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
  16 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  17 Cambridge, MA 02139, 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 *g;
  43   register size_t n;
  44   size_t ngroups;
  45   gid_t *groups;
  46 #ifdef NGROUPS_MAX
  47 # define limit NGROUPS_MAX
  48
  49   ngroups = limit;
  50 #else
  51   long int limit = sysconf (_SC_NGROUPS_MAX);
  52
  53   if (limit > 0)
  54     ngroups = limit;
  55   else
  56     /* No fixed limit on groups.  Pick a starting buffer size.  */
  57     ngroups = 16;
  58 #endif
  59
  60   groups = __alloca (ngroups * sizeof *groups);
  61
  62   setgrent ();
  63
  64   n = 0;
  65   groups[n++] = group;
  66
  67   while ((g = getgrent ()) != NULL)
  68     if (g->gr_gid != group)
  69       {
  70         register char **m;
  71
  72         for (m = g->gr_mem; *m != NULL; ++m)
  73           if (!strcmp (*m, user))
  74             break;
  75
  76         if (*m == NULL)
  77           {
  78             /* Matched the 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               break;
  92           }
  93       }
  94
  95   endgrent ();
  96
  97   return setgroups (n, groups);
  98 #endif
  99 }