getgroups.c 3.66 KB
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/* provide consistent interface to getgroups for systems that don't allow N==0

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   Copyright (C) 1996, 1999, 2003, 2006-2019 Free Software Foundation, Inc.
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   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
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   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
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/* written by Jim Meyering */

#include <config.h>

#include <unistd.h>

#include <errno.h>
#include <stdlib.h>
#include <stdint.h>

#if !HAVE_GETGROUPS

/* Provide a stub that fails with ENOSYS, since there is no group
   information available on mingw.  */
int
getgroups (int n _GL_UNUSED, GETGROUPS_T *groups _GL_UNUSED)
{
  errno = ENOSYS;
  return -1;
}

#else /* HAVE_GETGROUPS */

# undef getgroups
# ifndef GETGROUPS_ZERO_BUG
#  define GETGROUPS_ZERO_BUG 0
# endif

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/* On OS X 10.6 and later, use the usual getgroups, not the one
   supplied when _DARWIN_C_SOURCE is defined.  _DARWIN_C_SOURCE is
   normally defined, since it means "conform to POSIX, but add
   non-POSIX extensions even if that violates the POSIX namespace
   rules", which is what we normally want.  But with getgroups there
   is an inconsistency, and _DARWIN_C_SOURCE means "change getgroups()
   so that it no longer works right".  The BUGS section of compat(5)
   says that the behavior is dubious if you compile different sections
   of a program with different _DARWIN_C_SOURCE settings, so fix only
   the offending symbol.  */
# ifdef __APPLE__
int posix_getgroups (int, gid_t []) __asm ("_getgroups");
#  define getgroups posix_getgroups
# endif

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/* On at least NeXTstep 3.2, getgroups (0, NULL) always fails.
   On other systems, it returns the number of supplemental
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   groups for the process.  This function handles that special case
   and lets the system-provided function handle all others.  However,
   it can fail with ENOMEM if memory is tight.  It is unspecified
   whether the effective group id is included in the list.  */

int
rpl_getgroups (int n, gid_t *group)
{
  int n_groups;
  GETGROUPS_T *gbuf;
  int saved_errno;

  if (n < 0)
    {
      errno = EINVAL;
      return -1;
    }

  if (n != 0 || !GETGROUPS_ZERO_BUG)
    {
      int result;
      if (sizeof *group == sizeof *gbuf)
        return getgroups (n, (GETGROUPS_T *) group);

      if (SIZE_MAX / sizeof *gbuf <= n)
        {
          errno = ENOMEM;
          return -1;
        }
      gbuf = malloc (n * sizeof *gbuf);
      if (!gbuf)
        return -1;
      result = getgroups (n, gbuf);
      if (0 <= result)
        {
          n = result;
          while (n--)
            group[n] = gbuf[n];
        }
      saved_errno = errno;
      free (gbuf);
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      errno = saved_errno;
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      return result;
    }

  n = 20;
  while (1)
    {
      /* No need to worry about address arithmetic overflow here,
         since the ancient systems that we're running on have low
         limits on the number of secondary groups.  */
      gbuf = malloc (n * sizeof *gbuf);
      if (!gbuf)
        return -1;
      n_groups = getgroups (n, gbuf);
      if (n_groups == -1 ? errno != EINVAL : n_groups < n)
        break;
      free (gbuf);
      n *= 2;
    }

  saved_errno = errno;
  free (gbuf);
  errno = saved_errno;

  return n_groups;
}

#endif /* HAVE_GETGROUPS */