NAME

Unix::Groups::FFI - Interface to Unix group syscalls

SYNOPSIS

  use Unix::Groups::FFI qw(getgroups setgroups getgrouplist initgroups);

  my @gids = getgroups;
  setgroups(@gids);
  my @gids = getgrouplist($username, $gid);
  initgroups($username, $gid);

DESCRIPTION

This module provides a FFI interface to several syscalls related to Unix groups, including getgroups(2), setgroups(2), getgrouplist(3), and initgroups(3). As such it will only work on Unix-like operating systems.

FUNCTIONS

All functions are exported individually on demand. A function will not be available for export if the system does not implement the corresponding syscall.

getgroups

  my @gids = getgroups;

Returns the supplementary group IDs of the current process via getgroups(2).

setgroups

  setgroups(@gids);

Sets the supplementary group IDs for the current process via setgroups(2). Attempting to set more than NGROUPS_MAX groups (32 before Linux 2.6.4 or 65536 since Linux 2.6.4) will result in an EINVAL error. Passing an empty list of group IDs may result in unspecified behavior. The CAP_SETGID capability or equivalent privilege is required.

getgrouplist

  my @gids = getgrouplist($username, $gid);
  my @gids = getgrouplist($username);

Returns the group IDs for all groups of which $username is a member, also including $gid (without repetition), via getgrouplist(3). If $username does not exist on the system, an EINVAL error will result.

As a special case, the primary group ID of $username is included if $gid is not passed.

initgroups

  initgroups($username, $gid);
  initgroups($username);

Initializes the supplementary group access list for the current process to all groups of which $username is a member, also including $gid (without repetition), via initgroups(3). If $username does not exist on the system, an EINVAL error will result. The CAP_SETGID capability or equivalent privilege is required.

As a special case, the primary group ID of $username is included if $gid is not passed.

ERROR HANDLING

All functions will throw an exception containing the syscall error message in the event of an error. "$!" in perlvar will also have been set by the syscall, so you could check it after trapping the exception for finer exception handling:

  use Unix::Groups::FFI 'setgroups';
  use Syntax::Keyword::Try;
  use Errno qw(EINVAL EPERM ENOMEM);

  try { setgroups((0)x2**16) }
  catch {
    if ($! == EINVAL) {
      die 'Tried to set too many groups';
    } elsif ($! == EPERM) {
      die 'Insufficient privileges to set groups';
    } elsif ($! == ENOMEM) {
      die 'Out of memory';
    } else {
      die $@;
    }
  }

See the documentation for each syscall for details on the possible error codes.

BUGS

Report any issues on the public bugtracker.

AUTHOR

Dan Book <dbook@cpan.org>

COPYRIGHT AND LICENSE

This software is Copyright (c) 2018 by Dan Book.

This is free software, licensed under:

  The Artistic License 2.0 (GPL Compatible)

SEE ALSO

POSIX, credentials(7), capabilities(7)