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//
// Copyright (c) SAS Institute 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 authenticode
import (
"archive/tar"
"bytes"
"crypto"
"fmt"
"io"
"io/ioutil"
"github.com/sassoftware/relic/v7/lib/comdoc"
)
const (
msiTarExMeta = "__exmeta"
msiTarStorageUID = "__storage_uid"
)
// Convert MSI to a tar archive in a form that can be digested and signed as a
// stream
func MsiToTar(cdf *comdoc.ComDoc, w io.Writer) error {
tw := tar.NewWriter(w)
// First write the metadata that is needed for an extended signature
var buf bytes.Buffer
if err := prehashMsiDir(cdf, cdf.RootStorage(), &buf); err != nil {
return err
}
if err := tarAddFile(tw, msiTarExMeta, buf.Bytes()); err != nil {
return err
}
// Now all of the files in the same order they would get digested in
if err := msiToTarDir(cdf, tw, cdf.RootStorage(), ""); err != nil {
return err
}
return tw.Close()
}
// Digset a tarball produced by MsiToTar
func DigestMsiTar(r io.Reader, hash crypto.Hash, extended bool) ([]byte, error) {
tr := tar.NewReader(r)
d := hash.New()
for {
hdr, err := tr.Next()
if err == io.EOF {
break
} else if err != nil {
return nil, err
}
if hdr.Name == msiTarExMeta {
if !extended {
continue
}
exmeta, err := ioutil.ReadAll(tr)
if err != nil {
return nil, err
}
d2 := hash.New()
d2.Write(exmeta)
prehash := d2.Sum(nil)
d.Write(prehash)
} else if hdr.Name == msiDigitalSignature || hdr.Name == msiDigitalSignatureEx {
continue
}
if _, err := io.Copy(d, tr); err != nil {
return nil, err
}
}
return d.Sum(nil), nil
}
// Add a file with contents blob to an open tar.Writer
func tarAddFile(tw *tar.Writer, name string, contents []byte) error {
hdr := &tar.Header{Name: name, Mode: 0644, Size: int64(len(contents))}
if err := tw.WriteHeader(hdr); err != nil {
return err
}
_, err := tw.Write(contents)
return err
}
// Recursively copy streams from a MSI directory (storage) to a tar.Writer
func msiToTarDir(cdf *comdoc.ComDoc, tw *tar.Writer, parent *comdoc.DirEnt, path string) error {
files, err := cdf.ListDir(parent)
if err != nil {
if path == "" {
return fmt.Errorf("listing root storage: %w", err)
}
return fmt.Errorf("listing storage %q: %w", path, err)
}
sortMsiFiles(files)
for _, item := range files {
itemPath := path + msiDecodeName(item.Name())
switch item.Type {
case comdoc.DirStream:
r, err := cdf.ReadStream(item)
if err != nil {
return fmt.Errorf("reading MSI stream %q: %w", itemPath, err)
}
hdr := &tar.Header{
Name: itemPath,
Mode: 0644,
Size: int64(item.StreamSize),
}
if err := tw.WriteHeader(hdr); err != nil {
return err
}
if _, err := io.Copy(tw, r); err != nil {
return fmt.Errorf("transforming MSI stream %q: %w", itemPath, err)
}
case comdoc.DirStorage:
if err := msiToTarDir(cdf, tw, item, itemPath+"/"); err != nil {
return err
}
}
}
// The UID of each storage gets hashed after its contents so include that, too
return tarAddFile(tw, path+msiTarStorageUID, parent.UID[:])
}
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