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A script that uses redsocks to build a system-wide OpenSSH SOCKS proxy.
#!/bin/sh
########################################################################
#
# Usage: via-ssh.sh [-v] [-d] [USER@]SERVER[:PORT]
#
# -v Provide verbose output.
# -d Send all UDP on the DNS port 53 to 127.0.0.1.
# USER User name to use for SSH; default is current user.
# SERVER Server to use for SSH.
# PORT Port to use for SSH; default is 22.
#
# This experimental script illustrates the use redsocks to build a
# transparent SOCKS proxy that forces all TCP traffic to be routed
# over an encrypted SSH channel to a server. To use this script, you
# must be able to execute as root on the local computer, and you must
# be using OpenSSH and iptables.
#
# This script prints three IP addresses. The first is the externally
# visible IP address when you start the script. The second is the IP
# address after the script has activated the proxy; that address
# should correspond to your SSH server. After you use Control-C to
# terminate the proxy, the script will terminate the connection to
# your SSH server and then print a final IP address, which should
# match the first. If you use the "-v" (verbose) option, the script
# will also print the redsocks log and each of the major commands that
# it executes.
#
# The proxy that this script creates only carries the TCP protocol.
# In particular, it does not carry the UDP (e.g., DNS, NTP) and ICMP
# (e.g., ping, traceroute) protocols. You can use the proxy DNS
# server pdnsd with the "-mto" option to force TCP to be used for all
# DNS queries. If you pass the "-d" option to this script, it will
# enable an iptables rule that redirects all UDP traffic on the DNS
# port (53) to the DNS server that is listening on 127.0.0.1:53, which
# should be pdnsd or equivalent.
#
# CAUTION: Standard DNS queries over UDP do not travel on the
# encrypted channel to your server and can be observed by a
# local network monitor. Thus it is possible for a network
# monitor to observe the locations to which your TCP traffic
# is sent (but not the content of that traffic). If the
# destinations of your TCP traffic are sensitive, do not use
# this script unless you use pdnsd or some other DNS proxy to
# convert DNS queries from UDP to TCP so those queries are
# encrypted.
#
# ------------------------------------------------------------------------
#
# The script via-ssh.sh was written in 2011 by vitex from
# forum.tinycorelinux.net.
#
# To the extent possible under law, the author(s) have dedicated all
# copyright and related and neighboring rights to this software to the
# public domain worldwide. This software is distributed without any
# warranty.
#
# See http://creativecommons.org/publicdomain/zero/1.0/ for a copy of
# the CC0 Public Domain Dedication under which this work is
# distributed.
#
########################################################################
# Print usage information if there are no arguments on the command line.
[ "$#" = "0" ] &&
echo 'Usage: via-ssh.sh [ -v ] [ -d ] [USER@]SERVER[:PORT]' && exit 1
# Process the command line parameters.
while [ "$#" != '0' ] ; do
case "$1" in
-v) VERBOSE=1 ; shift ;;
-d) DNS=1 ; shift ;;
*) SSH_PORT=${1##*:}
SSH_USER_SERVER=${1%%:*}
[ "$SSH_USER_SERVER" = "$SSH_PORT" ] && SSH_PORT=22
shift ;;
esac
done
# Define various configuration parameters.
SOCKS_PORT=12345
REDSOCKS_TCP_PORT=$(expr $SOCKS_PORT + 1)
TMP=/tmp/via-ssh.sh ; mkdir -p $TMP
REDSOCKS_LOG=$TMP/redsocks.log
REDSOCKS_CONF=$TMP/redsocks.conf
# Verify that OpenSSH is installed.
ssh -V 2>&1 | grep -q OpenSSH ||
{ echo === You must install OpenSSH. ; exit 1 ; }
# Verify that iptables is installed.
sudo which iptables 1>/dev/null ||
{ echo === You must install iptables. ; exit 1 ; }
# Verify that redsocks is installed.
which redsocks 1>/dev/null ||
{ echo === You must install redsocks. ; exit 1 ; }
# Execute the command passed on the command line; print it if -v was specified.
CMD () {
[ -n "$VERBOSE" ] && echo "+++ $@"
"$@"
}
# Print the current IP address.
IPADDRESS () {
local IP=$(wget -qO- http://checkip.dyndns.com | grep -o '[0-9.]*')
echo $IP
}
# Activate OpenSSH, redsocks, and the iptables rules.
ACTIVATE () {
# Start the OpenSSH SOCKS proxy.
CMD ssh -fN -D $SOCKS_PORT -p $SSH_PORT $SSH_USER_SERVER || exit $?
# Start redsocks.
: >$REDSOCKS_LOG
CMD redsocks -c $REDSOCKS_CONF -p /dev/null
# Use iptables to direct all TCP traffic except 127.0.0.0/8 through the proxy.
CMD sudo iptables -t nat -N REDSOCKS
CMD sudo iptables -t nat -A REDSOCKS -d 127.0.0.0/8 -j RETURN
CMD sudo iptables -t nat -A REDSOCKS \
-p tcp -j REDIRECT --to-ports $REDSOCKS_TCP_PORT
CMD sudo iptables -t nat -A OUTPUT -p tcp -j REDSOCKS
# If -d is specified, direct UDP DNS queries to 127.0.0.1:53, which should
# be pdnsd (or equivalent) configured to convert UDP queries to TCP.
[ -n "$DNS" ] && CMD sudo iptables -t nat -A OUTPUT -p udp --dport 53 \
-j REDIRECT --to-ports 53
}
# Deactivate OpenSSH, redsocks, and the iptables rules.
DEACTIVATE () {
# Terminate the redsocks and ssh processes.
CMD pkill -f "redsocks -c $REDSOCKS_CONF -p /dev/null"
CMD pkill -f "ssh .*-D $SOCKS_PORT"
# Remove the iptables rules that were added to create the proxy.
sudo iptables -t nat -L -n |
egrep -q 'REDIRECT .* udp .* dpt:53 .* ports 53' &&
CMD sudo iptables -t nat -D OUTPUT -p udp --dport 53 \
-j REDIRECT --to-ports 53
CMD sudo iptables -t nat -D OUTPUT -p tcp -j REDSOCKS
CMD sudo iptables -t nat -F REDSOCKS
CMD sudo iptables -t nat -X REDSOCKS
}
# Define the trap handler that is used during UP processing.
QUIT () {
# Clear the trap handlers.
trap - INT TERM
# Clean up.
DEACTIVATE 1>/dev/null 2>&1
# Terminate.
exit 0
}
# Bring up the transparent proxy.
UP () {
# Set a trap handler in case the user uses Control-C or KILL.
trap QUIT INT TERM
# Silently clean up in case some part of the previous execution failed.
DEACTIVATE 1>/dev/null 2>&1
# Build the redsocks configuration file.
cat >$REDSOCKS_CONF <<EOF
base {
log_info = on;
log = "file:$REDSOCKS_LOG";
daemon = on;
redirector = iptables;
}
redsocks {
local_ip = 127.0.0.1;
local_port = $REDSOCKS_TCP_PORT;
ip = 127.0.0.1;
port = $SOCKS_PORT;
type = socks5;
}
EOF
# Print the current IP address, activate the proxy, and then print
# the new IP address, which should be different.
echo ===
echo === $(IPADDRESS) is your initial IP address.
[ -n "$VERBOSE" ] && echo ===
ACTIVATE
echo ===
echo === $(IPADDRESS) is your IP address after the proxy is activated.
echo ===
echo === Use Control-C to quit.
echo ===
}
# Bring down the transparent proxy.
DOWN () {
# Disable the special trap handling.
trap - 0 INT TERM
echo
# Deactivate the proxy.
DEACTIVATE
# Print the current IP address, which should be the same as the original one.
echo ===
echo === $(IPADDRESS) is your IP address after the proxy is deactivated.
echo ===
# Terminate this script.
exit 0
}
#----------------------------------------------------------------------------
# Start the transparent proxy.
UP
# Ensure that DOWN is executed following a normal exit, a Control-C, or TERM.
trap DOWN 0 INT TERM
# Wait for Control-C; display the redsocks log if in verbose mode.
if [ -n "$VERBOSE" ] ; then
tail -f $REDSOCKS_LOG
else
while true ; do sleep 10 ; done
fi
exit 0
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