ci: sign, scan and harden the docker image

.github/workflows/image-scan.yml

@@ -0,0 +1,47 @@
+name: Image scan
+
+# Vulnerabilities are published after an image is released: every week, scan
+# `latest` (its Debian packages and the crates in the binary); findings show in
+# the repository's Security tab.
+on:
+  schedule:
+    - cron: "17 5 * * 1"
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+env:
+  IMAGE: ghcr.io/${{ github.repository }}
+  # moved by hand, with the one in release.yml
+  TRIVY: ghcr.io/aquasecurity/trivy:0.76.2@sha256:8f6bb947dbc528902e11f2f5be52f7b519f6a39d5d148f41166f2040499768fb
+
+jobs:
+  trivy:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: read
+      security-events: write
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+
+      - uses: docker/login-action@8aa5831fb8d48d8f76594c7ddde61ae58019f550 # v4.8.0
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      # the login above: credentials for ghcr.io and nothing else
+      - name: Scan the latest image
+        run: |
+          mkdir -m 777 "$RUNNER_TEMP/trivy"
+          docker run --rm -e DOCKER_CONFIG=/docker -v "$HOME/.docker/config.json:/docker/config.json:ro" \
+            -v "$RUNNER_TEMP/trivy:/out" "$TRIVY" image \
+            --image-src remote --scanners vuln --ignore-unfixed \
+            --format sarif --output /out/image.sarif "$IMAGE:latest"
+
+      - uses: github/codeql-action/upload-sarif@33d7b85da1a04171e211befe2c739303b9a4c066 # v4.39.3
+        with:
+          sarif_file: ${{ runner.temp }}/trivy/image.sarif
+          category: image

.github/workflows/release.yml

@@ -3,6 +3,9 @@ name: Release
 # Pushing a tag vX.Y.Z publishes ghcr.io/forgust-dev/forgust:X.Y.Z (and X.Y,
 # latest) for amd64 and arm64, then opens a draft GitHub release with notes
 # grouped from the commit subjects since the last tag (.github/release-notes.sh).
+# The image carries an SBOM and BuildKit provenance, is scanned for known
+# vulnerabilities before it gets its tags, and is signed: a build provenance
+# attestation that `gh attestation verify` checks (see SECURITY.md).
 # Each architecture builds on its own runner: a Rust release build under
 # emulation would take hours.
 on:
@@ -15,6 +18,8 @@ permissions:
 env:
   IMAGE: ghcr.io/${{ github.repository }}
   DESCRIPTION: A fast, self-hosted code forge written in Rust
+  # moved by hand, with the one in image-scan.yml
+  TRIVY: ghcr.io/aquasecurity/trivy:0.76.2@sha256:8f6bb947dbc528902e11f2f5be52f7b519f6a39d5d148f41166f2040499768fb
 
 jobs:
   check:
@@ -94,13 +99,52 @@ jobs:
           if-no-files-found: error
           retention-days: 1
 
-  publish:
-    # one multi-arch image under the version tags
+  scan:
+    # the Debian packages and the crates in the binary: a high or critical
+    # vulnerability that has a fix stops the release before the image gets a tag.
+    # A job of its own, so that the scanner only ever sees a token that can read.
+    name: scan (${{ matrix.arch }})
     needs: build
+    strategy:
+      matrix:
+        arch: [amd64, arm64]
+    runs-on: ubuntu-latest
+    permissions:
+      packages: read
+    steps:
+      - uses: actions/download-artifact@9000827ccba6bdab643e8b6fd33ac0654aef8333 # v8.0.2
+        with:
+          path: /tmp/digests
+          name: digests-${{ matrix.arch }}
+
+      - uses: docker/login-action@8aa5831fb8d48d8f76594c7ddde61ae58019f550 # v4.8.0
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      # the login above, read-only: credentials for ghcr.io and nothing else
+      - name: Scan for vulnerabilities
+        working-directory: /tmp/digests
+        run: |
+          docker run --rm -e DOCKER_CONFIG=/docker -v "$HOME/.docker/config.json:/docker/config.json:ro" "$TRIVY" image \
+            --image-src remote --platform "linux/$ARCH" --scanners vuln \
+            --severity HIGH,CRITICAL --ignore-unfixed --exit-code 1 "$IMAGE@sha256:$(ls)"
+        env:
+          ARCH: ${{ matrix.arch }}
+
+  publish:
+    # one multi-arch image under the version tags, signed
+    needs: scan
     runs-on: ubuntu-latest
     permissions:
       contents: read
       packages: write
+      # the signature: a Sigstore certificate for this workflow run, stored with
+      # the repository's attestations and next to the image
+      id-token: write
+      attestations: write
+      artifact-metadata: write
     steps:
       - uses: actions/download-artifact@9000827ccba6bdab643e8b6fd33ac0654aef8333 # v8.0.2
         with:
@@ -130,17 +174,29 @@ jobs:
             org.opencontainers.image.description=${{ env.DESCRIPTION }}
 
       - name: Create the multi-arch image
+        id: image
         working-directory: /tmp/digests
         run: |
           # tags and the index's annotations (source, version, licenses...) from metadata-action
           mapfile -t args < <(jq -r '(.tags[] | "-t", .), (.annotations[] | "--annotation", .)' <<< "$DOCKER_METADATA_OUTPUT_JSON")
-          docker buildx imagetools create "${args[@]}" $(printf "$IMAGE@sha256:%s " *)
+          docker buildx imagetools create --metadata-file "$RUNNER_TEMP/image.json" "${args[@]}" $(printf "$IMAGE@sha256:%s " *)
+          # the digest of what was just pushed, for the signature: not read back from a tag
+          digest=$(jq -er '."containerimage.descriptor".digest' "$RUNNER_TEMP/image.json")
+          echo "digest=$digest" >> "$GITHUB_OUTPUT"
 
       - name: Inspect
         run: docker buildx imagetools inspect "$IMAGE:$VERSION"
         env:
           VERSION: ${{ steps.meta.outputs.version }}
 
+      # signed build provenance for the multi-arch image: which commit and which
+      # workflow run built this digest
+      - uses: actions/attest@1e69f48acb82d1966a394da916b4c1698aa569d6 # v4.2.2
+        with:
+          subject-name: ${{ env.IMAGE }}
+          subject-digest: ${{ steps.image.outputs.digest }}
+          push-to-registry: true
+
   release:
     # a draft: read the notes, then publish it
     needs: publish

Dockerfile

@@ -1,14 +1,26 @@
 # syntax=docker/dockerfile:1.7
 # Forgust: one binary + the web UI. Runtime needs git >= 2.45 (trixie ships 2.47).
+#
+# Base images are pinned by digest (Dependabot moves the tag and the digest
+# together). The image's SBOM (`docker buildx build --sbom=true`) lists the
+# Debian packages of the final stage and the crates in the binary, which
+# cargo-auditable records there; BUILDKIT_SBOM_SCAN_STAGE adds one more SBOM
+# per build stage, for the npm packages and the toolchains.
 
-FROM node:26.12-bookworm-slim AS web
+FROM node:26.12-bookworm-slim@sha256:88e480776c6149ff1d098cd304f44bf18057fb5d284a3329b78162d29821e28c AS web
+ARG BUILDKIT_SBOM_SCAN_STAGE=true
 WORKDIR /src/web
 COPY web/package.json web/package-lock.json ./
 RUN npm ci --no-audit --no-fund
 COPY web/ ./
 RUN npm run build
 
-FROM rust:1.99-trixie AS build
+FROM rust:1.99-trixie@sha256:8a4e90c7946b74626488b1446f712c0fe0ed1a596cbd3d871684bc9c5433ae07 AS build
+ARG BUILDKIT_SBOM_SCAN_STAGE=true
+# writes the dependency list into the binary: SBOM and vulnerability scanners read it
+ARG CARGO_AUDITABLE=0.7.7
+RUN --mount=type=cache,target=/usr/local/cargo/registry \
+    cargo install --locked cargo-auditable@${CARGO_AUDITABLE}
 WORKDIR /src
 ENV SQLX_OFFLINE=true CARGO_TERM_COLOR=never
 COPY Cargo.toml Cargo.lock ./
@@ -17,11 +29,13 @@ COPY crates crates
 COPY bench bench
 RUN --mount=type=cache,target=/usr/local/cargo/registry \
     --mount=type=cache,target=/src/target \
-    cargo build --release --locked -p forgust-server \
+    cargo auditable build --release --locked -p forgust-server \
  && cp target/release/forgust /usr/local/bin/forgust
 
-FROM debian:trixie-slim
+FROM debian:trixie-slim@sha256:a72b4433de1cf7d6bae0c4cee74d0547f58601a643b3375f070c51600d63b6b2
+# upgrade: security fixes Debian published after the pinned base image was built
 RUN apt-get update \
+ && apt-get upgrade -y \
  && apt-get install -y --no-install-recommends git ca-certificates postgresql-client tini \
  && rm -rf /var/lib/apt/lists/* \
  && useradd --system --home /var/lib/forgust --create-home --uid 10001 forgust

README.md

@@ -70,6 +70,10 @@ services:
   forgust:
     image: ghcr.io/forgust-dev/forgust:0.1
     restart: unless-stopped
+    read_only: true
+    tmpfs: [/tmp]
+    cap_drop: [ALL]
+    security_opt: ["no-new-privileges:true"]
     ports: ["8080:8080", "2222:2222"]
     environment:
       FORGUST_DATABASE__URL: postgres://forgust:change-me@db:5432/forgust
@@ -87,6 +91,8 @@ services:
 volumes: { forgust-data: {}, db-data: {} }
 ```
 
+- **Verify the image:** releases are signed and carry an SBOM, see
+  [SECURITY.md](SECURITY.md#verifying-a-release).
 - **First administrator:** the log prints a one-time link on first start
   (`docker compose logs forgust | grep setup`).
 - **Configuration:** every key in [`forgust.example.toml`](forgust.example.toml) can

SECURITY.md

@@ -14,6 +14,29 @@ published, unless you prefer not to be named.
 
 Forgust is before 1.0: only the latest release gets security fixes.
 
+## Verifying a release
+
+The release workflow builds `ghcr.io/forgust-dev/forgust` on GitHub's runners and
+signs it with a build provenance attestation: a Sigstore certificate that names the
+repository, the tag and the workflow run that built the image. To check an image
+before running it, with the [GitHub CLI](https://cli.github.com):
+
+```sh
+gh attestation verify oci://ghcr.io/forgust-dev/forgust:0.2.0 \
+  --repo forgust-dev/forgust --signer-workflow forgust-dev/forgust/.github/workflows/release.yml
+```
+
+Each image also carries an SBOM (SPDX): the Debian packages of the image, the crates
+compiled into the binary, and the packages of the build stages.
+
+```sh
+docker buildx imagetools inspect ghcr.io/forgust-dev/forgust:0.2.0 --format '{{ json .SBOM }}'
+```
+
+The image is scanned for known vulnerabilities at each release, and `latest` every
+week. Releases up to 0.1.0 were published before signing and have no attestation
+to verify.
+
 ## Scope
 
 Anything in this repository: the server and its APIs (`/api/v1`, `/api/v4`, the

compose.yml

@@ -17,6 +17,11 @@ services:
     image: forgust:local
     build: .
     restart: unless-stopped
+    # the server only writes to its volume and /tmp, and needs no capability
+    read_only: true
+    tmpfs: [/tmp]
+    cap_drop: [ALL]
+    security_opt: ["no-new-privileges:true"]
     depends_on:
       db: { condition: service_healthy }
       s3: { condition: service_healthy }