Make Netbird umount all of the NFS mounts which point to other devices on the Netbird mesh network when the Netbird service stops

mount-netbird-nfs.bash

#!/bin/bash

if [ -z "$1" -o "$1" = "mount" ]; then
  action=mount
elif [ "$1" = "umount" ]; then
  action=umount
else
  echo "missing action"
  exit 1
fi

if [ "$EUID" -ne 0 ]
  then echo "Please run as root"
  exit 1
fi

function in_subnet {
    # Determine whether IP address is in the specified subnet.
    #
    # Args:
    #   sub: Subnet, in CIDR notation.
    #   ip: IP address to check.
    #
    # Returns:
    #   1|0
    #
    # https://unix.stackexchange.com/a/465372/22701
    local ip ip_a mask netmask sub sub_ip rval start end

    # Define bitmask.
    local readonly BITMASK=0xFFFFFFFF

    # Read arguments.
    IFS=/ read sub mask <<< "${1}"
    IFS=. read -a sub_ip <<< "${sub}"
    IFS=. read -a ip_a <<< "${2}"

    # Calculate netmask.
    netmask=$(($BITMASK<<$((32-$mask)) & $BITMASK))

    # Determine address range.
    start=0
    for o in "${sub_ip[@]}"
    do
        start=$(($start<<8 | $o))
    done

    start=$(($start & $netmask))
    end=$(($start | ~$netmask & $BITMASK))

    # Convert IP address to 32-bit number.
    ip=0
    for o in "${ip_a[@]}"
    do
        ip=$(($ip<<8 | $o))
    done

    # Determine if IP in range.
    (( $ip >= $start )) && (( $ip <= $end )) && rval=1 || rval=0

    echo "${rval}"
}

# Carrier Grade NAT IP Range : 100.64.0.0/10

grep -Ev "^\s*#|^\s*$" /etc/fstab | grep -E '^[0-9.]+:' | while read -r line; do
  if [ $(in_subnet 100.64.0.0/10 ${line%%:*}) = 1 ]; then
    dir=$(awk -F' ' '{print $2}' <<< "$line")
    if [ "$action" = "umount" ]; then
      if mountpoint --quiet "$dir"; then
        echo "$action $dir"
        $action "$dir"
      fi
    else
      echo "$action $dir"
      $action "$dir"
    fi
  fi
done

override.conf

# https://github.com/netbirdio/netbird/discussions/570#discussioncomment-4189446
# Install this file at /etc/systemd/system/netbird.service.d/override.conf

[Service]
ExecStop=/usr/local/sbin/umount-netbird-nfs.bash

umount-netbird-nfs.bash

#!/bin/bash

mount-netbird-nfs.bash umount