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Store the digest of each verified attestation in the PolicyAttestation object #925

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merged 2 commits into from
Aug 8, 2023
Merged

Store the digest of each verified attestation in the PolicyAttestation object #925

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25ebebe
store attestation digest
hectorj2f Aug 8, 2023
3930192
add unit test to validate policy attestation digest
hectorj2f Aug 8, 2023
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9 changes: 9 additions & 0 deletions pkg/webhook/validator.go
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Original file line number Diff line number Diff line change
Expand Up @@ -713,6 +713,7 @@

PredicateType string
Payload []byte
Digest string
}

func attestationToPolicyAttestations(ctx context.Context, atts []attestation) []PolicyAttestation {
Expand Down Expand Up @@ -743,6 +744,7 @@
WorkflowRef: ce.GetCertExtensionGithubWorkflowRef(),
},
},
Digest: att.Digest,
PredicateType: att.PredicateType,
Payload: att.Payload,
})
Expand All @@ -754,6 +756,7 @@
},
PredicateType: att.PredicateType,
Payload: att.Payload,
Digest: att.Digest,

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})
}
}
Expand Down Expand Up @@ -890,6 +893,11 @@
// attestations and make sure that our particular one is satisfied.
checkedAttestations := make([]attestation, 0, len(verifiedAttestations))
for _, va := range verifiedAttestations {
attDigest, err := va.Digest()
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This is for the layer right? Just to make sure that with all the wonkiness for the OCI that we're getting the right one, that @wlynch had to make changes in here for:
#826

@wlynch could you take provide another set of 👀 here.

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@wlynch wlynch Aug 8, 2023 •
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This might be fine?

Digest (somewhat counterintuitively) is the SHA of the image layer.

For signatures this is problematic because because the signature bits are in the annotations, not the layer itself, so calling digest gets you the same value for different signatures.

But for attestations, the data is in the layer, so this might be fine? I'd spot check this with some real world examples first.

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Yes. The code is using VerifyImageAttestations which is also used in the mono PR, and cosign tree to show the digest of the attestation of an image.

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cosign tree ghcr.io/mattmoor/sbom-attestations/spdx-test@sha256:ba4037061b76ad8f306dd9e442877236015747ec42141caf504dc0df4d10708d
📦 Supply Chain Security Related artifacts for an image: ghcr.io/mattmoor/sbom-attestations/spdx-test@sha256:ba4037061b76ad8f306dd9e442877236015747ec42141caf504dc0df4d10708d
└── 💾 Attestations for an image tag: ghcr.io/mattmoor/sbom-attestations/spdx-test:sha256-ba4037061b76ad8f306dd9e442877236015747ec42141caf504dc0df4d10708d.att
   ├── 🍒 sha256:e9b75fb9a63666bd25c719a9fa3005ebd718e785d3a78844d5fcfd046e6bddc2
   ├── 🍒 sha256:f764a4251b2fe3c85dd46896b9d6e65361c9683755099d6dcd13009836d2e0e4
   └── 🍒 sha256:44726310314767412228d897a45943f158ef15a180270461b9f9847efa5c15de
└── 🔐 Signatures for an image tag: ghcr.io/mattmoor/sbom-attestations/spdx-test:sha256-ba4037061b76ad8f306dd9e442877236015747ec42141caf504dc0df4d10708d.sig
   └── 🍒 sha256:0f3404bb8c65cb8e1184c2d2fb3d1cec08771c1cd40c08f21b63cfaa96d13938

Found the att.Digest sha256:f764a4251b2fe3c85dd46896b9d6e65361c9683755099d6dcd13009836d2e0e4 for a spdx attestation.

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Thank you for checking!

if err != nil {
logging.FromContext(ctx).Errorf("failed to get the attestation digest for %s: %v", wantedAttestation.Name, err)
continue

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}
attBytes, gotPredicateType, err := policy.AttestationToPayloadJSON(ctx, wantedAttestation.PredicateType, va)
if gotPredicateType != "" {
checkedPredicateTypes[gotPredicateType] = struct{}{}
Expand Down Expand Up @@ -926,6 +934,7 @@
Signature: va,
PredicateType: wantedAttestation.PredicateType,
Payload: attBytes,
Digest: attDigest.String(),
})
}
if len(checkedAttestations) == 0 {
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3 changes: 3 additions & 0 deletions pkg/webhook/validator_result.go
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Expand Up @@ -119,6 +119,9 @@ type PolicyAttestation struct {
// not intended for consumption in the ClusterImagePolicy's outer policy
// block.
Payload []byte `json:"-"`

// Digest of the attestation
Digest string `json:"digest,omitempty"`
}

// GithubExtensions holds the Github-related OID extensions.
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1 change: 1 addition & 0 deletions pkg/webhook/validator_test.go
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Expand Up @@ -1776,6 +1776,7 @@ func TestValidatePolicy(t *testing.T) {
},
},
PredicateType: "vuln",
Digest: "sha256:01bd6aec99ad7c5d045d9aab649fd95b7af2b3b23887d34d7fce8b2e3c38ca0e",
Payload: []byte(`{"_type":"https://in-toto.io/Statement/v0.1","predicateType":"https://cosign.sigstore.dev/attestation/vuln/v1","subject":[{"name":"ghcr.io/distroless/static","digest":{"sha256":"a1e82f6a5f6dfc735165d3442e7cc5a615f72abac3db19452481f5f3c90fbfa8"}}],"predicate":{"invocation":{"parameters":null,"uri":"https://github.com/distroless/static/actions/runs/2757953139","event_id":"2757953139","builder.id":"Create Release"},"scanner":{"uri":"https://github.com/aquasecurity/trivy","version":"0.29.2","db":{"uri":"","version":""},"result":{"$schema":"https://json.schemastore.org/sarif-2.1.0-rtm.5.json","runs":[{"columnKind":"utf16CodeUnits","originalUriBaseIds":{"ROOTPATH":{"uri":"file:///"}},"results":[],"tool":{"driver":{"fullName":"Trivy Vulnerability Scanner","informationUri":"https://github.com/aquasecurity/trivy","name":"Trivy","rules":[],"version":"0.29.2"}}}],"version":"2.1.0"}},"metadata":{"scanStartedOn":"2022-07-29T02:28:42Z","scanFinishedOn":"2022-07-29T02:28:48Z"}}}`),
}},
},
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