crypto: make ALPN the same for OpenSSL 1.0.2 & 1.1.0

davidben · rvagg · commit 63c278959ad8 · 2017-11-11T20:42:50.000+11:00
This is kind of hairy. OpenSSL 1.0.2 ignored the return value and always treated everything as SSL_TLSEXT_ERR_NOACK (so the comment was wrong and Node was never sending a warning alert). OpenSSL 1.1.0 honors SSL_TLSEXT_ERR_NOACK vs SSL_TLSEXT_ERR_FATAL_ALERT and treats everything unknown as SSL_TLSEXT_ERR_FATAL_ALERT. Since this is a behavior change (tests break too), start by aligning everything on SSL_TLSEXT_ERR_NOACK. If sending no_application_protocol is desirable in the future, this can by changed to SSL_TLSEXT_ERR_FATAL_ALERT with whatever deprecation process is appropriate. However, note that, contrary to https://rt.openssl.org/Ticket/Display.html?id=3463#txn-54498, SSL_TLSEXT_ERR_FATAL_ALERT is *not* useful to a server with no fallback protocol. Even if such mismatches were rejected, such a server must *still* account for the fallback protocol case when the client does not advertise ALPN at all. Thus this may not be worth bothering. PR-URL: nodejs#16130 Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl> Reviewed-By: Rod Vagg <rod@vagg.org>
diff --git a/src/node_crypto.cc b/src/node_crypto.cc
@@ -2502,20 +2502,12 @@ int SSLWrap<Base>::SelectALPNCallback(SSL* s,
   unsigned alpn_protos_len = Buffer::Length(alpn_buffer);
   int status = SSL_select_next_proto(const_cast<unsigned char**>(out), outlen,
                                      alpn_protos, alpn_protos_len, in, inlen);
-
-  switch (status) {
-    case OPENSSL_NPN_NO_OVERLAP:
-      // According to 3.2. Protocol Selection of RFC7301,
-      // fatal no_application_protocol alert shall be sent
-      // but current openssl does not support it yet. See
-      // https://rt.openssl.org/Ticket/Display.html?id=3463&user=guest&pass=guest
-      // Instead, we send a warning alert for now.
-      return SSL_TLSEXT_ERR_ALERT_WARNING;
-    case OPENSSL_NPN_NEGOTIATED:
-      return SSL_TLSEXT_ERR_OK;
-    default:
-      return SSL_TLSEXT_ERR_ALERT_FATAL;
-  }
+  // According to 3.2. Protocol Selection of RFC7301, fatal
+  // no_application_protocol alert shall be sent but OpenSSL 1.0.2 does not
+  // support it yet. See
+  // https://rt.openssl.org/Ticket/Display.html?id=3463&user=guest&pass=guest
+  return status == OPENSSL_NPN_NEGOTIATED ? SSL_TLSEXT_ERR_OK
+                                          : SSL_TLSEXT_ERR_NOACK;
 }
 #endif  // TLSEXT_TYPE_application_layer_protocol_negotiation
 
