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utmp_file.c

/* Copyright (C) 1996,97,98,99,2000,01,02 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, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <utmp.h>

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


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

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


/* Locking timeout.  */
#ifndef TIMEOUT
# define TIMEOUT 1
#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 ((fd), F_SETLKW, &fl) < 0)

#define LOCKING_FAILED() \
  goto unalarm_return

#define UNLOCK_FILE(fd) \
  /* Unlock the file.  */                                               \
  fl.l_type = F_UNLCK;                                                  \
  __fcntl ((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.  */
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;
      int result;

      file_name = TRANSFORM_UTMP_FILE_NAME (__libc_utmp_file_name);

      file_fd = __open (file_name, O_RDWR);
      if (file_fd == -1)
      {
        /* Hhm, read-write access did not work.  Try read-only.  */
        file_fd = __open (file_name, O_RDONLY);
        if (file_fd == -1)
          return 0;
      }

      /* We have to make sure the file is `closed on exec'.  */
      result = __fcntl (file_fd, F_GETFD, 0);
      if (result >= 0)
      result = __fcntl (file_fd, F_SETFD, result | FD_CLOEXEC);
      if (result == -1)
      {
        __close (file_fd);
        return 0;
      }
    }

  __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 (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)
{
  int result = -1;

  LOCK_FILE (file_fd, F_RDLCK)
    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 (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 (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;
    }

  if (internal_getut_r (id, &last_entry) < 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 (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);

  /* 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
    found = internal_getut_r (data, &buffer);

  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 (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 (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 (file, O_WRONLY);
  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 (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 (fd);

  return result;
}

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