Add option to require encryption in S2S connections (EJAB-495)

doc/guide.tex

@@ -945,9 +945,10 @@ This is a detailed description of each option allowed by the listening modules:
 
 There are some additional global options that can be specified in the ejabberd configuration file (outside \term{listen}):
 \begin{description}
-  \titem{\{s2s\_use\_starttls, true|false\}}
-  \ind{options!s2s\_use\_starttls}\ind{STARTTLS}This option defines whether to
-  use STARTTLS for s2s connections.
+  \titem{\{s2s\_use\_starttls, false|optional|required\}}
+  \ind{options!s2s\_use\_starttls}\ind{STARTTLS}This option defines if 
+  s2s connections can optionally use STARTTLS encryption, or if it must be required.
+  The default value is to not use STARTTLS: \term{false}.
   \titem{\{s2s\_certfile, Path\}} \ind{options!s2s\_certificate}Full path to a
   file containing a SSL certificate.
   \titem{\{domain\_certfile, Domain, Path\}} \ind{options!domain\_certfile}
@@ -1046,7 +1047,7 @@ However, the c2s and s2s connections to the domain \term{example.com} use the fi
                                        ]}
  ]
 }.
-{s2s_use_starttls, true}.
+{s2s_use_starttls, optional}.
 {s2s_certfile, "/etc/ejabberd/server.pem"}.
 {domain_certfile, "example.com", "/etc/ejabberd/example_com.pem"}.
 {outgoing_s2s_options, [ipv4, ipv6], 10000}.
@@ -1058,7 +1059,7 @@ In this example, the following configuration defines that:
   on port 5223 (SSL, IP 192.168.0.1 and fdca:8ab6:a243:75ef::1) and denied
   for the user called `\term{bad}'.
 \item s2s connections are listened for on port 5269 (all IPv4 addresses) 
-  with STARTTLS for secured traffic enabled. 
+  with STARTTLS for secured traffic required. 
   Incoming and outgoing connections of remote XMPP servers are denied,
   only two servers can connect: "jabber.example.org" and "example.com".
 \item Port 5280 is serving the Web Admin and the HTTP Polling service
@@ -1139,7 +1140,7 @@ In this example, the following configuration defines that:
                             {service_check_from, false}]}
  ]
 }.
-{s2s_use_starttls, true}.
+{s2s_use_starttls, required}.
 {s2s_certfile, "/path/to/ssl.pem"}.
 {s2s_default_policy, deny}.
 {{s2s_host,"jabber.example.org"}, allow}.

src/ejabberd.cfg.example

@@ -180,10 +180,10 @@
 
 %%
 %% s2s_use_starttls: Enable STARTTLS + Dialback for S2S connections.
-%% Allowed values are: true or false.
+%% Allowed values are: false optional required
 %% You must specify a certificate file.
 %%
-%%{s2s_use_starttls, true}.
+%%{s2s_use_starttls, optional}.
 
 %%
 %% s2s_certfile: Specify a certificate file.

src/ejabberd_s2s_out.erl

@@ -146,11 +146,13 @@ stop_connection(Pid, Timeout) ->
 init([From, Server, Type]) ->
     process_flag(trap_exit, true),
     ?DEBUG("started: ~p", [{From, Server, Type}]),
-    TLS = case ejabberd_config:get_local_option(s2s_use_starttls) of
-	      undefined ->
-		  false;
-	      UseStartTLS ->
-		  UseStartTLS
+    {TLS, TLSRequired} = case ejabberd_config:get_local_option(s2s_use_starttls) of
+	      UseTls when (UseTls==undefined) or (UseTls==false) ->
+		  {false, false};
+	      UseTls when (UseTls==true) or (UseTls==optional) ->
+		  {true, false};
+	      required ->
+		  {true, true}
 	  end,
     UseV10 = TLS,
     TLSOpts = case ejabberd_config:get_local_option(s2s_certfile) of
@@ -169,6 +171,7 @@ init([From, Server, Type]) ->
     Timer = erlang:start_timer(?S2STIMEOUT, self(), []),
     {ok, open_socket, #state{use_v10 = UseV10,
 			     tls = TLS,
+			     tls_required = TLSRequired,
 			     tls_options = TLSOpts,
 			     queue = queue:new(),
 			     myname = From,
@@ -368,8 +371,8 @@ wait_for_validation({xmlstreamelement, El}, StateData) ->
     case is_verify_res(El) of
 	{result, To, From, Id, Type} ->
 	    ?DEBUG("recv result: ~p", [{From, To, Id, Type}]),
-	    case Type of
-		"valid" ->
+	    case {Type, StateData#state.tls_enabled, StateData#state.tls_required} of
+		{"valid", Enabled, Required} when (Enabled==true) or (Required==false) ->
 		    send_queue(StateData, StateData#state.queue),
 		    ?INFO_MSG("Connection established: ~s -> ~s with TLS=~p",
 			      [StateData#state.myname, StateData#state.server, StateData#state.tls_enabled]),
@@ -378,6 +381,11 @@ wait_for_validation({xmlstreamelement, El}, StateData) ->
 					StateData#state.server]),
 		    {next_state, stream_established,
 		     StateData#state{queue = queue:new()}};
+		{"valid", Enabled, Required} when (Enabled==false) and (Required==true) ->
+		    %% TODO: bounce packets
+		    ?INFO_MSG("Closing s2s connection: ~s -> ~s (TLS is required but unavailable)",
+			      [StateData#state.myname, StateData#state.server]),
+		    {stop, normal, StateData};
 		_ ->
 		    %% TODO: bounce packets
 		    ?INFO_MSG("Closing s2s connection: ~s -> ~s (invalid dialback key)",