#!/usr/bin/env bash
#
# JbTecWiz Support Centre -- generated fix script
#
# Fault : A firewall change has no effect, or locks the machine out
# Fix   : Use ufw without locking yourself out
# Source: https://jbtecwiz.com/support/lnx-net-firewalld
#
# Run as     : Root shell
# Expect     : 15 minutes
# Risk       : high
# Reversible : yes
#
# WHEN THIS IS THE RIGHT FIX
#   ufw is the manager. Enabling it with a default deny and no SSH rule is
#   the classic lockout.
#
# HOW TO UNDO IT
#   sudo ufw disable removes enforcement entirely, or delete a rule by its
#   number with sudo ufw delete N.
#
# Walks the fix one step at a time and asks before each. Steps with no
# command are yours to do -- it prints those and waits. DRYRUN=1 prints
# without executing; UNATTENDED=1 does not ask.
#
# --------------------------------------------------------------------
# NO WARRANTY - USE AT YOUR OWN RISK
#
# This script is provided by JbTecWiz as-is and with no warranty of any
# kind, express or implied. You run it entirely at your own risk.
#
# JbTecWiz accepts no liability for any loss or damage arising from its
# use, including but not limited to data loss, downtime, or configuration
# changes that turn out to be wrong for your system.
#
# You are responsible for reading this script before running it, for
# satisfying yourself that it suits the machine in front of you, and for
# having a working backup first. Some steps cannot be undone.
# --------------------------------------------------------------------

set -uo pipefail
DRYRUN="${DRYRUN:-0}"
UNATTENDED="${UNATTENDED:-0}"
failed=0

if [ "$(id -u)" -ne 0 ]; then
  echo "  This fix is documented as needing root. Re-run with sudo." >&2
  exit 3
fi

rule() { printf "\n%s\n" "$(printf '-%.0s' $(seq 1 70))"; if [ $# -gt 0 ]; then echo "$1"; fi; }
prose() { echo "$1" | fold -s -w 74 | sed "s/^/  /"; }

# Returns 0 when the caller should run the command, 1 when it should not.
# A manual step always returns 1 -- there is nothing for the caller to run.
step() {  # step <n> <do> <why> <manual|cmd> [command lines...]
  local n="$1" dotext="$2" why="$3" mode="$4"; shift 4
  rule "  Step $n of 5"
  prose "$dotext"
  if [ -n "$why" ]; then echo; prose "$why"; fi
  if [ "$mode" = "manual" ]; then
    echo; echo "  -> Do this yourself, then press Enter to carry on."
    if [ "$UNATTENDED" = "0" ] && [ "$DRYRUN" = "0" ]; then read -r _; fi
    return 1
  fi
  echo; printf "    %s\n" "$@"; echo
  if [ "$DRYRUN" = "1" ]; then echo "  (dry run -- not executed)"; return 1; fi
  if [ "$UNATTENDED" = "0" ]; then
    read -r -p "  Run this step? [Y]es / [S]kip / [Q]uit " a
    case "$a" in
      [Qq]*) echo "  Stopped at your request."; exit 0 ;;
      [Ss]*) echo "  Skipped."; return 1 ;;
    esac
  fi
  return 0
}

rule
echo "  A firewall change has no effect, or locks the machine out"
echo "  Use ufw without locking yourself out"
echo
echo "  Risk: high   Reversible   15 minutes"
echo
prose 'No warranty. Use at your own risk - JbTecWiz accepts no liability. Read it before you run it, and have a backup.'
rule
echo
if [ "$UNATTENDED" = "0" ] && [ "$DRYRUN" = "0" ]; then
  read -r -p "  Ready? [y/N] " go
  case "$go" in [Yy]*) ;; *) echo "  Nothing was changed."; exit 0;; esac
fi

if step 1 'Add the SSH rule before enabling anything. This order is not optional on a remote machine.' 'ufw enable applies a default deny immediately. Enabling first and adding SSH second means the second command never runs, because the session is already gone.' cmd 'sudo ufw allow OpenSSH' 'sudo ufw status verbose'; then
  sudo ufw allow OpenSSH
  sudo ufw status verbose
  if [ $? -ne 0 ]; then
    failed=$((failed+1))
    echo "  Step 1 failed. The rest of the fix may depend on it." >&2
  fi
fi

if step 2 'Enable it.' '' cmd 'sudo ufw enable'; then
  sudo ufw enable
  if [ $? -ne 0 ]; then
    failed=$((failed+1))
    echo "  Step 2 failed. The rest of the fix may depend on it." >&2
  fi
fi

if step 3 'Add the rules you need, with a source restriction where it makes sense.' '' cmd 'sudo ufw allow from 192.168.1.0/24 to any port 3306 proto tcp' 'sudo ufw allow 443/tcp'; then
  sudo ufw allow from 192.168.1.0/24 to any port 3306 proto tcp
  sudo ufw allow 443/tcp
  if [ $? -ne 0 ]; then
    failed=$((failed+1))
    echo "  Step 3 failed. The rest of the fix may depend on it." >&2
  fi
fi

if step 4 'Check the numbered list before deleting anything.' '' cmd 'sudo ufw status numbered'; then
  sudo ufw status numbered
  if [ $? -ne 0 ]; then
    failed=$((failed+1))
    echo "  Step 4 failed. The rest of the fix may depend on it." >&2
  fi
fi

step 5 'Remember that Docker publishes ports by writing directly to the kernel tables and bypasses ufw entirely -- a container published with -p is reachable regardless of what ufw says.' 'This surprises people badly. A machine that looks locked down by ufw status can have a database exposed to the internet by one docker run command.' manual || true

rule "  Confirm it worked"
prose 'ufw status shows the intended rules and a new SSH session still connects.'
if [ "$DRYRUN" = "0" ]; then
  sudo ufw status verbose
fi

rule
if [ "$failed" -gt 0 ]; then
  echo "  Finished with $failed failed step(s)."
  echo "  Read the full write-up at https://jbtecwiz.com/support/lnx-net-firewalld"
else
  echo "  Finished."
fi
echo
prose 'To undo: sudo ufw disable removes enforcement entirely, or delete a rule by its number with sudo ufw delete N.'
rule