WIP: Rough draft for updated generic OCI sealing by cgwalters · Pull Request #226 · composefs/composefs-rs

cgwalters · 2026-02-08T22:44:50Z

This is just some rough draft raw material that builds on:

oci: Add OCI-native manifest/config storage and image management #216 (🆕 now requires manifest/config as external not inline splitstream objeects, also the OCI artifact and referrer support was key)
doc/plans: Update OCI sealing spec (kernel sigs, flattened layers) #224 (Lots of updates there, I redid to go all-in on an external signature+digests by default)

cgwalters · 2026-02-12T16:53:07Z

crates/cfsctl/src/main.rs

+                    composefs_oci::signing::FsVeritySigningKey::from_pem(&cert_pem, &key_pem)?;
+
+                // Build subject descriptor from the source image's manifest
+                let manifest_json = img.manifest().to_string()?;


Hmm we actually need to operate on the raw original representation, can't rely on to_string() always giving us the same thing.

cgwalters · 2026-02-12T16:53:56Z

crates/cfsctl/src/main.rs

+        /// Image reference (tag name)
+        image: String,
+        /// Path to the OCI layout directory (must already exist)
+        oci_layout_path: PathBuf,


I think we can use clap(value_parser) into an ocidir directly or so

cgwalters · 2026-02-12T16:54:28Z

crates/composefs-oci/src/lib.rs

-/// the container to be mounted with integrity protection.
-///
-/// Returns a tuple of (sha256 content hash, fs-verity hash value) for the updated configuration.
-pub fn seal<ObjectID: FsVerityHashValue>(


Might be cleaner if we do a prep commit that removes the old sealing as we know we're not going to do it anymore.

cgwalters · 2026-02-12T16:54:45Z

crates/composefs-oci/src/oci_image.rs

+/// # Returns
+///
+/// The number of referrer artifacts exported.
+pub fn export_referrers_to_oci_layout<ObjectID: FsVerityHashValue>(


Something like this could land as a prep commit

cgwalters · 2026-02-12T16:54:50Z

crates/composefs-oci/src/oci_image.rs

+    use std::fs;
+    use std::io::Write;
+
+    let blobs_dir = oci_layout_path.join("blobs").join("sha256");


cgwalters · 2026-02-12T16:56:27Z

crates/composefs-oci/src/signature.rs

+        format!("{seed:02x}").repeat(32)
+    }
+
+    fn sample_subject() -> Descriptor {


Let's unify this stuff with shared infra to generate an ocidir with known content

crates/composefs/src/fsverity/ioctl.rs

crates/composefs/src/fsverity/keyring.rs

cgwalters · 2026-03-11T12:38:12Z

This one will need to logically depend on #225 because that one has a lot of hardening for the EROFS parser

The biggest goal here is support for Linux kernel-native fsverity signatures to be attached to layers, which enables integration with IPE. Add support for a fully separate OCI "composefs signature" artifact which can be attached to an image. Drop the -impl.md doc...it's not useful to try to write this stuff in markdown. The spec has some implementation considerations, but it's easier to look at implementation side from a code draft. Add standardized-erofs-meta.md as a placeholder document outlining the goal of standardizing composefs EROFS serialization across implementations (canonical model: tar -> dumpfile -> EROFS). Assisted-by: OpenCode (Claude Opus 4.5) Signed-off-by: Colin Walters <walters@verbum.org>

Implement end-to-end support for cryptographically signing composefs OCI images using PKCS#7/fsverity detached signatures, stored as OCI referrer artifacts following the 'composefs erofs-alongside' spec. Core signing infrastructure (composefs crate): - Add fsverity algorithm constants and ComposeFsAlgorithm type - Add formatted_digest module for kernel-compatible fsverity digest construction (the 12-byte header + raw hash used by the kernel's FS_IOC_ENABLE_VERITY ioctl) - Add kernel keyring support via composefs-ioctls keyring module (inject X.509 certs into .fs-verity keyring for kernel-level signature enforcement) OCI signing library (composefs-oci crate): - signing.rs: FsVeritySigningKey (sign) and FsVeritySignatureVerifier (verify) using openssl PKCS#7 with DETACHED|BINARY|NOATTR flags, compatible with Linux kernel fsverity builtin signature verification - signature.rs: OCI artifact manifest builder/parser for the 'application/vnd.composefs.erofs-alongside.v1' artifact type, storing per-layer and merged EROFS images alongside their PKCS#7 signatures as typed layers with composefs.* annotations - image.rs: compute_per_layer_digests() and compute_merged_digest() for deterministic EROFS image generation from OCI layer stacks - oci_image.rs: seal_image() to compute and embed the composefs fsverity digest into the OCI config, export/import to OCI layout directories (migrated to ocidir crate for atomic I/O), referrer index management CLI commands (cfsctl): - 'oci seal <image>' — compute composefs EROFS, embed fsverity digest - 'oci sign <image> --cert --key' — create signature artifact - 'oci verify <image> [--cert]' — verify signatures (digest-only without --cert, full PKCS#7 with --cert) - 'oci mount <name> <mountpoint> [--require-signature --trust-cert]' — verify signatures before kernel mount - 'oci pull ... --require-signature --trust-cert' — verify after pull - 'oci push <image> <dest> [--signatures]' — export to OCI layout - 'oci export-signatures <image> <dest>' — export just artifacts - 'oci inspect' — show referrer info in JSON output - 'keyring add-cert <pem>' — inject cert into kernel keyring The mount and pull --require-signature paths share a common verify_image_signatures() helper that recomputes expected EROFS digests and verifies each PKCS#7 signature blob against the trusted certificate. The mount command now also resolves tag names (via OciImage::open_ref) instead of requiring raw config digests, consistent with seal/sign/ verify. Integration tests: - signing.rs: 17 unprivileged tests covering sign, verify, wrong cert, export, seal+sign roundtrip, artifact structure, --require-signature on pull and mount - privileged.rs: 7 tests for real fsverity enforcement, kernel keyring injection, kernel signature acceptance/rejection - podman.rs: 3 tests building real container images via podman - cli.rs: updated for richer OCI test layout (4 entries) and new oci push/roundtrip tests - test-oci-sign-verify.sh: standalone shell-based integration tests Assisted-by: OpenCode (Claude claude-opus-4-6) Signed-off-by: Colin Walters <walters@verbum.org>

cgwalters force-pushed the sealing-impl branch 2 times, most recently from 1ce192a to 063ff54 Compare February 12, 2026 16:49

cgwalters commented Feb 12, 2026

View reviewed changes

cgwalters force-pushed the sealing-impl branch 3 times, most recently from 361eeb7 to 2f93e4a Compare March 6, 2026 12:24

cgwalters added 2 commits March 12, 2026 22:12

cgwalters force-pushed the sealing-impl branch from 2f93e4a to 6b676dd Compare March 13, 2026 00:29

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WIP: Rough draft for updated generic OCI sealing#226

WIP: Rough draft for updated generic OCI sealing#226
cgwalters wants to merge 2 commits intocomposefs:mainfrom
cgwalters:sealing-impl

cgwalters commented Feb 8, 2026

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