crypto/tls: fix ConnectionState().VerifiedChains for resumed connection

Strengthening VerifyHostname exposed the fact that for resumed
connections, ConnectionState().VerifiedChains was not being saved
and restored during the ClientSessionCache operations.
Do that.

This change just saves the verified chains in the client's session
cache. It does not re-verify the certificates when resuming a
connection.

There are arguments both ways about this: we want fast, light-weight
resumption connections (thus suggesting that we shouldn't verify) but
it could also be a little surprising that, if the verification config
is changed, that would be ignored if the same session cache is used.

On the server side we do re-verify client-auth certificates, but the
situation is a little different there. The client session cache is an
object in memory that's reset each time the process restarts. But the
server's session cache is a conceptual object, held by the clients, so
can persist across server restarts. Thus the chance of a change in
verification config being surprisingly ignored is much higher in the
server case.

Fixes #12024.

Change-Id: I3081029623322ce3d9f4f3819659fdd9a381db16
Reviewed-on: https://go-review.googlesource.com/13164
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Adam Langley <agl@golang.org>

common.go

@@ -196,6 +196,7 @@ type ClientSessionState struct {
 	cipherSuite        uint16                // Ciphersuite negotiated for the session
 	masterSecret       []byte                // MasterSecret generated by client on a full handshake
 	serverCertificates []*x509.Certificate   // Certificate chain presented by the server
+	verifiedChains     [][]*x509.Certificate // Certificate chains we built for verification
 }
 
 // ClientSessionCache is a cache of ClientSessionState objects that can be used

handshake_client.go

@@ -547,6 +547,7 @@ func (hs *clientHandshakeState) processServerHello() (bool, error) {
 		// Restore masterSecret and peerCerts from previous state
 		hs.masterSecret = hs.session.masterSecret
 		c.peerCertificates = hs.session.serverCertificates
+		c.verifiedChains = hs.session.verifiedChains
 		return true, nil
 	}
 	return false, nil
@@ -604,6 +605,7 @@ func (hs *clientHandshakeState) readSessionTicket() error {
 		cipherSuite:        hs.suite.id,
 		masterSecret:       hs.masterSecret,
 		serverCertificates: c.peerCertificates,
+		verifiedChains:     c.verifiedChains,
 	}
 
 	return nil

handshake_client_test.go

@@ -406,10 +406,20 @@ func TestClientResumption(t *testing.T) {
 		CipherSuites: []uint16{TLS_RSA_WITH_RC4_128_SHA, TLS_ECDHE_RSA_WITH_RC4_128_SHA},
 		Certificates: testConfig.Certificates,
 	}
+
+	issuer, err := x509.ParseCertificate(testRSACertificateIssuer)
+	if err != nil {
+		panic(err)
+	}
+
+	rootCAs := x509.NewCertPool()
+	rootCAs.AddCert(issuer)
+
 	clientConfig := &Config{
 		CipherSuites:       []uint16{TLS_RSA_WITH_RC4_128_SHA},
-		InsecureSkipVerify: true,
 		ClientSessionCache: NewLRUClientSessionCache(32),
+		RootCAs:            rootCAs,
+		ServerName:         "example.golang",
 	}
 
 	testResumeState := func(test string, didResume bool) {
@@ -420,6 +430,9 @@ func TestClientResumption(t *testing.T) {
 		if hs.DidResume != didResume {
 			t.Fatalf("%s resumed: %v, expected: %v", test, hs.DidResume, didResume)
 		}
+		if didResume && (hs.PeerCertificates == nil || hs.VerifiedChains == nil) {
+			t.Fatalf("expected non-nil certificates after resumption. Got peerCertificates: %#v, verifedCertificates: %#v", hs.PeerCertificates, hs.VerifiedChains)
+		}
 	}
 
 	getTicket := func() []byte {

tls_test.go

@@ -307,3 +307,28 @@ func TestVerifyHostname(t *testing.T) {
 		t.Fatalf("verify www.google.com succeeded with InsecureSkipVerify=true")
 	}
 }
+
+func TestVerifyHostnameResumed(t *testing.T) {
+	testenv.MustHaveExternalNetwork(t)
+
+	config := &Config{
+		ClientSessionCache: NewLRUClientSessionCache(32),
+	}
+	for i := 0; i < 2; i++ {
+		c, err := Dial("tcp", "www.google.com:https", config)
+		if err != nil {
+			t.Fatalf("Dial #%d: %v", i, err)
+		}
+		cs := c.ConnectionState()
+		if i > 0 && !cs.DidResume {
+			t.Fatalf("Subsequent connection unexpectedly didn't resume")
+		}
+		if cs.VerifiedChains == nil {
+			t.Fatalf("Dial #%d: cs.VerifiedChains == nil", i)
+		}
+		if err := c.VerifyHostname("www.google.com"); err != nil {
+			t.Fatalf("verify www.google.com #%d: %v", i, err)
+		}
+		c.Close()
+	}
+}