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validation.go
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validation.go
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//
// Copyright 2021 The Sigstore Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package webhook
import (
"context"
"crypto"
"crypto/x509"
"encoding/pem"
"errors"
"fmt"
"github.com/google/go-containerregistry/pkg/name"
"knative.dev/pkg/apis"
"knative.dev/pkg/logging"
"github.com/sigstore/cosign/cmd/cosign/cli/fulcio/fulcioroots"
v1alpha1 "github.com/sigstore/cosign/pkg/apis/cosigned/v1alpha1"
"github.com/sigstore/cosign/pkg/cosign"
"github.com/sigstore/cosign/pkg/oci"
ociremote "github.com/sigstore/cosign/pkg/oci/remote"
"github.com/sigstore/rekor/pkg/generated/client"
"github.com/sigstore/sigstore/pkg/signature"
)
func valid(ctx context.Context, ref name.Reference, keys []crypto.PublicKey, opts ...ociremote.Option) ([]oci.Signature, error) {
if len(keys) == 0 {
// If there are no keys, then verify against the fulcio root.
sps, err := validSignaturesWithFulcio(ctx, ref, fulcioroots.Get(), nil /* rekor */, nil /* no identities */, opts...)
if err != nil {
return nil, err
}
if len(sps) > 0 {
return sps, nil
}
return nil, errors.New("no valid signatures were found")
}
// We return nil if ANY key matches
var lastErr error
for _, k := range keys {
verifier, err := signature.LoadVerifier(k, crypto.SHA256)
if err != nil {
logging.FromContext(ctx).Errorf("error creating verifier: %v", err)
lastErr = err
continue
}
sps, err := validSignatures(ctx, ref, verifier, opts...)
if err != nil {
logging.FromContext(ctx).Errorf("error validating signatures: %v", err)
lastErr = err
continue
}
if len(sps) > 0 {
return sps, nil
}
}
logging.FromContext(ctx).Debug("No valid signatures were found.")
return nil, lastErr
}
// For testing
var cosignVerifySignatures = cosign.VerifyImageSignatures
func validSignatures(ctx context.Context, ref name.Reference, verifier signature.Verifier, opts ...ociremote.Option) ([]oci.Signature, error) {
sigs, _, err := cosignVerifySignatures(ctx, ref, &cosign.CheckOpts{
RegistryClientOpts: opts,
SigVerifier: verifier,
ClaimVerifier: cosign.SimpleClaimVerifier,
})
return sigs, err
}
// validSignaturesWithFulcio expects a Fulcio Cert to verify against. An
// optional rekorClient can also be given, if nil passed, default is assumed.
func validSignaturesWithFulcio(ctx context.Context, ref name.Reference, fulcioRoots *x509.CertPool, rekorClient *client.Rekor, identities []v1alpha1.Identity, opts ...ociremote.Option) ([]oci.Signature, error) {
ids := make([]cosign.Identity, len(identities))
for i, id := range identities {
ids[i] = cosign.Identity{Issuer: id.Issuer, Subject: id.Subject}
}
sigs, _, err := cosignVerifySignatures(ctx, ref, &cosign.CheckOpts{
RegistryClientOpts: opts,
RootCerts: fulcioRoots,
RekorClient: rekorClient,
ClaimVerifier: cosign.SimpleClaimVerifier,
Identities: ids,
})
return sigs, err
}
func getKeys(ctx context.Context, cfg map[string][]byte) ([]crypto.PublicKey, *apis.FieldError) {
keys := []crypto.PublicKey{}
errs := []error{}
logging.FromContext(ctx).Debugf("Got public key: %v", cfg["cosign.pub"])
pems := parsePems(cfg["cosign.pub"])
for _, p := range pems {
// TODO: (@dlorenc) check header
key, err := x509.ParsePKIXPublicKey(p.Bytes)
if err != nil {
errs = append(errs, err)
} else {
keys = append(keys, key.(crypto.PublicKey))
}
}
if keys == nil {
return nil, apis.ErrGeneric(fmt.Sprintf("malformed cosign.pub: %v", errs), apis.CurrentField)
}
return keys, nil
}
func parsePems(b []byte) []*pem.Block {
p, rest := pem.Decode(b)
if p == nil {
return nil
}
pems := []*pem.Block{p}
if rest != nil {
return append(pems, parsePems(rest)...)
}
return pems
}