lib/getugroups.c

/* getugroups.c -- return a list of the groups a user is in

   Copyright (C) 1990-1991, 1998-2000, 2003-2026 Free Software Foundation, Inc.

   This file is free software: you can redistribute it and/or modify
   it under the terms of the GNU Lesser General Public License as
   published by the Free Software Foundation; either version 2.1 of the
   License, or (at your option) any later version.

   This file 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 Lesser General Public License for more details.

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

/* Written by David MacKenzie. */

#include <config.h>

#include "getugroups.h"

#include <errno.h>
#include <limits.h>
#include <stdio.h> /* grp.h on alpha OSF1 V2.0 uses "FILE *". */
#include <string.h>
#include <unistd.h>

#if !HAVE_GRP_H || defined __ANDROID__

/* Mingw lacks all things related to group management.  The best we
   can do is fail with ENOSYS.

   Bionic declares e.g. getgrent() in <grp.h> but it isn't actually
   defined in the library.  */

int
getugroups (_GL_UNUSED int maxcount,
            _GL_UNUSED gid_t *grouplist,
            _GL_UNUSED char const *username,
            _GL_UNUSED gid_t gid)
{
  errno = ENOSYS;
  return -1;
}

#else /* HAVE_GRP_H */
# include <grp.h>

/* Like 'getgroups', but for user USERNAME instead of for the current
   process.  Store at most MAXCOUNT group IDs in the GROUPLIST array.
   If GID is not -1, store it first (if possible).  GID should be the
   group ID (pw_gid) obtained from getpwuid, in case USERNAME is not
   listed in /etc/groups.  Upon failure, set errno and return -1.
   Otherwise, return the number of IDs we've written into GROUPLIST.  */

int
getugroups (int maxcount, gid_t *grouplist, char const *username,
            gid_t gid)
{
  int count = 0;

  if (gid != (gid_t) -1)
    {
      if (maxcount != 0)
        grouplist[count] = gid;
      ++count;
    }

  setgrent ();
  while (1)
    {
      errno = 0;
      struct group *grp = getgrent ();
      if (grp == NULL)
        break;

      for (char **cp = grp->gr_mem; *cp; ++cp)
        {
          if (streq (username, *cp))
            {
              /* See if this group number is already on the list.  */
              int n;
              for (n = 0; n < count; ++n)
                if (grouplist && grouplist[n] == grp->gr_gid)
                  break;

              /* If it's a new group number, then try to add it to the list.  */
              if (n == count)
                {
                  if (maxcount != 0)
                    {
                      if (count >= maxcount)
                        goto done;
                      grouplist[count] = grp->gr_gid;
                    }
                  if (count == INT_MAX)
                    {
                      errno = EOVERFLOW;
                      goto done;
                    }
                  count++;
                }
            }
        }
    }

  if (errno != 0)
    count = -1;

 done:
  {
    int saved_errno = errno;
    endgrent ();
    errno = saved_errno;
  }

  return count;
}

#endif /* HAVE_GRP_H */