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sign.go
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sign.go
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// Copyright 2022 Chainguard, Inc.
//
// 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 cli
import (
"archive/tar"
"bytes"
"context"
"fmt"
"io"
"os"
"github.com/chainguard-dev/clog"
"github.com/chainguard-dev/go-apk/pkg/expandapk"
sign "github.com/chainguard-dev/go-apk/pkg/signature"
"github.com/klauspost/compress/gzip"
"github.com/spf13/cobra"
"golang.org/x/sync/errgroup"
"chainguard.dev/melange/pkg/build"
)
type signIndexOpts struct {
Key string
Force bool
}
// SignIndex is a constructor that returns a cobra.Command which wraps the SignIndexCmd() function.
func SignIndex() *cobra.Command {
o := &signIndexOpts{}
cmd := &cobra.Command{
Use: "sign-index",
Short: "Sign an APK index",
Long: `Sign an APK index.`,
Example: `
# Re-sign an index with the same signature
melange sign-index [--signing-key=key.rsa] <APKINDEX.tar.gz>
# Sign a new index with a new signature
melange sign-index [--signing-key=key.rsa] <APKINDEX.tar.gz> --force
`,
Args: cobra.MinimumNArgs(1),
RunE: func(cmd *cobra.Command, args []string) error {
return o.SignIndex(cmd.Context(), args[0])
},
}
cmd.Flags().StringVar(&o.Key, "signing-key", "melange.rsa", "the signing key to use")
cmd.Flags().BoolVarP(&o.Force, "force", "f", false, "when toggled, overwrites the specified index with a new index using the provided signature")
return cmd
}
func (o signIndexOpts) SignIndex(ctx context.Context, indexFile string) error {
log := clog.FromContext(ctx)
if !o.Force {
return sign.SignIndex(ctx, o.Key, indexFile)
}
idx, err := parseIndexWithoutSignature(ctx, indexFile)
if err != nil {
return err
}
t, err := os.Create(fmt.Sprintf("%s.new", indexFile))
if err != nil {
return err
}
if _, err := t.Write(idx); err != nil {
return err
}
if err := t.Sync(); err != nil {
return err
}
if _, err := t.Seek(0, io.SeekStart); err != nil {
return err
}
if err := sign.SignIndex(ctx, o.Key, t.Name()); err != nil {
return err
}
log.Infof("Replacing existing signed index (%s) with signed index with key %s", indexFile, o.Key)
return os.Rename(t.Name(), indexFile)
}
// parseIndexWithoutSignature takes in an index file and returns the unsigned []byte representation of it
func parseIndexWithoutSignature(_ context.Context, indexFile string) ([]byte, error) {
orig, err := os.Open(indexFile)
if err != nil {
return nil, err
}
defer orig.Close()
gr, err := gzip.NewReader(orig)
if err != nil {
return nil, err
}
defer gr.Close()
tr := tar.NewReader(gr)
var nb bytes.Buffer
gw := gzip.NewWriter(&nb)
tw := tar.NewWriter(gw)
for {
hdr, err := tr.Next()
if err == io.EOF {
break
}
if err != nil {
return nil, err
}
if hdr.Name == "DESCRIPTION" || hdr.Name == "APKINDEX" {
if err := tw.WriteHeader(hdr); err != nil {
return nil, err
}
if _, err := io.Copy(tw, tr); err != nil {
return nil, err
}
}
}
if err := tw.Close(); err != nil {
return nil, err
}
if err := gw.Close(); err != nil {
return nil, err
}
return nb.Bytes(), nil
}
type signOpts struct {
Key string
}
func Sign() *cobra.Command {
o := &signOpts{}
cmd := &cobra.Command{
Use: "sign",
Short: "Sign an APK package",
Long: "Signs an APK package on disk with the provided key. The package is replaced with the APK containing the new signature.",
Example: `
melange sign [--signing-key=key.rsa] package.apk
melange sign [--signing-key=key.rsa] *.apk
`,
Args: cobra.MinimumNArgs(1),
RunE: func(cmd *cobra.Command, args []string) error {
ctx := cmd.Context()
return o.RunAllE(ctx, args...)
},
}
cmd.Flags().StringVarP(&o.Key, "signing-key", "k", "local-melange.rsa", "The signing key to use.")
return cmd
}
func (o signOpts) RunAllE(ctx context.Context, pkgs ...string) error {
g, ctx := errgroup.WithContext(ctx)
for _, pkg := range pkgs {
p := pkg
g.Go(func() error {
return o.run(ctx, p)
})
}
return g.Wait()
}
func (o signOpts) run(ctx context.Context, pkg string) error {
clog.FromContext(ctx).Infof("Processing apk %s", pkg)
apkr, err := os.Open(pkg)
if err != nil {
return err
}
eapk, err := expandapk.ExpandApk(ctx, apkr, "")
if err != nil {
return fmt.Errorf("expanding apk: %w", err)
}
defer eapk.Close()
if err := apkr.Close(); err != nil {
return err
}
// Split the streams and then rebuild
cf, err := os.Open(eapk.ControlFile)
if err != nil {
return err
}
// Use the control sections ModTime (set to SDE) for the signature
cfinfo, err := os.Stat(eapk.ControlFile)
if err != nil {
return err
}
pc := &build.PackageBuild{
Build: &build.Build{
SigningKey: o.Key,
SigningPassphrase: "",
},
}
cdata, err := os.ReadFile(eapk.ControlFile)
if err != nil {
return err
}
sigData, err := build.EmitSignature(ctx, pc.Signer(), cdata, cfinfo.ModTime())
if err != nil {
return err
}
df, err := os.Open(eapk.PackageFile)
if err != nil {
return err
}
tf, err := os.CreateTemp("", "melange-signer")
if err != nil {
return err
}
defer os.RemoveAll(tf.Name())
for _, fp := range []io.Reader{bytes.NewBuffer(sigData), cf, df} {
if _, err := io.Copy(tf, fp); err != nil {
return err
}
}
if err := tf.Sync(); err != nil {
return err
}
if _, err := tf.Seek(0, io.SeekStart); err != nil {
return err
}
// Replace the package file with the new one
f, err := os.Create(pkg)
if err != nil {
return err
}
defer f.Close()
if _, err := io.Copy(f, tf); err != nil {
return err
}
return nil
}