[dev.boringcrypto] all: merge master into dev.boringcrypto

Change-Id: I31c69e54c904c66c10920e4c4caacfef08bb834f

1 files changed, 15 insertions, 18 deletions

diff --git a/src/crypto/tls/handshake_client.go b/src/crypto/tls/handshake_client.go
index 6d32a72fd3..ac19961d3c 100644
--- a/src/crypto/tls/handshake_client.go
+++ b/src/crypto/tls/handshake_client.go
@@ -708,18 +708,18 @@ func (hs *clientHandshakeState) processServerHello() (bool, error) {
 		}
 	}
 
-	clientDidALPN := len(hs.hello.alpnProtocols) > 0
-	serverHasALPN := len(hs.serverHello.alpnProtocol) > 0
-
-	if !clientDidALPN && serverHasALPN {
-		c.sendAlert(alertHandshakeFailure)
-		return false, errors.New("tls: server advertised unrequested ALPN extension")
-	}
-
-	if serverHasALPN {
+	if hs.serverHello.alpnProtocol != "" {
+		if len(hs.hello.alpnProtocols) == 0 {
+			c.sendAlert(alertUnsupportedExtension)
+			return false, errors.New("tls: server advertised unrequested ALPN extension")
+		}
+		if mutualProtocol([]string{hs.serverHello.alpnProtocol}, hs.hello.alpnProtocols) == "" {
+			c.sendAlert(alertUnsupportedExtension)
+			return false, errors.New("tls: server selected unadvertised ALPN protocol")
+		}
 		c.clientProtocol = hs.serverHello.alpnProtocol
-		c.clientProtocolFallback = false
 	}
+
 	c.scts = hs.serverHello.scts
 
 	if !hs.serverResumedSession() {
@@ -978,20 +978,17 @@ func clientSessionCacheKey(serverAddr net.Addr, config *Config) string {
 	return serverAddr.String()
 }
 
-// mutualProtocol finds the mutual Next Protocol Negotiation or ALPN protocol
-// given list of possible protocols and a list of the preference order. The
-// first list must not be empty. It returns the resulting protocol and flag
-// indicating if the fallback case was reached.
-func mutualProtocol(protos, preferenceProtos []string) (string, bool) {
+// mutualProtocol finds the mutual ALPN protocol given list of possible
+// protocols and a list of the preference order.
+func mutualProtocol(protos, preferenceProtos []string) string {
 	for _, s := range preferenceProtos {
 		for _, c := range protos {
 			if s == c {
-				return s, false
+				return s
 			}
 		}
 	}
-
-	return protos[0], true
+	return ""
 }
 
 // hostnameInSNI converts name into an appropriate hostname for SNI.