crypto/x509: add test for v1 intermediates.

X.509v1 certificates are ancient and should be dead. (They are even
prohibited by the Baseline requirements, section 7.1.1.)

However, there are a number of v1 roots from the 1990's that are still
in operation. Thus crypto/x509.Certificate.CheckSignatureFrom allows
X.509v1 certificates to sign other certificates.

The chain building code, however, only allows v1 certificates to sign
others if they're a root. This change adds a test to check that.

Change-Id: Ib8d81e522f30d41932b89bdf3b19ef3782d8ec12
Reviewed-on: https://go-review.googlesource.com/34383
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/crypto/x509/verify_test.go

@@ -263,6 +263,17 @@ var verifyTests = []verifyTest{
 
 		errorCallback: expectSubjectIssuerMismatcthError,
 	},
+	{
+		// An X.509 v1 certificate should not be accepted as an
+		// intermediate.
+		leaf:          x509v1TestLeaf,
+		intermediates: []string{x509v1TestIntermediate},
+		roots:         []string{x509v1TestRoot},
+		currentTime:   1481753183,
+		systemSkip:    true,
+
+		errorCallback: expectNotAuthorizedError,
+	},
 }
 
 func expectHostnameError(t *testing.T, i int, err error) (ok bool) {
@@ -330,6 +341,14 @@ func expectSubjectIssuerMismatcthError(t *testing.T, i int, err error) (ok bool)
 	return true
 }
 
+func expectNotAuthorizedError(t *testing.T, i int, err error) (ok bool) {
+	if inval, ok := err.(CertificateInvalidError); !ok || inval.Reason != NotAuthorizedToSign {
+		t.Errorf("#%d: error was not a NotAuthorizedToSign: %s", i, err)
+		return false
+	}
+	return true
+}
+
 func certificateFromPEM(pemBytes string) (*Certificate, error) {
 	block, _ := pem.Decode([]byte(pemBytes))
 	if block == nil {
@@ -1269,6 +1288,52 @@ vEA4PCJprUYmoj3q9MKSSRYDlq5kIbl87mSRR4GqtAwJKxIasvOvULOxziQ=
 -----END CERTIFICATE-----
 `
 
+const x509v1TestRoot = `
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----`
+
+const x509v1TestIntermediate = `
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----`
+
+const x509v1TestLeaf = `
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----`
+
 var unknownAuthorityErrorTests = []struct {
 	cert     string
 	expected string