Do not roll back to SSL 3.0 for Google properties.

net/socket/ssl_client_socket_nss.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This file includes code SSLClientSocketNSS::DoVerifyCertComplete() derived
 // from AuthCertificateCallback() in
 // mozilla/security/manager/ssl/src/nsNSSCallbacks.cpp.
 
 /* ***** BEGIN LICENSE BLOCK *****
  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
@@ skipping 3455 matching lines @@
         result = ERR_SSL_PINNED_KEY_NOT_IN_CERT_CHAIN;
         UMA_HISTOGRAM_BOOLEAN("Net.PublicKeyPinSuccess", false);
         TransportSecurityState::ReportUMAOnPinFailure(host);
       } else {
         UMA_HISTOGRAM_BOOLEAN("Net.PublicKeyPinSuccess", true);
       }
     }
   }
 #endif
 
+  // Persist the negotiated SSL version if it is newer than the minimum
+  // version. This is used to prevent SSLv3 fallback for domains known
+  // to support TLS.
+
+  // Note: this is effective only for non-preloaded HSTS hosts.
+
+  // TODO(thaidn): determine if the negotiated version is authenticated
+  // at this point. Chrome must not use it if it isn't; otherwise MITM
+  // attackers can perform a permanent DoS attack against users by setting
+  // the version to TLSv1.2 for non-TLSv1.2 servers.
+  if (transport_security_state_ &&
+      result == OK) {
+    bool sni_available =
+        ssl_config_.version_max >= SSL_PROTOCOL_VERSION_TLS1 ||
+        ssl_config_.version_fallback;
+    const std::string& host = host_and_port_.host();
+    TransportSecurityState::DomainState domain_state;
+
+    if (transport_security_state_->GetDomainState(host, sni_available,
+                                                  &domain_state)) {
+      // Update the minimum version of existing |domain_state| if necessary.
+      int ssl_version = SSLConnectionStatusToVersion(
+          core_->state().ssl_connection_status);
+      if (ssl_version > SSL_CONNECTION_VERSION_UNKNOWN &&
+          ssl_version < SSL_CONNECTION_VERSION_MAX &&
+          ssl_version > domain_state.ssl_version_min) {
+        domain_state.ssl_version_min =
+            static_cast<SSL_CONNECTION_VERSION>(ssl_version);
+      }
+    }
+    // Note: the default value of |domain_state.ssl_version_min| is SSLv3.
+    transport_security_state_->EnableHost(host, domain_state);
+  }
+
   // Exit DoHandshakeLoop and return the result to the caller to Connect.
   DCHECK_EQ(STATE_NONE, next_handshake_state_);
   return result;
 }
 
 void SSLClientSocketNSS::LogConnectionTypeMetrics() const {
   UpdateConnectionTypeHistograms(CONNECTION_SSL);
   if (server_cert_verify_result_.has_md5)
     UpdateConnectionTypeHistograms(CONNECTION_SSL_MD5);
   if (server_cert_verify_result_.has_md2)
@@ skipping 36 matching lines @@
   EnsureThreadIdAssigned();
   base::AutoLock auto_lock(lock_);
   return valid_thread_id_ == base::PlatformThread::CurrentId();
 }
 
 ServerBoundCertService* SSLClientSocketNSS::GetServerBoundCertService() const {
   return server_bound_cert_service_;
 }
 
 }  // namespace net