lib/getgroups.c

   1 /* provide consistent interface to getgroups for systems that don't allow N==0
   2
   3    Copyright (C) 1996, 1999, 2003, 2006-2015 Free Software Foundation,
   4    Inc.
   5
   6    This program is free software: you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 3 of the License, or
   9    (at your option) any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  18
  19 /* written by Jim Meyering */
  20
  21 #include <config.h>
  22
  23 #include <unistd.h>
  24
  25 #include <errno.h>
  26 #include <stdlib.h>
  27 #include <stdint.h>
  28
  29 #if !HAVE_GETGROUPS
  30
  31 /* Provide a stub that fails with ENOSYS, since there is no group
  32    information available on mingw.  */
  33 int
  34 getgroups (int n _GL_UNUSED, GETGROUPS_T *groups _GL_UNUSED)
  35 {
  36   errno = ENOSYS;
  37   return -1;
  38 }
  39
  40 #else /* HAVE_GETGROUPS */
  41
  42 # undef getgroups
  43 # ifndef GETGROUPS_ZERO_BUG
  44 #  define GETGROUPS_ZERO_BUG 0
  45 # endif
  46
  47 /* On OS X 10.6 and later, use the usual getgroups, not the one
  48    supplied when _DARWIN_C_SOURCE is defined.  _DARWIN_C_SOURCE is
  49    normally defined, since it means "conform to POSIX, but add
  50    non-POSIX extensions even if that violates the POSIX namespace
  51    rules", which is what we normally want.  But with getgroups there
  52    is an inconsistency, and _DARWIN_C_SOURCE means "change getgroups()
  53    so that it no longer works right".  The BUGS section of compat(5)
  54    says that the behavior is dubious if you compile different sections
  55    of a program with different _DARWIN_C_SOURCE settings, so fix only
  56    the offending symbol.  */
  57 # ifdef __APPLE__
  58 int posix_getgroups (int, gid_t []) __asm ("_getgroups");
  59 #  define getgroups posix_getgroups
  60 # endif
  61
  62 /* On at least Ultrix 4.3 and NextStep 3.2, getgroups (0, NULL) always
  63    fails.  On other systems, it returns the number of supplemental
  64    groups for the process.  This function handles that special case
  65    and lets the system-provided function handle all others.  However,
  66    it can fail with ENOMEM if memory is tight.  It is unspecified
  67    whether the effective group id is included in the list.  */
  68
  69 int
  70 rpl_getgroups (int n, gid_t *group)
  71 {
  72   int n_groups;
  73   GETGROUPS_T *gbuf;
  74   int saved_errno;
  75
  76   if (n < 0)
  77     {
  78       errno = EINVAL;
  79       return -1;
  80     }
  81
  82   if (n != 0 || !GETGROUPS_ZERO_BUG)
  83     {
  84       int result;
  85       if (sizeof *group == sizeof *gbuf)
  86         return getgroups (n, (GETGROUPS_T *) group);
  87
  88       if (SIZE_MAX / sizeof *gbuf <= n)
  89         {
  90           errno = ENOMEM;
  91           return -1;
  92         }
  93       gbuf = malloc (n * sizeof *gbuf);
  94       if (!gbuf)
  95         return -1;
  96       result = getgroups (n, gbuf);
  97       if (0 <= result)
  98         {
  99           n = result;
 100           while (n--)
 101             group[n] = gbuf[n];
 102         }
 103       saved_errno = errno;
 104       free (gbuf);
 105       errno = saved_errno;
 106       return result;
 107     }
 108
 109   n = 20;
 110   while (1)
 111     {
 112       /* No need to worry about address arithmetic overflow here,
 113          since the ancient systems that we're running on have low
 114          limits on the number of secondary groups.  */
 115       gbuf = malloc (n * sizeof *gbuf);
 116       if (!gbuf)
 117         return -1;
 118       n_groups = getgroups (n, gbuf);
 119       if (n_groups == -1 ? errno != EINVAL : n_groups < n)
 120         break;
 121       free (gbuf);
 122       n *= 2;
 123     }
 124
 125   saved_errno = errno;
 126   free (gbuf);
 127   errno = saved_errno;
 128
 129   return n_groups;
 130 }
 131
 132 #endif /* HAVE_GETGROUPS */