NAME
    Unix::Pledge - restrict system operations

SYNOPSIS
      use Unix::Pledge;

      # ...
      # Program initializtion, open files, drop privileges, fork, etc
      # ...

      # Now that we're initialized, limit our process to reading our .profile
      unveil("$ENV{HOME}/.profile", "r");
      unveil; # To ensure unveil can no longer be called
      pledge("stdio rpath"); # ... which this does also

      # Reading user's .profile works as expected
      open(my $fd, "<", "$ENV{HOME}/.profile");
      while(<$fd>) {
        print $_;
      }

      # Trying to open outside whitelisted path fails with file not found
      open($fd, "<", "/etc/passwd") or warn $!;

      # Trying to write will cause SIGABRT
      open($fd, ">", "$ENV{HOME}/.profile");

      # Abort trap (core dumped)

DESCRIPTION
    The current process is forced into a restricted-service operating mode.
    A few subsets are available, roughly described as computation, memory
    management, read-write operations on file descriptors, opening of files,
    networking. In general, these modes were selected by studying the
    operation of many programs using libc and other such interfaces, and
    setting promises or paths.

    Requires that the kernel supports the pledge(2) and unveil(2) system
    calls, which as of this writing are only available in OpenBSD.

    There are two types of restriction which can be made: Restrict the set
    of system calls which can be made with "pledge" or the files which can
    be accessed with "unveil".

pledge
    The pledge function takes one or two parameters: "promises" and
    optionally "execpromises".

    Both parameters are space-delimited strings listing modes of operation
    which represent system calls that a process is asserting are the only
    calls that it will make from then on. "promises" lists the modes this
    process will adhere to while "execpromises" lists the modes that will be
    adhered to after calling exec.

    To set "execpromises" only, "promises" can be passed as undef or the
    empty string. A detailed description of which calls are restricted by
    which modes is available in the pledge(2) manpage.

    Process violations of the previously "pledged" modes will result in the
    process being forcibly terminated via SIGABRT, which under normal
    circumstances will dump perl's core as it quits. In this way pledge
    serves as a capabilities framework like capsicum, systrace, AppArmor,
    etc. The difference is that pledge aims to be very easy to use for the
    typical developer to sandbox their process.

    Note that restrictions are one way only: you can only increase the
    restrictions on your process, not relax them.

    Also note that if either list of promises includes "error" then further
    attempts to raise privileges will fail silently and illegal system calls
    will fail rather than abort.

unveil
    The unveil function takes two parameters - a directory/file path and
    access mode - or none. After it has been called with no parameters
    further calls to unveil will fail.

    Each successive call to unveil adds a path which this process is
    permitted to access. Any attempt to access a file not previously
    unveiled will fail.

    Full details on the difference between naming files and directories, and
    their access modes are in the unveil(2) manpage.

    Note that, on OpenBSD at least, the kernel associates the unveiling with
    the file itself not the textual path, so unveiled files which are
    subsequently renamed or removed will be "lost". OpenBSD's manpage
    recommends only unveiling directories.

  ERRORS
    Unix::Pledge will croak on any errors.

  EXPORT
    The "pledge" and "unveil" functions are exported by default.

SEE ALSO
    For detailed information on pledge and unveil, their parameters and
    errors, please see the OpenBSD pledge(2)
    <http://www.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man2/pledge.2>
    and unveil(2)
    <http://www.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man2/unveil.2>
    man pages.

    Github repo <https://github.com/rfarr/Unix-Pledge>

AUTHOR
    Richard Farr "<richard@nxbit.io>"

COPYRIGHT AND LICENSE
    Copyright (C) 2016 by Richard Farr

    This module is licensed under the same terms as Perl itself.

