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https://github.com/rfarr/Unix-Pledge

Perl support for pledge(2) syscall
https://github.com/rfarr/Unix-Pledge

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Perl support for pledge(2) syscall

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package Unix::Pledge;



use strict;



require Exporter;



our @ISA = qw{Exporter};

our @EXPORT = qw{pledge unveil};



our $VERSION = '0.006';



require XSLoader;

XSLoader::load('Unix::Pledge', $VERSION);



1;

__END__



=head1 NAME



Unix::Pledge - restrict system operations



=head1 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)



=head1 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 L and L

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 L or the files which

can be accessed with L.



=head1 pledge



The pledge function takes one or two parameters: C and

optionally C.



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. C lists the modes this

process will adhere to while C lists the modes that

will be adhered to after calling L.



To set C only, C can be passed as undef or the

empty string. A detailed description of which calls are restricted by

which modes is available in the L 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 C then

further attempts to raise privileges will fail silently and illegal

system calls will fail rather than abort.



=head1 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 L 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.



=head2 ERRORS



Unix::Pledge will croak on any errors.



=head2 EXPORT



The L and L functions are exported by default.



=head1 SEE ALSO



For detailed information on pledge and unveil, their parameters and errors, please see the

OpenBSD L

and L

man pages.



L



=head1 AUTHOR



Richard Farr C<<  >>



=head1 COPYRIGHT AND LICENSE



Copyright (C) 2016 by Richard Farr



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



=cut