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package attestation
import (
"context"
"encoding/json"
"os"
"path"
"strings"
"github.com/containerd/continuity/fs"
intoto "github.com/in-toto/in-toto-golang/in_toto"
"github.com/moby/buildkit/exporter"
gatewaypb "github.com/moby/buildkit/frontend/gateway/pb"
"github.com/moby/buildkit/session"
"github.com/moby/buildkit/snapshot"
"github.com/moby/buildkit/solver/result"
"github.com/pkg/errors"
"golang.org/x/sync/errgroup"
)
// Unbundle iterates over all provided result attestations and un-bundles any
// bundled attestations by loading them from the provided refs map.
func Unbundle(ctx context.Context, s session.Group, bundled []exporter.Attestation) ([]exporter.Attestation, error) {
if err := Validate(bundled); err != nil {
return nil, err
}
eg, ctx := errgroup.WithContext(ctx)
unbundled := make([][]exporter.Attestation, len(bundled))
for i, att := range bundled {
i, att := i, att
eg.Go(func() error {
switch att.Kind {
case gatewaypb.AttestationKindInToto:
if strings.HasPrefix(att.InToto.PredicateType, "https://slsa.dev/provenance/") {
if att.ContentFunc == nil {
// provenance may only be set buildkit-side using ContentFunc
return errors.New("frontend may not set provenance attestations")
}
}
unbundled[i] = append(unbundled[i], att)
case gatewaypb.AttestationKindBundle:
if att.ContentFunc != nil {
return errors.New("attestation bundle cannot have callback")
}
if att.Ref == nil {
return errors.Errorf("no ref provided for attestation bundle")
}
mount, err := att.Ref.Mount(ctx, true, s)
if err != nil {
return err
}
lm := snapshot.LocalMounter(mount)
src, err := lm.Mount()
if err != nil {
return err
}
defer lm.Unmount()
atts, err := unbundle(ctx, src, att)
if err != nil {
return err
}
for _, att := range atts {
if strings.HasPrefix(att.InToto.PredicateType, "https://slsa.dev/provenance/") {
return errors.New("frontend may not bundle provenance attestations")
}
}
unbundled[i] = append(unbundled[i], atts...)
}
return nil
})
}
if err := eg.Wait(); err != nil {
return nil, err
}
var joined []exporter.Attestation
for _, atts := range unbundled {
joined = append(joined, atts...)
}
joined = sort(joined)
if err := Validate(joined); err != nil {
return nil, err
}
return joined, nil
}
func sort(atts []exporter.Attestation) []exporter.Attestation {
isCore := make([]bool, len(atts))
for i, att := range atts {
name, ok := att.Metadata[result.AttestationSBOMCore]
if !ok {
continue
}
if n, _, _ := strings.Cut(att.Path, "."); n != string(name) {
continue
}
isCore[i] = true
}
result := make([]exporter.Attestation, 0, len(atts))
for i, att := range atts {
if isCore[i] {
result = append(result, att)
}
}
for i, att := range atts {
if !isCore[i] {
result = append(result, att)
}
}
return result
}
func unbundle(ctx context.Context, root string, bundle exporter.Attestation) ([]exporter.Attestation, error) {
dir, err := fs.RootPath(root, bundle.Path)
if err != nil {
return nil, err
}
entries, err := os.ReadDir(dir)
if err != nil {
return nil, err
}
var unbundled []exporter.Attestation
for _, entry := range entries {
p, err := fs.RootPath(dir, entry.Name())
if err != nil {
return nil, err
}
f, err := os.Open(p)
if err != nil {
return nil, err
}
dec := json.NewDecoder(f)
var stmt intoto.Statement
if err := dec.Decode(&stmt); err != nil {
return nil, errors.Wrap(err, "cannot decode in-toto statement")
}
if bundle.InToto.PredicateType != "" && stmt.PredicateType != bundle.InToto.PredicateType {
return nil, errors.Errorf("bundle entry %s does not match required predicate type %s", stmt.PredicateType, bundle.InToto.PredicateType)
}
predicate, err := json.Marshal(stmt.Predicate)
if err != nil {
return nil, err
}
subjects := make([]result.InTotoSubject, len(stmt.Subject))
for i, subject := range stmt.Subject {
subjects[i] = result.InTotoSubject{
Kind: gatewaypb.InTotoSubjectKindRaw,
Name: subject.Name,
Digest: result.FromDigestMap(subject.Digest),
}
}
unbundled = append(unbundled, exporter.Attestation{
Kind: gatewaypb.AttestationKindInToto,
Metadata: bundle.Metadata,
Path: path.Join(bundle.Path, entry.Name()),
ContentFunc: func() ([]byte, error) { return predicate, nil },
InToto: result.InTotoAttestation{
PredicateType: stmt.PredicateType,
Subjects: subjects,
},
})
}
return unbundled, nil
}
func Validate(atts []exporter.Attestation) error {
for _, att := range atts {
if err := validate(att); err != nil {
return err
}
}
return nil
}
func validate(att exporter.Attestation) error {
if att.Kind != gatewaypb.AttestationKindBundle && att.Path == "" {
return errors.New("attestation does not have set path")
}
if att.Ref == nil && att.ContentFunc == nil {
return errors.New("attestation does not have available content")
}
return nil
}
|
