crypto/x509: parse SAN DirectoryName

[tracefinder]

What version of Go are you using (go version)?

$ go version
go version go1.16.6 linux/amd64

Does this issue reproduce with the latest release?

Yes, according to the sources.

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/user/.cache/go-build"
GOENV="/home/user/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/user/repos/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/user/repos/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.16.6"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/dev/null"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build169247540=/tmp/go-build -gno-record-gcc-switches"

What did you do?

I'm playing around TPM Endorsement Key certificates. One of the things I want to archive is to verify a EK certificate against the root CA. The function looks like

func (v *Verifier) VerifyEK(ekPem []byte) (bool, error) {
	block, _ := pem.Decode(ekPem)
	if block == nil {
		return false, errors.New("failed to parse certificate PEM")
	}

	ek, err := x509.ParseCertificate(block.Bytes)
	if err != nil {
		return false, fmt.Errorf("failed to parse certificate: %w", err)
	}

	opts := x509.VerifyOptions{
		Roots: v.ekRoots,
		Intermediates: v.ekIntermediates,
	}
	if _, err := ek.Verify(opts); err != nil {
		return false, fmt.Errorf("failed to verify certificate: %w", err)
	}

	return true, nil
}

What did you expect to see?

I expect the verification process to complete.

What did you see instead?

Verification fails with x509: unhandled critical extension . The unhandled critical extension is SubjectAltName.

The reason

RFC 5280, 4.2.1.6 defines 9 types of general names. However, parseSANExtension function (crypto/x509) supports only 4 (email, dns, uri, ip).

The proposal

Support other types of general names for SubjectAltName (or add some of them).

[seankhliao]

Duplicate of #15196