grp/initgroups.c

   1 /* Copyright (C) 1989, 1991, 1993, 1996 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Library General Public License as
   6    published by the Free Software Foundation; either version 2 of the
   7    License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Library General Public License for more details.
  13
  14    You should have received a copy of the GNU Library General Public
  15    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  16    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  17    Boston, MA 02111-1307, USA.  */
  18
  19 #include <alloca.h>
  20 #include <unistd.h>
  21 #include <string.h>
  22 #include <grp.h>
  23 #include <limits.h>
  24 #include <sys/types.h>
  25
  26
  27 /* Initialize the group set for the current user
  28    by reading the group database and using all groups
  29    of which USER is a member.  Also include GROUP.  */
  30 int
  31 initgroups (user, group)
  32      const char *user;
  33      gid_t group;
  34 {
  35 #if defined (NGROUPS_MAX) && NGROUPS_MAX == 0
  36
  37   /* No extra groups allowed.  */
  38   return 0;
  39
  40 #else
  41
  42   struct group grpbuf, *g;
  43   size_t buflen = sysconf (_SC_GETPW_R_SIZE_MAX);
  44   char *tmpbuf;
  45   register size_t n;
  46   size_t ngroups;
  47   gid_t *groups;
  48 #ifdef NGROUPS_MAX
  49 # define limit NGROUPS_MAX
  50
  51   ngroups = limit;
  52 #else
  53   long int limit = sysconf (_SC_NGROUPS_MAX);
  54
  55   if (limit > 0)
  56     ngroups = limit;
  57   else
  58     /* No fixed limit on groups.  Pick a starting buffer size.  */
  59     ngroups = 16;
  60 #endif
  61
  62   groups = __alloca (ngroups * sizeof *groups);
  63   tmpbuf = __alloca (buflen);
  64
  65   setgrent ();
  66
  67   n = 0;
  68   groups[n++] = group;
  69
  70   while (__getgrent_r (&grpbuf, tmpbuf, buflen, &g) >= 0)
  71     if (g->gr_gid != group)
  72       {
  73         register char **m;
  74
  75         for (m = g->gr_mem; *m != NULL; ++m)
  76           if (strcmp (*m, user) == 0)
  77             {
  78               /* Matches user.  Insert this group.  */
  79               if (n == ngroups && limit <= 0)
  80                 {
  81                   /* Need a bigger buffer.  */
  82                   groups = memcpy (__alloca (ngroups * 2 * sizeof *groups),
  83                                    groups, ngroups * sizeof *groups);
  84                   ngroups *= 2;
  85                 }
  86
  87               groups[n++] = g->gr_gid;
  88
  89               if (n == limit)
  90                 /* Can't take any more groups; stop searching.  */
  91                 goto done;
  92
  93               break;
  94             }
  95       }
  96 done:
  97   endgrent ();
  98
  99   return setgroups (n, groups);
 100 #endif
 101 }