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Support tag-based refs in ec.oci.blob #3214

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82 changes: 67 additions & 15 deletions internal/rego/oci/oci.go
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Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,7 @@ import (
"fmt"
"io"
"path"
"regexp"
"runtime"
"strings"
"sync"
Expand Down Expand Up @@ -68,6 +69,10 @@ const (

var maxTarEntrySize int64 = maxTarEntrySizeConst // Use var to allow override in tests

// cosignTagPattern matches legacy cosign tag refs produced by ec.oci.image_tag_refs.
// Format: sha256-<hex>.(sbom|att|sig) — e.g. "sha256-d34db33f...abcd.sbom"
var cosignTagPattern = regexp.MustCompile(`:sha256-[0-9a-f]+\.(sbom|att|sig)$`)

func registerOCIBlob() {
decl := rego.Function{
Name: ociBlobName,
Expand Down Expand Up @@ -515,22 +520,70 @@ func ociBlobInternal(bctx rego.BuiltinContext, a *ast.Term, verifyDigest bool) (
}
logger.Debug("Starting blob retrieval")

ref, err := name.NewDigest(refStr)
if err != nil {
logger.WithFields(log.Fields{
"action": "new digest",
"error": err,
}).Error("failed to create new digest")
return nil, nil //nolint:nilerr // intentional: return nil to signal failure without OPA error
}
client := oci.NewClient(bctx.Context)

rawLayer, err := oci.NewClient(bctx.Context).Layer(ref)
var rawLayer v1.Layer
var expectedDigest string
ref, err := name.NewDigest(refStr)
if err != nil {
logger.WithFields(log.Fields{
"action": "fetch layer",
"error": err,
}).Error("failed to fetch OCI layer")
return nil, nil //nolint:nilerr
// Fall back to tag-based fetch: resolve the tag to an image and
// extract the first layer. This supports legacy cosign tag refs
// (e.g. .sbom, .att) returned by ec.oci.image_tag_refs.
if !cosignTagPattern.MatchString(refStr) {
logger.WithFields(log.Fields{
"action": "parse digest",
"error": err,
// Debug, not Error: this is the expected path for non-cosign refs, not a failure.
}).Debug("ref is not a digest ref and not a cosign tag artifact")
return nil, nil //nolint:nilerr
}
tagRef, tagErr := name.ParseReference(refStr)
if tagErr != nil {
logger.WithFields(log.Fields{
"action": "parse reference",
"error": tagErr,
}).Error("failed to parse reference")
return nil, nil //nolint:nilerr
}
img, imgErr := client.Image(tagRef)
if imgErr != nil {
logger.WithFields(log.Fields{
"action": "fetch image",
"error": imgErr,
}).Error("failed to fetch image for tag reference")
return nil, nil //nolint:nilerr
}
layers, layersErr := img.Layers()
if layersErr != nil || len(layers) == 0 {
logger.WithFields(log.Fields{
"action": "get layers",
"error": layersErr,
}).Error("failed to get layers from image")
return nil, nil //nolint:nilerr
}
rawLayer = layers[0]
layerDigest, digestErr := rawLayer.Digest()
if digestErr != nil {
logger.WithFields(log.Fields{
"action": "get layer digest",
"error": digestErr,
}).Error("failed to get layer digest")
return nil, nil //nolint:nilerr
}
// For tag refs, digest verification is intentionally weak: it only checks
// transport integrity (computed vs registry-reported digest), not a
// caller-specified expectation, since there is no digest in the ref.
expectedDigest = layerDigest.String()
} else {
expectedDigest = ref.DigestStr()
rawLayer, err = client.Layer(ref)
if err != nil {
logger.WithFields(log.Fields{
"action": "fetch layer",
"error": err,
}).Error("failed to fetch OCI layer")
return nil, nil //nolint:nilerr
}
}

layer, err := rawLayer.Uncompressed()
Expand Down Expand Up @@ -572,7 +625,6 @@ func ociBlobInternal(bctx rego.BuiltinContext, a *ast.Term, verifyDigest bool) (
// that's not as easy as it sounds, since it may require another
// io.Copy which could be inefficient. For now let's just skip it.
//
expectedDigest := ref.DigestStr()
if verifyDigest {
computedDigest := fmt.Sprintf("sha256:%x", hasher.Sum(nil))
if computedDigest != expectedDigest {
Expand Down
76 changes: 75 additions & 1 deletion internal/rego/oci/oci_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -35,6 +35,7 @@ import (
"github.com/google/go-containerregistry/pkg/name"
"github.com/google/go-containerregistry/pkg/registry"
v1 "github.com/google/go-containerregistry/pkg/v1"
"github.com/google/go-containerregistry/pkg/v1/empty"
v1fake "github.com/google/go-containerregistry/pkg/v1/fake"
"github.com/google/go-containerregistry/pkg/v1/mutate"
"github.com/google/go-containerregistry/pkg/v1/partial"
Expand Down Expand Up @@ -62,6 +63,10 @@ func TestOCIBlob(t *testing.T) {
uri *ast.Term
err bool
remoteErr error
tagRef bool // when true, mock Image() instead of Layer() for tag-based fetch
imageErr error
noLayers bool // when true with tagRef, mock Image() to return an image with no layers
layersErr error // when set with tagRef, mock Image() to return a fake image that errors on Layers()
}{
{
name: "success",
Expand Down Expand Up @@ -99,14 +104,83 @@ func TestOCIBlob(t *testing.T) {
uri: ast.StringTerm("registry.local/spam@sha256:4bbf56a3a9231f752d3b9c174637975f0f83ed2b15e65799837c571e4ef3374b"),
err: true,
},
{
name: "tag reference fetches first layer from image",
data: `{"bomFormat": "CycloneDX", "specVersion": "1.6"}`,
uri: ast.StringTerm("registry.local/spam:sha256-abc123def456.sbom"),
tagRef: true,
},
{
name: "tag reference with image fetch error",
data: `{"spam": "maps"}`,
uri: ast.StringTerm("registry.local/spam:sha256-abc123def456.sbom"),
tagRef: true,
imageErr: errors.New("image not found"),
err: true,
},
{
name: "tag reference with no layers",
data: `{"spam": "maps"}`,
uri: ast.StringTerm("registry.local/spam:sha256-abc123def456.sbom"),
tagRef: true,
noLayers: true,
err: true,
},
{
name: "tag reference layers error",
data: `{"spam": "maps"}`,
uri: ast.StringTerm("registry.local/spam:sha256-abc123def456.sbom"),
tagRef: true,
layersErr: errors.New("layers failed"),
err: true,
},
{
name: "non-cosign tag reference returns nil without image fetch",
data: `{"spam": "maps"}`,
uri: ast.StringTerm("registry.local/spam:latest"),
err: true,
},
{
name: "non-cosign tag with cosign suffix but wrong format",
data: `{"spam": "maps"}`,
uri: ast.StringTerm("registry.local/spam:release.sbom"),
err: true,
},
{
name: "tag reference fetches first layer from image with .att suffix",
data: `{"bomFormat": "CycloneDX", "specVersion": "1.6"}`,
uri: ast.StringTerm("registry.local/spam:sha256-abc123def456.att"),
tagRef: true,
},
{
name: "tag reference fetches first layer from image with .sig suffix",
data: `{"bomFormat": "CycloneDX", "specVersion": "1.6"}`,
uri: ast.StringTerm("registry.local/spam:sha256-abc123def456.sig"),
tagRef: true,
},
}

for _, c := range cases {
t.Run(c.name, func(t *testing.T) {
ClearCaches() // Clear cache before each subtest

client := fake.FakeClient{}
if c.remoteErr != nil {
if c.tagRef {
if c.imageErr != nil {
client.On("Image", mock.Anything).Return(nil, c.imageErr)
} else if c.noLayers {
client.On("Image", mock.Anything).Return(empty.Image, nil)
} else if c.layersErr != nil {
fakeImg := &v1fake.FakeImage{}
fakeImg.LayersReturns(nil, c.layersErr)
client.On("Image", mock.Anything).Return(fakeImg, nil)
} else {
layer := static.NewLayer([]byte(c.data), types.OCIUncompressedLayer)
img, imgErr := mutate.AppendLayers(empty.Image, layer)
require.NoError(t, imgErr)
client.On("Image", mock.Anything).Return(img, nil)
}
} else if c.remoteErr != nil {
client.On("Layer", mock.Anything, mock.Anything).Return(nil, c.remoteErr)
} else {
layer := static.NewLayer([]byte(c.data), types.OCIUncompressedLayer)
Expand Down
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