Add support for multiple architecture manifests in an image scan

[mbrancato]

Description

Proposing here that trivy add support for muti-arch containers containing application/vnd.oci.image.index.v1+json types, listing multiple items in the manifests array. This is a standard index, that can be tagged for a single app that can run on multiple architectures. At runtime, clients will pull the correct architecture. But it could be used to scan all architectures for the index and combined into a single report.

Example index:

{
  "schemaVersion": 2,
  "mediaType": "application/vnd.oci.image.index.v1+json",
  "manifests": [
    {
      "mediaType": "application/vnd.oci.image.manifest.v1+json",
      "size": 479,
      "digest": "sha256:79d83d0a795f541712e512e4c2e6dfd033d97d88b509d20edf670d138aba59ca",
      "platform": {
        "architecture": "amd64",
        "os": "linux"
      }
    },
    {
      "mediaType": "application/vnd.oci.image.manifest.v1+json",
      "size": 479,
      "digest": "sha256:32cb0987f1baf24ce74e75c94ca49867252508c7c308bec2b4b473237ce3d3ff",
      "platform": {
        "architecture": "arm64",
        "os": "linux"
      }
    }
  ],
  "annotations": {
    "org.opencontainers.image.created": "2024-10-30T20:07:30Z",
    "org.opencontainers.image.revision": "68757c1e4818c1f9291ba0b9022a7e9a44c1fa77",
    "org.opencontainers.image.source": "git+ssh://github.com/myorg/myapp.git"
  }
}

When scanning a multi-arch TAR file today, trivy fails. Providing --platform as an option to trivy image produces the same error. (note: I tried aarch64 and arm64 formats)

% trivy image --input test.tar  --platform aarch64
2024-10-31T20:42:30-04:00	INFO	[vuln] Vulnerability scanning is enabled
2024-10-31T20:42:30-04:00	INFO	[secret] Secret scanning is enabled
2024-10-31T20:42:30-04:00	INFO	[secret] If your scanning is slow, please try '--scanners vuln' to disable secret scanning
2024-10-31T20:42:30-04:00	INFO	[secret] Please see also https://aquasecurity.github.io/trivy/v0.56/docs/scanner/secret#recommendation for faster secret detection
2024-10-31T20:42:30-04:00	FATAL	Fatal error	image scan error: scan error: unable to initialize a scanner: unable to initialize the archive scanner: 2 errors occurred:
	* unable to open test.tar as a Docker image: tarball must contain only a single image to be used with tarball.Image
	* unable to open test.tar as an OCI Image: stat test.tar/index.json: not a directory

Target

Container Image

Scanner

None