lib/getgroups.c

   1 /* provide consistent interface to getgroups for systems that don't allow N==0
   2
   3    Copyright (C) 1996, 1999, 2003, 2006-2013 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 <http://www.gnu.org/licenses/>.  */
  17
  18 /* written by Jim Meyering */
  19
  20 #include <config.h>
  21
  22 #include <unistd.h>
  23
  24 #include <errno.h>
  25 #include <stdlib.h>
  26 #include <stdint.h>
  27
  28 #if !HAVE_GETGROUPS
  29
  30 /* Provide a stub that fails with ENOSYS, since there is no group
  31    information available on mingw.  */
  32 int
  33 getgroups (int n _GL_UNUSED, GETGROUPS_T *groups _GL_UNUSED)
  34 {
  35   errno = ENOSYS;
  36   return -1;
  37 }
  38
  39 #else /* HAVE_GETGROUPS */
  40
  41 # undef getgroups
  42 # ifndef GETGROUPS_ZERO_BUG
  43 #  define GETGROUPS_ZERO_BUG 0
  44 # endif
  45
  46 /* On at least Ultrix 4.3 and NextStep 3.2, getgroups (0, NULL) always
  47    fails.  On other systems, it returns the number of supplemental
  48    groups for the process.  This function handles that special case
  49    and lets the system-provided function handle all others.  However,
  50    it can fail with ENOMEM if memory is tight.  It is unspecified
  51    whether the effective group id is included in the list.  */
  52
  53 int
  54 rpl_getgroups (int n, gid_t *group)
  55 {
  56   int n_groups;
  57   GETGROUPS_T *gbuf;
  58   int saved_errno;
  59
  60   if (n < 0)
  61     {
  62       errno = EINVAL;
  63       return -1;
  64     }
  65
  66   if (n != 0 || !GETGROUPS_ZERO_BUG)
  67     {
  68       int result;
  69       if (sizeof *group == sizeof *gbuf)
  70         return getgroups (n, (GETGROUPS_T *) group);
  71
  72       if (SIZE_MAX / sizeof *gbuf <= n)
  73         {
  74           errno = ENOMEM;
  75           return -1;
  76         }
  77       gbuf = malloc (n * sizeof *gbuf);
  78       if (!gbuf)
  79         return -1;
  80       result = getgroups (n, gbuf);
  81       if (0 <= result)
  82         {
  83           n = result;
  84           while (n--)
  85             group[n] = gbuf[n];
  86         }
  87       saved_errno = errno;
  88       free (gbuf);
  89       errno == saved_errno;
  90       return result;
  91     }
  92
  93   n = 20;
  94   while (1)
  95     {
  96       /* No need to worry about address arithmetic overflow here,
  97          since the ancient systems that we're running on have low
  98          limits on the number of secondary groups.  */
  99       gbuf = malloc (n * sizeof *gbuf);
 100       if (!gbuf)
 101         return -1;
 102       n_groups = getgroups (n, gbuf);
 103       if (n_groups == -1 ? errno != EINVAL : n_groups < n)
 104         break;
 105       free (gbuf);
 106       n *= 2;
 107     }
 108
 109   saved_errno = errno;
 110   free (gbuf);
 111   errno = saved_errno;
 112
 113   return n_groups;
 114 }
 115
 116 #endif /* HAVE_GETGROUPS */