login/utmp_file.c

   1 /* Copyright (C) 1996-2017 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Ulrich Drepper <drepper@cygnus.com>
   4    and Paul Janzen <pcj@primenet.com>, 1996.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <http://www.gnu.org/licenses/>.  */
  19
  20 #include <assert.h>
  21 #include <errno.h>
  22 #include <fcntl.h>
  23 #include <signal.h>
  24 #include <stdbool.h>
  25 #include <stdio.h>
  26 #include <string.h>
  27 #include <unistd.h>
  28 #include <utmp.h>
  29 #include <not-cancel.h>
  30 #include <kernel-features.h>
  31
  32 #include "utmp-private.h"
  33 #include "utmp-equal.h"
  34
  35
  36 /* Descriptor for the file and position.  */
  37 static int file_fd = -1;
  38 static bool file_writable;
  39 static off64_t file_offset;
  40
  41 /* Cache for the last read entry.  */
  42 static struct utmp last_entry;
  43
  44
  45 /* Locking timeout.  */
  46 #ifndef TIMEOUT
  47 # define TIMEOUT 10
  48 #endif
  49
  50 /* Do-nothing handler for locking timeout.  */
  51 static void timeout_handler (int signum) {};
  52
  53 /* LOCK_FILE(fd, type) failure_statement
  54      attempts to get a lock on the utmp file referenced by FD.  If it fails,
  55      the failure_statement is executed, otherwise it is skipped.
  56    LOCKING_FAILED()
  57      jumps into the UNLOCK_FILE macro and ensures cleanup of LOCK_FILE.
  58    UNLOCK_FILE(fd)
  59      unlocks the utmp file referenced by FD and performs the cleanup of
  60      LOCK_FILE.
  61  */
  62 #define LOCK_FILE(fd, type) \
  63 {                                                                             \
  64   struct flock fl;                                                            \
  65   struct sigaction action, old_action;                                        \
  66   unsigned int old_timeout;                                                   \
  67                                                                               \
  68   /* Cancel any existing alarm.  */                                           \
  69   old_timeout = alarm (0);                                                    \
  70                                                                               \
  71   /* Establish signal handler.  */                                            \
  72   action.sa_handler = timeout_handler;                                        \
  73   __sigemptyset (&action.sa_mask);                                            \
  74   action.sa_flags = 0;                                                        \
  75   __sigaction (SIGALRM, &action, &old_action);                                \
  76                                                                               \
  77   alarm (TIMEOUT);                                                            \
  78                                                                               \
  79   /* Try to get the lock.  */                                                 \
  80   memset (&fl, '\0', sizeof (struct flock));                                  \
  81   fl.l_type = (type);                                                         \
  82   fl.l_whence = SEEK_SET;                                                     \
  83   if (fcntl_not_cancel ((fd), F_SETLKW, &fl) < 0)
  84
  85 #define LOCKING_FAILED() \
  86   goto unalarm_return
  87
  88 #define UNLOCK_FILE(fd) \
  89   /* Unlock the file.  */                                                     \
  90   fl.l_type = F_UNLCK;                                                        \
  91   fcntl_not_cancel ((fd), F_SETLKW, &fl);                                     \
  92                                                                               \
  93  unalarm_return:                                                              \
  94   /* Reset the signal handler and alarm.  We must reset the alarm             \
  95      before resetting the handler so our alarm does not generate a            \
  96      spurious SIGALRM seen by the user.  However, we cannot just set          \
  97      the user's old alarm before restoring the handler, because then          \
  98      it's possible our handler could catch the user alarm's SIGARLM           \
  99      and then the user would never see the signal he expected.  */            \
 100   alarm (0);                                                                  \
 101   __sigaction (SIGALRM, &old_action, NULL);                                   \
 102   if (old_timeout != 0)                                                       \
 103     alarm (old_timeout);                                                      \
 104 } while (0)
 105
 106
 107 /* Functions defined here.  */
 108 static int setutent_file (void);
 109 static int getutent_r_file (struct utmp *buffer, struct utmp **result);
 110 static int getutid_r_file (const struct utmp *key, struct utmp *buffer,
 111                            struct utmp **result);
 112 static int getutline_r_file (const struct utmp *key, struct utmp *buffer,
 113                              struct utmp **result);
 114 static struct utmp *pututline_file (const struct utmp *data);
 115 static void endutent_file (void);
 116 static int updwtmp_file (const char *file, const struct utmp *utmp);
 117
 118 /* Jump table for file functions.  */
 119 const struct utfuncs __libc_utmp_file_functions =
 120 {
 121   setutent_file,
 122   getutent_r_file,
 123   getutid_r_file,
 124   getutline_r_file,
 125   pututline_file,
 126   endutent_file,
 127   updwtmp_file
 128 };
 129
 130
 131 #ifndef TRANSFORM_UTMP_FILE_NAME
 132 # define TRANSFORM_UTMP_FILE_NAME(file_name) (file_name)
 133 #endif
 134
 135 static int
 136 setutent_file (void)
 137 {
 138   if (file_fd < 0)
 139     {
 140       const char *file_name;
 141
 142       file_name = TRANSFORM_UTMP_FILE_NAME (__libc_utmp_file_name);
 143
 144       file_writable = false;
 145       file_fd = open_not_cancel_2
 146         (file_name, O_RDONLY | O_LARGEFILE | O_CLOEXEC);
 147       if (file_fd == -1)
 148         return 0;
 149     }
 150
 151   __lseek64 (file_fd, 0, SEEK_SET);
 152   file_offset = 0;
 153
 154   /* Make sure the entry won't match.  */
 155 #if _HAVE_UT_TYPE - 0
 156   last_entry.ut_type = -1;
 157 #else
 158   last_entry.ut_line[0] = '\177';
 159 # if _HAVE_UT_ID - 0
 160   last_entry.ut_id[0] = '\0';
 161 # endif
 162 #endif
 163
 164   return 1;
 165 }
 166
 167
 168 static int
 169 getutent_r_file (struct utmp *buffer, struct utmp **result)
 170 {
 171   ssize_t nbytes;
 172
 173   assert (file_fd >= 0);
 174
 175   if (file_offset == -1l)
 176     {
 177       /* Not available.  */
 178       *result = NULL;
 179       return -1;
 180     }
 181
 182   LOCK_FILE (file_fd, F_RDLCK)
 183     {
 184       nbytes = 0;
 185       LOCKING_FAILED ();
 186     }
 187
 188   /* Read the next entry.  */
 189   nbytes = read_not_cancel (file_fd, &last_entry, sizeof (struct utmp));
 190
 191   UNLOCK_FILE (file_fd);
 192
 193   if (nbytes != sizeof (struct utmp))
 194     {
 195       if (nbytes != 0)
 196         file_offset = -1l;
 197       *result = NULL;
 198       return -1;
 199     }
 200
 201   /* Update position pointer.  */
 202   file_offset += sizeof (struct utmp);
 203
 204   memcpy (buffer, &last_entry, sizeof (struct utmp));
 205   *result = buffer;
 206
 207   return 0;
 208 }
 209
 210
 211 static int
 212 internal_getut_r (const struct utmp *id, struct utmp *buffer,
 213                   bool *lock_failed)
 214 {
 215   int result = -1;
 216
 217   LOCK_FILE (file_fd, F_RDLCK)
 218     {
 219       *lock_failed = true;
 220       LOCKING_FAILED ();
 221     }
 222
 223 #if _HAVE_UT_TYPE - 0
 224   if (id->ut_type == RUN_LVL || id->ut_type == BOOT_TIME
 225       || id->ut_type == OLD_TIME || id->ut_type == NEW_TIME)
 226     {
 227       /* Search for next entry with type RUN_LVL, BOOT_TIME,
 228          OLD_TIME, or NEW_TIME.  */
 229
 230       while (1)
 231         {
 232           /* Read the next entry.  */
 233           if (read_not_cancel (file_fd, buffer, sizeof (struct utmp))
 234               != sizeof (struct utmp))
 235             {
 236               __set_errno (ESRCH);
 237               file_offset = -1l;
 238               goto unlock_return;
 239             }
 240           file_offset += sizeof (struct utmp);
 241
 242           if (id->ut_type == buffer->ut_type)
 243             break;
 244         }
 245     }
 246   else
 247 #endif /* _HAVE_UT_TYPE */
 248     {
 249       /* Search for the next entry with the specified ID and with type
 250          INIT_PROCESS, LOGIN_PROCESS, USER_PROCESS, or DEAD_PROCESS.  */
 251
 252       while (1)
 253         {
 254           /* Read the next entry.  */
 255           if (read_not_cancel (file_fd, buffer, sizeof (struct utmp))
 256               != sizeof (struct utmp))
 257             {
 258               __set_errno (ESRCH);
 259               file_offset = -1l;
 260               goto unlock_return;
 261             }
 262           file_offset += sizeof (struct utmp);
 263
 264           if (__utmp_equal (buffer, id))
 265             break;
 266         }
 267     }
 268
 269   result = 0;
 270
 271 unlock_return:
 272   UNLOCK_FILE (file_fd);
 273
 274   return result;
 275 }
 276
 277
 278 /* For implementing this function we don't use the getutent_r function
 279    because we can avoid the reposition on every new entry this way.  */
 280 static int
 281 getutid_r_file (const struct utmp *id, struct utmp *buffer,
 282                 struct utmp **result)
 283 {
 284   assert (file_fd >= 0);
 285
 286   if (file_offset == -1l)
 287     {
 288       *result = NULL;
 289       return -1;
 290     }
 291
 292   /* We don't have to distinguish whether we can lock the file or
 293      whether there is no entry.  */
 294   bool lock_failed = false;
 295   if (internal_getut_r (id, &last_entry, &lock_failed) < 0)
 296     {
 297       *result = NULL;
 298       return -1;
 299     }
 300
 301   memcpy (buffer, &last_entry, sizeof (struct utmp));
 302   *result = buffer;
 303
 304   return 0;
 305 }
 306
 307
 308 /* For implementing this function we don't use the getutent_r function
 309    because we can avoid the reposition on every new entry this way.  */
 310 static int
 311 getutline_r_file (const struct utmp *line, struct utmp *buffer,
 312                   struct utmp **result)
 313 {
 314   assert (file_fd >= 0);
 315
 316   if (file_offset == -1l)
 317     {
 318       *result = NULL;
 319       return -1;
 320     }
 321
 322   LOCK_FILE (file_fd, F_RDLCK)
 323     {
 324       *result = NULL;
 325       LOCKING_FAILED ();
 326     }
 327
 328   while (1)
 329     {
 330       /* Read the next entry.  */
 331       if (read_not_cancel (file_fd, &last_entry, sizeof (struct utmp))
 332           != sizeof (struct utmp))
 333         {
 334           __set_errno (ESRCH);
 335           file_offset = -1l;
 336           *result = NULL;
 337           goto unlock_return;
 338         }
 339       file_offset += sizeof (struct utmp);
 340
 341       /* Stop if we found a user or login entry.  */
 342       if (
 343 #if _HAVE_UT_TYPE - 0
 344           (last_entry.ut_type == USER_PROCESS
 345            || last_entry.ut_type == LOGIN_PROCESS)
 346           &&
 347 #endif
 348           !strncmp (line->ut_line, last_entry.ut_line, sizeof line->ut_line))
 349         break;
 350     }
 351
 352   memcpy (buffer, &last_entry, sizeof (struct utmp));
 353   *result = buffer;
 354
 355 unlock_return:
 356   UNLOCK_FILE (file_fd);
 357
 358   return ((*result == NULL) ? -1 : 0);
 359 }
 360
 361
 362 static struct utmp *
 363 pututline_file (const struct utmp *data)
 364 {
 365   struct utmp buffer;
 366   struct utmp *pbuf;
 367   int found;
 368
 369   assert (file_fd >= 0);
 370
 371   if (! file_writable)
 372     {
 373       /* We must make the file descriptor writable before going on.  */
 374       const char *file_name = TRANSFORM_UTMP_FILE_NAME (__libc_utmp_file_name);
 375
 376       int new_fd = open_not_cancel_2
 377         (file_name, O_RDWR | O_LARGEFILE | O_CLOEXEC);
 378       if (new_fd == -1)
 379         return NULL;
 380
 381       if (__lseek64 (new_fd, __lseek64 (file_fd, 0, SEEK_CUR), SEEK_SET) == -1
 382           || __dup2 (new_fd, file_fd) < 0)
 383         {
 384           close_not_cancel_no_status (new_fd);
 385           return NULL;
 386         }
 387       close_not_cancel_no_status (new_fd);
 388       file_writable = true;
 389     }
 390
 391   /* Find the correct place to insert the data.  */
 392   if (file_offset > 0
 393       && (
 394 #if _HAVE_UT_TYPE - 0
 395           (last_entry.ut_type == data->ut_type
 396            && (last_entry.ut_type == RUN_LVL
 397                || last_entry.ut_type == BOOT_TIME
 398                || last_entry.ut_type == OLD_TIME
 399                || last_entry.ut_type == NEW_TIME))
 400           ||
 401 #endif
 402           __utmp_equal (&last_entry, data)))
 403     found = 1;
 404   else
 405     {
 406       bool lock_failed = false;
 407       found = internal_getut_r (data, &buffer, &lock_failed);
 408
 409       if (__builtin_expect (lock_failed, false))
 410         {
 411           __set_errno (EAGAIN);
 412           return NULL;
 413         }
 414     }
 415
 416   LOCK_FILE (file_fd, F_WRLCK)
 417     {
 418       pbuf = NULL;
 419       LOCKING_FAILED ();
 420     }
 421
 422   if (found < 0)
 423     {
 424       /* We append the next entry.  */
 425       file_offset = __lseek64 (file_fd, 0, SEEK_END);
 426       if (file_offset % sizeof (struct utmp) != 0)
 427         {
 428           file_offset -= file_offset % sizeof (struct utmp);
 429           __ftruncate64 (file_fd, file_offset);
 430
 431           if (__lseek64 (file_fd, 0, SEEK_END) < 0)
 432             {
 433               pbuf = NULL;
 434               goto unlock_return;
 435             }
 436         }
 437     }
 438   else
 439     {
 440       /* We replace the just read entry.  */
 441       file_offset -= sizeof (struct utmp);
 442       __lseek64 (file_fd, file_offset, SEEK_SET);
 443     }
 444
 445   /* Write the new data.  */
 446   if (write_not_cancel (file_fd, data, sizeof (struct utmp))
 447       != sizeof (struct utmp))
 448     {
 449       /* If we appended a new record this is only partially written.
 450          Remove it.  */
 451       if (found < 0)
 452         (void) __ftruncate64 (file_fd, file_offset);
 453       pbuf = NULL;
 454     }
 455   else
 456     {
 457       file_offset += sizeof (struct utmp);
 458       pbuf = (struct utmp *) data;
 459     }
 460
 461  unlock_return:
 462   UNLOCK_FILE (file_fd);
 463
 464   return pbuf;
 465 }
 466
 467
 468 static void
 469 endutent_file (void)
 470 {
 471   assert (file_fd >= 0);
 472
 473   close_not_cancel_no_status (file_fd);
 474   file_fd = -1;
 475 }
 476
 477
 478 static int
 479 updwtmp_file (const char *file, const struct utmp *utmp)
 480 {
 481   int result = -1;
 482   off64_t offset;
 483   int fd;
 484
 485   /* Open WTMP file.  */
 486   fd = open_not_cancel_2 (file, O_WRONLY | O_LARGEFILE);
 487   if (fd < 0)
 488     return -1;
 489
 490   LOCK_FILE (fd, F_WRLCK)
 491     LOCKING_FAILED ();
 492
 493   /* Remember original size of log file.  */
 494   offset = __lseek64 (fd, 0, SEEK_END);
 495   if (offset % sizeof (struct utmp) != 0)
 496     {
 497       offset -= offset % sizeof (struct utmp);
 498       __ftruncate64 (fd, offset);
 499
 500       if (__lseek64 (fd, 0, SEEK_END) < 0)
 501         goto unlock_return;
 502     }
 503
 504   /* Write the entry.  If we can't write all the bytes, reset the file
 505      size back to the original size.  That way, no partial entries
 506      will remain.  */
 507   if (write_not_cancel (fd, utmp, sizeof (struct utmp))
 508       != sizeof (struct utmp))
 509     {
 510       __ftruncate64 (fd, offset);
 511       goto unlock_return;
 512     }
 513
 514   result = 0;
 515
 516 unlock_return:
 517   UNLOCK_FILE (fd);
 518
 519   /* Close WTMP file.  */
 520   close_not_cancel_no_status (fd);
 521
 522   return result;
 523 }