fix(ci): emit CycloneDX SBOM so attestation fits the 16 MiB cap

The v0.2.1 release failed at "Attest image SBOM":
  Error: SBOM file exceeds maximum allowed size: 16777216 bytes

A full Kairos OS-image SBOM in SPDX-json is ~23.4 MiB, over the
actions/attest-sbom 16 MiB predicate cap. The same SBOM in CycloneDX-json is
~2.8 MiB (measured with syft on kairos-kubeadm:v1.34.0). Switch both the image
and binary SBOMs to cyclonedx-json (one consistent, compact format).

Also drop the predicate-typed SBOM self-verify: the Attest-*-SBOM step failing
(as it just did) is the real guard, and a predicate-type filter couples R-4 to
the SBOM spec version. R-4 keeps the load-bearing provenance verify. This is
the zero-coupling option the security review flagged.

Docs updated: SBOMs are CycloneDX; verify with
--predicate-type https://cyclonedx.org/bom. actionlint clean.

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: William Rizzo <william.rizzo@gmail.com>

Author: wrkode

.github/workflows/release.yml

@@ -8,7 +8,7 @@ name: Release
 #     ghcr.io/<owner>/provider-kubernetes:<tag>-k8s<minor> (e.g. v0.1.0-k8s1.34).
 #     The newest supported minor is additionally tagged <tag> and latest.
 #   - a GitHub Release with the provider binary + sha256 checksum.
-#   - SLSA build-provenance + SPDX SBOM attestations for every image (by digest)
+#   - SLSA build-provenance + CycloneDX SBOM attestations for every image (by digest)
 #     and for the binary, signed keyless via the workflow's OIDC identity (ADR-15).
 #     Verify with `gh attestation verify` -- see the GitHub Release notes / README.
 #
@@ -144,12 +144,15 @@ jobs:
             done
           fi
 
-      - name: Generate image SBOM (SPDX)
+      # CycloneDX, not SPDX: a full OS-image SPDX SBOM is ~23 MiB and exceeds the
+      # actions/attest-sbom 16 MiB predicate cap; the equivalent CycloneDX SBOM is
+      # ~3 MiB. CycloneDX is the compact format for image-scale SBOMs.
+      - name: Generate image SBOM (CycloneDX)
         uses: anchore/sbom-action@e22c389904149dbc22b58101806040fa8d37a610 # v0.24.0
         with:
           image: ${{ steps.build.outputs.image }}@${{ steps.build.outputs.digest }}
-          format: spdx-json
-          output-file: image.spdx.json
+          format: cyclonedx-json
+          output-file: image.cdx.json
           upload-artifact: false
           upload-release-assets: false # we attest the SBOM; do not auto-attach it to the Release
 
@@ -165,24 +168,23 @@ jobs:
         with:
           subject-name: ${{ steps.build.outputs.image }}
           subject-digest: ${{ steps.build.outputs.digest }}
-          sbom-path: image.spdx.json
+          sbom-path: image.cdx.json
           push-to-registry: true
 
-      # R-4: prove the attestations are real before a tester relies on them. A
-      # broken signing step fails the release here, not in the field.
-      - name: Self-verify image attestations
+      # R-4: prove the attestation is real before a tester relies on it. A broken
+      # signing step fails the release here, not in the field. We verify provenance
+      # (the load-bearing integrity check); the SBOM attestation's existence is
+      # already guaranteed by the Attest-image-SBOM step above failing otherwise, so
+      # we do not add a predicate-type filter here (avoids coupling to the SBOM
+      # format/spec version).
+      - name: Self-verify image attestation
         env:
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: |
           set -euo pipefail
           ref="${{ steps.build.outputs.image }}@${{ steps.build.outputs.digest }}"
           echo "verifying provenance for oci://${ref}"
           gh attestation verify "oci://${ref}" --repo "${{ github.repository }}"
-          echo "verifying SBOM attestation for oci://${ref}"
-          # The SPDX predicate-type suffix tracks the SBOM's spdxVersion (syft emits
-          # SPDX-2.3 -> /v2.3). Bump this if the SBOM SPDX version changes.
-          gh attestation verify "oci://${ref}" --repo "${{ github.repository }}" \
-            --predicate-type https://spdx.dev/Document/v2.3
 
   # Build the provider binary and publish a GitHub Release with a checksum.
   binary:
@@ -214,12 +216,14 @@ jobs:
           sha256sum agent-provider-kubernetes_*.tar.gz > checksums.txt
           cat checksums.txt
 
-      - name: Generate binary SBOM (SPDX)
+      # CycloneDX for consistency with the image SBOM (one SBOM format across all
+      # published artifacts; well under the attest-sbom 16 MiB cap).
+      - name: Generate binary SBOM (CycloneDX)
         uses: anchore/sbom-action@e22c389904149dbc22b58101806040fa8d37a610 # v0.24.0
         with:
           file: bin/agent-provider-kubernetes
-          format: spdx-json
-          output-file: binary.spdx.json
+          format: cyclonedx-json
+          output-file: binary.cdx.json
           upload-artifact: false
           upload-release-assets: false # we attest the SBOM; do not auto-attach it to the Release
 
@@ -232,9 +236,10 @@ jobs:
         uses: actions/attest-sbom@c604332985a26aa8cf1bdc465b92731239ec6b9e # v4.1.0
         with:
           subject-path: bin/agent-provider-kubernetes_*.tar.gz
-          sbom-path: binary.spdx.json
+          sbom-path: binary.cdx.json
 
-      # R-4: verify the binary attestation before publishing the Release.
+      # R-4: verify provenance before publishing the Release (the SBOM attestation's
+      # existence is guaranteed by the Attest-binary-SBOM step failing otherwise).
       - name: Self-verify binary attestation
         env:
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
@@ -243,10 +248,6 @@ jobs:
           tarball="$(ls bin/agent-provider-kubernetes_*.tar.gz)"
           echo "verifying provenance for ${tarball}"
           gh attestation verify "${tarball}" --repo "${{ github.repository }}"
-          echo "verifying SBOM attestation for ${tarball}"
-          # SPDX predicate-type suffix tracks the SBOM spdxVersion (SPDX-2.3 -> /v2.3).
-          gh attestation verify "${tarball}" --repo "${{ github.repository }}" \
-            --predicate-type https://spdx.dev/Document/v2.3
 
       - name: Create GitHub Release
         env:
@@ -264,7 +265,7 @@ jobs:
           for m in $(echo "${MINORS}" | jq -r '.[]'); do
             imglist="${imglist}${repo}:${TAG}-k8s${m}"$'\n'
           done
-          verify="$(printf 'Verifying (every image + the binary carry keyless SLSA provenance + SPDX SBOM attestations):\n```\n# image (resolve the digest first, then verify by digest)\ngh attestation verify oci://%s:%s --repo %s\n# binary\ngh attestation verify agent-provider-kubernetes_%s_linux_amd64.tar.gz --repo %s\n```\n' \
+          verify="$(printf 'Verifying (every image + the binary carry keyless SLSA provenance + CycloneDX SBOM attestations):\n```\n# image (resolve the digest first, then verify by digest)\ngh attestation verify oci://%s:%s --repo %s\n# binary\ngh attestation verify agent-provider-kubernetes_%s_linux_amd64.tar.gz --repo %s\n```\n' \
             "${repo}" "${TAG}" "${REPO_SLUG}" "${TAG}" "${REPO_SLUG}")"
           notes="$(printf 'Kairos images (one per supported Kubernetes minor):\n```\n%s```\nThe newest supported minor (%s) is also published as `%s:%s` and `%s:latest`.\n\n%s\nProvider binary (linux/amd64) attached below. This is a development release; not yet field-ready.\n' \
             "${imglist}" "${LATEST_MINOR}" "${repo}" "${TAG}" "${repo}" "${verify}")"

README.md

@@ -149,7 +149,7 @@ checksum. **These are development releases and are not field-ready.**
 ### Verifying a release
 
 Every published image and the release binary carry **keyless SLSA build-provenance
-and SPDX SBOM attestations**, signed via the release workflow's OIDC identity (no
+and CycloneDX SBOM attestations**, signed via the release workflow's OIDC identity (no
 private key). Verify them with the GitHub CLI -- no extra tooling:
 
 ```sh
@@ -168,8 +168,9 @@ gh attestation verify \
 ```
 
 A successful verification confirms the artifact was built by this repository's
-`Release` workflow from a tagged commit. Add `--predicate-type
-https://spdx.dev/Document/v2.3` to verify the SBOM attestation specifically. See
+`Release` workflow from a tagged commit. That command checks the provenance; add
+`--predicate-type https://cyclonedx.org/bom` to verify the CycloneDX SBOM
+attestation specifically. See
 [`docs/testing.md`](./docs/testing.md) for the full supply-chain picture.
 
 Maintainers cut a release by pushing a signed semver tag; the `Release` workflow

docs/testing.md

@@ -177,7 +177,7 @@ is the one CI built. The two halves of the supply chain:
   HTTPS-served `.sha256`.
 - **Publish-time (outputs):** the `Release` workflow attaches, to every published
   image (by digest) and to the release binary, a **keyless SLSA build-provenance
-  attestation** and an **SPDX SBOM attestation**, signed via the workflow's OIDC
+  attestation** and a **CycloneDX SBOM attestation**, signed via the workflow's OIDC
   identity (no private key, ADR-15). The release job self-verifies its own
   attestations before publishing, so a broken signing step fails the release rather
   than reaching a tester.
@@ -193,8 +193,9 @@ gh attestation verify agent-provider-kubernetes_<tag>_linux_amd64.tar.gz \
   --repo kairos-io/provider-kubernetes
 ```
 
-Add `--predicate-type https://spdx.dev/Document/v2.3` to check the SBOM
-attestation specifically (the version suffix tracks the SBOM's SPDX version). See the [README](../README.md#verifying-a-release) for the
+The command above checks the build-provenance attestation. The SBOM is attested
+separately as CycloneDX; to verify it specifically add
+`--predicate-type https://cyclonedx.org/bom`. See the [README](../README.md#verifying-a-release) for the
 digest-resolution one-liner.
 
 ## See also