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 #ifdef O_CLOEXEC
 145 # define O_flags O_LARGEFILE | O_CLOEXEC
 146 #else
 147 # define O_flags O_LARGEFILE
 148 #endif
 149       file_writable = false;
 150       file_fd = open_not_cancel_2 (file_name, O_RDONLY | O_flags);
 151       if (file_fd == -1)
 152         return 0;
 153
 154 #ifndef __ASSUME_O_CLOEXEC
 155 # ifdef O_CLOEXEC
 156       if (__have_o_cloexec <= 0)
 157 # endif
 158         {
 159           /* We have to make sure the file is `closed on exec'.  */
 160           int result = fcntl_not_cancel (file_fd, F_GETFD, 0);
 161           if (result >= 0)
 162             {
 163 # ifdef O_CLOEXEC
 164               if (__have_o_cloexec == 0)
 165                 __have_o_cloexec = (result & FD_CLOEXEC) ? 1 : -1;
 166
 167               if (__have_o_cloexec < 0)
 168 # endif
 169                 result = fcntl_not_cancel (file_fd, F_SETFD,
 170                                            result | FD_CLOEXEC);
 171             }
 172
 173           if (result == -1)
 174             {
 175               close_not_cancel_no_status (file_fd);
 176               return 0;
 177             }
 178         }
 179 #endif
 180     }
 181
 182   __lseek64 (file_fd, 0, SEEK_SET);
 183   file_offset = 0;
 184
 185   /* Make sure the entry won't match.  */
 186 #if _HAVE_UT_TYPE - 0
 187   last_entry.ut_type = -1;
 188 #else
 189   last_entry.ut_line[0] = '\177';
 190 # if _HAVE_UT_ID - 0
 191   last_entry.ut_id[0] = '\0';
 192 # endif
 193 #endif
 194
 195   return 1;
 196 }
 197
 198
 199 static int
 200 getutent_r_file (struct utmp *buffer, struct utmp **result)
 201 {
 202   ssize_t nbytes;
 203
 204   assert (file_fd >= 0);
 205
 206   if (file_offset == -1l)
 207     {
 208       /* Not available.  */
 209       *result = NULL;
 210       return -1;
 211     }
 212
 213   LOCK_FILE (file_fd, F_RDLCK)
 214     {
 215       nbytes = 0;
 216       LOCKING_FAILED ();
 217     }
 218
 219   /* Read the next entry.  */
 220   nbytes = read_not_cancel (file_fd, &last_entry, sizeof (struct utmp));
 221
 222   UNLOCK_FILE (file_fd);
 223
 224   if (nbytes != sizeof (struct utmp))
 225     {
 226       if (nbytes != 0)
 227         file_offset = -1l;
 228       *result = NULL;
 229       return -1;
 230     }
 231
 232   /* Update position pointer.  */
 233   file_offset += sizeof (struct utmp);
 234
 235   memcpy (buffer, &last_entry, sizeof (struct utmp));
 236   *result = buffer;
 237
 238   return 0;
 239 }
 240
 241
 242 static int
 243 internal_getut_r (const struct utmp *id, struct utmp *buffer,
 244                   bool *lock_failed)
 245 {
 246   int result = -1;
 247
 248   LOCK_FILE (file_fd, F_RDLCK)
 249     {
 250       *lock_failed = true;
 251       LOCKING_FAILED ();
 252     }
 253
 254 #if _HAVE_UT_TYPE - 0
 255   if (id->ut_type == RUN_LVL || id->ut_type == BOOT_TIME
 256       || id->ut_type == OLD_TIME || id->ut_type == NEW_TIME)
 257     {
 258       /* Search for next entry with type RUN_LVL, BOOT_TIME,
 259          OLD_TIME, or NEW_TIME.  */
 260
 261       while (1)
 262         {
 263           /* Read the next entry.  */
 264           if (read_not_cancel (file_fd, buffer, sizeof (struct utmp))
 265               != sizeof (struct utmp))
 266             {
 267               __set_errno (ESRCH);
 268               file_offset = -1l;
 269               goto unlock_return;
 270             }
 271           file_offset += sizeof (struct utmp);
 272
 273           if (id->ut_type == buffer->ut_type)
 274             break;
 275         }
 276     }
 277   else
 278 #endif /* _HAVE_UT_TYPE */
 279     {
 280       /* Search for the next entry with the specified ID and with type
 281          INIT_PROCESS, LOGIN_PROCESS, USER_PROCESS, or DEAD_PROCESS.  */
 282
 283       while (1)
 284         {
 285           /* Read the next entry.  */
 286           if (read_not_cancel (file_fd, buffer, sizeof (struct utmp))
 287               != sizeof (struct utmp))
 288             {
 289               __set_errno (ESRCH);
 290               file_offset = -1l;
 291               goto unlock_return;
 292             }
 293           file_offset += sizeof (struct utmp);
 294
 295           if (__utmp_equal (buffer, id))
 296             break;
 297         }
 298     }
 299
 300   result = 0;
 301
 302 unlock_return:
 303   UNLOCK_FILE (file_fd);
 304
 305   return result;
 306 }
 307
 308
 309 /* For implementing this function we don't use the getutent_r function
 310    because we can avoid the reposition on every new entry this way.  */
 311 static int
 312 getutid_r_file (const struct utmp *id, struct utmp *buffer,
 313                 struct utmp **result)
 314 {
 315   assert (file_fd >= 0);
 316
 317   if (file_offset == -1l)
 318     {
 319       *result = NULL;
 320       return -1;
 321     }
 322
 323   /* We don't have to distinguish whether we can lock the file or
 324      whether there is no entry.  */
 325   bool lock_failed = false;
 326   if (internal_getut_r (id, &last_entry, &lock_failed) < 0)
 327     {
 328       *result = NULL;
 329       return -1;
 330     }
 331
 332   memcpy (buffer, &last_entry, sizeof (struct utmp));
 333   *result = buffer;
 334
 335   return 0;
 336 }
 337
 338
 339 /* For implementing this function we don't use the getutent_r function
 340    because we can avoid the reposition on every new entry this way.  */
 341 static int
 342 getutline_r_file (const struct utmp *line, struct utmp *buffer,
 343                   struct utmp **result)
 344 {
 345   assert (file_fd >= 0);
 346
 347   if (file_offset == -1l)
 348     {
 349       *result = NULL;
 350       return -1;
 351     }
 352
 353   LOCK_FILE (file_fd, F_RDLCK)
 354     {
 355       *result = NULL;
 356       LOCKING_FAILED ();
 357     }
 358
 359   while (1)
 360     {
 361       /* Read the next entry.  */
 362       if (read_not_cancel (file_fd, &last_entry, sizeof (struct utmp))
 363           != sizeof (struct utmp))
 364         {
 365           __set_errno (ESRCH);
 366           file_offset = -1l;
 367           *result = NULL;
 368           goto unlock_return;
 369         }
 370       file_offset += sizeof (struct utmp);
 371
 372       /* Stop if we found a user or login entry.  */
 373       if (
 374 #if _HAVE_UT_TYPE - 0
 375           (last_entry.ut_type == USER_PROCESS
 376            || last_entry.ut_type == LOGIN_PROCESS)
 377           &&
 378 #endif
 379           !strncmp (line->ut_line, last_entry.ut_line, sizeof line->ut_line))
 380         break;
 381     }
 382
 383   memcpy (buffer, &last_entry, sizeof (struct utmp));
 384   *result = buffer;
 385
 386 unlock_return:
 387   UNLOCK_FILE (file_fd);
 388
 389   return ((*result == NULL) ? -1 : 0);
 390 }
 391
 392
 393 static struct utmp *
 394 pututline_file (const struct utmp *data)
 395 {
 396   struct utmp buffer;
 397   struct utmp *pbuf;
 398   int found;
 399
 400   assert (file_fd >= 0);
 401
 402   if (! file_writable)
 403     {
 404       /* We must make the file descriptor writable before going on.  */
 405       const char *file_name = TRANSFORM_UTMP_FILE_NAME (__libc_utmp_file_name);
 406
 407       int new_fd = open_not_cancel_2 (file_name, O_RDWR | O_flags);
 408       if (new_fd == -1)
 409         return NULL;
 410
 411 #ifndef __ASSUME_O_CLOEXEC
 412 # ifdef O_CLOEXEC
 413       if (__have_o_cloexec <= 0)
 414 # endif
 415         {
 416           /* We have to make sure the file is `closed on exec'.  */
 417           int result = fcntl_not_cancel (file_fd, F_GETFD, 0);
 418           if (result >= 0)
 419             {
 420 # ifdef O_CLOEXEC
 421               if (__have_o_cloexec == 0)
 422                 __have_o_cloexec = (result & FD_CLOEXEC) ? 1 : -1;
 423
 424               if (__have_o_cloexec < 0)
 425 # endif
 426                 result = fcntl_not_cancel (file_fd, F_SETFD,
 427                                            result | FD_CLOEXEC);
 428             }
 429
 430           if (result == -1)
 431             {
 432               close_not_cancel_no_status (file_fd);
 433               return NULL;
 434             }
 435         }
 436 #endif
 437
 438       if (__lseek64 (new_fd, __lseek64 (file_fd, 0, SEEK_CUR), SEEK_SET) == -1
 439           || __dup2 (new_fd, file_fd) < 0)
 440         {
 441           close_not_cancel_no_status (new_fd);
 442           return NULL;
 443         }
 444       close_not_cancel_no_status (new_fd);
 445       file_writable = true;
 446     }
 447
 448   /* Find the correct place to insert the data.  */
 449   if (file_offset > 0
 450       && (
 451 #if _HAVE_UT_TYPE - 0
 452           (last_entry.ut_type == data->ut_type
 453            && (last_entry.ut_type == RUN_LVL
 454                || last_entry.ut_type == BOOT_TIME
 455                || last_entry.ut_type == OLD_TIME
 456                || last_entry.ut_type == NEW_TIME))
 457           ||
 458 #endif
 459           __utmp_equal (&last_entry, data)))
 460     found = 1;
 461   else
 462     {
 463       bool lock_failed = false;
 464       found = internal_getut_r (data, &buffer, &lock_failed);
 465
 466       if (__builtin_expect (lock_failed, false))
 467         {
 468           __set_errno (EAGAIN);
 469           return NULL;
 470         }
 471     }
 472
 473   LOCK_FILE (file_fd, F_WRLCK)
 474     {
 475       pbuf = NULL;
 476       LOCKING_FAILED ();
 477     }
 478
 479   if (found < 0)
 480     {
 481       /* We append the next entry.  */
 482       file_offset = __lseek64 (file_fd, 0, SEEK_END);
 483       if (file_offset % sizeof (struct utmp) != 0)
 484         {
 485           file_offset -= file_offset % sizeof (struct utmp);
 486           __ftruncate64 (file_fd, file_offset);
 487
 488           if (__lseek64 (file_fd, 0, SEEK_END) < 0)
 489             {
 490               pbuf = NULL;
 491               goto unlock_return;
 492             }
 493         }
 494     }
 495   else
 496     {
 497       /* We replace the just read entry.  */
 498       file_offset -= sizeof (struct utmp);
 499       __lseek64 (file_fd, file_offset, SEEK_SET);
 500     }
 501
 502   /* Write the new data.  */
 503   if (write_not_cancel (file_fd, data, sizeof (struct utmp))
 504       != sizeof (struct utmp))
 505     {
 506       /* If we appended a new record this is only partially written.
 507          Remove it.  */
 508       if (found < 0)
 509         (void) __ftruncate64 (file_fd, file_offset);
 510       pbuf = NULL;
 511     }
 512   else
 513     {
 514       file_offset += sizeof (struct utmp);
 515       pbuf = (struct utmp *) data;
 516     }
 517
 518  unlock_return:
 519   UNLOCK_FILE (file_fd);
 520
 521   return pbuf;
 522 }
 523
 524
 525 static void
 526 endutent_file (void)
 527 {
 528   assert (file_fd >= 0);
 529
 530   close_not_cancel_no_status (file_fd);
 531   file_fd = -1;
 532 }
 533
 534
 535 static int
 536 updwtmp_file (const char *file, const struct utmp *utmp)
 537 {
 538   int result = -1;
 539   off64_t offset;
 540   int fd;
 541
 542   /* Open WTMP file.  */
 543   fd = open_not_cancel_2 (file, O_WRONLY | O_LARGEFILE);
 544   if (fd < 0)
 545     return -1;
 546
 547   LOCK_FILE (fd, F_WRLCK)
 548     LOCKING_FAILED ();
 549
 550   /* Remember original size of log file.  */
 551   offset = __lseek64 (fd, 0, SEEK_END);
 552   if (offset % sizeof (struct utmp) != 0)
 553     {
 554       offset -= offset % sizeof (struct utmp);
 555       __ftruncate64 (fd, offset);
 556
 557       if (__lseek64 (fd, 0, SEEK_END) < 0)
 558         goto unlock_return;
 559     }
 560
 561   /* Write the entry.  If we can't write all the bytes, reset the file
 562      size back to the original size.  That way, no partial entries
 563      will remain.  */
 564   if (write_not_cancel (fd, utmp, sizeof (struct utmp))
 565       != sizeof (struct utmp))
 566     {
 567       __ftruncate64 (fd, offset);
 568       goto unlock_return;
 569     }
 570
 571   result = 0;
 572
 573 unlock_return:
 574   UNLOCK_FILE (fd);
 575
 576   /* Close WTMP file.  */
 577   close_not_cancel_no_status (fd);
 578
 579   return result;
 580 }