lxc-oci.in

#!/bin/bash

# Create application containers from OCI images

# Copyright © 2014 Stéphane Graber <stgraber@ubuntu.com>
# Copyright © 2017 Serge Hallyn <serge@hallyn.com>
#
#  This library is free software; you can redistribute it and/or
#  modify it under the terms of the GNU Lesser General Public
#  License as published by the Free Software Foundation; either
#  version 2.1 of the License, or (at your option) any later version.

#  This library is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
#  Lesser General Public License for more details.

#  You should have received a copy of the GNU Lesser General Public
#  License along with this library; if not, write to the Free Software
#  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301
#  USA

set -eu

# Make sure the usual locations are in PATH
export PATH=$PATH:/usr/sbin:/usr/bin:/sbin:/bin

# Check for required binaries
for bin in skopeo umoci jq; do
  if ! which $bin >/dev/null 2>&1; then
    echo "ERROR: Missing required tool: $bin" 1>&2
    exit 1
  fi
done

LOCALSTATEDIR="@LOCALSTATEDIR@"
LXC_TEMPLATE_CONFIG="@LXCTEMPLATECONFIG@"
LXC_HOOK_DIR="@LXCHOOKDIR@"

# Some useful functions
cleanup() {
  if [ -d "${DOWNLOAD_TEMP}" ]; then
    rm -Rf "${DOWNLOAD_TEMP}"
  fi

  if [ -d "${LXC_ROOTFS}.tmp" ]; then
    rm -Rf "${LXC_ROOTFS}.tmp"
  fi
}

in_userns() {
  [ -e /proc/self/uid_map ] || { echo no; return; }
  while read -r line; do
    fields="$(echo "$line" | awk '{ print $1 " " $2 " " $3 }')"
    if [ "${fields}" = "0 0 4294967295" ]; then
      echo no;
      return;
    fi
    if echo "${fields}" | grep -q " 0 1$"; then
      echo userns-root;
      return;
    fi
  done < /proc/self/uid_map

  if [ -e /proc/1/uid_map ]; then
    if [ "$(cat /proc/self/uid_map)" = "$(cat /proc/1/uid_map)" ]; then
      echo userns-root
      return
    fi
  fi
  echo yes
}

getconfigpath() {
  basedir="$1"
  q="$2"

  digest=$(jq -c -r --arg q "$q" '.manifests[] | if .annotations."org.opencontainers.image.ref.name" == $q then .digest else empty end' < "${basedir}/index.json")
  if [ -z "${digest}" ]; then
    echo "$q not found in index.json" >&2
    return
  fi

  # Ok we have the image config digest, now get the config from that
  # shellcheck disable=SC2039
  d=${digest:7}
  cdigest=$(jq -c -r '.config.digest' < "${basedir}/blobs/sha256/${d}")
  if [ -z "${cdigest}" ]; then
    echo "container config not found" >&2
    return
  fi

  # shellcheck disable=SC2039
  d2=${cdigest:7}
  echo "${basedir}/blobs/sha256/${d2}"
  return
}

# Get entrypoint from oci image. Use sh if unspecified
getep() {
  if [ "$#" -eq 0 ]; then
    echo "/bin/sh"
    return
  fi

  configpath="$1"

  ep=$(jq -c '.config.Entrypoint[]?'< "${configpath}" | tr '\n' ' ')
  cmd=$(jq -c '.config.Cmd[]?'< "${configpath}" | tr '\n' ' ')
  if [ -z "${ep}" ]; then
    ep="${cmd}"
    if [ -z "${ep}" ]; then
      ep="/bin/sh"
    fi
  elif [ -n "${cmd}" ]; then
    ep="${ep} ${cmd}"
  fi

  echo "${ep}"
  return
}

# get environment from oci image.
getenv() {
  if [ "$#" -eq 0 ]; then
    return
  fi

  configpath="$1"

  env=$(jq -c -r '.config.Env[]'< "${configpath}")

  echo "${env}"
  return
}

# check var is decimal.
isdecimal() {
  var="$1"
  if [ "${var}" -eq "${var}" ] 2> /dev/null; then
    return 0
  else 
    return 1
  fi
}

# get uid, gid from oci image.
getuidgid() {
  configpath="$1"
  rootpath="$2"
  passwdpath="${rootpath}/etc/passwd"
  grouppath="${rootpath}/etc/group"

  usergroup=$(jq -c -r '.config.User' < "${configpath}")
  # shellcheck disable=SC2039
  usergroup=(${usergroup//:/ })

  user=${usergroup[0]:-0}
  if ! isdecimal "${user}"; then
    if [ -f ${passwdpath} ]; then
      user=$(grep "^${user}:" "${passwdpath}" | awk -F: '{print $3}')
    else
      user=0
    fi
  fi

  group=${usergroup[1]:-}
  if [ -z "${group}" ]; then
    if [ -f "${passwdpath}" ]; then
      group=$(grep "^[^:]*:[^:]*:${user}:" "${passwdpath}" | awk -F: '{print $4}')
    else
      group=0
    fi
  elif ! isdecimal "${group}"; then
    if [ -f "${grouppath}" ]; then
      group=$(grep "^${group}:" "${grouppath}" | awk -F: '{print $3}')
    else
      group=0
    fi
  fi

  echo "${user:-0} ${group:-0}"
  return
}

# get cwd from oci image.
getcwd() {
  if [ "$#" -eq 0 ]; then
    echo "/"
    return
  fi

  configpath="$1"

  cwd=$(jq -c -r '.config.WorkingDir // "/"' < "${configpath}")

  echo "${cwd}"
  return
}

usage() {
  cat <<EOF
LXC container template for OCI images

Special arguments:
[ -h | --help ]: Print this help message and exit.

Required arguments:
[ -u | --url <url> ]: The OCI image URL

Optional arguments:
[ --username <username> ]: The username for the registry
[ --password <password> ]: The password for the registry

LXC internal arguments (do not pass manually!):
[ --name <name> ]: The container name
[ --path <path> ]: The path to the container
[ --rootfs <rootfs> ]: The path to the container's rootfs
[ --mapped-uid <map> ]: A uid map (user namespaces)
[ --mapped-gid <map> ]: A gid map (user namespaces)
EOF
  return 0
}

if ! options=$(getopt -o u:h -l help,url:,username:,password:,no-cache,dhcp,name:,path:,rootfs:,mapped-uid:,mapped-gid: -- "$@"); then
    usage
    exit 1
fi
eval set -- "$options"

OCI_URL=""
OCI_USERNAME=
OCI_PASSWORD=
OCI_USE_CACHE="true"
OCI_USE_DHCP="false"

LXC_MAPPED_GID=
LXC_MAPPED_UID=
LXC_NAME=
LXC_PATH=
LXC_ROOTFS=

while :; do
  case "$1" in
    -h|--help)    usage && exit 1;;
    -u|--url)     OCI_URL=$2; shift 2;;
    --username)   OCI_USERNAME=$2; shift 2;;
    --password)   OCI_PASSWORD=$2; shift 2;;
    --no-cache)   OCI_USE_CACHE="false"; shift 1;;
    --dhcp)       OCI_USE_DHCP="true"; shift 1;;
    --name)       LXC_NAME=$2; shift 2;;
    --path)       LXC_PATH=$2; shift 2;;
    --rootfs)     LXC_ROOTFS=$2; shift 2;;
    --mapped-uid) LXC_MAPPED_UID=$2; shift 2;;
    --mapped-gid) LXC_MAPPED_GID=$2; shift 2;;
    *)            break;;
  esac
done

# Check that we have all variables we need
if [ -z "$LXC_NAME" ] || [ -z "$LXC_PATH" ] || [ -z "$LXC_ROOTFS" ]; then
  echo "ERROR: Not running through LXC" 1>&2
  exit 1
fi

if [ -z "$OCI_URL" ]; then
  echo "ERROR: no OCI URL given"
  exit 1
fi

if [ -n "$OCI_PASSWORD" ] && [ -z "$OCI_USERNAME" ]; then
  echo "ERROR: password given but no username specified"
  exit 1
fi

if [ "${OCI_USE_CACHE}" = "true" ]; then
  if ! skopeo copy --help | grep -q 'dest-shared-blob-dir'; then
    echo "INFO: skopeo doesn't support blob caching"
    OCI_USE_CACHE="false"
  fi
fi

USERNS=$(in_userns)

if [ "$USERNS" = "yes" ]; then
  if [ -z "$LXC_MAPPED_UID" ] || [ "$LXC_MAPPED_UID" = "-1" ]; then
    echo "ERROR: In a user namespace without a map" 1>&2
    exit 1
  fi
fi

if [ "${OCI_USE_CACHE}" = "true" ]; then
  if [ "$USERNS" = "yes" ]; then
    DOWNLOAD_BASE="${HOME}/.cache/lxc"
  else
    DOWNLOAD_BASE="${LOCALSTATEDIR}/cache/lxc"
  fi
else
  DOWNLOAD_BASE=/tmp
fi
mkdir -p "${DOWNLOAD_BASE}"

# Trap all exit signals
trap cleanup EXIT HUP INT TERM

if ! which mktemp >/dev/null 2>&1; then
  DOWNLOAD_TEMP="${DOWNLOAD_BASE}/lxc-oci.$$"
  mkdir -p "${DOWNLOAD_TEMP}"
else
  DOWNLOAD_TEMP=$(mktemp -d -p "${DOWNLOAD_BASE}")
fi

# Download the image
# shellcheck disable=SC2039
skopeo_args=("")
if [ -n "$OCI_USERNAME" ]; then
  CREDENTIALS="${OCI_USERNAME}"

  if [ -n "$OCI_PASSWORD" ]; then
    CREDENTIALS="${CREDENTIALS}:${OCI_PASSWORD}"
  fi

  # shellcheck disable=SC2039
  skopeo_args+=(--src-creds "${CREDENTIALS}")
fi

if [ "${OCI_USE_CACHE}" = "true" ]; then
  # shellcheck disable=SC2039
  # shellcheck disable=SC2068
  skopeo_args+=(--dest-shared-blob-dir "${DOWNLOAD_BASE}")
  # shellcheck disable=SC2039
  # shellcheck disable=SC2068
  skopeo copy ${skopeo_args[@]} "${OCI_URL}" "oci:${DOWNLOAD_TEMP}:latest"
  ln -s "${DOWNLOAD_BASE}/sha256" "${DOWNLOAD_TEMP}/blobs/sha256"
else
  # shellcheck disable=SC2039
  # shellcheck disable=SC2068
  skopeo copy ${skopeo_args[@]} "${OCI_URL}" "oci:${DOWNLOAD_TEMP}:latest"
fi

echo "Unpacking the rootfs"
# shellcheck disable=SC2039
umoci_args=("")
if [ -n "$LXC_MAPPED_UID" ] && [ "$LXC_MAPPED_UID" != "-1" ]; then
  # shellcheck disable=SC2039
  umoci_args+=(--rootless)
fi
# shellcheck disable=SC2039
# shellcheck disable=SC2068
umoci --log=error unpack ${umoci_args[@]} --image "${DOWNLOAD_TEMP}:latest" "${LXC_ROOTFS}.tmp"
find "${LXC_ROOTFS}.tmp/rootfs" -mindepth 1 -maxdepth 1 -exec mv '{}' "${LXC_ROOTFS}/" \;

OCI_CONF_FILE=$(getconfigpath "${DOWNLOAD_TEMP}" latest)
LXC_CONF_FILE="${LXC_PATH}/config"
entrypoint=$(getep "${OCI_CONF_FILE}")
echo "lxc.execute.cmd = '${entrypoint}'" >> "${LXC_CONF_FILE}"
echo "lxc.mount.auto = proc:mixed sys:mixed cgroup:mixed" >> "${LXC_CONF_FILE}"

environment=$(getenv "${OCI_CONF_FILE}")
# shellcheck disable=SC2039
while read -r line; do
  echo "lxc.environment = ${line}" >> "${LXC_CONF_FILE}"
done <<< "${environment}"

if [ -e "${LXC_TEMPLATE_CONFIG}/common.conf" ]; then
  echo "lxc.include = ${LXC_TEMPLATE_CONFIG}/common.conf" >> "${LXC_CONF_FILE}"
fi

if [ -n "$LXC_MAPPED_UID" ] && [ "$LXC_MAPPED_UID" != "-1" ] && [ -e "${LXC_TEMPLATE_CONFIG}/userns.conf" ]; then
  echo "lxc.include = ${LXC_TEMPLATE_CONFIG}/userns.conf" >> "${LXC_CONF_FILE}"
fi

if [ -e "${LXC_TEMPLATE_CONFIG}/oci.common.conf" ]; then
  echo "lxc.include = ${LXC_TEMPLATE_CONFIG}/oci.common.conf" >> "${LXC_CONF_FILE}"
fi

if [ "${OCI_USE_DHCP}" = "true" ]; then
  echo "lxc.hook.start-host = ${LXC_HOOK_DIR}/dhclient" >> "${LXC_CONF_FILE}"
  echo "lxc.hook.stop = ${LXC_HOOK_DIR}/dhclient" >> "${LXC_CONF_FILE}"
fi

echo "lxc.uts.name = ${LXC_NAME}" >> "${LXC_CONF_FILE}"
# set the hostname
cat <<EOF > "${LXC_ROOTFS}/etc/hostname"
${LXC_NAME}
EOF

# set minimal hosts
cat <<EOF > "${LXC_ROOTFS}/etc/hosts"
127.0.0.1   localhost
127.0.1.1   ${LXC_NAME}
::1     localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
EOF

# shellcheck disable=SC2039
uidgid=($(getuidgid "${OCI_CONF_FILE}" "${LXC_ROOTFS}" ))
# shellcheck disable=SC2039
echo "lxc.init.uid = ${uidgid[0]}" >> "${LXC_CONF_FILE}"
# shellcheck disable=SC2039
echo "lxc.init.gid = ${uidgid[1]}" >> "${LXC_CONF_FILE}"

cwd=$(getcwd "${OCI_CONF_FILE}")
echo "lxc.init.cwd = ${cwd}" >> "${LXC_CONF_FILE}"

if [ -n "$LXC_MAPPED_UID" ] && [ "$LXC_MAPPED_UID" != "-1" ]; then
  chown "$LXC_MAPPED_UID" "$LXC_PATH/config" "$LXC_PATH/fstab" > /dev/null 2>&1 || true
fi
if [ -n "$LXC_MAPPED_GID" ] && [ "$LXC_MAPPED_GID" != "-1" ]; then
  chgrp "$LXC_MAPPED_GID" "$LXC_PATH/config" "$LXC_PATH/fstab" > /dev/null 2>&1 || true
fi

exit 0