msantos/sredird

RFC 2217 network serial port redirector

SYNOPSIS

sredird option loglevel device [pollinginterval]

DESCRIPTION

sredird is:

• an RFC 2217 compliant serial port redirector

• maps a network port to a serial device: serial port parameters are configured using an extension to the telnet protocol

• runs under a UCSPI or other inetd style service such as systemd for process level isolation

• restricts process operations using seccomp(2), pledge(2), capsicum(4) or setrlimit(2)

sredird can be used as a minimal serial console server on a device like a raspberry pi zero w.

A picocom branch supports RFC 2217.

This version of sredird is a fork of sredird 2.2.1-1.1 taken from Ubuntu 16.04 (there does not seem to be a canonical source repository for this project). sredird 2.2.1-1.1 is the last C version: later versions of sredird (2.2.1-2) switched to C++.

EXAMPLES

apt install daemontools

• unixexec
• hexlog
• tscat

Here is my setup:

• raspberry pi zero w acting as a console server for other raspberry pi's
• example of setup using unixexec
• TODO: show example xmppbot

SUBSYSTEM=="tty", ATTRS{idProduct}=="6001", ATTRS{idVendor}=="0403", ATTRS{serial}=="FTG9GBNY", SYMLINK+="console@getpid"
SUBSYSTEM=="tty", ATTRS{idProduct}=="2008", ATTRS{idVendor}=="0557", SYMLINK+="console@switch"
SUBSYSTEM=="tty", ATTRS{idProduct}=="2303", ATTRS{idVendor}=="067b", ATTRS{version}==" 1.10", SYMLINK+="console@getsid"
SUBSYSTEM=="tty", ATTRS{idProduct}=="2303", ATTRS{idVendor}=="067b", ATTRS{version}==" 2.00", SYMLINK+="console@sigquit"

service run

• service/console@getpid/run

#!/bin/bash

umask 077

mkdir -p /tmp/sredird

exec 2>&1
exec unixexec /tmp/sredird/console@getpid \
  hexlog none \
  sredird -t 900 5 /dev/console@getpid

service run log

• service/console@getpid/log/run

#!/bin/bash

set -o errexit
set -o nounset
set -o pipefail

SERVICE="$(basename $(dirname $PWD))"
exec tscat -o 2 "$SERVICE"

USAGE

loglevel : numeric syslog level, see syslog(3)

device : serial device

pollinginterval : Poll interval is in milliseconds, default is 100, 0 means no polling

OPTIONS

-i, --cisco-compatibility : indicates Cisco IOS Bug compatibility

-t, --timeout seconds :set inactivity timeout

BUILDING

make

# selecting process restrictions
RESTRICT_PROCESS=seccomp make clean all

# rlimit
RESTRICT_PROCESS=rlimit make clean all

# disable process restrictions
RESTRICT_PROCESS=null make clean all

#### using musl
# sudo apt install musl-dev musl-tools

RESTRICT_PROCESS=rlimit ./musl-make clean all

## linux seccomp sandbox: requires kernel headers

# clone the kernel headers somewhere
cd /path/to/dir
git clone https://github.com/sabotage-linux/kernel-headers.git

# then compile
MUSL_INCLUDE=/path/to/dir ./musl-make clean all

ALTERNATIVES