, data)))
    found = 1;
  else
    {
      bool lock_failed = false;
      found = internal_getut_r (data, &buffer, &lock_failed);

      if (__builtin_expect (lock_failed, false))
	{
	  __set_errno (EAGAIN);
	  return NULL;
	}
    }

  LOCK_FILE (file_fd, F_WRLCK)
    {
      pbuf = NULL;
      LOCKING_FAILED ();
    }

  if (found < 0)
    {
      /* We append the next entry.  */
      file_offset = __lseek64 (file_fd, 0, SEEK_END);
      if (file_offset % sizeof (struct utmp) != 0)
	{
	  file_offset -= file_offset % sizeof (struct utmp);
	  __ftruncate64 (file_fd, file_offset);

	  if (__lseek64 (file_fd, 0, SEEK_END) < 0)
	    {
	      pbuf = NULL;
	      goto unlock_return;
	    }
	}
    }
  else
    {
      /* We replace the just read entry.  */
      file_offset -= sizeof (struct utmp);
      __lseek64 (file_fd, file_offset, SEEK_SET);
    }

  /* Write the new data.  */
  if (write_not_cancel (file_fd, data, sizeof (struct utmp))
      != sizeof (struct utmp))
    {
      /* If we appended a new record this is only partially written.
	 Remove it.  */
      if (found < 0)
	(void) __ftruncate64 (file_fd, file_offset);
      pbuf = NULL;
    }
  else
    {
      file_offset += sizeof (struct utmp);
      pbuf = (struct utmp *) data;
    }

 unlock_return:
  UNLOCK_FILE (file_fd);

  return pbuf;
}


static void
endutent_file (void)
{
  assert (file_fd >= 0);

  close_not_cancel_no_status (file_fd);
  file_fd = -1;
}


static int
updwtmp_file (const char *file, const struct utmp *utmp)
{
  int result = -1;
  off64_t offset;
  int fd;

  /* Open WTMP file.  */
  fd = open_not_cancel_2 (file, O_WRONLY | O_LARGEFILE);
  if (fd < 0)
    return -1;

  LOCK_FILE (fd, F_WRLCK)
    LOCKING_FAILED ();

  /* Remember original size of log file.  */
  offset = __lseek64 (fd, 0, SEEK_END);
  if (offset % sizeof (struct utmp) != 0)
    {
      offset -= offset % sizeof (struct utmp);
      __ftruncate64 (fd, offset);

      if (__lseek64 (fd, 0, SEEK_END) < 0)
	goto unlock_return;
    }

  /* Write the entry.  If we can't write all the bytes, reset the file
     size back to the original size.  That way, no partial entries
     will remain.  */
  if (write_not_cancel (fd, utmp, sizeof (struct utmp))
      != sizeof (struct utmp))
    {
      __ftruncate64 (fd, offset);
      goto unlock_return;
    }

  result = 0;

unlock_return:
  UNLOCK_FILE (fd);

  /* Close WTMP file.  */
  close_not_cancel_no_status (fd);

  return result;
}