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attest.go
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attest.go
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package attest
import (
"bytes"
"context"
"encoding/json"
"fmt"
"os"
"strings"
"github.com/anchore/stereoscope"
"github.com/anchore/stereoscope/pkg/image"
"github.com/anchore/syft/cmd/syft/cli/eventloop"
"github.com/anchore/syft/cmd/syft/cli/options"
"github.com/anchore/syft/cmd/syft/cli/packages"
"github.com/anchore/syft/internal/bus"
"github.com/anchore/syft/internal/config"
"github.com/anchore/syft/internal/formats/cyclonedxjson"
"github.com/anchore/syft/internal/formats/spdx22json"
"github.com/anchore/syft/internal/formats/syftjson"
"github.com/anchore/syft/internal/ui"
"github.com/anchore/syft/syft"
"github.com/anchore/syft/syft/event"
"github.com/anchore/syft/syft/sbom"
"github.com/anchore/syft/syft/source"
"github.com/in-toto/in-toto-golang/in_toto"
"github.com/pkg/errors"
"github.com/sigstore/cosign/cmd/cosign/cli/sign"
"github.com/sigstore/cosign/pkg/cosign/attestation"
"github.com/sigstore/sigstore/pkg/signature/dsse"
"github.com/wagoodman/go-partybus"
signatureoptions "github.com/sigstore/sigstore/pkg/signature/options"
)
var allowedAttestFormats = []sbom.FormatID{
syftjson.ID,
spdx22json.ID,
cyclonedxjson.ID,
}
var intotoJSONDsseType = `application/vnd.in-toto+json`
func Run(ctx context.Context, app *config.Application, args []string) error {
// We cannot generate an attestation for more than one output
if len(app.Outputs) > 1 {
return fmt.Errorf("unable to generate attestation for more than one output")
}
// can only be an image for attestation or OCI DIR
userInput := args[0]
si, err := sourceFromInput(userInput, app)
if err != nil {
return err
}
format := syft.FormatByName(app.Outputs[0])
predicateType := formatPredicateType(format)
if predicateType == "" {
return fmt.Errorf("could not produce attestation predicate for given format: %q. Available formats: %+v", options.FormatAliases(format.ID()), options.FormatAliases(allowedAttestFormats...))
}
passFunc, err := selectPassFunc(app.Attest.Key, app.Attest.Password)
if err != nil {
return err
}
ko := sign.KeyOpts{
KeyRef: app.Attest.Key,
PassFunc: passFunc,
}
sv, err := sign.SignerFromKeyOpts(ctx, "", "", ko)
if err != nil {
return err
}
defer sv.Close()
eventBus := partybus.NewBus()
stereoscope.SetBus(eventBus)
syft.SetBus(eventBus)
return eventloop.EventLoop(
execWorker(app, *si, format, predicateType, sv),
eventloop.SetupSignals(),
eventBus.Subscribe(),
stereoscope.Cleanup,
ui.Select(options.IsVerbose(app), app.Quiet)...,
)
}
func sourceFromInput(userInput string, app *config.Application) (s *source.Input, err error) {
si, err := source.ParseInput(userInput, app.Platform, false)
if err != nil {
return nil, fmt.Errorf("could not generate source input for attest command: %w", err)
}
switch si.Scheme {
case source.ImageScheme, source.UnknownScheme:
// at this point we know that it cannot be dir: or file: schemes;
// we will assume that the unknown scheme could represent an image;
si.Scheme = source.ImageScheme
default:
return nil, fmt.Errorf("attest command can only be used with image sources but discovered %q when given %q", si.Scheme, userInput)
}
// if the original detection was from the local daemon we want to short circuit
// that and attempt to generate the image source from its current registry source instead
switch si.ImageSource {
case image.UnknownSource, image.OciRegistrySource:
si.ImageSource = image.OciRegistrySource
default:
return nil, fmt.Errorf("attest command can only be used with image sources fetch directly from the registry, but discovered an image source of %q when given %q", si.ImageSource, userInput)
}
return si, nil
}
func execWorker(app *config.Application, sourceInput source.Input, format sbom.Format, predicateType string, sv *sign.SignerVerifier) <-chan error {
errs := make(chan error)
go func() {
defer close(errs)
src, cleanup, err := source.NewFromRegistry(sourceInput, app.Registry.ToOptions(), app.Exclusions)
if cleanup != nil {
defer cleanup()
}
if err != nil {
errs <- fmt.Errorf("failed to construct source from user input %q: %w", sourceInput.UserInput, err)
return
}
s, err := packages.GenerateSBOM(src, errs, app)
if err != nil {
errs <- err
return
}
sbomBytes, err := syft.Encode(*s, format)
if err != nil {
errs <- err
return
}
err = generateAttestation(sbomBytes, src, sv, predicateType)
if err != nil {
errs <- err
return
}
}()
return errs
}
func generateAttestation(predicate []byte, src *source.Source, sv *sign.SignerVerifier, predicateType string) error {
switch len(src.Image.Metadata.RepoDigests) {
case 0:
return fmt.Errorf("cannot generate attestation since no repo digests were found; make sure you're passing an OCI registry source for the attest command")
case 1:
default:
return fmt.Errorf("cannot generate attestation since multiple repo digests were found for the image: %+v", src.Image.Metadata.RepoDigests)
}
wrapped := dsse.WrapSigner(sv, intotoJSONDsseType)
sh, err := attestation.GenerateStatement(attestation.GenerateOpts{
Predicate: bytes.NewBuffer(predicate),
Type: predicateType,
Digest: findValidDigest(src.Image.Metadata.RepoDigests),
})
if err != nil {
return err
}
payload, err := json.Marshal(sh)
if err != nil {
return err
}
signedPayload, err := wrapped.SignMessage(bytes.NewReader(payload), signatureoptions.WithContext(context.Background()))
if err != nil {
return errors.Wrap(err, "unable to sign SBOM")
}
bus.Publish(partybus.Event{
Type: event.Exit,
Value: func() error {
_, err := os.Stdout.Write(signedPayload)
return err
},
})
return nil
}
func findValidDigest(digests []string) string {
// since we are only using the OCI repo provider for this source we are safe that this is only 1 value
// see https://github.com/anchore/stereoscope/blob/25ebd49a842b5ac0a20c2e2b4b81335b64ad248c/pkg/image/oci/registry_provider.go#L57-L63
split := strings.Split(digests[0], "sha256:")
return split[1]
}
func formatPredicateType(format sbom.Format) string {
switch format.ID() {
case spdx22json.ID:
return in_toto.PredicateSPDX
case cyclonedxjson.ID:
// Tentative see https://github.com/in-toto/attestation/issues/82
return "https://cyclonedx.org/bom"
case syftjson.ID:
return "https://syft.dev/bom"
default:
return ""
}
}