path: root/nixos/modules/system/boot/luksroot.nix

{ config, lib, pkgs, ... }:

with lib;

let
  luks = config.boot.initrd.luks;

  commonFunctions = ''
    die() {
        echo "$@" >&2
        exit 1
    }

    dev_exist() {
        local target="$1"
        if [ -e $target ]; then
            return 0
        else
            local uuid=$(echo -n $target | sed -e 's,UUID=\(.*\),\1,g')
            blkid --uuid $uuid >/dev/null
            return $?
        fi
    }

    wait_target() {
        local name="$1"
        local target="$2"
        local secs="''${3:-10}"
        local desc="''${4:-$name $target to appear}"

        if ! dev_exist $target; then
            echo -n "Waiting $secs seconds for $desc..."
            local success=false;
            for try in $(seq $secs); do
                echo -n "."
                sleep 1
                if dev_exist $target; then
                    success=true
                    break
                fi
            done
            if [ $success == true ]; then
                echo " - success";
                return 0
            else
                echo " - failure";
                return 1
            fi
        fi
        return 0
    }

    wait_yubikey() {
        local secs="''${1:-10}"

        ykinfo -v 1>/dev/null 2>&1
        if [ $? != 0 ]; then
            echo -n "Waiting $secs seconds for Yubikey to appear..."
            local success=false
            for try in $(seq $secs); do
                echo -n .
                sleep 1
                ykinfo -v 1>/dev/null 2>&1
                if [ $? == 0 ]; then
                    success=true
                    break
                fi
            done
            if [ $success == true ]; then
                echo " - success";
                return 0
            else
                echo " - failure";
                return 1
            fi
        fi
        return 0
    }

    wait_gpgcard() {
        local secs="''${1:-10}"

        gpg --card-status > /dev/null 2> /dev/null
        if [ $? != 0 ]; then
            echo -n "Waiting $secs seconds for GPG Card to appear"
            local success=false
            for try in $(seq $secs); do
                echo -n .
                sleep 1
                gpg --card-status > /dev/null 2> /dev/null
                if [ $? == 0 ]; then
                    success=true
                    break
                fi
            done
            if [ $success == true ]; then
                echo " - success";
                return 0
            else
                echo " - failure";
                return 1
            fi
        fi
        return 0
    }
  '';

  preCommands = ''
    # A place to store crypto things

    # A ramfs is used here to ensure that the file used to update
    # the key slot with cryptsetup will never get swapped out.
    # Warning: Do NOT replace with tmpfs!
    mkdir -p /crypt-ramfs
    mount -t ramfs none /crypt-ramfs

    # Cryptsetup locking directory
    mkdir -p /run/cryptsetup

    # For Yubikey salt storage
    mkdir -p /crypt-storage

    ${optionalString luks.gpgSupport ''
    export GPG_TTY=$(tty)
    export GNUPGHOME=/crypt-ramfs/.gnupg

    gpg-agent --daemon --scdaemon-program $out/bin/scdaemon > /dev/null 2> /dev/null
    ''}
        
    # Disable all input echo for the whole stage. We could use read -s
    # instead but that would ocasionally leak characters between read
    # invocations.
    stty -echo
  '';

  postCommands = ''
    stty echo
    umount /crypt-storage 2>/dev/null
    umount /crypt-ramfs 2>/dev/null
  '';

  openCommand = name': { name, device, header, keyFile, keyFileSize, keyFileOffset, allowDiscards, yubikey, gpgCard, fallbackToPassword, ... }: assert name' == name;
  let
    csopen   = "cryptsetup luksOpen ${device} ${name} ${optionalString allowDiscards "--allow-discards"} ${optionalString (header != null) "--header=${header}"}";
    cschange = "cryptsetup luksChangeKey ${device} ${optionalString (header != null) "--header=${header}"}";
  in ''
    # Wait for luksRoot (and optionally keyFile and/or header) to appear, e.g.
    # if on a USB drive.
    wait_target "device" ${device} || die "${device} is unavailable"

    ${optionalString (header != null) ''
      wait_target "header" ${header} || die "${header} is unavailable"
    ''}

    do_open_passphrase() {
        local passphrase

        while true; do
            echo -n "Passphrase for ${device}: "
            passphrase=
            while true; do
                if [ -e /crypt-ramfs/passphrase ]; then
                    echo "reused"
                    passphrase=$(cat /crypt-ramfs/passphrase)
                    break
                else
                    # ask cryptsetup-askpass
                    echo -n "${device}" > /crypt-ramfs/device

                    # and try reading it from /dev/console with a timeout
                    IFS= read -t 1 -r passphrase
                    if [ -n "$passphrase" ]; then
                       ${if luks.reusePassphrases then ''
                         # remember it for the next device
                         echo -n "$passphrase" > /crypt-ramfs/passphrase
                       '' else ''
                         # Don't save it to ramfs. We are very paranoid
                       ''}
                       echo
                       break
                    fi
                fi
            done
            echo -n "Verifying passphrase for ${device}..."
            echo -n "$passphrase" | ${csopen} --key-file=-
            if [ $? == 0 ]; then
                echo " - success"
                ${if luks.reusePassphrases then ''
                  # we don't rm here because we might reuse it for the next device
                '' else ''
                  rm -f /crypt-ramfs/passphrase
                ''}
                break
            else
                echo " - failure"
                # ask for a different one
                rm -f /crypt-ramfs/passphrase
            fi
        done
    }

    # LUKS
    open_normally() {
        ${if (keyFile != null) then ''
        if wait_target "key file" ${keyFile}; then
            ${csopen} --key-file=${keyFile} \
              ${optionalString (keyFileSize != null) "--keyfile-size=${toString keyFileSize}"} \
              ${optionalString (keyFileOffset != null) "--keyfile-offset=${toString keyFileOffset}"}
        else
            ${if fallbackToPassword then "echo" else "die"} "${keyFile} is unavailable"
            echo " - failing back to interactive password prompt"
            do_open_passphrase
        fi
        '' else ''
        do_open_passphrase
        ''}
    }

    ${optionalString (luks.yubikeySupport && (yubikey != null)) ''
    # Yubikey
    rbtohex() {
        ( od -An -vtx1 | tr -d ' \n' )
    }

    hextorb() {
        ( tr '[:lower:]' '[:upper:]' | sed -e 's/\([0-9A-F]\{2\}\)/\\\\\\x\1/gI' | xargs printf )
    }

    do_open_yubikey() {
        # Make all of these local to this function
        # to prevent their values being leaked
        local salt
        local iterations
        local k_user
        local challenge
        local response
        local k_luks
        local opened
        local new_salt
        local new_iterations
        local new_challenge
        local new_response
        local new_k_luks

        mount -t ${yubikey.storage.fsType} ${yubikey.storage.device} /crypt-storage || \
          die "Failed to mount Yubikey salt storage device"

        salt="$(cat /crypt-storage${yubikey.storage.path} | sed -n 1p | tr -d '\n')"
        iterations="$(cat /crypt-storage${yubikey.storage.path} | sed -n 2p | tr -d '\n')"
        challenge="$(echo -n $salt | openssl-wrap dgst -binary -sha512 | rbtohex)"
        response="$(ykchalresp -${toString yubikey.slot} -x $challenge 2>/dev/null)"

        for try in $(seq 3); do
            ${optionalString yubikey.twoFactor ''
            echo -n "Enter two-factor passphrase: "
            read -r k_user
            echo
            ''}

            if [ ! -z "$k_user" ]; then
                k_luks="$(echo -n $k_user | pbkdf2-sha512 ${toString yubikey.keyLength} $iterations $response | rbtohex)"
            else
                k_luks="$(echo | pbkdf2-sha512 ${toString yubikey.keyLength} $iterations $response | rbtohex)"
            fi

            echo -n "$k_luks" | hextorb | ${csopen} --key-file=-

            if [ $? == 0 ]; then
                opened=true
                break
            else
                opened=false
                echo "Authentication failed!"
            fi
        done

        [ "$opened" == false ] && die "Maximum authentication errors reached"

        echo -n "Gathering entropy for new salt (please enter random keys to generate entropy if this blocks for long)..."
        for i in $(seq ${toString yubikey.saltLength}); do
            byte="$(dd if=/dev/random bs=1 count=1 2>/dev/null | rbtohex)";
            new_salt="$new_salt$byte";
            echo -n .
        done;
        echo "ok"

        new_iterations="$iterations"
        ${optionalString (yubikey.iterationStep > 0) ''
        new_iterations="$(($new_iterations + ${toString yubikey.iterationStep}))"
        ''}

        new_challenge="$(echo -n $new_salt | openssl-wrap dgst -binary -sha512 | rbtohex)"

        new_response="$(ykchalresp -${toString yubikey.slot} -x $new_challenge 2>/dev/null)"

        if [ ! -z "$k_user" ]; then
            new_k_luks="$(echo -n $k_user | pbkdf2-sha512 ${toString yubikey.keyLength} $new_iterations $new_response | rbtohex)"
        else
            new_k_luks="$(echo | pbkdf2-sha512 ${toString yubikey.keyLength} $new_iterations $new_response | rbtohex)"
        fi

        echo -n "$new_k_luks" | hextorb > /crypt-ramfs/new_key
        echo -n "$k_luks" | hextorb | ${cschange} --key-file=- /crypt-ramfs/new_key