xcage

#!/bin/sh

# Copyright (C)2011 Laurence Tratt <http://tratt.net/laurie/>
#
# Permission is hereby granted, free of charge, to any person obtaining a
# copy of this software and associated documentation files (the "Software"),
# to deal in the Software without restriction, including without limitation
# the rights to use, copy, modify, merge, publish, distribute, sublicense,
# and/or sell copies of the Software, and to permit persons to whom the
# Software is furnished to do so, subject to the following conditions:
# 
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
# 
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
# THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
# FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
# DEALINGS IN THE SOFTWARE.


# http://tratt.net/laurie/src/xcage/
#
# This utility runs an Xnest (i.e. X Windows-inside-X Windows), and inside
# that executes a command as another user. This allows one to conveniently
# run an X Windows "jail" or "sandbox" where programs can execute without
# impacting upon one's normal user account.
#
# This utility requires sudo to work appropriately.
#
# This utility was inspired by xsandbox:
#   http://shoestringfoundation.org/cgi-bin/blosxom.cgi/2005/11/16


which sudo 2> /dev/null > /dev/null
if [ $? -eq 0 ]; then
    sudo="sudo"
else
    which doas 2> /dev/null > /dev/null
    if [ $? -eq 0 ]; then
        sudo="doas"
    else
        sudo=""
    fi
fi
user=""
cmd=""
xnest_args=""
if [ -f ~/.xcagerc ]; then
    . ~/.xcagerc
fi

ae=0
while getopts ":hc:u:" f
do
    case "$f" in
        c)   cmd="$OPTARG";;
        u)   user="$OPTARG";;
        h)   ae=1; break;;
        s)   sudo="$OPTARG";;
        [?]) ae=2; break;;
    esac
done

if [ "$sudo" == "" ]; then
    echo "No sudo-esque command specified." > /dev/stderr
    exit 1
fi

if [[ "X$user" = "X" || "X$cmd" = "X" ]]; then
    ae=2
fi

if [ $ae -gt 0 ]; then
    echo "Usage: xcage [-c <cmd>] [-u <user>] [-- <arguments for Xnest>]" >&2
    if [ $ae -eq 1 ]; then
        exit 0
    else
        exit 1
    fi
fi

shift $((OPTIND-1))

function die {
    echo $1
    exit $2
}

# Setup the appropriate authorisation - we use two files to ensure that only
# the current user and $user can access the X authorisation files.

which jot > /dev/null 2> /dev/null
if [ $? -eq 0 ]; then
    hexkey=`jot -p 8 -s "" -r -w "%.2x" 16 0 255`
else
    hexkey=`head -c 16 < /dev/urandom | hexdump -v -e '/1 "%02x"'` ||
      die "Can't create hex key" $?
fi
umask 022
xauthmef=`mktemp` ||
  die "Can't create temporary file" $?
trap "rm -f $xauthmef" 0 1 2 3 13 15
xauthof=`$sudo su -l $user -c mktemp` ||
  die "Can't create temporary file as user $user" $?
trap "rm -f $xauthmef; $sudo -u $user rm -f $xauthof" 0 1 2 3 13 15

xauth -i -f $xauthmef add :1.0 . $hexkey ||
  exit $?
xauth -i -f $xauthmef nextract - :1.0 |
  $sudo -u $user xauth -f $xauthof nmerge - ||
  exit $?

# Run Xnest using the override args or not, as appropriate.

if [ $# -eq 0 ]; then
    Xnest :1 -auth $xauthmef -sss $xnest_args &
else
    Xnest :1 -auth $xauthmef -sss $* &
fi

# Run the specified command $cmd as $user.

$sudo su -l $user -c "XAUTHORITY=$xauthof DISPLAY=:1.0 $cmd"

# Sometimes Xnest exits unexpectedly, and there may be other Xnests running
# in the system, so we're careful only to kill an Xnest process (should
# there be any running) if it was started by this script.

pkill -P $$ Xnest