From 27a91f9a0ec89580cda842fd0f54ba5f60fea49c Mon Sep 17 00:00:00 2001
From: Alex Pyrgiotis <alex.p@freedom.press>
Date: Tue, 11 Feb 2025 19:15:49 +0100
Subject: [PATCH] Publish and attest multi-architecture container images

A new `dangerzone-image attest-provenance` script is now available,
making it possible to verify the attestations of an image published on
the github container registry.

Container images are now build nightly and uploaded to the container
registry.
---
 dangerzone/updater/attestations.py | 90 ++++++++++++++++++++++++++++++
 dangerzone/updater/cli.py          | 49 ++++++++++++++++
 2 files changed, 139 insertions(+)
 create mode 100644 dangerzone/updater/attestations.py

diff --git a/dangerzone/updater/attestations.py b/dangerzone/updater/attestations.py
new file mode 100644
index 0000000..bdf1ef6
--- /dev/null
+++ b/dangerzone/updater/attestations.py
@@ -0,0 +1,90 @@
+import subprocess
+from tempfile import NamedTemporaryFile
+
+from . import cosign
+
+# NOTE: You can grab the SLSA attestation for an image/tag pair with the following
+# commands:
+#
+#     IMAGE=ghcr.io/apyrgio/dangerzone/dangerzone
+#     TAG=20250129-0.8.0-149-gbf2f5ac
+#     DIGEST=$(crane digest ${IMAGE?}:${TAG?})
+#     ATT_MANIFEST=${IMAGE?}:${DIGEST/:/-}.att
+#     ATT_BLOB=${IMAGE?}@$(crane manifest ${ATT_MANIFEST?} | jq -r '.layers[0].digest')
+#     crane blob ${ATT_BLOB?} | jq -r '.payload' | base64 -d | jq
+CUE_POLICY = r"""
+// The predicateType field must match this string
+predicateType: "https://slsa.dev/provenance/v0.2"
+
+predicate: {{
+  // This condition verifies that the builder is the builder we
+  // expect and trust. The following condition can be used
+  // unmodified. It verifies that the builder is the container
+  // workflow.
+  builder: {{
+    id: =~"^https://github.com/slsa-framework/slsa-github-generator/.github/workflows/generator_container_slsa3.yml@refs/tags/v[0-9]+.[0-9]+.[0-9]+$"
+  }}
+  invocation: {{
+    configSource: {{
+      // This condition verifies the entrypoint of the workflow.
+      // Replace with the relative path to your workflow in your
+      // repository.
+      entryPoint: "{workflow}"
+
+      // This condition verifies that the image was generated from
+      // the source repository we expect. Replace this with your
+      // repository.
+      uri: =~"^git\\+https://github.com/{repository}@refs/heads/{branch}"
+      // Add a condition to check for a specific commit hash
+      digest: {{
+        sha1: "{commit}"
+      }}
+    }}
+  }}
+}}
+"""
+
+
+def verify(
+    image_name: str,
+    branch: str,
+    commit: str,
+    repository: str,
+    workflow: str,
+) -> bool:
+    """
+    Look up the image attestation to see if the image has been built
+    on Github runners, and from a given repository.
+    """
+    cosign.ensure_installed()
+    policy = CUE_POLICY.format(
+        repository=repository, workflow=workflow, commit=commit, branch=branch
+    )
+
+    # Put the value in files and verify with cosign
+    with (
+        NamedTemporaryFile(mode="w", suffix=".cue") as policy_f,
+    ):
+        policy_f.write(policy)
+        policy_f.flush()
+
+        # Call cosign with the temporary file paths
+        cmd = [
+            "cosign",
+            "verify-attestation",
+            "--type",
+            "slsaprovenance",
+            "--policy",
+            policy_f.name,
+            "--certificate-oidc-issuer",
+            "https://token.actions.githubusercontent.com",
+            "--certificate-identity-regexp",
+            "^https://github.com/slsa-framework/slsa-github-generator/.github/workflows/generator_container_slsa3.yml@refs/tags/v[0-9]+.[0-9]+.[0-9]+$",
+            image_name,
+        ]
+
+        result = subprocess.run(cmd, capture_output=True)
+        if result.returncode != 0:
+            error = result.stderr.decode()
+            raise Exception(f"Attestation cannot be verified. {error}")
+        return True
diff --git a/dangerzone/updater/cli.py b/dangerzone/updater/cli.py
index 9363d51..ede57d8 100644
--- a/dangerzone/updater/cli.py
+++ b/dangerzone/updater/cli.py
@@ -103,5 +103,54 @@ def get_manifest(image: str) -> None:
     click.echo(registry.get_manifest(image).content)
 
 
+@main.command()
+@click.argument("image_name")
+# XXX: Do we really want to check against this?
+@click.option(
+    "--branch",
+    default=DEFAULT_BRANCH,
+    help="The Git branch that the image was built from",
+)
+@click.option(
+    "--commit",
+    required=True,
+    help="The Git commit the image was built from",
+)
+@click.option(
+    "--repository",
+    default=DEFAULT_REPOSITORY,
+    help="The github repository to check the attestation for",
+)
+@click.option(
+    "--workflow",
+    default=".github/workflows/release-container-image.yml",
+    help="The path of the GitHub actions workflow this image was created from",
+)
+def attest_provenance(
+    image_name: str,
+    branch: str,
+    commit: str,
+    repository: str,
+    workflow: str,
+) -> None:
+    """
+    Look up the image attestation to see if the image has been built
+    on Github runners, and from a given repository.
+    """
+    # TODO: Parse image and make sure it has a tag. Might even check for a digest.
+    # parsed = registry.parse_image_location(image)
+
+    verified = attestations.verify(image_name, branch, commit, repository, workflow)
+    if verified:
+        click.echo(
+            f"🎉 Successfully verified image '{image_name}' and its associated claims:"
+        )
+        click.echo(f"- ✅ SLSA Level 3 provenance")
+        click.echo(f"- ✅ GitHub repo: {repository}")
+        click.echo(f"- ✅ GitHub actions workflow: {workflow}")
+        click.echo(f"- ✅ Git branch: {branch}")
+        click.echo(f"- ✅ Git commit: {commit}")
+
+
 if __name__ == "__main__":
     main()