V9.14.022.2026.06.10: Attest selected decrypted rootfs mapper

2026-06-10 23:13:23 +02:00
parent b78779e790
commit 42e2ae6b0e
3 changed files with 207 additions and 27 deletions
@@ -9,17 +9,90 @@
 # SPDX-LicenseComment: This file is part of the CISS.debian.installer.secure framework.
 # SPDX-PackageName: CISS.debian.live.builder
 # SPDX-Security-Contact: security@coresecret.eu
+# shellcheck disable=SC2154
 set -Ceuo pipefail

-# Final live-build binary hook for encrypted root filesystem packaging. Preallocate a LUKS2 container, formats it with the
-# generated build secret, copies the generated filesystem.squashfs into the opened encrypted mapping, then closes the container,
-# shreds the temporary LUKS secret, and removes the plaintext SquashFS from the ISO payload.
+# Final live-build binary hook for encrypted root filesystem packaging. Preallocate a LUKS2 container, format it with the
+# generated build secret, copy the generated filesystem.squashfs into the opened encrypted mapping, generate and sign a
+# SHA-512 attestation manifest for the complete decrypted mapper, then close the container, shred the temporary LUKS secret,
+# and remove the plaintext SquashFS from the ISO payload.

 printf "\e[95m🧪 '%s' starting ... \e[0m\n" "${0}"

 __umask=$(umask)
 umask 0077

+#######################################
+# Prints a fatal error message and terminates the hook.
+# Globals:
+#   None
+# Arguments:
+#   1: Error message
+# Returns:
+#   42: always exits with failure
+#######################################
+die() {
+  declare message="${1}"
+  printf "\e[91m❌ %s \e[0m\n" "${message}" >&2
+  exit 42
+}
+
+#######################################
+# Checks whether a required command exists.
+# Globals:
+#   None
+# Arguments:
+#   1: Command name
+# Returns:
+#   0: on success
+#   42: if the command is missing
+#######################################
+require_command() {
+  declare command_name="${1}"
+
+  command -v "${command_name}" >/dev/null 2>&1 || die "Required command not found: '${command_name}'."
+
+  return 0
+}
+
+#######################################
+# Checks whether a required file exists and is readable.
+# Globals:
+#   None
+# Arguments:
+#   1: File path
+#   2: Human-readable file description
+# Returns:
+#   0: on success
+#   42: if the file is missing or unreadable
+#######################################
+require_file() {
+  declare file_path="${1}"
+  declare description="${2}"
+
+  [[ -f "${file_path}" && -r "${file_path}" ]] || die "Missing or unreadable ${description}: '${file_path}'."
+
+  return 0
+}
+
+#######################################
+# Checks whether a required environment variable is non-empty.
+# Globals:
+#   None
+# Arguments:
+#   1: Variable name
+# Returns:
+#   0: on success
+#   42: if the variable is empty or unset
+#######################################
+require_variable() {
+  declare variable_name="${1}"
+
+  [[ -n "${!variable_name:-}" ]] || die "Required environment variable is empty or unset: '${variable_name}'."
+
+  return 0
+}
+
 #######################################
 # Pre allocates space for LUKS container.
 # Globals:
@@ -65,8 +138,25 @@ readonly -f preallocate

 declare ROOTFS="${VAR_HANDLER_BUILD_DIR}/binary/live/filesystem.squashfs"
 declare LUKSFS="${VAR_HANDLER_BUILD_DIR}/binary/live/ciss_rootfs.crypt"
+declare MAPPER_DEV="/dev/mapper/crypt_liveiso"
+declare ROOTFS_ATTESTATION="${LUKSFS}.decrypted.sha512sum.txt"
+declare ROOTFS_ATTESTATION_SIG="${ROOTFS_ATTESTATION}.sig"
 declare KEYFD=""

+require_command gpg
+require_command gpgv
+require_command sha512sum
+require_file "${ROOTFS}" "final SquashFS payload"
+require_variable VAR_SIGNING_KEY_FPR
+require_variable VAR_SIGNING_KEY_PASSFILE
+require_variable VAR_VERIFY_KEYRING
+require_file "${VAR_SIGNING_KEY_PASSFILE}" "GPG signing passphrase file"
+require_file "${VAR_VERIFY_KEYRING}" "GPG verification keyring"
+
+[[ "${VAR_SIGNER:-false}" == "true" ]] || die "Rootfs attestation requires an enabled artifact signer."
+
+rm -f -- "${ROOTFS_ATTESTATION}" "${ROOTFS_ATTESTATION_SIG}"
+
 # shellcheck disable=SC2155
 declare -i VAR_ROOTFS_SIZE=$(stat -c%s -- "${ROOTFS}")

@@ -126,7 +216,7 @@ fi
 cryptsetup open --key-file "/proc/$$/fd/${KEYFD}" "${LUKSFS}" crypt_liveiso

 # shellcheck disable=SC2155
-declare -i LUKS_FREE=$(blockdev --getsize64 /dev/mapper/crypt_liveiso)
+declare -i LUKS_FREE=$(blockdev --getsize64 "${MAPPER_DEV}")
 declare -i SQUASH_FS="${VAR_ROOTFS_SIZE}"

 if (( LUKS_FREE >= SQUASH_FS )); then
@@ -140,8 +230,22 @@ else

 fi

-dd if="${ROOTFS}" of=/dev/mapper/crypt_liveiso bs=8M status=progress conv=fsync
+dd if="${ROOTFS}" of="${MAPPER_DEV}" bs=8M status=progress conv=fsync
 sync
+
+# The selected boot root is the complete decrypted mapper. Hashing this exact block payload binds the signed manifest to the
+# bytes later mounted as SquashFS, including the mapper padding after the SquashFS image.
+LC_ALL=C sha512sum "${MAPPER_DEV}" >| "${ROOTFS_ATTESTATION}"
+
+gpg --batch --yes --pinentry-mode loopback --passphrase-file "${VAR_SIGNING_KEY_PASSFILE}" --local-user "${VAR_SIGNING_KEY_FPR}" \
+  --detach-sign --output "${ROOTFS_ATTESTATION_SIG}" "${ROOTFS_ATTESTATION}"
+
+gpgv --keyring "${VAR_VERIFY_KEYRING}" "${ROOTFS_ATTESTATION_SIG}" "${ROOTFS_ATTESTATION}"
+
+(cd / && LC_ALL=C sha512sum -c --strict --quiet "${ROOTFS_ATTESTATION}")
+
+chmod 0444 "${ROOTFS_ATTESTATION}" "${ROOTFS_ATTESTATION_SIG}"
+
 cryptsetup close crypt_liveiso

 exec {KEYFD}<&-
@@ -15,14 +15,11 @@
 # SPDX-Security-Contact: security@coresecret.eu

 # Module summary:
-# - Runs after the encrypted live root filesystem has been decrypted.
-# - Requires the pinned public key, attestation hash file, and detached signature to exist as readable, non-empty regular files
-#   inside the decrypted rootfs.
-# - Verifies the attestation signature with gpgv against the pinned key material.
-# - Confirms that the signature fingerprint matches the build-time expected rootfs fingerprint and panics on missing, malformed,
-#   or mismatched evidence.
-
-_SAVED_SET_OPTS="$(set +o)"
+# - Runs after the encrypted live root filesystem has been decrypted and selected for the SquashFS root mount.
+# - Requires the pinned public key and the signed decrypted-mapper SHA-512 manifest from the mounted live medium.
+# - Verifies the manifest signature and pinned signer fingerprint, then verifies the complete selected decrypted mapper against
+#   the manifest.
+# - Panics on missing, malformed, mismatched, or unverifiable evidence.

 set -eu

@@ -37,9 +34,12 @@ export CDLB_EXP_CA_FPR="@EXP_CA_FPR@"
 ### Name of the top-level dm-crypt mapping (e.g., cryptsetup --label): zzzz_ciss_crypt_squash.hook.binary ----------------------
 export CDLB_MAPPER_NAME="${CDLB_MAPPER_NAME:-crypt_liveiso}"

-### Attestation file locations inside decrypted rootfs. ------------------------------------------------------------------------
-CDLB_ATTEST_FPR_SHA="${CDLB_ATTEST_FPR_SHA:-/root/root/.ciss/attestation/${CDLB_EXP_FPR}.gpg.sha512sum.txt}"
-CDLB_ATTEST_FPR_SIG="${CDLB_ATTEST_FPR_SIG:-/root/root/.ciss/attestation/${CDLB_EXP_FPR}.gpg.sha512sum.txt.sig}"
+### Rootfs selection and attestation file locations. ---------------------------------------------------------------------------
+CDLB_LUKS_FS="${CDLB_LUKS_FS:-/live/ciss_rootfs.crypt}"
+CDLB_MAPPER_DEV="${CDLB_MAPPER_DEV:-/dev/mapper/${CDLB_MAPPER_NAME}}"
+CDLB_MNT_MEDIUM="${CDLB_MNT_MEDIUM:-/run/live/medium}"
+CDLB_ATTEST_ROOTFS_SHA="${CDLB_ATTEST_ROOTFS_SHA:-${CDLB_MNT_MEDIUM}${CDLB_LUKS_FS}.decrypted.sha512sum.txt}"
+CDLB_ATTEST_ROOTFS_SIG="${CDLB_ATTEST_ROOTFS_SIG:-${CDLB_ATTEST_ROOTFS_SHA}.sig}"
 CDLB_KEY_DIR="${CDLB_KEY_DIR:-/etc/ciss/keys}"

 ### Declare functions ----------------------------------------------------------------------------------------------------------
@@ -91,11 +91,13 @@ require_attestation_file() {

      log_er "0042()              : ${artifact_label} is a broken symlink, not a regular file: [${artifact_path}]"
      panic  "0042()              : ${artifact_label} is a broken symlink, not a regular file: [${artifact_path}]"
+      return 1

    fi

    log_er "0042()              : ${artifact_label} missing: [${artifact_path}]"
    panic  "0042()              : ${artifact_label} missing: [${artifact_path}]"
+    return 1

  fi

@@ -103,6 +105,7 @@ require_attestation_file() {

    log_er "0042()              : ${artifact_label} is not a regular file: [${artifact_path}]"
    panic  "0042()              : ${artifact_label} is not a regular file: [${artifact_path}]"
+    return 1

  fi

@@ -110,6 +113,7 @@ require_attestation_file() {

    log_er "0042()              : ${artifact_label} is empty: [${artifact_path}]"
    panic  "0042()              : ${artifact_label} is empty: [${artifact_path}]"
+    return 1

  fi

@@ -117,23 +121,56 @@ require_attestation_file() {

    log_er "0042()              : ${artifact_label} is not readable: [${artifact_path}]"
    panic  "0042()              : ${artifact_label} is not readable: [${artifact_path}]"
+    return 1

  fi

  return 0
 }

-HASH_FILE="${CDLB_ATTEST_FPR_SHA}"
-SIGN_FILE="${CDLB_ATTEST_FPR_SIG}"
+#######################################
+# Validate the selected decrypted rootfs payload.
+# Globals:
+#   None
+# Arguments:
+#   1: Absolute payload path
+# Returns:
+#   0: on success
+#######################################
+require_rootfs_payload() {
+  payload_path="${1}"
+
+  if [ ! -b "${payload_path}" ]; then
+
+    log_er "0042()              : Selected rootfs payload is not a block device: [${payload_path}]"
+    panic  "0042()              : Selected rootfs payload is not a block device: [${payload_path}]"
+    return 1
+
+  fi
+
+  if [ ! -r "${payload_path}" ]; then
+
+    log_er "0042()              : Selected rootfs payload is not readable: [${payload_path}]"
+    panic  "0042()              : Selected rootfs payload is not readable: [${payload_path}]"
+    return 1
+
+  fi
+
+  return 0
+}
+
+HASH_FILE="${CDLB_ATTEST_ROOTFS_SHA}"
+SIGN_FILE="${CDLB_ATTEST_ROOTFS_SIG}"
 KEYFILE="${CDLB_KEY_DIR}/${CDLB_EXP_FPR}.gpg"

 require_attestation_file "Public key"            "${KEYFILE}"
-require_attestation_file "Attestation data"      "${HASH_FILE}"
-require_attestation_file "Attestation signature" "${SIGN_FILE}"
+require_attestation_file "Rootfs attestation manifest"  "${HASH_FILE}"
+require_attestation_file "Rootfs attestation signature" "${SIGN_FILE}"
+require_rootfs_payload "${CDLB_MAPPER_DEV}"

-log_in "0042()               : Verifying rootfs attestation with 'gpgv' and inside LUKS encrypted rootfs pinned GPG FPR."
+log_in "0042()               : Verifying signed rootfs attestation manifest with pinned GPG FPR."

-if ! _STATUS="$(/usr/bin/gpgv --keyring "${KEYFILE}" --status-fd 1 "${SIGN_FILE}" "${HASH_FILE}" 2>&1)"; then
+if ! _STATUS="$(/usr/bin/gpgv --no-default-keyring --keyring "${KEYFILE}" --status-fd 1 "${SIGN_FILE}" "${HASH_FILE}" 2>&1)"; then

  log_er "0042()              : gpgv verification failed for signature: [${SIGN_FILE}]"

@@ -145,6 +182,7 @@ if ! _STATUS="$(/usr/bin/gpgv --keyring "${KEYFILE}" --status-fd 1 "${SIGN_FILE}

  sleep 8
  panic  "0042()              : gpgv verification failed for signature: [${SIGN_FILE}]"
+  exit 1

 fi

@@ -160,10 +198,51 @@ else
  log_er "0042()              : Signature FPR mismatch: got: [${_CDLB_SIG_FILE_FPR}] expected: [${CDLB_EXP_FPR}]"
  sleep 8
  panic "[FATAL] Signature FPR mismatch: got: [${_CDLB_SIG_FILE_FPR}] expected: [${CDLB_EXP_FPR}]."
+  exit 1

 fi

-eval "${_SAVED_SET_OPTS}"
+_ATTEST_RECORD_COUNT="$(awk 'NF && $1 !~ /^#/ { count++ } END { print count + 0 }' "${HASH_FILE}")"
+
+if [ "${_ATTEST_RECORD_COUNT}" -ne 1 ]; then
+
+  log_er "0042()              : Rootfs attestation manifest must contain exactly one checksum record: [${HASH_FILE}]"
+  sleep 8
+  panic  "0042()              : Rootfs attestation manifest must contain exactly one checksum record: [${HASH_FILE}]"
+  exit 1
+
+fi
+
+_ATTESTED_PAYLOAD="$(awk 'NF && $1 !~ /^#/ { print $2; exit }' "${HASH_FILE}")"
+
+if [ "${_ATTESTED_PAYLOAD}" != "${CDLB_MAPPER_DEV}" ]; then
+
+  log_er "0042()              : Rootfs attestation manifest targets [${_ATTESTED_PAYLOAD}], expected selected payload [${CDLB_MAPPER_DEV}]"
+  sleep 8
+  panic  "0042()              : Rootfs attestation manifest does not target the selected rootfs payload."
+  exit 1
+
+fi
+
+log_in "0042()               : Verifying selected decrypted rootfs mapper content: [${CDLB_MAPPER_DEV}]"
+
+if ! _CHECKSUM_STATUS="$(cd / && LC_ALL=C /usr/bin/sha512sum -c --strict --quiet "${HASH_FILE}" 2>&1)"; then
+
+  log_er "0042()              : Rootfs payload checksum verification failed: [${CDLB_MAPPER_DEV}]"
+
+  if [ -n "${_CHECKSUM_STATUS}" ]; then
+
+    printf '%s\n' "${_CHECKSUM_STATUS}" >&2
+
+  fi
+
+  sleep 8
+  panic  "0042()              : Rootfs payload checksum verification failed: [${CDLB_MAPPER_DEV}]"
+  exit 1
+
+fi
+
+log_ok "0042()               : Rootfs payload checksum verification successful: [${CDLB_MAPPER_DEV}]"

 printf "\e[92m[INFO] Successfully applied : [/usr/lib/live/boot/0042_ciss_post_decrypt_attest] \n\e[0m"

@@ -9,12 +9,12 @@
 # SPDX-LicenseComment: This file is part of the CISS.debian.installer.secure framework.
 # SPDX-PackageName: CISS.debian.live.builder
 # SPDX-Security-Contact: security@coresecret.eu
+# shellcheck disable=SC2154

 guard_sourcing || return "${ERR_GUARD_SRCE}"

 #######################################
 # Integrates and generates sha512sum and GPG signatures on CISS specific LIVE boot artifacts:
-#  - /root/.ciss/attestation/VAR_SIGNING_KEY_FPR.*
 #  - /etc/initramfs-tools/files/unlock_wrapper.sh
 #  - /usr/lib/live/boot/0030-ciss-verify-checksums
 # Globals:
@@ -31,10 +31,7 @@ guard_sourcing || return "${ERR_GUARD_SRCE}"
 ciss_upgrades_boot() {
  printf "\e[95m🧪 %s starting ... \e[0m\n" "${BASH_SOURCE[0]}"

-  gpg --batch --yes --export "${VAR_SIGNING_KEY_FPR}" >| "${VAR_HANDLER_BUILD_DIR}/config/includes.chroot/root/.ciss/attestation/${VAR_SIGNING_KEY_FPR}.gpg"
-
  declare -ar _ary_target=(
-    "/root/.ciss/attestation/${VAR_SIGNING_KEY_FPR}.gpg"
    "/etc/initramfs-tools/files/unlock_wrapper.sh"
    "/usr/lib/live/boot/0030-ciss-verify-checksums"
  )