Add ability for application to control which TLS extensions are used

GH #1186

9 files changed, 56 insertions, 1 deletions

diff --git a/src/lib/tls/msg_client_hello.cpp b/src/lib/tls/msg_client_hello.cpp
index eeeaf8c71..77068a928 100644
--- a/src/lib/tls/msg_client_hello.cpp
+++ b/src/lib/tls/msg_client_hello.cpp
@@ -10,6 +10,7 @@
 #include <botan/tls_messages.h>
 #include <botan/tls_alert.h>
 #include <botan/tls_exceptn.h>
+#include <botan/tls_callbacks.h>
 #include <botan/rng.h>
 #include <botan/hash.h>
 
@@ -81,6 +82,7 @@ std::vector<uint8_t> Hello_Request::serialize() const
 Client_Hello::Client_Hello(Handshake_IO& io,
                            Handshake_Hash& hash,
                            const Policy& policy,
+                           Callbacks& cb,
                            RandomNumberGenerator& rng,
                            const std::vector<uint8_t>& reneg_info,
                            const Client_Hello::Settings& client_settings,
@@ -140,6 +142,8 @@ Client_Hello::Client_Hello(Handshake_IO& io,
       m_extensions.add(new Signature_Algorithms(policy.allowed_signature_hashes(),
                                                 policy.allowed_signature_methods()));
 
+   cb.tls_modify_extensions(m_extensions);
+
    if(policy.send_fallback_scsv(client_settings.protocol_version()))
       m_suites.push_back(TLS_FALLBACK_SCSV);
 
@@ -152,6 +156,7 @@ Client_Hello::Client_Hello(Handshake_IO& io,
 Client_Hello::Client_Hello(Handshake_IO& io,
                            Handshake_Hash& hash,
                            const Policy& policy,
+                           Callbacks& cb,
                            RandomNumberGenerator& rng,
                            const std::vector<uint8_t>& reneg_info,
                            const Session& session,
@@ -201,6 +206,8 @@ Client_Hello::Client_Hello(Handshake_IO& io,
    if(reneg_info.empty() && !next_protocols.empty())
       m_extensions.add(new Application_Layer_Protocol_Notification(next_protocols));
 
+   cb.tls_modify_extensions(m_extensions);
+
    hash.update(io.send(*this));
    }
 
diff --git a/src/lib/tls/msg_server_hello.cpp b/src/lib/tls/msg_server_hello.cpp
index 5e290eb68..815fd37f0 100644
--- a/src/lib/tls/msg_server_hello.cpp
+++ b/src/lib/tls/msg_server_hello.cpp
@@ -9,6 +9,7 @@
 
 #include <botan/tls_messages.h>
 #include <botan/tls_extensions.h>
+#include <botan/tls_callbacks.h>
 #include <botan/internal/tls_reader.h>
 #include <botan/internal/tls_session_key.h>
 #include <botan/internal/tls_handshake_io.h>
@@ -23,6 +24,7 @@ namespace TLS {
 Server_Hello::Server_Hello(Handshake_IO& io,
                            Handshake_Hash& hash,
                            const Policy& policy,
+                           Callbacks& cb,
                            RandomNumberGenerator& rng,
                            const std::vector<uint8_t>& reneg_info,
                            const Client_Hello& client_hello,
@@ -83,6 +85,8 @@ Server_Hello::Server_Hello(Handshake_IO& io,
          }
       }
 
+   cb.tls_modify_extensions(m_extensions);
+
    hash.update(io.send(*this));
    }
 
@@ -90,6 +94,7 @@ Server_Hello::Server_Hello(Handshake_IO& io,
 Server_Hello::Server_Hello(Handshake_IO& io,
                            Handshake_Hash& hash,
                            const Policy& policy,
+                           Callbacks& cb,
                            RandomNumberGenerator& rng,
                            const std::vector<uint8_t>& reneg_info,
                            const Client_Hello& client_hello,
@@ -130,6 +135,8 @@ Server_Hello::Server_Hello(Handshake_IO& io,
    if(!next_protocol.empty() && client_hello.supports_alpn())
       m_extensions.add(new Application_Layer_Protocol_Notification(next_protocol));
 
+   cb.tls_modify_extensions(m_extensions);
+
    hash.update(io.send(*this));
    }
 
diff --git a/src/lib/tls/tls_callbacks.cpp b/src/lib/tls/tls_callbacks.cpp
index b8f38589e..b13aa2406 100644
--- a/src/lib/tls/tls_callbacks.cpp
+++ b/src/lib/tls/tls_callbacks.cpp
@@ -32,6 +32,10 @@ std::string TLS::Callbacks::tls_server_choose_app_protocol(const std::vector<std
    return "";
    }
 
+void TLS::Callbacks::tls_modify_extensions(Extensions&)
+   {
+   }
+
 void TLS::Callbacks::tls_verify_cert_chain(
    const std::vector<X509_Certificate>& cert_chain,
    const std::vector<std::shared_ptr<const OCSP::Response>>& ocsp_responses,
diff --git a/src/lib/tls/tls_callbacks.h b/src/lib/tls/tls_callbacks.h
index 4437a222a..3ac1a9d2f 100644
--- a/src/lib/tls/tls_callbacks.h
+++ b/src/lib/tls/tls_callbacks.h
@@ -30,6 +30,7 @@ namespace TLS {
 
 class Handshake_Message;
 class Policy;
+class Extensions;
 
 /**
 * Encapsulates the callbacks that a TLS channel will make which are due to
@@ -250,6 +251,17 @@ class BOTAN_PUBLIC_API(2,0) Callbacks
        virtual std::string tls_server_choose_app_protocol(const std::vector<std::string>& client_protos);
 
        /**
+       * Optional callback: examine/modify Extensions before sending.  Both
+       * client and server will call this callback on the Extensions object
+       * before serializing it in the client/server hellos. This allows a client
+       * to modify which extensions are sent during the handshake. This also
+       * allows creating custom extensions.
+       *
+       * Default implementation does nothing.
+       */
+       virtual void tls_modify_extensions(Extensions& extn);
+
+       /**
        * Optional callback: error logging. (not currently called)
        * @param err An error message related to this connection.
        */
diff --git a/src/lib/tls/tls_client.cpp b/src/lib/tls/tls_client.cpp
index c88b6a7db..e041c1a77 100644
--- a/src/lib/tls/tls_client.cpp
+++ b/src/lib/tls/tls_client.cpp
@@ -169,6 +169,7 @@ void Client::send_client_hello(Handshake_State& state_base,
                   new Client_Hello(state.handshake_io(),
                                    state.hash(),
                                    policy(),
+                                   callbacks(),
                                    rng(),
                                    secure_renegotiation_data_for_client_hello(),
                                    session_info,
@@ -188,6 +189,7 @@ void Client::send_client_hello(Handshake_State& state_base,
          state.handshake_io(),
          state.hash(),
          policy(),
+         callbacks(),
          rng(),
          secure_renegotiation_data_for_client_hello(),
          client_settings,
diff --git a/src/lib/tls/tls_extensions.cpp b/src/lib/tls/tls_extensions.cpp
index d521f6bf8..6497c3c11 100644
--- a/src/lib/tls/tls_extensions.cpp
+++ b/src/lib/tls/tls_extensions.cpp
@@ -124,6 +124,15 @@ std::vector<uint8_t> Extensions::serialize() const
    return buf;
    }
 
+bool Extensions::remove_extension(Handshake_Extension_Type typ)
+   {
+   auto i = m_extensions.find(typ);
+   if(i == m_extensions.end())
+      return false;
+   m_extensions.erase(i);
+   return true;
+   }
+
 std::set<Handshake_Extension_Type> Extensions::extension_types() const
    {
    std::set<Handshake_Extension_Type> offers;
diff --git a/src/lib/tls/tls_extensions.h b/src/lib/tls/tls_extensions.h
index 221d8b46f..7b7b645bf 100644
--- a/src/lib/tls/tls_extensions.h
+++ b/src/lib/tls/tls_extensions.h
@@ -466,6 +466,13 @@ class BOTAN_UNSTABLE_API Extensions final
 
       void deserialize(TLS_Data_Reader& reader);
 
+      /**
+      * Remvoe an extension from this extensions object, if it exists.
+      * Returns true if the extension existed (and thus is now removed),
+      * otherwise false (the extension wasn't set in the first place).
+      */
+      bool remove_extension(Handshake_Extension_Type typ);
+
       Extensions() = default;
 
       explicit Extensions(TLS_Data_Reader& reader) { deserialize(reader); }
diff --git a/src/lib/tls/tls_messages.h b/src/lib/tls/tls_messages.h
index 35ec3c83c..471467fc2 100644
--- a/src/lib/tls/tls_messages.h
+++ b/src/lib/tls/tls_messages.h
@@ -38,9 +38,10 @@ namespace TLS {
 class Session;
 class Handshake_IO;
 class Handshake_State;
+class Callbacks;
 
 std::vector<uint8_t> make_hello_random(RandomNumberGenerator& rng,
-                                    const Policy& policy);
+                                       const Policy& policy);
 
 /**
 * DTLS Hello Verify Request
@@ -148,6 +149,7 @@ class BOTAN_UNSTABLE_API Client_Hello final : public Handshake_Message
       Client_Hello(Handshake_IO& io,
                    Handshake_Hash& hash,
                    const Policy& policy,
+                   Callbacks& cb,
                    RandomNumberGenerator& rng,
                    const std::vector<uint8_t>& reneg_info,
                    const Client_Hello::Settings& client_settings,
@@ -156,6 +158,7 @@ class BOTAN_UNSTABLE_API Client_Hello final : public Handshake_Message
       Client_Hello(Handshake_IO& io,
                    Handshake_Hash& hash,
                    const Policy& policy,
+                   Callbacks& cb,
                    RandomNumberGenerator& rng,
                    const std::vector<uint8_t>& reneg_info,
                    const Session& resumed_session,
@@ -286,6 +289,7 @@ class BOTAN_UNSTABLE_API Server_Hello final : public Handshake_Message
       Server_Hello(Handshake_IO& io,
                    Handshake_Hash& hash,
                    const Policy& policy,
+                   Callbacks& cb,
                    RandomNumberGenerator& rng,
                    const std::vector<uint8_t>& secure_reneg_info,
                    const Client_Hello& client_hello,
@@ -295,6 +299,7 @@ class BOTAN_UNSTABLE_API Server_Hello final : public Handshake_Message
       Server_Hello(Handshake_IO& io,
                    Handshake_Hash& hash,
                    const Policy& policy,
+                   Callbacks& cb,
                    RandomNumberGenerator& rng,
                    const std::vector<uint8_t>& secure_reneg_info,
                    const Client_Hello& client_hello,
diff --git a/src/lib/tls/tls_server.cpp b/src/lib/tls/tls_server.cpp
index 2d2fb769b..3ed1b120d 100644
--- a/src/lib/tls/tls_server.cpp
+++ b/src/lib/tls/tls_server.cpp
@@ -703,6 +703,7 @@ void Server::session_resume(Server_Handshake_State& pending_state,
                                  pending_state.handshake_io(),
                                  pending_state.hash(),
                                  policy(),
+                                 callbacks(),
                                  rng(),
                                  secure_renegotiation_data_for_server_hello(),
                                  *pending_state.client_hello(),
@@ -794,6 +795,7 @@ void Server::session_create(Server_Handshake_State& pending_state,
                                  pending_state.handshake_io(),
                                  pending_state.hash(),
                                  policy(),
+                                 callbacks(),
                                  rng(),
                                  secure_renegotiation_data_for_server_hello(),
                                  *pending_state.client_hello(),