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lib/App/EvalServerAdvanced/Sandbox.pm  view on Meta::CPAN

use Data::Dumper;
use Sys::Linux::Syscall::Execve qw/execve_byref/;

my %sig_map;
do {
  my @sig_names = split ' ', $Config{sig_name};
  my @sig_nums = split ' ', $Config{sig_num};
  @sig_map{@sig_nums} = map {'SIG' . $_} @sig_names;
  $sig_map{31} = "SIGSYS (Illegal Syscall)";
};

my $namespace = Sys::Linux::Namespace->new(private_pid => 1, no_proc => 1, private_mount => 1, private_uts => 1,  private_ipc => 0, private_sysvsem => 1);

sub _rel2abs {
  my $base = config->sandbox->mount_base;
  die "sandbox.mount_base must be set" unless defined $base;
  my $p = shift;
  if ($p !~ m|^/|) {
    $p = path("$base/$p")->realpath;
  }
  return "".$p
}

my $seccomp;

sub run_eval {
  my $code = shift; # TODO this should be more than just code
  my $language = shift;
  my $files = shift;
  my $work_path = Path::Tiny->tempdir("eval-XXXXXXXX");

  $|++;

  chmod(0555, $work_path); # have to fix permissions on the new / or nobody can do anything!

  unless ($seccomp) {
    App::EvalServerAdvanced::Sandbox::Internal->load_plugins();
    $seccomp = App::EvalServerAdvanced::Seccomp->new();
    $seccomp->load_yaml(config->sandbox->seccomp->yaml); # TODO allow multiple yamls
    $seccomp->build_seccomp;
  }

  my @binds = config->sandbox->bind_mounts->@*;

  # Setup SECCOMP for us
  my $lang_config = config->language->$language;
  die "Language $language not configured." unless $lang_config;

  my $profile = $lang_config->seccomp_profile // "default";

	# Get the nobody uid before we chroot, namespace and do other funky stuff.
	my $nobody_uid = getpwnam("nobody");
	die "Error, can't find a uid for 'nobody'. Replace with someone who exists" unless $nobody_uid;

  my $exitcode = $namespace->run(code => sub {
    delete $SIG{CHLD};
    select(STDERR);
    $|++;
    select(STDOUT);
    $|++;
    binmode STDOUT, ":encoding(utf8)"; # Enable utf8 output.
    binmode STDERR, ":encoding(utf8)"; # Enable utf8 output.

    # This should end up actually reading from the IO::Async::Process stdin filehandle eventually
    # but I'm not ready to setup the protocol for that yet.
    # redirect STDIN to /dev/null, to avoid warnings in convoluted cases.
    close(STDIN);
    open STDIN, '<', '/dev/null' or die "Can't open /dev/null: $!";

    my $tmpfs_size = config->sandbox->tmpfs_size // "16m"; # / # fix syntax in kate

    my $jail_path = $work_path . "/jail";

    my $jail_home = $jail_path . (config->sandbox->home_dir // "/home"); # " # ditto
    my $jail_tmp  = "$jail_path/tmp";

    mount("tmpfs", $work_path, "tmpfs", 0, {size => $tmpfs_size});
    mount("tmpfs", $work_path, "tmpfs", MS_PRIVATE, {size => $tmpfs_size});

    path($jail_path)->mkpath();
    # put this all in a tmpfs, so that we don't pollute anywhere if possible.  TODO this should be overlayfs!
    path("$work_path/tmp/.overlayfs")->mkpath();
    # setup /tmp
    path($jail_tmp)->mkpath;

    umask(0);
    for my $bind (@binds) {
      my $src = _rel2abs($bind->{src});
      my $target = $bind->{target};

      if ($target eq config->sandbox->home_dir) {
        # We need to use overlayfs to bring the homedir in, so it's writable inside
        # without being writable to the outside

        $target = $work_path . "/home";
      } else {
        $target = $jail_path . $target;
      }

      path($target)->mkpath;

      eval {
        mount($src, $target, undef, MS_BIND|MS_PRIVATE|MS_RDONLY, undef)
      };
      if ($@) {
        die "Failed to mount ", $src, " to ", $target, ": $@\n";
      }
    }

    my $overlay_opts = {upperdir => $jail_tmp, lowerdir => "$work_path/home", workdir => "$work_path/tmp/.overlayfs"};
    path("$work_path/home")->mkpath; # Make sure it's made, even if it's not being mounted
    path($jail_home)->mkpath;
    mount("overlay", $jail_home, "overlay", 0, $overlay_opts);

    # Setup /dev
    path("$jail_path/dev")->mkpath;
    for my $dev_name (keys config->sandbox->devices->%*) {
      my ($type, $major, $minor) = config->sandbox->devices->$dev_name->@*;

      _exit(213) unless $type eq 'c';
      mknod("$jail_path/dev/$dev_name", S_IFCHR|0666, makedev($major, $minor));
    }