lib/readutmp.c

   1 /* GNU's read utmp module.
   2
   3    Copyright (C) 1992-2001, 2003-2006, 2009-2021 Free Software Foundation, Inc.
   4
   5    This program is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  17
  18 /* Written by jla; revised by djm */
  19
  20 #include <config.h>
  21
  22 #include "readutmp.h"
  23
  24 #include <errno.h>
  25 #include <stdio.h>
  26
  27 #include <sys/types.h>
  28 #include <sys/stat.h>
  29 #include <signal.h>
  30 #include <stdbool.h>
  31 #include <string.h>
  32 #include <stdlib.h>
  33 #include <stdint.h>
  34
  35 #include "xalloc.h"
  36
  37 #if USE_UNLOCKED_IO
  38 # include "unlocked-io.h"
  39 #endif
  40
  41 #if 8 <= __GNUC__
  42 # pragma GCC diagnostic ignored "-Wsizeof-pointer-memaccess"
  43 #endif
  44
  45 /* Copy UT->ut_name into storage obtained from malloc.  Then remove any
  46    trailing spaces from the copy, NUL terminate it, and return the copy.  */
  47
  48 char *
  49 extract_trimmed_name (const STRUCT_UTMP *ut)
  50 {
  51   char *p, *trimmed_name;
  52
  53   trimmed_name = xmalloc (sizeof (UT_USER (ut)) + 1);
  54   strncpy (trimmed_name, UT_USER (ut), sizeof (UT_USER (ut)));
  55   /* Append a trailing NUL.  Some systems pad names shorter than the
  56      maximum with spaces, others pad with NULs.  Remove any trailing
  57      spaces.  */
  58   trimmed_name[sizeof (UT_USER (ut))] = '\0';
  59   for (p = trimmed_name + strlen (trimmed_name);
  60        trimmed_name < p && p[-1] == ' ';
  61        *--p = '\0')
  62     continue;
  63   return trimmed_name;
  64 }
  65
  66 /* Is the utmp entry U desired by the user who asked for OPTIONS?  */
  67
  68 static bool
  69 desirable_utmp_entry (STRUCT_UTMP const *u, int options)
  70 {
  71   bool user_proc = IS_USER_PROCESS (u);
  72   if ((options & READ_UTMP_USER_PROCESS) && !user_proc)
  73     return false;
  74   if ((options & READ_UTMP_CHECK_PIDS)
  75       && user_proc
  76       && 0 < UT_PID (u)
  77       && (kill (UT_PID (u), 0) < 0 && errno == ESRCH))
  78     return false;
  79   return true;
  80 }
  81
  82 /* Read the utmp entries corresponding to file FILE into freshly-
  83    malloc'd storage, set *UTMP_BUF to that pointer, set *N_ENTRIES to
  84    the number of entries, and return zero.  If there is any error,
  85    return -1, setting errno, and don't modify the parameters.
  86    If OPTIONS & READ_UTMP_CHECK_PIDS is nonzero, omit entries whose
  87    process-IDs do not currently exist.  */
  88
  89 #ifdef UTMP_NAME_FUNCTION
  90
  91 int
  92 read_utmp (char const *file, size_t *n_entries, STRUCT_UTMP **utmp_buf,
  93            int options)
  94 {
  95   size_t n_read = 0;
  96   size_t n_alloc = 0;
  97   STRUCT_UTMP *utmp = NULL;
  98   STRUCT_UTMP *u;
  99
 100   /* Ignore the return value for now.
 101      Solaris' utmpname returns 1 upon success -- which is contrary
 102      to what the GNU libc version does.  In addition, older GNU libc
 103      versions are actually void.   */
 104   UTMP_NAME_FUNCTION ((char *) file);
 105
 106   SET_UTMP_ENT ();
 107
 108   while ((u = GET_UTMP_ENT ()) != NULL)
 109     if (desirable_utmp_entry (u, options))
 110       {
 111         if (n_read == n_alloc)
 112           utmp = x2nrealloc (utmp, &n_alloc, sizeof *utmp);
 113
 114         utmp[n_read++] = *u;
 115       }
 116
 117   END_UTMP_ENT ();
 118
 119   *n_entries = n_read;
 120   *utmp_buf = utmp;
 121
 122   return 0;
 123 }
 124
 125 #else
 126
 127 int
 128 read_utmp (char const *file, size_t *n_entries, STRUCT_UTMP **utmp_buf,
 129            int options)
 130 {
 131   size_t n_read = 0;
 132   size_t n_alloc = 0;
 133   STRUCT_UTMP *utmp = NULL;
 134   int saved_errno;
 135   FILE *f = fopen (file, "re");
 136
 137   if (! f)
 138     return -1;
 139
 140   for (;;)
 141     {
 142       if (n_read == n_alloc)
 143         utmp = x2nrealloc (utmp, &n_alloc, sizeof *utmp);
 144       if (fread (&utmp[n_read], sizeof utmp[n_read], 1, f) == 0)
 145         break;
 146       n_read += desirable_utmp_entry (&utmp[n_read], options);
 147     }
 148
 149   saved_errno = ferror (f) ? errno : 0;
 150   if (fclose (f) != 0)
 151     saved_errno = errno;
 152   if (saved_errno != 0)
 153     {
 154       free (utmp);
 155       errno = saved_errno;
 156       return -1;
 157     }
 158
 159   *n_entries = n_read;
 160   *utmp_buf = utmp;
 161
 162   return 0;
 163 }
 164
 165 #endif