Add the ability to generate rootfs signatures using openssl CMS module if ``-c`` is given.

(gitlab ci)

Added a CA structure to the codesigning certificates.
This to test the functionality of optional CA being in the signing message.

(mkarchiso)
Removed the ``sign_netboot_artifacts`` variable and instead
we'll now rely on ``if [[ -v cert_list ]]; then``.

Added ``ARCHISO_TLS_FD`` and ``ARCHISO_TLSCA_FD`` environment variables
to override the certificates used. This is so that third party CA's can
be used during building in a meaningful way without distrupting the
CA trust that is shipped by default.

_cms_sign_artifact() was added which signs the rootfs using OpenSSL CMS.
The files will be saved as "${artifact}.cms.sig". That would be for instance
"${isofs_dir}/${install_dir}/${arch}/airootfs.sfs.cms.sig".

4 files changed, 165 insertions, 48 deletions

diff --git a/.gitlab/ci/build_archiso.sh b/.gitlab/ci/build_archiso.sh
index 5250b51..104792a 100755
--- a/.gitlab/ci/build_archiso.sh
+++ b/.gitlab/ci/build_archiso.sh
@@ -30,6 +30,8 @@ gnupg_homedir=""
 codesigning_dir=""
 codesigning_cert=""
 codesigning_key=""
+ca_cert=""
+ca_key=""
 pgp_key_id=""
 
 print_section_start() {
@@ -204,43 +206,103 @@ EOF
   print_section_end "ephemeral_pgp_key"
 }
 
-create_ephemeral_codesigning_key() {
+create_ephemeral_codesigning_keys() {
   # create ephemeral certificates used for codesigning
-  print_section_start "ephemeral_codesigning_key" "Creating ephemeral codesigning key"
+  print_section_start "ephemeral_codesigning_key" "Creating ephemeral codesigning keys"
 
+  # The exact steps in creating a CA with Codesigning being signed was taken from
+  # https://jamielinux.com/docs/openssl-certificate-authority/introduction.html
+  # (slight modifications to the process to not disturb default values of /etc/ssl/openssl.cnf)
+  
   codesigning_dir="${tmpdir}/.codesigning/"
-  local codesigning_conf="${codesigning_dir}/openssl.cnf"
+  local ca_dir="${codesigning_dir}/ca/"
+
+  local ca_conf="${ca_dir}/certificate_authority.cnf"
+  local ca_subj="/C=DE/ST=Berlin/L=Berlin/O=Arch Linux/OU=Release Engineering/CN=archlinux.org"
+  ca_cert="${ca_dir}/cacert.pem"
+  ca_key="${ca_dir}/private/cakey.pem"
+
+  local codesigning_conf="${codesigning_dir}/code_signing.cnf"
   local codesigning_subj="/C=DE/ST=Berlin/L=Berlin/O=Arch Linux/OU=Release Engineering/CN=archlinux.org"
   codesigning_cert="${codesigning_dir}/codesign.crt"
   codesigning_key="${codesigning_dir}/codesign.key"
+
+  mkdir -p "${ca_dir}/"{private,newcerts,crl}
   mkdir -p "${codesigning_dir}"
   cp -- /etc/ssl/openssl.cnf "${codesigning_conf}"
-  printf "\n[codesigning]\nkeyUsage=digitalSignature\nextendedKeyUsage=codeSigning\n" >> "${codesigning_conf}"
+  cp -- /etc/ssl/openssl.cnf "${ca_conf}"
+  touch "${ca_dir}/index.txt"
+  echo "1000" > "${ca_dir}/serial"
+
+  # Prepare the ca configuration for the change in directory
+  sed -i "s#/etc/ssl#${ca_dir}#g" "${ca_conf}"
+
+  # Create the Certificate Authority
+  openssl req \
+      -newkey rsa:4096 \
+      -sha256 \
+      -nodes \
+      -x509 \
+      -new \
+      -sha256 \
+      -keyout "${ca_key}" \
+      -config "${ca_conf}" \
+      -subj "${ca_subj}" \
+      -out "${ca_cert}"
+
+  cat << EOF >> "${ca_conf}"
+
+[ v3_intermediate_ca ]
+# Extensions for a typical intermediate CA ('man x509v3_config').
+subjectKeyIdentifier = hash
+authorityKeyIdentifier = keyid:always,issuer
+basicConstraints = critical, CA:true, pathlen:0
+keyUsage = critical, digitalSignature, cRLSign, keyCertSign
+
+EOF
+
+  cat << EOF >> "${codesigning_conf}"
+
+[codesigning]
+keyUsage=digitalSignature
+extendedKeyUsage=codeSigning, clientAuth, emailProtection
+
+EOF
+
   openssl req \
       -newkey rsa:4096 \
       -keyout "${codesigning_key}" \
       -nodes \
       -sha256 \
-      -x509 \
-      -days 365 \
-      -out "${codesigning_cert}" \
+      -out "${codesigning_cert}.csr" \
       -config "${codesigning_conf}" \
       -subj "${codesigning_subj}" \
       -extensions codesigning
 
+  # Sign the code signing certificate with the CA
+  openssl ca \
+      -batch \
+      -config "${ca_conf}" \
+      -extensions v3_intermediate_ca \
+      -days 3650 \
+      -notext \
+      -md sha256 \
+      -in "${codesigning_cert}.csr" \
+      -out "${codesigning_cert}"
+
   print_section_end "ephemeral_codesigning_key"
 }
 
 run_mkarchiso() {
   # run mkarchiso
   create_ephemeral_pgp_key
-  create_ephemeral_codesigning_key
+  create_ephemeral_codesigning_keys
 
   print_section_start "mkarchiso" "Running mkarchiso"
   mkdir -p "${output}/" "${tmpdir}/"
   GNUPGHOME="${gnupg_homedir}" ./archiso/mkarchiso \
       -D "${install_dir}" \
-      -c "${codesigning_cert} ${codesigning_key}" \
+      -c "${codesigning_cert} ${codesigning_key} ${ca_cert}" \
       -g "${pgp_key_id}" \
       -G "${pgp_sender}" \
       -o "${output}/" \
diff --git a/AUTHORS.rst b/AUTHORS.rst
index b03b91e..18207eb 100644
--- a/AUTHORS.rst
+++ b/AUTHORS.rst
@@ -36,3 +36,4 @@ Archiso Authors
 * Øyvind Heggstad <heggstad@gmail.com>
 * plain linen <bcdedit@hotmail.com>
 * Pellegrino Prevete <pellegrinoprevete@gmail.com>
+* Anton Hvornum <anton@hvornum.se>
diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 687b413..1d9eeea 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -8,6 +8,8 @@ Changelog
 Added
 -----
 
+- The ability to generate rootfs signatures using openssl CMS module if ``-c`` is given.
+
 Changed
 -------
 
diff --git a/archiso/mkarchiso b/archiso/mkarchiso
index 5f0c79b..2fbbf66 100755
--- a/archiso/mkarchiso
+++ b/archiso/mkarchiso
@@ -43,7 +43,6 @@ bootmodes=()
 airootfs_image_type=""
 airootfs_image_tool_options=()
 cert_list=()
-sign_netboot_artifacts=""
 declare -A file_permissions=()
 efibootimg=""
 efiboot_files=()
@@ -94,10 +93,11 @@ usage: ${app_name} [options] <profile_dir>
                       Default: '${iso_label}'
      -P <publisher>   Set the ISO publisher
                       Default: '${iso_publisher}'
-     -c [cert ..]     Provide certificates for codesigning of netboot artifacts
+     -c [cert ..]     Provide certificates for codesigning of netboot artifacts as
+                      well as the rootfs artifact.
                       Multiple files are provided as quoted, space delimited list.
                       The first file is considered as the signing certificate,
-                      the second as the key.
+                      the second as the key and the third as the optional certificate authority.
      -g <gpg_key>     Set the PGP key ID to be used for signing the rootfs image.
                       Passed to gpg as the value for --default-key
      -G <mbox>        Set the PGP signer (must include an email address)
@@ -250,14 +250,11 @@ _mkchecksum() {
 }
 
 # GPG sign the root file system image.
-_mksignature() {
-    local airootfs_image_filename gpg_options=()
-    _msg_info "Signing rootfs image..."
-    if [[ -e "${isofs_dir}/${install_dir}/${arch}/airootfs.sfs" ]]; then
-        airootfs_image_filename="${isofs_dir}/${install_dir}/${arch}/airootfs.sfs"
-    elif [[ -e "${isofs_dir}/${install_dir}/${arch}/airootfs.erofs" ]]; then
-        airootfs_image_filename="${isofs_dir}/${install_dir}/${arch}/airootfs.erofs"
-    fi
+_mk_pgp_signature() {
+    local gpg_options=()
+    local airootfs_image_filename="${1}"
+    _msg_info "Signing rootfs image using GPG..."
+   
     rm -f -- "${airootfs_image_filename}.sig"
     # Add gpg sender option if the value is provided
     [[ -z "${gpg_sender}" ]] || gpg_options+=('--sender' "${gpg_sender}")
@@ -342,6 +339,15 @@ _make_packages() {
         exec {ARCHISO_GNUPG_FD}<>"${work_dir}/pubkey.gpg"
         export ARCHISO_GNUPG_FD
     fi
+    if [[ -v cert_list[0] ]]; then
+        exec {ARCHISO_TLS_FD}<>"${cert_list[0]}"
+        export ARCHISO_TLS_FD
+    fi
+    if [[ -v cert_list[2] ]]; then
+        exec {ARCHISO_TLSCA_FD}<>"${cert_list[2]}"
+        export ARCHISO_TLSCA_FD
+    fi
+
 
     # Unset TMPDIR to work around https://bugs.archlinux.org/task/70580
     if [[ "${quiet}" = "y" ]]; then
@@ -350,6 +356,14 @@ _make_packages() {
         env -u TMPDIR pacstrap -C "${work_dir}/${buildmode}.pacman.conf" -c -G -M -- "${pacstrap_dir}" "${buildmode_pkg_list[@]}"
     fi
 
+    if [[ -v cert_list[0] ]]; then
+        exec {ARCHISO_TLS_FD}<&-
+        unset ARCHISO_TLS_FD
+    fi
+    if [[ -v cert_list[2] ]]; then
+        exec {ARCHISO_TLSCA_FD}<&-
+        unset ARCHISO_TLSCA_FD
+    fi
     if [[ -n "${gpg_key}" ]]; then
         exec {ARCHISO_GNUPG_FD}<&-
         unset ARCHISO_GNUPG_FD
@@ -998,8 +1012,18 @@ _validate_requirements_bootmode_uefi-x64.grub.eltorito() {
 _prepare_airootfs_image() {
     _run_once "_mkairootfs_${airootfs_image_type}"
     _mkchecksum
+
+    if [[ -e "${isofs_dir}/${install_dir}/${arch}/airootfs.sfs" ]]; then
+        airootfs_image_filename="${isofs_dir}/${install_dir}/${arch}/airootfs.sfs"
+    elif [[ -e "${isofs_dir}/${install_dir}/${arch}/airootfs.erofs" ]]; then
+        airootfs_image_filename="${isofs_dir}/${install_dir}/${arch}/airootfs.erofs"
+    fi
+
     if [[ -n "${gpg_key}" ]]; then
-        _mksignature
+        _mk_pgp_signature "${airootfs_image_filename}"
+    fi
+    if [[ -v cert_list ]]; then
+        _cms_sign_artifact "${airootfs_image_filename}"
     fi
 }
 
@@ -1012,6 +1036,32 @@ _export_netboot_artifacts() {
     du -hs -- "${out_dir}/${install_dir}"
 }
 
+_cms_sign_artifact() {
+    local artifact="${1}"
+    local openssl_flags=(
+        "-sign"
+        "-binary"
+        "-nocerts"
+        "-noattr"
+        "-outform" "DER" "-out" "${artifact}.cms.sig"
+        "-in" "${artifact}"
+        "-signer" "${cert_list[0]}"
+        "-inkey" "${cert_list[1]}"
+    )
+
+    if (( ${#cert_list[@]} > 2 )); then
+        openssl_flags+=("-certfile" "${cert_list[2]}")
+    fi
+
+    _msg_info "Signing ${artifact} image using openssl cms..."
+   
+    rm -f -- "${artifact}.cms.sig"
+
+    openssl cms "${openssl_flags[@]}"
+
+    _msg_info "Done!"
+}
+
 # sign build artifacts for netboot
 _sign_netboot_artifacts() {
     local _file _dir
@@ -1115,6 +1165,26 @@ _validate_common_requirements_buildmode_iso_netboot() {
         _msg_error "Packages file '${packages}' does not exist." 0
     fi
 
+    if [[ -v cert_list ]]; then
+        # Check if the certificate files exist
+        for _cert in "${cert_list[@]}"; do
+            if [[ ! -e "${_cert}" ]]; then
+                (( validation_error=validation_error+1 ))
+                _msg_error "File '${_cert}' does not exist." 0
+            fi
+        done
+        # Check if there are at least three certificate files to sign netboot and rootfs.
+        if (( ${#cert_list[@]} < 2 )); then
+            (( validation_error=validation_error+1 ))
+            _msg_error "Two certificates are required for codesigning netboot artifacts, but '${cert_list[*]}' is provided." 0
+        fi
+
+        if ! command -v openssl &> /dev/null; then
+            (( validation_error=validation_error+1 ))
+            _msg_error "Validating build mode '${_buildmode}': openssl is not available on this host. Install 'openssl'!" 0
+        fi
+    fi
+
     # Check if the specified airootfs_image_type is supported
     if typeset -f "_mkairootfs_${airootfs_image_type}" &> /dev/null; then
         if typeset -f "_validate_requirements_airootfs_image_type_${airootfs_image_type}" &> /dev/null; then
@@ -1156,31 +1226,8 @@ _validate_requirements_buildmode_iso() {
 }
 
 _validate_requirements_buildmode_netboot() {
-    local _override_cert_list=()
-
-    if [[ "${sign_netboot_artifacts}" == "y" ]]; then
-        # Check if the certificate files exist
-        for _cert in "${cert_list[@]}"; do
-            if [[ -e "${_cert}" ]]; then
-                _override_cert_list+=("$(realpath -- "${_cert}")")
-            else
-                (( validation_error=validation_error+1 ))
-                _msg_error "File '${_cert}' does not exist." 0
-            fi
-        done
-        cert_list=("${_override_cert_list[@]}")
-        # Check if there are at least two certificate files
-        if (( ${#cert_list[@]} < 2 )); then
-            (( validation_error=validation_error+1 ))
-            _msg_error "Two certificates are required for codesigning, but '${cert_list[*]}' is provided." 0
-        fi
-    fi
     _validate_common_requirements_buildmode_iso_netboot
     _validate_common_requirements_buildmode_all
-    if ! command -v openssl &> /dev/null; then
-        (( validation_error=validation_error+1 ))
-        _msg_error "Validating build mode '${_buildmode}': openssl is not available on this host. Install 'openssl'!" 0
-    fi
 }
 
 # SYSLINUX El Torito
@@ -1541,10 +1588,7 @@ _set_overrides() {
     fi
     [[ ! -v override_gpg_key ]] || gpg_key="$override_gpg_key"
     [[ ! -v override_gpg_sender ]] || gpg_sender="$override_gpg_sender"
-    if [[ -v override_cert_list ]]; then
-        sign_netboot_artifacts="y"
-    fi
-    [[ ! -v override_cert_list ]] || cert_list+=("${override_cert_list[@]}")
+    [[ ! -v override_cert_list ]] || mapfile -t cert_list < <(realpath -- "${override_cert_list[@]}")
     if [[ -v override_quiet ]]; then
         quiet="$override_quiet"
     elif [[ -z "$quiet" ]]; then
@@ -1675,8 +1719,16 @@ _build_buildmode_netboot() {
     local run_once_mode="${buildmode}"
 
     _build_iso_base
+
+    if [[ -e "${isofs_dir}/${install_dir}/${arch}/airootfs.sfs" ]]; then
+        airootfs_image_filename="${isofs_dir}/${install_dir}/${arch}/airootfs.sfs"
+    elif [[ -e "${isofs_dir}/${install_dir}/${arch}/airootfs.erofs" ]]; then
+        airootfs_image_filename="${isofs_dir}/${install_dir}/${arch}/airootfs.erofs"
+    fi
+
     if [[ -v cert_list ]]; then
         _run_once _sign_netboot_artifacts
+        _cms_sign_artifact "${airootfs_image_filename}"
     fi
     _run_once _export_netboot_artifacts
 }