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tailscale/util/winutil/authenticode/authenticode_windows.go

520 lines
13 KiB
Go

// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
// Package authenticode contains Windows Authenticode signature verification code.
package authenticode
import (
"encoding/hex"
"errors"
"fmt"
"path/filepath"
"strings"
"unsafe"
"github.com/dblohm7/wingoes"
"github.com/dblohm7/wingoes/pe"
"golang.org/x/sys/windows"
)
var (
// ErrSigNotFound is returned if no authenticode signature could be found.
ErrSigNotFound = errors.New("authenticode signature not found")
// ErrUnexpectedCertSubject is wrapped with the actual cert subject and
// returned when the binary is signed by a different subject than expected.
ErrUnexpectedCertSubject = errors.New("unexpected cert subject")
errCertSubjectNotFound = errors.New("cert subject not found")
errCertSubjectDecodeLenMismatch = errors.New("length mismatch while decoding cert subject")
)
const (
_CERT_STRONG_SIGN_OID_INFO_CHOICE = 2
_CMSG_SIGNER_CERT_INFO_PARAM = 7
_MSI_INVALID_HASH_IS_FATAL = 1
_TRUST_E_NOSIGNATURE = wingoes.HRESULT(-((0x800B0100 ^ 0xFFFFFFFF) + 1))
)
// Verify performs authenticode verification on the file at path, and also
// ensures that expectedCertSubject matches the actual cert subject. path may
// point to either a PE binary or an MSI package. ErrSigNotFound is returned if
// no signature is found.
func Verify(path string, expectedCertSubject string) error {
path16, err := windows.UTF16PtrFromString(path)
if err != nil {
return err
}
var subject string
if strings.EqualFold(filepath.Ext(path), ".msi") {
subject, err = verifyMSI(path16)
} else {
subject, _, err = queryPE(path16, true)
}
if err != nil {
return err
}
if subject != expectedCertSubject {
return fmt.Errorf("%w %q", ErrUnexpectedCertSubject, subject)
}
return nil
}
// SigProvenance indicates whether an authenticode signature was embedded within
// the file itself, or the signature applies to an associated catalog file.
type SigProvenance int
const (
SigProvUnknown = SigProvenance(iota)
SigProvEmbedded
SigProvCatalog
)
// QueryCertSubject obtains the subject associated with the certificate used to
// sign the PE binary located at path. When err == nil, it also returns the
// provenance of that signature. ErrSigNotFound is returned if no signature
// is found. Note that this function does *not* validate the chain of trust; use
// Verify for that purpose!
func QueryCertSubject(path string) (certSubject string, provenance SigProvenance, err error) {
path16, err := windows.UTF16PtrFromString(path)
if err != nil {
return "", SigProvUnknown, err
}
return queryPE(path16, false)
}
func queryPE(utf16Path *uint16, verify bool) (string, SigProvenance, error) {
certSubject, err := queryEmbeddedCertSubject(utf16Path, verify)
switch {
case err == ErrSigNotFound:
// Try looking for the signature in a catalog file.
default:
return certSubject, SigProvEmbedded, err
}
certSubject, err = queryCatalogCertSubject(utf16Path, verify)
switch {
case err == ErrSigNotFound:
return "", SigProvUnknown, err
default:
return certSubject, SigProvCatalog, err
}
}
// CertSubjectError is returned if a cert subject was successfully resolved but
// there was a problem encountered during its extraction. The Subject is
// provided for informational purposes but is not presumed to be accurate.
type CertSubjectError struct {
Err error // The error that occurred while extracting the cert subject.
Subject string // The (possibly invalid) cert subject that was extracted.
}
func (e *CertSubjectError) Error() string {
if e == nil {
return "<nil>"
}
if e.Subject == "" {
return e.Err.Error()
}
return fmt.Sprintf("cert subject %q: %v", e.Subject, e.Err)
}
func (e *CertSubjectError) Unwrap() error {
return e.Err
}
func verifyMSI(path *uint16) (string, error) {
var certCtx *windows.CertContext
hr := msiGetFileSignatureInformation(path, _MSI_INVALID_HASH_IS_FATAL, &certCtx, nil, nil)
if e := wingoes.ErrorFromHRESULT(hr); e.Failed() {
if e == wingoes.ErrorFromHRESULT(_TRUST_E_NOSIGNATURE) {
return "", ErrSigNotFound
}
return "", e
}
defer windows.CertFreeCertificateContext(certCtx)
return certSubjectFromCertContext(certCtx)
}
func certSubjectFromCertContext(certCtx *windows.CertContext) (string, error) {
desiredLen := windows.CertGetNameString(
certCtx,
windows.CERT_NAME_SIMPLE_DISPLAY_TYPE,
0,
nil,
nil,
0,
)
if desiredLen <= 1 {
return "", errCertSubjectNotFound
}
buf := make([]uint16, desiredLen)
actualLen := windows.CertGetNameString(
certCtx,
windows.CERT_NAME_SIMPLE_DISPLAY_TYPE,
0,
nil,
&buf[0],
desiredLen,
)
if actualLen != desiredLen {
return "", errCertSubjectDecodeLenMismatch
}
return windows.UTF16ToString(buf), nil
}
type objectQuery struct {
certStore windows.Handle
cryptMsg windows.Handle
encodingType uint32
}
func newObjectQuery(utf16Path *uint16) (*objectQuery, error) {
var oq objectQuery
if err := windows.CryptQueryObject(
windows.CERT_QUERY_OBJECT_FILE,
unsafe.Pointer(utf16Path),
windows.CERT_QUERY_CONTENT_FLAG_PKCS7_SIGNED_EMBED,
windows.CERT_QUERY_FORMAT_FLAG_BINARY,
0,
&oq.encodingType,
nil,
nil,
&oq.certStore,
&oq.cryptMsg,
nil,
); err != nil {
return nil, err
}
return &oq, nil
}
func (oq *objectQuery) Close() error {
if oq.certStore != 0 {
if err := windows.CertCloseStore(oq.certStore, 0); err != nil {
return err
}
oq.certStore = 0
}
if oq.cryptMsg != 0 {
if err := cryptMsgClose(oq.cryptMsg); err != nil {
return err
}
oq.cryptMsg = 0
}
return nil
}
func (oq *objectQuery) certSubject() (string, error) {
var certInfoLen uint32
if err := cryptMsgGetParam(
oq.cryptMsg,
_CMSG_SIGNER_CERT_INFO_PARAM,
0,
unsafe.Pointer(nil),
&certInfoLen,
); err != nil {
return "", err
}
buf := make([]byte, certInfoLen)
if err := cryptMsgGetParam(
oq.cryptMsg,
_CMSG_SIGNER_CERT_INFO_PARAM,
0,
unsafe.Pointer(&buf[0]),
&certInfoLen,
); err != nil {
return "", err
}
certInfo := (*windows.CertInfo)(unsafe.Pointer(&buf[0]))
certCtx, err := windows.CertFindCertificateInStore(
oq.certStore,
oq.encodingType,
0,
windows.CERT_FIND_SUBJECT_CERT,
unsafe.Pointer(certInfo),
nil,
)
if err != nil {
return "", err
}
defer windows.CertFreeCertificateContext(certCtx)
return certSubjectFromCertContext(certCtx)
}
func extractCertBlob(hfile windows.Handle) ([]byte, error) {
pef, err := pe.NewPEFromFileHandle(hfile)
if err != nil {
return nil, err
}
defer pef.Close()
certsAny, err := pef.DataDirectoryEntry(pe.IMAGE_DIRECTORY_ENTRY_SECURITY)
if err != nil {
if errors.Is(err, pe.ErrNotPresent) {
err = ErrSigNotFound
}
return nil, err
}
certs, ok := certsAny.([]pe.AuthenticodeCert)
if !ok || len(certs) == 0 {
return nil, ErrSigNotFound
}
for _, cert := range certs {
if cert.Revision() != pe.WIN_CERT_REVISION_2_0 || cert.Type() != pe.WIN_CERT_TYPE_PKCS_SIGNED_DATA {
continue
}
return cert.Data(), nil
}
return nil, ErrSigNotFound
}
type _HCRYPTPROV windows.Handle
type _CRYPT_VERIFY_MESSAGE_PARA struct {
CBSize uint32
MsgAndCertEncodingType uint32
HCryptProv _HCRYPTPROV
FNGetSignerCertificate uintptr
GetArg uintptr
StrongSignPara *windows.CertStrongSignPara
}
func querySubjectFromBlob(blob []byte) (string, error) {
para := _CRYPT_VERIFY_MESSAGE_PARA{
CBSize: uint32(unsafe.Sizeof(_CRYPT_VERIFY_MESSAGE_PARA{})),
MsgAndCertEncodingType: windows.X509_ASN_ENCODING | windows.PKCS_7_ASN_ENCODING,
}
var certCtx *windows.CertContext
if err := cryptVerifyMessageSignature(&para, 0, &blob[0], uint32(len(blob)), nil, nil, &certCtx); err != nil {
return "", err
}
defer windows.CertFreeCertificateContext(certCtx)
return certSubjectFromCertContext(certCtx)
}
func queryEmbeddedCertSubject(utf16Path *uint16, verify bool) (string, error) {
peBinary, err := windows.CreateFile(
utf16Path,
windows.GENERIC_READ,
windows.FILE_SHARE_READ,
nil,
windows.OPEN_EXISTING,
0,
0,
)
if err != nil {
return "", err
}
defer windows.CloseHandle(peBinary)
blob, err := extractCertBlob(peBinary)
if err != nil {
return "", err
}
certSubj, err := querySubjectFromBlob(blob)
if err != nil {
return "", err
}
if !verify {
return certSubj, nil
}
wintrustArg := unsafe.Pointer(&windows.WinTrustFileInfo{
Size: uint32(unsafe.Sizeof(windows.WinTrustFileInfo{})),
FilePath: utf16Path,
File: peBinary,
})
if err := verifyTrust(windows.WTD_CHOICE_FILE, wintrustArg); err != nil {
// We might still want to know who the cert subject claims to be
// even if the validation has failed (eg for troubleshooting purposes),
// so we return a CertSubjectError.
return "", &CertSubjectError{Err: err, Subject: certSubj}
}
return certSubj, nil
}
var (
_BCRYPT_SHA256_ALGORITHM = &([]uint16{'S', 'H', 'A', '2', '5', '6', 0})[0]
_OID_CERT_STRONG_SIGN_OS_1 = &([]byte("1.3.6.1.4.1.311.72.1.1\x00"))[0]
)
type _HCATADMIN windows.Handle
type _HCATINFO windows.Handle
type _CATALOG_INFO struct {
size uint32
catalogFile [windows.MAX_PATH]uint16
}
type _WINTRUST_CATALOG_INFO struct {
size uint32
catalogVersion uint32
catalogFilePath *uint16
memberTag *uint16
memberFilePath *uint16
memberFile windows.Handle
pCalculatedFileHash *byte
cbCalculatedFileHash uint32
catalogContext uintptr
catAdmin _HCATADMIN
}
func queryCatalogCertSubject(utf16Path *uint16, verify bool) (string, error) {
var catAdmin _HCATADMIN
policy := windows.CertStrongSignPara{
Size: uint32(unsafe.Sizeof(windows.CertStrongSignPara{})),
InfoChoice: _CERT_STRONG_SIGN_OID_INFO_CHOICE,
InfoOrSerializedInfoOrOID: unsafe.Pointer(_OID_CERT_STRONG_SIGN_OS_1),
}
if err := cryptCATAdminAcquireContext2(
&catAdmin,
nil,
_BCRYPT_SHA256_ALGORITHM,
&policy,
0,
); err != nil {
return "", err
}
defer cryptCATAdminReleaseContext(catAdmin, 0)
// We use windows.CreateFile instead of standard library facilities because:
// 1. Subsequent API calls directly utilize the file's Win32 HANDLE;
// 2. We're going to be hashing the contents of this file, so we want to
// provide a sequential-scan hint to the kernel.
memberFile, err := windows.CreateFile(
utf16Path,
windows.GENERIC_READ,
windows.FILE_SHARE_READ,
nil,
windows.OPEN_EXISTING,
windows.FILE_FLAG_SEQUENTIAL_SCAN,
0,
)
if err != nil {
return "", err
}
defer windows.CloseHandle(memberFile)
var hashLen uint32
if err := cryptCATAdminCalcHashFromFileHandle2(
catAdmin,
memberFile,
&hashLen,
nil,
0,
); err != nil {
return "", err
}
hashBuf := make([]byte, hashLen)
if err := cryptCATAdminCalcHashFromFileHandle2(
catAdmin,
memberFile,
&hashLen,
&hashBuf[0],
0,
); err != nil {
return "", err
}
catInfoCtx, err := cryptCATAdminEnumCatalogFromHash(
catAdmin,
&hashBuf[0],
hashLen,
0,
nil,
)
if err != nil {
if err == windows.ERROR_NOT_FOUND {
err = ErrSigNotFound
}
return "", err
}
defer cryptCATAdminReleaseCatalogContext(catAdmin, catInfoCtx, 0)
catInfo := _CATALOG_INFO{
size: uint32(unsafe.Sizeof(_CATALOG_INFO{})),
}
if err := cryptCATAdminCatalogInfoFromContext(catInfoCtx, &catInfo, 0); err != nil {
return "", err
}
oq, err := newObjectQuery(&catInfo.catalogFile[0])
if err != nil {
return "", err
}
defer oq.Close()
certSubj, err := oq.certSubject()
if err != nil {
return "", err
}
if !verify {
return certSubj, nil
}
// memberTag is required to be formatted this way.
hbh := strings.ToUpper(hex.EncodeToString(hashBuf))
memberTag, err := windows.UTF16PtrFromString(hbh)
if err != nil {
return "", err
}
wintrustArg := unsafe.Pointer(&_WINTRUST_CATALOG_INFO{
size: uint32(unsafe.Sizeof(_WINTRUST_CATALOG_INFO{})),
catalogFilePath: &catInfo.catalogFile[0],
memberTag: memberTag,
memberFilePath: utf16Path,
memberFile: memberFile,
catAdmin: catAdmin,
})
if err := verifyTrust(windows.WTD_CHOICE_CATALOG, wintrustArg); err != nil {
// We might still want to know who the cert subject claims to be
// even if the validation has failed (eg for troubleshooting purposes),
// so we return a CertSubjectError.
return "", &CertSubjectError{Err: err, Subject: certSubj}
}
return certSubj, nil
}
func verifyTrust(infoType uint32, info unsafe.Pointer) error {
data := &windows.WinTrustData{
Size: uint32(unsafe.Sizeof(windows.WinTrustData{})),
UIChoice: windows.WTD_UI_NONE,
RevocationChecks: windows.WTD_REVOKE_WHOLECHAIN, // Full revocation checking, as this is called with network connectivity.
UnionChoice: infoType,
StateAction: windows.WTD_STATEACTION_VERIFY,
FileOrCatalogOrBlobOrSgnrOrCert: info,
}
err := windows.WinVerifyTrustEx(windows.InvalidHWND, &windows.WINTRUST_ACTION_GENERIC_VERIFY_V2, data)
data.StateAction = windows.WTD_STATEACTION_CLOSE
windows.WinVerifyTrustEx(windows.InvalidHWND, &windows.WINTRUST_ACTION_GENERIC_VERIFY_V2, data)
return err
}