Mitigate Computational DoS attack

2 files changed, 75 insertions, 7 deletions

diff --git a/lib/ssl/src/ssl_connection.erl b/lib/ssl/src/ssl_connection.erl
index cec81d551b..c87ea22cf8 100644
--- a/lib/ssl/src/ssl_connection.erl
+++ b/lib/ssl/src/ssl_connection.erl
@@ -91,12 +91,14 @@
 	  renegotiation,        % {boolean(), From | internal | peer}
 	  recv_during_renegotiation,  %boolean() 
 	  send_queue,           % queue()
-	  terminated = false   %
+	  terminated = false,   %
+	  allow_renegotiate = true
 	 }).
 
 -define(DEFAULT_DIFFIE_HELLMAN_PARAMS, 
-	#'DHParameter'{prime = ?DEFAULT_DIFFIE_HELLMAN_PRIME, 
+	#'DHParameter'{prime = ?DEFAULT_DIFFIE_HELLMAN_PRIME,
 		       base = ?DEFAULT_DIFFIE_HELLMAN_GENERATOR}).
+-define(WAIT_TO_ALLOW_RENEGOTIATION, 12000).
 
 -type state_name()           :: hello | abbreviated | certify | cipher | connection.
 -type gen_fsm_state_return() :: {next_state, state_name(), #state{}} |
@@ -707,9 +709,25 @@ connection(#hello_request{}, #state{host = Host, port = Port,
 					       ConnectionStates1,
 					       tls_handshake_hashes = Hashes1}),
     next_state(hello, Record, State);
-connection(#client_hello{} = Hello, #state{role = server} = State) ->
-    hello(Hello, State);
-
+connection(#client_hello{} = Hello, #state{role = server, allow_renegotiate = true} = State) ->
+    %% Mitigate Computational DoS attack http://www.educatedguesswork.org/2011/10/ssltls_and_computational_dos.html
+    %% http://www.thc.org/thc-ssl-dos/ Rather than disabling client initiated renegotiation
+    %% we will disallow many client initiated renegotiations immediately after each other.
+    erlang:send_after(?WAIT_TO_ALLOW_RENEGOTIATION, self(), allow_renegotiate),
+    hello(Hello, State#state{allow_renegotiate = false});
+
+connection(#client_hello{}, #state{role = server, allow_renegotiate = false,
+				   connection_states = ConnectionStates0,
+				   socket = Socket, transport_cb = Transport,
+				   negotiated_version = Version} = State0) ->
+    Alert = ?ALERT_REC(?WARNING, ?NO_RENEGOTIATION),
+    {BinMsg, ConnectionStates} =
+	encode_alert(Alert, Version, ConnectionStates0),
+    Transport:send(Socket, BinMsg),
+    {Record, State} = next_record(State0#state{connection_states = 
+     						   ConnectionStates}),
+    next_state(connection, Record, State);
+  
 connection(timeout, State) ->
     {next_state, connection, State, hibernate};
 
@@ -984,6 +1002,9 @@ handle_info({'DOWN', MonitorRef, _, _, _}, _,
 	    State = #state{user_application={MonitorRef,_Pid}}) ->
     {stop, normal, State};   
 
+handle_info(allow_renegotiate, StateName, State) ->
+    {next_state, StateName, State#state{allow_renegotiate = true}, get_timeout(State)};
+    
 handle_info(Msg, StateName, State) ->
     Report = io_lib:format("SSL: Got unexpected info: ~p ~n", [Msg]),
     error_logger:info_report(Report),
@@ -2257,7 +2278,7 @@ renegotiate(#state{role = server,
     {Record, State} = next_record(State0#state{connection_states = 
 					       ConnectionStates,
 					       tls_handshake_hashes = Hs0}),
-    next_state(hello, Record, State).
+    next_state(hello, Record, State#state{allow_renegotiate = true}).
 
 notify_senders(SendQueue) -> 
     lists:foreach(fun({From, _}) ->
diff --git a/lib/ssl/test/ssl_basic_SUITE.erl b/lib/ssl/test/ssl_basic_SUITE.erl
index 8da1d947d3..f1ebac8845 100644
--- a/lib/ssl/test/ssl_basic_SUITE.erl
+++ b/lib/ssl/test/ssl_basic_SUITE.erl
@@ -37,6 +37,7 @@
 -define(LONG_TIMEOUT, 600000).
 -define(EXPIRE, 10).
 -define(SLEEP, 500).
+-define(RENEGOTIATION_DISABLE_TIME, 12000).
 
 %% Test server callback functions
 %%--------------------------------------------------------------------
@@ -257,7 +258,7 @@ all() ->
      %%different_ca_peer_sign,
      no_reuses_session_server_restart_new_cert,
      no_reuses_session_server_restart_new_cert_file, reuseaddr,
-     hibernate, connect_twice
+     hibernate, connect_twice, renegotiate_dos_mitigate
     ].
 
 groups() -> 
@@ -3655,7 +3656,40 @@ connect_twice(Config) when is_list(Config) ->
     ssl_test_lib:close(Client),
     ssl_test_lib:close(Client1).
 
+%%--------------------------------------------------------------------
+renegotiate_dos_mitigate(doc) -> 
+    ["Mitigate DOS computational attack by not allowing client to renegotiate many times in a row",
+    "immediately after each other"];
+
+renegotiate_dos_mitigate(suite) -> 
+    [];
+
+renegotiate_dos_mitigate(Config) when is_list(Config) -> 
+    ServerOpts = ?config(server_opts, Config),  
+    ClientOpts = ?config(client_opts, Config),  
+
+    {ClientNode, ServerNode, Hostname} = ssl_test_lib:run_where(Config),
+    
+    Server = 
+	ssl_test_lib:start_server([{node, ServerNode}, {port, 0}, 
+				   {from, self()},
+				   {mfa, {?MODULE, send_recv_result_active, []}},
+				   {options, [ServerOpts]}]),
+    Port = ssl_test_lib:inet_port(Server),
+ 
+    Client = ssl_test_lib:start_client([{node, ClientNode}, {port, Port},
+					{host, Hostname},
+					{from, self()}, 
+					{mfa, {?MODULE, 
+					       renegotiate_immediately, []}},
+					{options, ClientOpts}]),
+    
+    ssl_test_lib:check_result(Client, ok, Server, ok), 
+    ssl_test_lib:close(Server),
+    ssl_test_lib:close(Client).
 
+  
+    
 %%--------------------------------------------------------------------
 %%% Internal functions
 %%--------------------------------------------------------------------
@@ -3698,6 +3732,19 @@ renegotiate_reuse_session(Socket, Data) ->
     test_server:sleep(?SLEEP),
     renegotiate(Socket, Data).
 
+renegotiate_immediately(Socket) ->
+    receive 
+	{ssl, Socket, "Hello world"} ->
+	    ok
+    end,
+    ok = ssl:renegotiate(Socket),  
+    {error, renegotiation_rejected} = ssl:renegotiate(Socket),
+    test_server:sleep(?RENEGOTIATION_DISABLE_TIME +1),
+    ok = ssl:renegotiate(Socket),
+    test_server:format("Renegotiated again"),
+    ssl:send(Socket, "Hello world"),
+    ok.
+    
 new_config(PrivDir, ServerOpts0) ->
     CaCertFile = proplists:get_value(cacertfile, ServerOpts0),
     CertFile = proplists:get_value(certfile, ServerOpts0),