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cmd/tailscale/cli, util/winutil/authenticode: flesh out authenticode support
Previously, tailscale upgrade was doing the bare minimum for checking authenticode signatures via `WinVerifyTrustEx`. This is fine, but we can do better: * WinVerifyTrustEx verifies that the binary's signature is valid, but it doesn't determine *whose* signature is valid; tailscale upgrade should also ensure that the binary is actually signed *by us*. * I added the ability to check the signatures of MSI files. * In future PRs I will be adding diagnostic logging that lists details about every module (ie, DLL) loaded into our process. As part of that metadata, I want to be able to extract information about who signed the binaries. This code is modelled on some C++ I wrote for Firefox back in the day. See https://searchfox.org/mozilla-central/rev/27e4816536c891d85d63695025f2549fd7976392/toolkit/xre/dllservices/mozglue/Authenticode.cpp for reference. Fixes #8284 Signed-off-by: Aaron Klotz <aaron@tailscale.com>
This commit is contained in:
Aaron Klotz
512
util/winutil/authenticode/authenticode_windows.go
Normal file
512
util/winutil/authenticode/authenticode_windows.go
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@@ -0,0 +1,512 @@
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// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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package authenticode
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import (
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"encoding/hex"
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"errors"
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"fmt"
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"path/filepath"
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"strings"
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"unsafe"
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"github.com/dblohm7/wingoes"
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"github.com/dblohm7/wingoes/pe"
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"golang.org/x/sys/windows"
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)
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var (
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// ErrSigNotFound is returned if no authenticode signature could be found.
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ErrSigNotFound = errors.New("authenticode signature not found")
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// ErrUnexpectedCertSubject is wrapped with the actual cert subject and
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// returned when the binary is signed by a different subject than expected.
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ErrUnexpectedCertSubject = errors.New("unexpected cert subject")
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errCertSubjectNotFound = errors.New("cert subject not found")
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errCertSubjectDecodeLenMismatch = errors.New("length mismatch while decoding cert subject")
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)
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const (
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_CERT_STRONG_SIGN_OID_INFO_CHOICE = 2
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_CMSG_SIGNER_CERT_INFO_PARAM = 7
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_MSI_INVALID_HASH_IS_FATAL = 1
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_TRUST_E_NOSIGNATURE = wingoes.HRESULT(-((0x800B0100 ^ 0xFFFFFFFF) + 1))
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)
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// Verify performs authenticode verification on the file at path, and also
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// ensures that expectedCertSubject was the entity who signed it. path may point
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// to either a PE binary or an MSI package. ErrSigNotFound is returned if no
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// signature is found.
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func Verify(path string, expectedCertSubject string) error {
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path16, err := windows.UTF16PtrFromString(path)
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if err != nil {
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return err
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}
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var subject string
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if strings.EqualFold(filepath.Ext(path), ".msi") {
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subject, err = verifyMSI(path16)
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} else {
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subject, _, err = queryPE(path16, true)
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}
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if err != nil {
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return err
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}
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if subject != expectedCertSubject {
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return fmt.Errorf("%w %q", ErrUnexpectedCertSubject, subject)
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}
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return nil
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}
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// SigProvenance indicates whether an authenticode signature was embedded within
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// the file itself, or the signature applies to an associated catalog file.
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type SigProvenance int
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const (
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SigProvUnknown = SigProvenance(iota)
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SigProvEmbedded
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SigProvCatalog
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)
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// QueryCertSubject obtains the subject associated with the certificate used to
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// sign the PE binary located at path. When err == nil, it also returns the
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// provenance of that signature. ErrSigNotFound is returned if no signature
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// is found. Note that this function does *not* validate the chain of trust; use
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// Verify for that purpose!
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func QueryCertSubject(path string) (certSubject string, provenance SigProvenance, err error) {
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path16, err := windows.UTF16PtrFromString(path)
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if err != nil {
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return "", SigProvUnknown, err
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}
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return queryPE(path16, false)
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}
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func queryPE(utf16Path *uint16, verify bool) (string, SigProvenance, error) {
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certSubject, err := queryEmbeddedCertSubject(utf16Path, verify)
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switch {
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case err == ErrSigNotFound:
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// Try looking for the signature in a catalog file.
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default:
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return certSubject, SigProvEmbedded, err
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}
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certSubject, err = queryCatalogCertSubject(utf16Path, verify)
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switch {
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case err == ErrSigNotFound:
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return "", SigProvUnknown, err
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default:
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return certSubject, SigProvCatalog, err
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}
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}
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type CertSubjectError struct {
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Err error
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Subject string
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}
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func (e *CertSubjectError) Error() string {
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if e == nil {
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return "<nil>"
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}
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if e.Subject == "" {
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return e.Err.Error()
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}
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return fmt.Sprintf("cert subject %q: %v", e.Subject, e.Err)
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}
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func (e *CertSubjectError) Unwrap() error {
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return e.Err
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}
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func verifyMSI(path *uint16) (string, error) {
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var certCtx *windows.CertContext
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hr := msiGetFileSignatureInformation(path, _MSI_INVALID_HASH_IS_FATAL, &certCtx, nil, nil)
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if e := wingoes.ErrorFromHRESULT(hr); e.Failed() {
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if e == wingoes.ErrorFromHRESULT(_TRUST_E_NOSIGNATURE) {
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return "", ErrSigNotFound
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}
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return "", e
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}
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defer windows.CertFreeCertificateContext(certCtx)
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return certSubjectFromCertContext(certCtx)
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}
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func certSubjectFromCertContext(certCtx *windows.CertContext) (string, error) {
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desiredLen := windows.CertGetNameString(
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certCtx,
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windows.CERT_NAME_SIMPLE_DISPLAY_TYPE,
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0,
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nil,
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nil,
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0,
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)
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if desiredLen <= 1 {
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return "", errCertSubjectNotFound
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}
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buf := make([]uint16, desiredLen)
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actualLen := windows.CertGetNameString(
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certCtx,
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windows.CERT_NAME_SIMPLE_DISPLAY_TYPE,
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0,
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nil,
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&buf[0],
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desiredLen,
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)
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if actualLen != desiredLen {
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return "", errCertSubjectDecodeLenMismatch
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}
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return windows.UTF16ToString(buf), nil
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}
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type objectQuery struct {
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certStore windows.Handle
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cryptMsg windows.Handle
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encodingType uint32
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}
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func newObjectQuery(utf16Path *uint16) (*objectQuery, error) {
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var oq objectQuery
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if err := windows.CryptQueryObject(
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windows.CERT_QUERY_OBJECT_FILE,
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unsafe.Pointer(utf16Path),
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windows.CERT_QUERY_CONTENT_FLAG_PKCS7_SIGNED_EMBED,
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windows.CERT_QUERY_FORMAT_FLAG_BINARY,
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0,
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&oq.encodingType,
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nil,
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nil,
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&oq.certStore,
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&oq.cryptMsg,
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nil,
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); err != nil {
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return nil, err
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}
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return &oq, nil
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}
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func (oq *objectQuery) Close() error {
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if oq.certStore != 0 {
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if err := windows.CertCloseStore(oq.certStore, 0); err != nil {
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return err
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}
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oq.certStore = 0
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}
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if oq.cryptMsg != 0 {
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if err := cryptMsgClose(oq.cryptMsg); err != nil {
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return err
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}
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oq.cryptMsg = 0
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}
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return nil
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}
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func (oq *objectQuery) certSubject() (string, error) {
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var certInfoLen uint32
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if err := cryptMsgGetParam(
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oq.cryptMsg,
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_CMSG_SIGNER_CERT_INFO_PARAM,
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0,
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unsafe.Pointer(nil),
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&certInfoLen,
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); err != nil {
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return "", err
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}
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buf := make([]byte, certInfoLen)
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if err := cryptMsgGetParam(
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oq.cryptMsg,
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_CMSG_SIGNER_CERT_INFO_PARAM,
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0,
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unsafe.Pointer(&buf[0]),
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&certInfoLen,
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); err != nil {
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return "", err
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}
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certInfo := (*windows.CertInfo)(unsafe.Pointer(&buf[0]))
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certCtx, err := windows.CertFindCertificateInStore(
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oq.certStore,
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oq.encodingType,
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0,
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windows.CERT_FIND_SUBJECT_CERT,
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unsafe.Pointer(certInfo),
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nil,
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)
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if err != nil {
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return "", err
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}
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defer windows.CertFreeCertificateContext(certCtx)
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return certSubjectFromCertContext(certCtx)
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}
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func extractCertBlob(hfile windows.Handle) ([]byte, error) {
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pef, err := pe.NewPEFromFileHandle(hfile)
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if err != nil {
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return nil, err
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}
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defer pef.Close()
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certsAny, err := pef.DataDirectoryEntry(pe.IMAGE_DIRECTORY_ENTRY_SECURITY)
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if err != nil {
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return nil, err
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}
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certs, ok := certsAny.([]pe.AuthenticodeCert)
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if !ok || len(certs) == 0 {
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return nil, ErrSigNotFound
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}
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for _, cert := range certs {
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if cert.Revision() != pe.WIN_CERT_REVISION_2_0 || cert.Type() != pe.WIN_CERT_TYPE_PKCS_SIGNED_DATA {
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continue
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}
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return cert.Data(), nil
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}
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return nil, ErrSigNotFound
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}
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type _HCRYPTPROV windows.Handle
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type _CRYPT_VERIFY_MESSAGE_PARA struct {
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CBSize uint32
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MsgAndCertEncodingType uint32
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HCryptProv _HCRYPTPROV
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FNGetSignerCertificate uintptr
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GetArg uintptr
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StrongSignPara *windows.CertStrongSignPara
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}
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func querySubjectFromBlob(blob []byte) (string, error) {
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para := _CRYPT_VERIFY_MESSAGE_PARA{
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CBSize: uint32(unsafe.Sizeof(_CRYPT_VERIFY_MESSAGE_PARA{})),
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MsgAndCertEncodingType: windows.X509_ASN_ENCODING | windows.PKCS_7_ASN_ENCODING,
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}
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var certCtx *windows.CertContext
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if err := cryptVerifyMessageSignature(¶, 0, &blob[0], uint32(len(blob)), nil, nil, &certCtx); err != nil {
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return "", err
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}
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defer windows.CertFreeCertificateContext(certCtx)
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return certSubjectFromCertContext(certCtx)
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}
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func queryEmbeddedCertSubject(utf16Path *uint16, verify bool) (string, error) {
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peBinary, err := windows.CreateFile(
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utf16Path,
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windows.GENERIC_READ,
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windows.FILE_SHARE_READ,
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nil,
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windows.OPEN_EXISTING,
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0,
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0,
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)
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if err != nil {
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return "", err
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}
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defer windows.CloseHandle(peBinary)
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blob, err := extractCertBlob(peBinary)
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if err != nil {
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return "", err
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}
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certSubj, err := querySubjectFromBlob(blob)
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if err != nil {
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return "", err
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}
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if !verify {
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return certSubj, nil
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}
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wintrustArg := unsafe.Pointer(&windows.WinTrustFileInfo{
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Size: uint32(unsafe.Sizeof(windows.WinTrustFileInfo{})),
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FilePath: utf16Path,
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File: peBinary,
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})
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if err := verifyTrust(windows.WTD_CHOICE_FILE, wintrustArg); err != nil {
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// We might still want to know who the cert subject claims to be
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// even if the validation has failed (eg for troubleshooting purposes),
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// so we return a CertSubjectError.
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return "", &CertSubjectError{Err: err, Subject: certSubj}
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}
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return certSubj, nil
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}
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var (
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_BCRYPT_SHA256_ALGORITHM = &([]uint16{'S', 'H', 'A', '2', '5', '6', 0})[0]
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_OID_CERT_STRONG_SIGN_OS_1 = &([]byte("1.3.6.1.4.1.311.72.1.1\x00"))[0]
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)
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type _HCATADMIN windows.Handle
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type _HCATINFO windows.Handle
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type _CATALOG_INFO struct {
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size uint32
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catalogFile [windows.MAX_PATH]uint16
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}
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type _WINTRUST_CATALOG_INFO struct {
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size uint32
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catalogVersion uint32
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catalogFilePath *uint16
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memberTag *uint16
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memberFilePath *uint16
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memberFile windows.Handle
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pCalculatedFileHash *byte
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cbCalculatedFileHash uint32
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catalogContext uintptr
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catAdmin _HCATADMIN
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}
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func queryCatalogCertSubject(utf16Path *uint16, verify bool) (string, error) {
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var catAdmin _HCATADMIN
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policy := windows.CertStrongSignPara{
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Size: uint32(unsafe.Sizeof(windows.CertStrongSignPara{})),
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InfoChoice: _CERT_STRONG_SIGN_OID_INFO_CHOICE,
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InfoOrSerializedInfoOrOID: unsafe.Pointer(_OID_CERT_STRONG_SIGN_OS_1),
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}
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if err := cryptCATAdminAcquireContext2(
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&catAdmin,
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nil,
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_BCRYPT_SHA256_ALGORITHM,
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&policy,
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0,
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); err != nil {
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return "", err
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}
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defer cryptCATAdminReleaseContext(catAdmin, 0)
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// We use windows.CreateFile instead of standard library facilities because:
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// 1. Subsequent API calls directly utilize the file's Win32 HANDLE;
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// 2. We're going to be hashing the contents of this file, so we want to
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// provide a sequential-scan hint to the kernel.
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memberFile, err := windows.CreateFile(
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utf16Path,
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windows.GENERIC_READ,
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windows.FILE_SHARE_READ,
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nil,
|
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windows.OPEN_EXISTING,
|
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windows.FILE_FLAG_SEQUENTIAL_SCAN,
|
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0,
|
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)
|
||||
if err != nil {
|
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return "", err
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||||
}
|
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defer windows.CloseHandle(memberFile)
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|
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var hashLen uint32
|
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if err := cryptCATAdminCalcHashFromFileHandle2(
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catAdmin,
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memberFile,
|
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&hashLen,
|
||||
nil,
|
||||
0,
|
||||
); err != nil {
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return "", err
|
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}
|
||||
|
||||
hashBuf := make([]byte, hashLen)
|
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if err := cryptCATAdminCalcHashFromFileHandle2(
|
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catAdmin,
|
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memberFile,
|
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&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
|
||||
}
|
||||
Reference in New Issue
Block a user