From 09e33934867936399b5f6d81920b871da192b859 Mon Sep 17 00:00:00 2001
From: firest <blankalupo@163.com>
Date: Wed, 13 Apr 2022 10:28:21 +0800
Subject: [PATCH] fix(frame): prohibit empty topic in strict mode

---
 src/emqx_frame.erl        | 11 +++++++++++
 test/emqx_frame_SUITE.erl | 17 +++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/src/emqx_frame.erl b/src/emqx_frame.erl
index 2149833d6..8dd657253 100644
--- a/src/emqx_frame.erl
+++ b/src/emqx_frame.erl
@@ -252,6 +252,7 @@ parse_packet(#mqtt_packet_header{type = ?PUBLISH, qos = QoS}, Bin,
     (PacketId =/= undefined) andalso
       StrictMode andalso validate_packet_id(PacketId),
     {Properties, Payload} = parse_properties(Rest1, Ver, StrictMode),
+    ok = ensure_topic_name_valid(StrictMode, TopicName, Properties),
     Publish = #mqtt_packet_publish{topic_name = TopicName,
                                    packet_id  = PacketId,
                                    properties = Properties
@@ -338,6 +339,7 @@ parse_will_message(Packet = #mqtt_packet_connect{will_flag = true,
     {Props, Rest} = parse_properties(Bin, Ver, StrictMode),
     {Topic, Rest1} = parse_utf8_string(Rest, StrictMode),
     {Payload, Rest2} = parse_binary_data(Rest1),
+    ok = ensure_topic_name_valid(StrictMode, Topic, Props),
     {Packet#mqtt_packet_connect{will_props   = Props,
                                 will_topic   = Topic,
                                 will_payload = Payload
@@ -503,6 +505,15 @@ parse_binary_data(Bin)
   when 2 > byte_size(Bin) ->
     error(malformed_binary_data_length).
 
+ensure_topic_name_valid(false, _TopicName, _Properties) ->
+    ok;
+ensure_topic_name_valid(true, TopicName, _Properties) when TopicName =/= <<>> ->
+    ok;
+ensure_topic_name_valid(true, <<>>, #{'Topic-Alias' := _}) ->
+    ok;
+ensure_topic_name_valid(true, <<>>, _) ->
+    error(empty_topic_name).
+
 %%--------------------------------------------------------------------
 %% Serialize MQTT Packet
 %%--------------------------------------------------------------------
diff --git a/test/emqx_frame_SUITE.erl b/test/emqx_frame_SUITE.erl
index c51ab8d7f..eca130bbe 100644
--- a/test/emqx_frame_SUITE.erl
+++ b/test/emqx_frame_SUITE.erl
@@ -46,6 +46,8 @@ groups() ->
        t_parse_frame_malformed_variable_byte_integer,
        t_parse_frame_variable_byte_integer,
        t_parse_malformed_utf8_string,
+       t_parse_empty_topic_name,
+       t_parse_empty_topic_name_with_alias,
        t_parse_frame_proxy_protocol %% proxy_protocol_config_disabled packet.
       ]},
      {connect, [parallel],
@@ -161,6 +163,21 @@ t_parse_malformed_utf8_string(_) ->
     ParseState = emqx_frame:initial_parse_state(#{strict_mode => true}),
     ?catch_error(utf8_string_invalid, emqx_frame:parse(MalformedPacket, ParseState)).
 
+t_parse_empty_topic_name(_) ->
+    Packet = ?PUBLISH_PACKET(?QOS_1, <<>>, 1, #{}, <<>>),
+    ?assertEqual(Packet, parse_serialize(Packet, #{strict_mode => false})),
+    ?catch_error(empty_topic_name, parse_serialize(Packet, #{strict_mode => true})).
+
+t_parse_empty_topic_name_with_alias(_) ->
+    Props = #{'Topic-Alias' => 16#AB},
+    Packet = ?PUBLISH_PACKET(?QOS_1, <<>>, 1, Props, <<>>),
+    ?assertEqual(
+       Packet, parse_serialize(Packet, #{strict_mode => false, version => ?MQTT_PROTO_V5})
+      ),
+    ?assertEqual(
+       Packet, parse_serialize(Packet, #{strict_mode => true, version => ?MQTT_PROTO_V5})
+      ).
+
 t_parse_frame_proxy_protocol(_) ->
     BinList = [ <<"PROXY TCP4 ">>, <<"PROXY TCP6 ">>, <<"PROXY UNKNOWN">>
               , <<"\r\n\r\n\0\r\nQUIT\n">>],