#!/bin/sh
#
#    Copyright (C) 2009-2010 Canonical Ltd.
#
#    This program is free software; you can redistribute it and/or
#    modify it under the terms of version 2 of the GNU General Public
#    License as published by the Free Software Foundation.
#
#    This program is distributed in the hope that it will be useful,
#    but WITHOUT ANY WARRANTY; without even the implied warranty of
#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#    GNU General Public License for more details.
#
#    You should have received a copy of the GNU General Public License
#    along with this program; if not, contact Canonical, Ltd.
#

set -e

help() {
    cat <<EOM
USAGE: aa-decode [OPTIONS] <encoded string>
Decode a hex-encoded string to ASCII. It will also take an audit log on
standard input and convert any hex-encoded AppArmor log entries and display
them on standard output.

OPTIONS:
  --help	display this help

EXAMPLES:
$ aa-decode 2F746D702F666F6F20626172
Decoded: /tmp/foo bar
$ cat /var/log/kern.log | aa-decode
... denied_mask="r::" fsuid=1000 ouid=1000 name=/tmp/foo bar
EOM
}

decode() {
    decoded=`perl -le "\\$s = '$1' ; print pack 'H*', \\$s"`
    echo "$decoded"
}

if [ "$1" = "-h" ] || [ "$1" = "--help" ]; then
    help
    exit
fi

# if have an argument, then use it, otherwise process stdin
if [ -n "$1" ]; then
    e=`echo "$1" | tr -s '[:lower:]' '[:upper:]'`
    if ! echo "$e" | egrep -q "^[0-9A-F]+$" ; then
        echo "String should only contain hex characters (0-9, a-f, A-F)"
        return
    fi

    d=`decode $e`
    if [ -z "$d" ]; then
        echo "Could not decode string"
        exit 1
    fi

    echo "Decoded: $d"
    exit 0
fi

# For now just look at 'name=...' which is usually the last in the log entry,
# so validate input against this and output based on it.
# TODO: better handle other cases too
egrep ' name=2[fF][0-9a-fA-F]*$' | while read line ; do
    e=`echo "$line" | sed 's/.* name=\(.*\)/\\1/g' | tr -s '[:lower:]' '[:upper:]'`
    d=`decode $e`
    echo -n "$line" | sed "s/\(.*\) name=.*/\1 name=/g"
    echo "'$d'"
done