#!/usr/bin/env bash
#
# Script to corrupt a linux ext3/4 partition
#
# SPDX-License-Identifier: MIT

# Check usage
if [ "$#" != "1" ]
then
 echo "Usage: $0 /dev/sdb1"
 exit 1
fi

# Check if the invoking user is root
if [ "$EUID" != "0" ]
then
 echo 'Please run this script as a root privileged user'
 exit 2
fi

# Find mount and check it's actually mounted
MOUNT=$(mount | grep "$1" | awk '{print $3}')
if [ -z "$MOUNT" ]
then
 echo "$1 is not mounted, please mount it first"
 exit 3
fi

# Find journal inode and block size from device
DUMP=$(dumpe2fs "$1" 2>&1 | grep -E -i "^Journal\ inode|^Block\ size")
INODE=$(echo "$DUMP" | grep inode | awk '{print $3}')
SIZE=$(echo "$DUMP" | grep size | awk '{print $3}')

# If foo exists delete it, then create it
if [ -e "$MOUNT/foo" ]
then
 rm -f "$MOUNT/foo"
fi
touch "$MOUNT/foo"
sync

# Find block location of the journal
echo "stat <${INODE}>" > debugfs.cmd
BLOCK=$(debugfs -f debugfs.cmd "$1" 2>&1 | sed -nr 's/\([0-9-]+\):\ ?([0-9]+)-[0-9].+/\1/p')
rm -f debugfs.cmd

# Overwrite the first block of the journal
# shellcheck disable=SC2086
dd if=/dev/urandom of="$1" bs=$SIZE count=1 skip=$BLOCK > /dev/null 2>&1
sync

# Attempt to write to foo, and then remove it, at least one should fail
rm -f "$MOUNT/foo"
echo foo > "$MOUNT/bar"

# Exit
exit 0