#!/usr/bin/env bash
#
# JbTecWiz Support Centre -- generated fix script
#
# Fault : "Permission denied (publickey)"
# Fix   : Fix the server side
# Source: https://jbtecwiz.com/support/lnx-ssh-publickey
#
# Run as     : Console or another session on the server
# Expect     : 20 minutes
# Risk       : medium
# Reversible : yes
#
# WHEN THIS IS THE RIGHT FIX
#   You have another way in. Keep that session open until SSH is confirmed
#   working from a second terminal.
#
# HOW TO UNDO IT
#   Restore the previous sshd_config and restart. Keep the working session
#   open until the new one is proven.
#
# 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

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 "  "Permission denied (publickey)""
echo "  Fix the server side"
echo
echo "  Risk: medium   Reversible   20 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 'Read the server'\''s own reason for refusing.' '' cmd 'sudo journalctl -u ssh -u sshd -n 50 --no-pager'; then
  sudo journalctl -u ssh -u sshd -n 50 --no-pager
  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 'Fix permissions. sshd refuses group- or world-writable paths anywhere in the chain.' 'This is the cause the overwhelming majority of the time, and sshd logs it as '\''Authentication refused: bad ownership or modes'\''.' cmd 'sudo chown -R user:user /home/user/.ssh' 'sudo chmod 700 /home/user/.ssh' 'sudo chmod 600 /home/user/.ssh/authorized_keys' 'sudo chmod 755 /home/user'; then
  sudo chown -R user:user /home/user/.ssh
  sudo chmod 700 /home/user/.ssh
  sudo chmod 600 /home/user/.ssh/authorized_keys
  sudo chmod 755 /home/user
  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 'On RHEL, Rocky, Alma or Fedora, restore the SELinux context.' 'A file created by copying rather than by ssh-copy-id often ends up with the wrong context, and sshd cannot read it even though the mode bits look right.' cmd 'sudo restorecon -Rv /home/user/.ssh'; then
  sudo restorecon -Rv /home/user/.ssh
  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 'Confirm the daemon config allows key auth and check for a Match block overriding it.' 'sshd -T prints the effective configuration after all includes and defaults, which is not always what the config file appears to say.' cmd 'sudo sshd -T | grep -Ei '\''pubkeyauthentication|authorizedkeysfile|permitrootlogin|allowusers|allowgroups'\'''; then
  sudo sshd -T | grep -Ei 'pubkeyauthentication|authorizedkeysfile|permitrootlogin|allowusers|allowgroups'
  if [ $? -ne 0 ]; then
    failed=$((failed+1))
    echo "  Step 4 failed. The rest of the fix may depend on it." >&2
  fi
fi

if step 5 'Test the config before restarting, so a typo cannot lock everyone out.' '' cmd 'sudo sshd -t && sudo systemctl restart ssh'; then
  sudo sshd -t && sudo systemctl restart ssh
  if [ $? -ne 0 ]; then
    failed=$((failed+1))
    echo "  Step 5 failed. The rest of the fix may depend on it." >&2
  fi
fi

rule "  Confirm it worked"
prose 'A brand new SSH session connects while the original one is still open.'
if [ "$DRYRUN" = "0" ]; then
  ssh -o IdentitiesOnly=yes -i ~/.ssh/id_ed25519 user@host 'echo connected'
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-ssh-publickey"
else
  echo "  Finished."
fi
echo
prose 'To undo: Restore the previous sshd_config and restart. Keep the working session open until the new one is proven.'
rule