lxc-download: Rely on HTTPS only

GPG has been a major source of issues over the years with various
attacks on the key network as well as client side issues making it hard
to retrieve our keys.

Back when we introduced the image server, SSL certificates were still
expensive and annoying to setup, so not something we'd have expected
potential mirrors to setup for us. They were also issued for multiple
years, making a compromise of such a certificate quite problematic.

But things have changed since, we now have completely free, very easily
deployable SSL certificates everywhere with the majority of those being
shortlived and with good reporting of issued certificates.

With that, we can now deprecate the GPG validation, disable the fallback
to non-HTTPS download and rely on our indices being accurate because
they've been downloaded from a server with a valid certificate.

This puts LXC more in line with what LXD has done since the beginning
and should offer a more reliable user experience.

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>

templates/lxc-download.in

@@ -33,21 +33,15 @@ DOWNLOAD_DIST=
 DOWNLOAD_FLUSH_CACHE="false"
 DOWNLOAD_FORCE_CACHE="false"
 DOWNLOAD_INTERACTIVE="false"
-DOWNLOAD_KEYID="0xE7FB0CAEC8173D669066514CBAEFF88C22F6E216"
 DOWNLOAD_LIST_IMAGES="false"
 DOWNLOAD_MODE="system"
-DOWNLOAD_READY_GPG="false"
 DOWNLOAD_RELEASE=
 DOWNLOAD_SERVER="images.linuxcontainers.org"
-DOWNLOAD_SHOW_GPG_WARNING="true"
-DOWNLOAD_SHOW_HTTP_WARNING="true"
 DOWNLOAD_TARGET="system"
 DOWNLOAD_URL=
 DOWNLOAD_USE_CACHE="false"
-DOWNLOAD_VALIDATE="true"
 DOWNLOAD_VARIANT="default"
 DOWNLOAD_TEMP=
-DOWNLOAD_STANDARD_RESOLVER="false"
 
 LXC_MAPPED_GID=
 LXC_MAPPED_UID=
@@ -55,16 +49,6 @@ LXC_NAME=
 LXC_PATH=
 LXC_ROOTFS=
 
-if [ -z "${DOWNLOAD_KEYSERVER:-}" ]; then
-  DOWNLOAD_KEYSERVER="hkp://keyserver.ubuntu.com"
-
-  # Deal with GPG over http proxy
-  if [ -n "${http_proxy:-}" ]; then
-    DOWNLOAD_KEYSERVER="hkp://keyserver.ubuntu.com:80"
-    DOWNLOAD_GPG_PROXY="--keyserver-options http-proxy=\"${http_proxy}\""
-  fi
-fi
-
 # Make sure the usual locations are in PATH
 export PATH="$PATH:/usr/sbin:/usr/bin:/sbin:/bin"
 
@@ -87,88 +71,15 @@ wget_wrapper() {
 
 download_file() {
   if ! wget_wrapper --user-agent="lxc/@PACKAGE_VERSION@ compat:${DOWNLOAD_COMPAT_LEVEL}" -T 30 -q "https://${DOWNLOAD_SERVER}/$1" -O "$2" >/dev/null 2>&1; then
-    if ! wget_wrapper --user-agent="lxc/@PACKAGE_VERSION@ compat:${DOWNLOAD_COMPAT_LEVEL}" -T 30 -q "http://${DOWNLOAD_SERVER}/$1" -O "$2" >/dev/null 2>&1; then
+    if [ "$3" = "noexit" ]; then
-      if [ "$3" = "noexit" ]; then
+      return 1
-        return 1
-      else
-        echo "ERROR: Failed to download http://${DOWNLOAD_SERVER}/$1" 1>&2
-        exit 1
-      fi
-    elif [ "${DOWNLOAD_SHOW_HTTP_WARNING}" = "true" ]; then
-      DOWNLOAD_SHOW_HTTP_WARNING="false"
-      echo "WARNING: Failed to download the file over HTTPs" 1>&2
-      echo "         The file was instead download over HTTP " 1>&2
-      echo "A server replay attack may be possible!" 1>&2
-    fi
-  fi
-}
-
-download_sig() {
-  if ! download_file "$1" "$2" noexit; then
-    if [ "${DOWNLOAD_VALIDATE}" = "true" ]; then
-      if [ "$3" = "normal" ]; then
-        echo "ERROR: Failed to download http://${DOWNLOAD_SERVER}/$1" 1>&2
-        exit 1
-      else
-        return 1
-      fi
     else
-      return 0
+      echo "ERROR: Failed to download https://${DOWNLOAD_SERVER}/$1" 1>&2
+      exit 1
     fi
   fi
 }
 
-gpg_setup() {
-  if [ "${DOWNLOAD_VALIDATE}" = "false" ]; then
-    return
-  fi
-
-  if [ "${DOWNLOAD_READY_GPG}" = "true" ]; then
-    return
-  fi
-
-  echo "Setting up the GPG keyring"
-
-  mkdir -p "${DOWNLOAD_TEMP}/gpg"
-  chmod 700 "${DOWNLOAD_TEMP}/gpg"
-
-  if [ "${DOWNLOAD_STANDARD_RESOLVER}" = "true" ]; then
-    echo "standard-resolver" > "${DOWNLOAD_TEMP}/gpg/dirmngr.conf"
-  fi
-  export GNUPGHOME="${DOWNLOAD_TEMP}/gpg"
-
-  success=
-  for _ in $(seq 3); do
-    if gpg --keyserver "${DOWNLOAD_KEYSERVER}" ${DOWNLOAD_GPG_PROXY:-} \
-      --recv-keys "${DOWNLOAD_KEYID}" >/dev/null 2>&1; then
-      success=1
-      break
-    fi
-  done
-
-  if [ -z "${success}" ]; then
-    echo "ERROR: Unable to fetch GPG key from keyserver"
-    exit 1
-  fi
-
-  DOWNLOAD_READY_GPG="true"
-}
-
-gpg_validate() {
-  if [ "${DOWNLOAD_VALIDATE}" = "false" ]; then
-    if [ "${DOWNLOAD_SHOW_GPG_WARNING}" = "true" ]; then
-      echo "WARNING: Running without gpg validation!" 1>&2
-    fi
-    DOWNLOAD_SHOW_GPG_WARNING="false"
-    return 0
-  fi
-
-  if ! gpg --verify "$1" >/dev/null 2>&1; then
-    echo "ERROR: Invalid signature for $1" 1>&2
-    exit 1
-  fi
-}
-
 in_userns() {
   [ -e /proc/self/uid_map ] || { echo no; return; }
   while read -r line; do
@@ -222,12 +133,8 @@ Required arguments:
 Optional arguments:
 [ --variant <variant> ]: Variant of the image (default: "default")
 [ --server <server> ]: Image server (default: "images.linuxcontainers.org")
-[ --keyid <keyid> ]: GPG keyid (default: 0x...)
-[ --keyserver <keyserver> ]: GPG keyserver to use. Environment variable: DOWNLOAD_KEYSERVER
-[ --no-validate ]: Disable GPG validation (not recommended)
 [ --flush-cache ]: Flush the local copy (if present)
 [ --force-cache ]: Force the use of the local copy even if expired
-[ --standard-resolver ]: Force the use of the standard resolver
 
 LXC internal arguments (do not pass manually!):
 [ --name <name> ]: The container name
@@ -236,16 +143,12 @@ LXC internal arguments (do not pass manually!):
 [ --mapped-uid <map> ]: A uid map (user namespaces)
 [ --mapped-gid <map> ]: A gid map (user namespaces)
 
-Environment Variables:
-DOWNLOAD_KEYSERVER : The URL of the key server to use, instead of the default.
-                     Can be further overridden by using optional argument --keyserver
-
 EOF
   return 0
 }
 
 if ! options=$(getopt -o d:r:a:hl -l dist:,release:,arch:,help,list,variant:,\
-server:,keyid:,keyserver:,no-validate,flush-cache,force-cache,name:,path:,\
+server:,flush-cache,force-cache,name:,path:,\
 rootfs:,mapped-uid:,mapped-gid: -- "$@"); then
   usage
   exit 1
@@ -261,12 +164,8 @@ while :; do
     -a|--arch)     DOWNLOAD_ARCH="$2"; shift 2;;
     --variant)     DOWNLOAD_VARIANT="$2"; shift 2;;
     --server)      DOWNLOAD_SERVER="$2"; shift 2;;
-    --keyid)       DOWNLOAD_KEYID="$2"; shift 2;;
-    --keyserver)   DOWNLOAD_KEYSERVER="$2"; shift 2;;
-    --no-validate) DOWNLOAD_VALIDATE="false"; shift 1;;
     --flush-cache) DOWNLOAD_FLUSH_CACHE="true"; shift 1;;
     --force-cache) DOWNLOAD_FORCE_CACHE="true"; shift 1;;
-    --standard-resolver) STANDARD_RESOLVER="true"; shift 1;;
     --name)        LXC_NAME="$2"; shift 2;;
     --path)        LXC_PATH="$2"; shift 2;;
     --rootfs)      LXC_ROOTFS="$2"; shift 2;;
@@ -284,15 +183,6 @@ for bin in tar xz wget; do
   fi
 done
 
-# Check for GPG
-if [ "${DOWNLOAD_VALIDATE}" = "true" ]; then
-  if ! command -V gpg >/dev/null 2>&1; then
-    echo "ERROR: Missing recommended tool: gpg" 1>&2
-    echo "You can workaround this by using --no-validate" 1>&2
-    exit 1
-  fi
-fi
-
 # Check that we have all variables we need
 if [ -z "${LXC_NAME}" ] || [ -z "${LXC_PATH}" ] || [ -z "${LXC_ROOTFS}" ]; then
   if [ "${DOWNLOAD_LIST_IMAGES}" != "true" ]; then
@@ -340,21 +230,14 @@ fi
 
 # Simply list images
 if [ "${DOWNLOAD_LIST_IMAGES}" = "true" ] || [ "${DOWNLOAD_INTERACTIVE}" = "true" ]; then
-  # Initialize GPG
-  gpg_setup
-
   # Grab the index
   DOWNLOAD_INDEX_PATH="/meta/1.0/index-${DOWNLOAD_MODE}"
 
   echo "Downloading the image index"
-  if ! download_file "${DOWNLOAD_INDEX_PATH}.${DOWNLOAD_COMPAT_LEVEL}" "${DOWNLOAD_TEMP}/index" noexit ||
+  if ! download_file "${DOWNLOAD_INDEX_PATH}.${DOWNLOAD_COMPAT_LEVEL}" "${DOWNLOAD_TEMP}/index" noexit; then
-     ! download_sig "${DOWNLOAD_INDEX_PATH}.${DOWNLOAD_COMPAT_LEVEL}.asc" "${DOWNLOAD_TEMP}/index.asc" noexit; then
     download_file "${DOWNLOAD_INDEX_PATH}" "${DOWNLOAD_TEMP}/index" normal
-    download_sig "${DOWNLOAD_INDEX_PATH}.asc" "${DOWNLOAD_TEMP}/index.asc" normal
   fi
 
-  gpg_validate "${DOWNLOAD_TEMP}/index.asc"
-
   # Parse it
   echo ""
   echo "---"
@@ -429,21 +312,14 @@ fi
 
 # Download what's needed
 if [ "${DOWNLOAD_USE_CACHE}" = "false" ]; then
-  # Initialize GPG
-  gpg_setup
-
   # Grab the index
   DOWNLOAD_INDEX_PATH="/meta/1.0/index-${DOWNLOAD_MODE}"
 
   echo "Downloading the image index"
-  if ! download_file "${DOWNLOAD_INDEX_PATH}.${DOWNLOAD_COMPAT_LEVEL}" "${DOWNLOAD_TEMP}/index" noexit ||
+  if ! download_file "${DOWNLOAD_INDEX_PATH}.${DOWNLOAD_COMPAT_LEVEL}" "${DOWNLOAD_TEMP}/index" noexit; then
-     ! download_sig "${DOWNLOAD_INDEX_PATH}.${DOWNLOAD_COMPAT_LEVEL}.asc" "${DOWNLOAD_TEMP}/index.asc" noexit; then
     download_file "${DOWNLOAD_INDEX_PATH}" "${DOWNLOAD_TEMP}/index" normal
-    download_sig "${DOWNLOAD_INDEX_PATH}.asc" "${DOWNLOAD_TEMP}/index.asc" normal
   fi
 
-  gpg_validate "${DOWNLOAD_TEMP}/index.asc"
-
   # Parse it
   while IFS=';' read -r f1 f2 f3 f4 f5 f6; do
     if [ "${f1}" != "${DOWNLOAD_DIST}" ] || \
@@ -474,13 +350,9 @@ if [ "${DOWNLOAD_USE_CACHE}" = "false" ]; then
     # Download the actual files
     echo "Downloading the rootfs"
     download_file "${DOWNLOAD_URL}/rootfs.tar.xz" "${DOWNLOAD_TEMP}/rootfs.tar.xz" normal
-    download_sig "${DOWNLOAD_URL}/rootfs.tar.xz.asc" "${DOWNLOAD_TEMP}/rootfs.tar.xz.asc" normal
-    gpg_validate "${DOWNLOAD_TEMP}/rootfs.tar.xz.asc"
 
     echo "Downloading the metadata"
     download_file "${DOWNLOAD_URL}/meta.tar.xz" "${DOWNLOAD_TEMP}/meta.tar.xz" normal
-    download_sig "$DOWNLOAD_URL/meta.tar.xz.asc" "${DOWNLOAD_TEMP}/meta.tar.xz.asc" normal
-    gpg_validate "${DOWNLOAD_TEMP}/meta.tar.xz.asc"
 
     if [ -d "${LXC_CACHE_PATH}" ]; then
       rm -Rf "${LXC_CACHE_PATH}"