grp/initgroups.c

   1 /* Copyright (C) 1989, 1991, 1993, 1996, 1997 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 <errno.h>
  21 #include <grp.h>
  22 #include <limits.h>
  23 #include <string.h>
  24 #include <unistd.h>
  25 #include <sys/types.h>
  26
  27
  28 /* Initialize the group set for the current user
  29    by reading the group database and using all groups
  30    of which USER is a member.  Also include GROUP.  */
  31 int
  32 initgroups (user, group)
  33      const char *user;
  34      gid_t group;
  35 {
  36 #if defined NGROUPS_MAX && NGROUPS_MAX == 0
  37
  38   /* No extra groups allowed.  */
  39   return 0;
  40
  41 #else
  42
  43   struct group grpbuf, *g;
  44   size_t buflen = sysconf (_SC_GETPW_R_SIZE_MAX);
  45   char *tmpbuf;
  46   size_t n;
  47   size_t ngroups;
  48   gid_t *groups;
  49   int status;
  50 #ifdef NGROUPS_MAX
  51 # define limit NGROUPS_MAX
  52
  53   ngroups = limit;
  54 #else
  55   long int limit = sysconf (_SC_NGROUPS_MAX);
  56
  57   if (limit > 0)
  58     ngroups = limit;
  59   else
  60     /* No fixed limit on groups.  Pick a starting buffer size.  */
  61     ngroups = 16;
  62 #endif
  63
  64   groups = __alloca (ngroups * sizeof *groups);
  65   tmpbuf = __alloca (buflen);
  66
  67   setgrent ();
  68
  69   n = 0;
  70   groups[n++] = group;
  71
  72   do
  73     {
  74       while ((status = __getgrent_r (&grpbuf, tmpbuf, buflen, &g)) != 0
  75              && errno == ERANGE)
  76         {
  77           buflen *= 2;
  78           tmpbuf = __alloca (buflen);
  79         }
  80
  81       if (status == 0 && g->gr_gid != group)
  82         {
  83           char **m;
  84
  85           for (m = g->gr_mem; *m != NULL; ++m)
  86             if (strcmp (*m, user) == 0)
  87               {
  88                 /* Matches user.  Insert this group.  */
  89                 if (n == ngroups && limit <= 0)
  90                   {
  91                     /* Need a bigger buffer.  */
  92                     gid_t *newgrp;
  93                     newgrp = __alloca (ngroups * 2 * sizeof *groups);
  94                     groups = memcpy (newgrp, groups, ngroups * sizeof *groups);
  95                     ngroups *= 2;
  96                   }
  97
  98                 groups[n++] = g->gr_gid;
  99
 100                 if (n == limit)
 101                   /* Can't take any more groups; stop searching.  */
 102                   goto done;
 103
 104                 break;
 105               }
 106         }
 107     }
 108   while (status == 0);
 109
 110 done:
 111   endgrent ();
 112
 113   return setgroups (n, groups);
 114 #endif
 115 }