Allow disabling certificate_authorities extension on server with `v…

…erify_peer` Fixes erlang#6106 Based on the discussion from the issue (and erlang#6204), it was decided that adding the ability to disable the `certificate_authorities` extension on the server would be the fitting resolution for situations where you do not want that extension forced in TLS 1.3. This adds that ability to specify as a server option and defaults to `true` to keep with existing expected functionality.
jjcarstens · Sep 10, 2022 · e3c1793 · e3c1793
1 parent 088797a
commit e3c1793
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Showing 4 changed files with 74 additions and 19 deletions.
diff --git a/lib/ssl/doc/src/ssl.xml b/lib/ssl/doc/src/ssl.xml
@@ -1033,7 +1033,7 @@ fun(srp, Username :: binary(), UserState :: term()) ->
     </datatype>
 
     <datatype>
-      <name name="certificate_authorities"/>
+      <name name="client_certificate_authorities"/>
       <desc>
 	<p>If set to true, sends the certificate authorities extension in TLS-1.3 client hello.
 	The default is false. Note that setting it to true may result in a big overhead if you
@@ -1248,6 +1248,15 @@ fun(srp, Username :: binary(), UserState :: term()) ->
       is supplied it overrides option <c>cacertfile</c>.</p>
 	</desc>
       </datatype>
+
+  <datatype>
+    <name name="server_certificate_authorities"/>
+      <desc>
+      <p>When used with <c>{verify, verify_peer}</c> on the server with TLS-1.3, the certificate
+      authorities extension will be included or excluded from the certificate request. The Default
+      is true.</p>
+      </desc>
+  </datatype>
 
       <datatype>
 	<name name="server_cafile"/>
@@ -1287,8 +1296,9 @@ fun(srp, Username :: binary(), UserState :: term()) ->
 	A server only does x509-certificate path validation in mode
 	<c>verify_peer</c>. By default the server is in <c>verify_none</c> mode
 	an hence will not send an certificate request to the client.
-	When using <c>verify_peer</c> you may also want to specify the option
-	<seetype marker="#fail_if_no_peer_cert">fail_if_no_peer_cert</seetype>.</p>
+	When using <c>verify_peer</c> you may also want to specify the options
+	<seetype marker="#fail_if_no_peer_cert">fail_if_no_peer_cert</seetype> and
+  <seetype marker="#certificate_authorities">certificate_authorities</seetype>.</p>
       </desc>
       </datatype>
 

diff --git a/lib/ssl/src/ssl.erl b/lib/ssl/src/ssl.erl
@@ -418,7 +418,7 @@
                                 {customize_hostname_check, customize_hostname_check()} |
                                 {fallback, fallback()} |
                                 {middlebox_comp_mode, middlebox_comp_mode()} |
-                                {certificate_authorities, certificate_authorities()} |
+                                {certificate_authorities, client_certificate_authorities()} |
                                 {session_tickets, client_session_tickets()} |
                                 {use_ticket, use_ticket()} |
                                 {early_data, client_early_data()}.
@@ -429,7 +429,7 @@
 -type client_verify_type()       :: verify_type().
 -type client_reuse_session()     :: session_id() | {session_id(), SessionData::binary()}.
 -type client_reuse_sessions()    :: boolean() | save.
--type certificate_authorities()  :: boolean().
+-type client_certificate_authorities()  :: boolean().
 -type client_cacerts()           :: [public_key:der_encoded()] | [public_key:combined_cert()].
 -type client_cafile()            :: file:filename().
 -type app_level_protocol()       :: binary().
@@ -458,6 +458,7 @@
                                 {dhfile, dh_file()} |
                                 {verify, server_verify_type()} |
                                 {fail_if_no_peer_cert, fail_if_no_peer_cert()} |
+                                {certificate_authorities, server_certificate_authorities()} |
                                 {reuse_sessions, server_reuse_sessions()} |
                                 {reuse_session, server_reuse_session()} |
                                 {alpn_preferred_protocols, server_alpn()} |
@@ -490,6 +491,7 @@
 -type honor_ecc_order()          :: boolean().
 -type client_renegotiation()     :: boolean().
 -type cookie()                   :: boolean().
+-type server_certificate_authorities() :: boolean().
 %% -------------------------------------------------------------------------------------------------------
 -type prf_random() :: client_random | server_random. % exported
 -type protocol_extensions()  :: #{renegotiation_info => binary(),
@@ -1684,11 +1686,11 @@ handle_option(fallback = Option, Value0, OptionsMap, #{role := Role}) ->
     assert_role(client_only, Role, Option, Value0),
     Value = validate_option(Option, Value0),
     OptionsMap#{Option => Value};
-handle_option(certificate_authorities = Option, unbound, OptionsMap, #{role := Role}) ->
-    Value = default_option_role(client, false, Role),
-    OptionsMap#{Option => Value};
-handle_option(certificate_authorities = Option, Value0, #{versions := Versions} = OptionsMap, #{role := Role}) ->
-    assert_role(client_only, Role, Option, Value0),
+handle_option(certificate_authorities = Option, unbound, OptionsMap, #{role := server}) ->
+    OptionsMap#{Option => true};
+handle_option(certificate_authorities = Option, unbound, OptionsMap, #{role := client}) ->
+    OptionsMap#{Option => false};
+handle_option(certificate_authorities = Option, Value0, #{versions := Versions} = OptionsMap, _Env) ->
     assert_option_dependency(Option, versions, Versions, ['tlsv1.3']),
     Value = validate_option(Option, Value0),
     OptionsMap#{Option => Value};

diff --git a/lib/ssl/src/tls_handshake_1_3.erl b/lib/ssl/src/tls_handshake_1_3.erl
@@ -204,18 +204,23 @@ encrypted_extensions(#state{handshake_env = HandshakeEnv}) ->
       }.
 
 
-certificate_request(SignAlgs0, SignAlgsCert0, CertDbHandle, CertDbRef) ->
+certificate_request(SignAlgs0, SignAlgsCert0, CertDbHandle, CertDbRef, CertAuthBool) ->
     %% Input arguments contain TLS 1.2 algorithms due to backward compatibility
     %% reasons. These {Hash, Algo} tuples must be filtered before creating the
     %% the extensions.
     SignAlgs = filter_tls13_algs(SignAlgs0),
     SignAlgsCert = filter_tls13_algs(SignAlgsCert0),
     Extensions0 = add_signature_algorithms(#{}, SignAlgs),
-    Extensions = add_signature_algorithms_cert(Extensions0, SignAlgsCert),
-    Auths = ssl_handshake:certificate_authorities(CertDbHandle, CertDbRef),
+    Extensions1 = add_signature_algorithms_cert(Extensions0, SignAlgsCert),
+    Extensions = if CertAuthBool =:= true ->
+                        Auths = ssl_handshake:certificate_authorities(CertDbHandle, CertDbRef),
+                        Extensions1#{certificate_authorities => #certificate_authorities{authorities = Auths}};    
+                    true ->
+                        Extensions1
+                 end,
     #certificate_request_1_3{
       certificate_request_context = <<>>,
-      extensions = Extensions#{certificate_authorities => #certificate_authorities{authorities = Auths}}}.
+      extensions = Extensions}.
 
 
 add_signature_algorithms(Extensions, SignAlgs) ->
@@ -1346,8 +1351,9 @@ maybe_send_certificate_request(#state{static_env = #static_env{protocol_cb = Con
                                                                cert_db_ref = CertDbRef}} = State, 
                                #{verify := verify_peer,
                                  signature_algs := SignAlgs,
-                                 signature_algs_cert := SignAlgsCert}, _) ->
-    CertificateRequest = certificate_request(SignAlgs, SignAlgsCert, CertDbHandle, CertDbRef),
+                                 signature_algs_cert := SignAlgsCert,
+                                 certificate_authorities := CertAuthBool}, _) ->
+    CertificateRequest = certificate_request(SignAlgs, SignAlgsCert, CertDbHandle, CertDbRef, CertAuthBool),
     {Connection:queue_handshake(CertificateRequest, State), wait_cert}.
 
 maybe_send_certificate(State, PSK) when  PSK =/= undefined ->
@@ -3080,4 +3086,3 @@ plausible_missing_chain([_] = EncodedChain, undefined, SignAlg, Key, Session0) -
                     };
 plausible_missing_chain(_,Plausible,_,_,_) ->
     Plausible.
-
diff --git a/lib/ssl/test/ssl_cert_SUITE.erl b/lib/ssl/test/ssl_cert_SUITE.erl
@@ -123,7 +123,9 @@
          signature_algorithms_bad_curve_secp384r1/0,
          signature_algorithms_bad_curve_secp384r1/1,
          signature_algorithms_bad_curve_secp521r1/0,
-         signature_algorithms_bad_curve_secp521r1/1
+         signature_algorithms_bad_curve_secp521r1/1,
+         server_certificate_authorities_disabled/0,
+         server_certificate_authorities_disabled/1
          ]).
 
 %%--------------------------------------------------------------------
@@ -191,7 +193,8 @@ tls_1_3_tests() ->
      client_auth_no_suitable_chain,
      hello_retry_client_auth,
      hello_retry_client_auth_empty_cert_accepted,
-     hello_retry_client_auth_empty_cert_rejected
+     hello_retry_client_auth_empty_cert_rejected,
+     server_certificate_authorities_disabled
     ].
 
 pre_tls_1_3_rsa_tests() ->
@@ -1287,6 +1290,41 @@ basic_rsa_1024(Config) ->
                   {fail_if_no_peer_cert, true} | ServerOpts1],
     ssl_test_lib:basic_test(ClientOpts, ServerOpts, Config).
 
+%%--------------------------------------------------------------------
+server_certificate_authorities_disabled() ->
+     [{doc,"TLS 1.3: Disabling certificate_authorities extension on the server when verify_peer is set to true" 
+       " allows client auth with empty chain"}].
+
+server_certificate_authorities_disabled(Config) ->
+    ClientOpts0 = ssl_test_lib:ssl_options(client_cert_opts, Config),
+    ServerOpts0 = ssl_test_lib:ssl_options(server_cert_opts, Config),
+
+    % Strip out the ClientRoot to simulate cases where the they are manually managed and
+    % not expected to be included in certificate requests during mutual authentication.
+    {ok, CACerts0} = ssl_pkix_db:decode_pem_file(proplists:get_value(cacertfile, ServerOpts0)),
+    [_ClientRoot | ServerCACerts] = [CertDER || {_, CertDER, _} <- CACerts0],
+
+    FunAndState =  {fun(_,{extension, _}, UserState) ->
+        {unknown, UserState};
+        (_, valid, UserState) ->
+        {valid, UserState};
+        % Because this is a manually managed setup, we also need to manually verify
+        % an unknown_ca (ClientCert) as expected. Typically you would have custom logic
+        % here to decide if you know the cert (like looking up pinned values in a DB)
+        % but for testing purposes, we'll allow everything
+        (_, {bad_cert, unknown_ca}, UserState) ->
+        {valid, UserState};
+        (_, valid_peer, UserState) ->
+        {valid, UserState}
+    end, [0]},
+
+    ClientOpts = [{versions, ['tlsv1.3']}, {verify, verify_peer} | ClientOpts0],
+    ServerOpts = [{versions, ['tlsv1.3']}, {verify, verify_peer},
+                  {fail_if_no_peer_cert, true}, {cacerts, ServerCACerts},
+                  {verify_fun, FunAndState} | ServerOpts0],
+    ssl_test_lib:basic_alert(ClientOpts, ServerOpts, Config, certificate_required),
+    ssl_test_lib:basic_test(ClientOpts, [{certificate_authorities, false} | ServerOpts], Config).
+
 %%--------------------------------------------------------------------
 %% Internal functions  -----------------------------------------------
 %%--------------------------------------------------------------------