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Verifying Assets

Inspektor Gadget container image and release assets are signed using cosign. In this guide, we will see how you can verify them with this tool. Note that, You would need to have cosign v2.0 installed.

Verify the container image manually​

Verifying the container image is pretty straightforward:

$ RELEASE='v0.27.0'
$ cosign verify --key https://raw.githubusercontent.com/inspektor-gadget/inspektor-gadget/${RELEASE}/inspektor-gadget.pub ghcr.io/inspektor-gadget/inspektor-gadget:${RELEASE}
The following checks were performed on each of these signatures:
  - The cosign claims were validated
  - Existence of the claims in the transparency log was verified offline
  - The signatures were verified against the specified public key

[{"critical":{"identity":{"docker-reference":"ghcr.io/inspektor-gadget/inspektor-gadget"}, ...
]

Getting the above output followed by a JSON array of payloads, ensures you the container image was signed using our private key.

Verify the container Source Code Bill Of Materials (SBOMs)​

A Software Bill of Materials (SBOM) is a detailed list of all the components of a software. It facilitates security and license compliance assessments. The Inspektor Gadget project publishes SBOMs in the CycloneDX format for all our container images and CLI tools:

  • SBOMs for container images are attached to the corresponding image and can be found in our registry.
  • SBOMs for CLI tools are available as release assets.

In this section, we will see how you can verify and inspect the SBOMs attached to our container images. To do so, you will need cosign, oras and Inspektor Gadget public key.

# We will demo this for amd64, but it works the same for arm64.
$ arch=amd64
$ oras discover --platform linux/${arch} --artifact-type example/sbom ghcr.io/inspektor-gadget/inspektor-gadget:latest
Discovered 1 artifact referencing latest
Digest: sha256:...

Artifact Type   Digest
example/sbom    sha256:hash_of_sbom_manifest
# As we include SBOMs in our multi architecture container image, they are also
# signed.
# So, let's check the SBOM is signed with our private key:
$ cosign verify --key inspektor-gadget.pub ghcr.io/inspektor-gadget/inspektor-gadget@sha256:hash_of_sbom_manifest

Verification for ghcr.io/inspektor-gadget/inspektor-gadget@sha256:hash_of_sbom_manifest
The following checks were performed on each of these signatures:
  - The cosign claims were validated
  - Existence of the claims in the transparency log was verified offline
  - The signatures were verified against the specified public key

[{"critical":{"identity":{"docker-reference":"ghcr.io/inspektor-gadget/inspektor-gadget"}, ...
]
# Let's download the SBOM and look at it:
$ oras pull --allow-path-traversal ghcr.io/inspektor-gadget/inspektor-gadget@sha256:hash_of_sbom_manifest
Downloading 1d479bb51392 /tmp/gadget-container-image-linux-amd64/sbom_cyclonedx.json
Downloaded  1d479bb51392 /tmp/gadget-container-image-linux-amd64/sbom_cyclonedx.json
Pulled [registry] ghcr.io/eiffel-fl/inspektor-gadget@sha256:hash_of_sbom_manifest
Digest: sha256:hash_of_sbom_manifest
$ jq '' /tmp/gadget-container-image-linux-amd64/sbom_cyclonedx.json
{
  "$schema": "http://cyclonedx.org/schema/bom-1.5.schema.json",
  "bomFormat": "CycloneDX",
  "specVersion": "1.5",
  "serialNumber": "urn:uuid:cf132c3d-5960-4536-9c03-9724babd76e9",
  "version": 1,
  "metadata": {
    "timestamp": "2024-03-21T17:22:38Z",
    "tools": {
      "components": [
        {
          "type": "application",
          "author": "anchore",
          "name": "syft",
          "version": "1.0.1"
        }
      ]
    },
    "component": {
      "bom-ref": "af63bd4c8601b7f1",
      "type": "file",
      "name": "."
    }
  },
  "components": [
    {
      "bom-ref": "pkg:deb/debian/[email protected]+deb12u5?arch=amd64&distro=debian-12&package-id=854ccee33785ad46",
      "type": "library",
      "publisher": "Santiago Vila <[email protected]>",
      "name": "base-files",
...
}

As the SBOM was signed with our private key, you can now inspect it to track down every dependencies we use to build our container image.

Verify image-based gadgets​

Like our container image, we sign all our image-based gadgets. The signatures are by default verified against the official Inspektor Gadget public key.

Compared to ig, you cannot specify information with regard to verification when calling kubectl gadget run:

$ kubectl gadget run --public-keys="$(cat your-key.pub)" trace_exec
Error: unknown flag: --public-keys
$ kubectl gadget run --verify-image=false trace_exec
Error: unknown flag: --verify-image

When using Inspektor Gadget on Kubernetes, you have to configure these features at deploy time. This enforces the policies so that users cannot override them. By default all image-based gadgets are verified using Inspektor Gadget public key:

$ kubectl gadget deploy
...
Inspektor Gadget successfully deployed
$ kubectl gadget run ghcr.io/your_repo/trace_exec -A
Error: fetching gadget information: getting gadget info: rpc error: code = Unknown desc = getting gadget info: initializing and preparing operators: instantiating operator "oci": ensuring image: verifying image "ghcr.io/your_repo/trace_exec": verifying signature: invalid signature when validating ASN.1 encoded signature
$ kubectl gadget run trace_exec -A
K8S.NAMESP… K8S.PODNAME K8S.CONTAI… MNTNS… TIMES… PID    PPID   UID    GID    LOGIN… SESSI… RETVAL ARGS_… UPPER… ARGS_… COMM  ARGS  K8S.…
gadget      gadge…hbh8n gadget      40265… 22867… 53386  53368  0      0      42949… 42949… 0      2      false  35     gadg… /bin… mini…
gadget      gadge…hbh8n gadget      40265… 22867… 53387  53369  0      0      42949… 42949… 0      2      false  35     gadg… /bin… mini…
...

You can specify a custom public key at deploy time using --gadgets-public-keys:

$ kubectl gadget deploy --gadgets-public-keys="$(cat your-key.pub)"
...
Inspektor Gadget successfully deployed
# Without the official public key, official gadgets will be rejected.
$ kubectl gadget run trace_exec -A
Error: fetching gadget information: getting gadget info: rpc error: code = Unknown desc = getting gadget info: initializing and preparing operators: instantiating operator "oci": ensuring image: verifying image "trace_exec": verifying signature: invalid signature when validating ASN.1 encoded signature
$ kubectl-gadget run ghcr.io/your_repo/trace_exec -A
K8S.NAMESP… K8S.PODNAME K8S.CONTAI… MNTNS… TIMES… PID    PPID   UID    GID    LOGIN… SESSI… RETVAL ARGS_… UPPER… ARGS_… COMM  ARGS  K8S.…
gadget      gadge…hbh8n gadget      40265… 22867… 53386  53368  0      0      42949… 42949… 0      2      false  35     gadg… /bin… mini…
gadget      gadge…hbh8n gadget      40265… 22867… 53387  53369  0      0      42949… 42949… 0      2      false  35     gadg… /bin… mini…
...

You can also instruct Inspektor Gadget to skip the verification by disabling it at deploy time. Please note that we do not recommend doing so and that it should only be used for development purposes.

$ kubectl gadget deploy --verify-gadgets=false
...
Inspektor Gadget successfully deployed
$ kubectl gadget run trace_exec -A
WARN[0001] minikube-docker      | image signature verification is disabled due to using corresponding option
K8S.NAMESPACE       K8S.PODNAME         K8S.CONTAINERNAME          PID       PPID RE… COMM      ARGS      K8S.NODE  TIMESTAMP
gadget              gadget-z55jq        gadget                   55376      55357   0 gadgettr… /bin/gad… minikube… 2024-07-17T07:39:07.…
gadget              gadget-z55jq        gadget                   55375      55358   0 gadgettr… /bin/gad… minikube… 2024-07-17T07:39:07.…
...

Verify the ebpf-builder image​

We also sign the ebpf-builder image which is used to build gadgets. You can verify it using the following command:

$ cosign verify --key inspektor-gadget.pub ghcr.io/inspektor-gadget/ebpf-builder:latest

We highly recommend you to verify by digest and specify the digest when building. This helps to protect against TOCTOU issue, as the image tag that got verified could have been manipulated to point to another malicious image after the check.

$ DIGEST='sha256:4967ad1a11a9ed32867dc0d63e137dc2196c560db4b3644c7c0c97fccea7c522'
$ cosign verify --key inspektor-gadget.pub ghcr.io/inspektor-gadget/ebpf-builder@$DIGEST

Verification for ghcr.io/inspektor-gadget/ebpf-builder@sha256:4967ad1a11a9ed32867dc0d63e137dc2196c560db4b3644c7c0c97fccea7c522 --
The following checks were performed on each of these signatures:
  - The cosign claims were validated
  - Existence of the claims in the transparency log was verified offline
  - The signatures were verified against the specified public key

[{"critical":{"identity":{"docker-reference":"ghcr.io/inspektor-gadget/ebpf-builder"}, ...
]
$ sudo ig image build -t trace_exec:build-verified -f gadgets/trace_exec/gadget.yaml --builder-image ghcr.io/inspektor-gadget/ebpf-builder@$DIGEST gadgets/trace_exec
Pulling builder image ghcr.io/inspektor-gadget/ebpf-builder@sha256:4967ad1a11a9ed32867dc0d63e137dc2196c560db4b3644c7c0c97fccea7c522
ghcr.io/inspektor-gadget/ebpf-builder@sha256:4967ad1a11a9ed32867dc0d63e137dc2196c560db4b3644c7c0c97fccea7c522: Pulling from inspektor-gadget/ebpf-builder
...
Digest: sha256:4967ad1a11a9ed32867dc0d63e137dc2196c560db4b3644c7c0c97fccea7c522
Status: Downloaded newer image for ghcr.io/inspektor-gadget/ebpf-builder@sha256:4967ad1a11a9ed32867dc0d63e137dc2196c560db4b3644c7c0c97fccea7c522
Successfully built ghcr.io/inspektor-gadget/gadget/trace_exec:build-verified@sha256:c85eac1e4615a08c74883402f73c5f8667b64597bd51f9e46275dfdbb0a04703

Verify an asset​

Rather than signing all the assets, we only sign the checksums file. So, by verifying this file, you can then verify the assets themselves by checking their checksums.

Verifying the checksums file​

The following snippet show you how to verify the checksums file:

$ RELEASE='v0.19.0'
$ ASSET="SHA256SUMS"
$ URL="https://github.com/inspektor-gadget/inspektor-gadget/releases/download/${RELEASE}"
# We need to get the asset itself, its signature file and the corresponding bundle:
$ for i in $URL/$ASSET $URL/$ASSET.sig $URL/$ASSET.bundle; do
	wget $i
done
...
# We need to get the public key too.
$ wget $URL/inspektor-gadget.pub
...
$ cosign verify-blob $ASSET --bundle ${ASSET}.bundle --signature ${ASSET}.sig --key inspektor-gadget.pub --offline
Verified OK

As you can see, the checksum file was correctly verified which means this file was indeed signed by us. So, you can use this file to verify other release assets.

Verify an asset​

Once you verified the checksums file, you can now verify the integrity of an asset using such checksums file:

$ RELEASE='v0.19.0'
$ ASSET="inspektor-gadget-${RELEASE}.yaml"
$ URL="https://github.com/inspektor-gadget/inspektor-gadget/releases/download/${RELEASE}"
$ wget $URL/$ASSET
$ grep $ASSET SHA256SUMS | shasum -a 256 -c -s || echo "Error: ${ASSET} didn't pass the checksum verification. You must not use it!"