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#!/usr/bin/env perl
# SPDX-License-Identifier: GPL-2.0-or-later
#
# Copyright (C) 2018 Red Hat, Inc.
#
# $ perldoc modemu.pl for eye-pleasing view of the manual:
=head1 NAME
modemu.pl - emulate a serial modem
=head1 SYNOPSIS
modemu.pl [<name>] [-- <pppd> ...]
=head1 DESCRIPTION
B<modemu.pl> opens a PTY, links the slave side to F</dev> and announces a
fake kobject via netlink as if it were a real serial device, so that
ModemManager picks it up.
Then it answers to a very basic subset of AT commands, sufficient making
ModemManager recognize it as a 3GPP capable modem registered to a network.
Upon receiving the dial (ATD) command, it spawns C<pppd> so that
NetworkManager can establish a connection.
B<modemu.pl> needs superuser privileges to be able to announce a kobject
and create a F</dev> node.
=head1 OPTIONS
=over 4
=item B<< <name> >>
Create a modem of given name. Links it to F<< /dev/<name> >>.
Defaults to I<modemu>.
=item B<< <pppd> >>
Specifies extra arguments to be prepended before C<pppd> to the default
set of I<nodetach notty local logfd 2 nopersist>.
Defaults to I<pppd dump debug 172.31.82.1:172.31.82.2>.
=back
=cut
use strict;
use warnings;
use Errno;
use Socket;
use IO::Pty;
use IO::Handle;
use constant AF_NETLINK => 16;
use constant NETLINK_KOBJECT_UEVENT => 15;
# This allows us to use buffered read for lines from ModemManager
# despite not ending with \n
IO::Handle->input_record_separator ("\r");
# Parse command line arguments
my $name;
my @pppd = qw/pppd dump debug 172.31.82.1:172.31.82.2/;
while (@ARGV) {
$_ = shift @ARGV;
if ($_ eq '--') {
@pppd = @ARGV;
last;
} else {
die "Extra argument: '$_'" if $name;
$name = $_;
}
};
$name ||= 'modemu';
socket my $fd, AF_NETLINK, SOCK_RAW, NETLINK_KOBJECT_UEVENT
or die "Can't create a netlink socket: $!";
my $seqnum = 666;
sub send_netlink
{
my %props = (@_, SEQNUM => $seqnum++);
my $props = join '', map { $_, '=', $props{$_}, "\0" } keys %props;
my $head = pack 'a8NLLLNLLL',
# signature + magic
'libudev',
0xfeedcafe,
# 40 octets is the length of this header
40, 40, 40 + length ($props),
# Digest::MurmurHash2::Neutral::murmur_hash2_neutral("tty")
0x8afa90c8,
0x00000000,
0x00040002,
0x00008010;
$! = undef;
send $fd, "$head$props", 0, pack 'SSLL', AF_NETLINK, 0, 0, 0x0002;
# RHEL 7 kernel responds ECONNREFUSED even thoguh the sendto succeeded. Weird.
die "Can't send a netlink message: $!" if $! and not $!{ECONNREFUSED};
}
my $devpath = '/devices/pci0000:00/0000:00:00.0';
unless (-d "/sys/$devpath") {
# Create a virtual device. Older ModemManager likes a hotpluggable bus
# (USB, PCI), but there's none on an IBM POWER lpar...
warn "No PCI bus to use for parent. Don't expect this to work with ModemManager 1.6";
$devpath = '/devices/virtual';
}
my %props = (
DEVPATH => "$devpath/$name",
SUBSYSTEM => 'tty',
DEVNAME => "/dev/$name",
# Whitelisting that works for both ModemManager 1.6 and 1.8
ID_MM_CANDIDATE => '1',
ID_MM_DEVICE_PROCESS => '1',
);
sub cleanup
{
unlink "/dev/$name";
send_netlink (ACTION => 'remove', %props) if $fd;
}
# Ensure we clean up before and after.
END { cleanup };
$SIG{INT} = sub { cleanup; die };
$SIG{TERM} = sub { cleanup; die };
cleanup;
my $pty = new IO::Pty;
my $ptyname = ttyname $pty;
symlink $ptyname, "/dev/$name" or die "Can't create /dev/$name: $!";
send_netlink (ACTION => 'add', %props);
while (<$pty>) {
chomp;
if (/^AT$/ or /^ATE0$/ or /^ATV1$/ or /^AT\+CMEE=1$/ or /^ATX4$/ or /^AT&C1$/ or /^ATZ$/) {
# Standard Hayes commands that are basically used to
# ensure the modem is in a known state. Accept them all.
print $pty "\r\n";
print $pty "OK\r\n";
} elsif (/^AT\+CPIN\?$/) {
# PIN unlocked. Required.
print $pty "\r\n";
print $pty "+CPIN:READY\r\n";
print $pty "\r\n";
print $pty "OK\r\n";
} elsif (/^AT\+COPS=0$/) {
# Select access technology (we just accept 0=automatic)
print $pty "\r\n";
print $pty "OK\r\n";
} elsif (/^AT\+CGREG\?$/) {
# 3GPP Registration status.
print $pty "\r\n";
print $pty "+CGREG: 0,1\r\n";
print $pty "\r\n";
print $pty "OK\r\n";
} elsif (/^AT\+CGDCONT=\?$/) {
# Get supported PDP contexts
print $pty "\r\n";
print $pty "+CGDCONT: (1-10),(\"IP\"),,,(0-1),(0-1)\r\n";
print $pty "+CGDCONT: (1-10),(\"IPV6\"),,,(0-1),(0-1)\r\n";
print $pty "OK\r\n";
} elsif (/^AT\+CGACT=0,1$/) {
# Activate a PDP context
print $pty "\r\n";
print $pty "OK\r\n";
} elsif (/^AT\+CGDCONT=1,"(.*)","(.*)"$/) {
# Set PDP context. We accept any.
print $pty "\r\n";
print $pty "OK\r\n";
} elsif (/^ATD/) {
print $pty "\r\n";
print $pty "CONNECT 28800000\r\n";
my $ppp = fork;
die "Can't fork: $!" unless defined $ppp;
if ($ppp == 0) {
close STDIN;
close STDOUT;
open STDIN, '<&', $pty or die "Can't dup pty to a pppd stdin: $!";
open STDOUT, '>&', $pty or die "Can't dup pty to a pppd stdout: $!";
close $pty;
exec @pppd, qw/nodetach notty local logfd 2 nopersist/;
die "Can't exec pppd: $!";
}
waitpid $ppp, 0;
} else {
print $pty "\r\n";
print $pty "ERROR\r\n";
}
}
=head1 EXAMPLES
=over
=item B<modemu.pl>
Just create a modem named I<modemu>, with the default PPP arguments.
=item B<modemu.pl ttyS666>
Same as above, just name the modem I<ttyS666>.
=item B<modemu.pl -- unshare --net pppd 172.31.82.1:172.31.82.2>
Avoid polluting the namespace with the modem end of PPP connection.
=item B<modemu.pl -- pppd 10.0.0.1:10.0.0.2>
Override the C<pppd> parameters: no debug logging and different set of
addresses.
=item B<modemu.pl mymodem -- pppd 10.0.0.1:10.0.0.2>
Same as above, with a modem name different from default.
=back
=head1 BUGS
Only works on machines with a PCI bus. ModemManager is picky about platform
devices and accepts PCI and USB buses easily. Which is why pretent to have
our tty on the PCI root device.
Terminates after a single PPP session. C<pppd> seems to hang up the PTY.
=head1 SEE ALSO
L<ModemManager(8)>, L<pppd(8)>
=head1 COPYRIGHT
Copyright (C) 2018 Lubomir Rintel
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
=head1 AUTHOR
Lubomir Rintel C<lkundrak@v3.sk>
=cut
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