Add the ability to do unsafe SSL renegotiation as a fallback.

This commit adds the ability to perform legacy SSL renegotiation as
a fallback via QSsl::SslOptions. This is something that used to work,
but has been disabled by default in newer versions of openssl. The
need for this has been reported by users (eg. in QTBUG-14983).

Change-Id: I5b80f3ffd07e0c5faddc469f6a8f857bac5740f7
Reviewed-by: Corentin Chary <corentin.chary@gmail.com>
Reviewed-by: Peter Hartmann <peter.hartmann@nokia.com>

src/network/ssl/qssl.cpp

@@ -141,9 +141,15 @@ QT_BEGIN_NAMESPACE
     \value SslOptionDisableServerNameIndication Disables the SSL server
     name indication extension. When enabled, this tells the server the virtual
     host being accessed allowing it to respond with the correct certificate.
+    \value SslOptionDisableLegacyRenegotiation Disables the older insecure
+    mechanism for renegotiating the connection parameters. When enabled, this
+    option can allow connections for legacy servers, but it introduces the
+    possibility that an attacker could inject plaintext into the SSL session.
 
     By default, SslOptionDisableEmptyFragments is turned on since this causes
-    problems with a large number of servers, but the other options are disabled.
+    problems with a large number of servers. SslOptionDisableLegacyRenegotiation
+    is also turned on, since it introduces a security risk. The other options
+    are turned off.
 
     Note: Availability of above options depends on the version of the SSL
     backend in use.

src/network/ssl/qssl.h

@@ -92,7 +92,8 @@ namespace QSsl {
         SslOptionDisableEmptyFragments = 0x01,
         SslOptionDisableSessionTickets = 0x02,
         SslOptionDisableCompression = 0x04,
-        SslOptionDisableServerNameIndication = 0x08
+        SslOptionDisableServerNameIndication = 0x08,
+        SslOptionDisableLegacyRenegotiation = 0x10
     };
     Q_DECLARE_FLAGS(SslOptions, SslOption)
 }

src/network/ssl/qsslconfiguration.cpp

@@ -201,7 +201,7 @@ bool QSslConfiguration::isNull() const
             d->privateKey.isNull() &&
             d->peerCertificate.isNull() &&
             d->peerCertificateChain.count() == 0 &&
-            d->sslOptions == 0);
+            d->sslOptions == QSsl::SslOptionDisableEmptyFragments|QSsl::SslOptionDisableLegacyRenegotiation);
 }
 
 /*!

src/network/ssl/qsslconfiguration_p.h

@@ -82,7 +82,8 @@ public:
     QSslConfigurationPrivate()
         : protocol(QSsl::SecureProtocols),
           peerVerifyMode(QSslSocket::AutoVerifyPeer),
-          peerVerifyDepth(0)
+          peerVerifyDepth(0),
+          sslOptions(QSsl::SslOptionDisableEmptyFragments|QSsl::SslOptionDisableLegacyRenegotiation)
     { }
 
     QSslCertificate peerCertificate;

src/network/ssl/qsslsocket_openssl.cpp

@@ -287,6 +287,14 @@ init_context:
     else
         options &= ~SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS;
 
+#ifdef SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
+    // This option is disabled by default, so we need to be able to clear it
+    if (configuration.sslOptions & QSsl::SslOptionDisableLegacyRenegotiation)
+        options &= ~SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION;
+    else
+        options |= SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION;
+#endif
+
 #ifdef SSL_OP_NO_TICKET
     if (configuration.sslOptions & QSsl::SslOptionDisableSessionTickets)
         options |= SSL_OP_NO_TICKET;

tests/manual/qssloptions/main.cpp

@@ -56,6 +56,7 @@ int main(int argc, char **argv)
         out << "disable_session_tickets" << endl;
         out << "disable_compression" << endl;
         out << "disable_sni" << endl;
+        out << "enable_unsafe_reneg" << endl;
         return 1;
     }
 
@@ -75,6 +76,8 @@ int main(int argc, char **argv)
             config.setSslOption(QSsl::SslOptionDisableCompression, true);
         else if (option == QStringLiteral("disable_sni"))
             config.setSslOption(QSsl::SslOptionDisableServerNameIndication, true);
+        else if (option == QStringLiteral("enable_unsafe_reneg"))
+            config.setSslOption(QSsl::SslOptionDisableLegacyRenegotiation, false);
     }
 
     QSslConfiguration::setDefaultConfiguration(config);