fix: check willretain and willqos when WillFlag set to `true`

apps/emqx/src/emqx_frame.erl

@@ -287,14 +287,25 @@ parse_connect(FrameBin, StrictMode) ->
 % Note: return malformed if reserved flag is not 0.
 parse_connect2(
     ProtoName,
-    <<BridgeTag:4, ProtoVer:4, UsernameFlag:1, PasswordFlag:1, WillRetain:1, WillQoS:2, WillFlag:1,
-        CleanStart:1, Reserved:1, KeepAlive:16/big, Rest2/binary>>,
+    <<BridgeTag:4, ProtoVer:4, UsernameFlag:1, PasswordFlag:1, WillRetainB:1, WillQoS:2,
+        WillFlagB:1, CleanStart:1, Reserved:1, KeepAlive:16/big, Rest2/binary>>,
     StrictMode
 ) ->
     case Reserved of
         0 -> ok;
         1 -> ?PARSE_ERR(reserved_connect_flag)
     end,
+    WillFlag = bool(WillFlagB),
+    WillRetain = bool(WillRetainB),
+    case WillFlag of
+        %% MQTT-v3.1.1-[MQTT-3.1.2-13], MQTT-v5.0-[MQTT-3.1.2-11]
+        false when WillQoS > 0 -> ?PARSE_ERR(invalid_will_qos);
+        %% MQTT-v3.1.1-[MQTT-3.1.2-14], MQTT-v5.0-[MQTT-3.1.2-12]
+        true when WillQoS > 2 -> ?PARSE_ERR(invalid_will_qos);
+        %% MQTT-v3.1.1-[MQTT-3.1.2-15], MQTT-v5.0-[MQTT-3.1.2-13]
+        false when WillRetain -> ?PARSE_ERR(invalid_will_retain);
+        _ -> ok
+    end,
     {Properties, Rest3} = parse_properties(Rest2, ProtoVer, StrictMode),
     {ClientId, Rest4} = parse_utf8_string_with_cause(Rest3, StrictMode, invalid_clientid),
     ConnPacket = #mqtt_packet_connect{
@@ -304,9 +315,9 @@ parse_connect2(
         %% Invented by mosquitto, named 'try_private': https://mosquitto.org/man/mosquitto-conf-5.html
         is_bridge = (BridgeTag =:= 8),
         clean_start = bool(CleanStart),
-        will_flag = bool(WillFlag),
+        will_flag = WillFlag,
         will_qos = WillQoS,
-        will_retain = bool(WillRetain),
+        will_retain = WillRetain,
         keepalive = KeepAlive,
         properties = Properties,
         clientid = ClientId

apps/emqx/src/emqx_schema.erl

@@ -3491,6 +3491,7 @@ mqtt_general() ->
             )},
         {"max_clientid_len",
             sc(
+                %% MQTT-v3.1.1-[MQTT-3.1.3-5], MQTT-v5.0-[MQTT-3.1.3-5]
                 range(23, 65535),
                 #{
                     default => 65535,

changes/ce/fix-13222.en.md

@@ -0,0 +1,5 @@
+Fix the flags check and error handling related to the Will message in the `CONNECT` packet.
+See also:
+- MQTT-v3.1.1-[MQTT-3.1.2-13], MQTT-v5.0-[MQTT-3.1.2-11]
+- MQTT-v3.1.1-[MQTT-3.1.2-14], MQTT-v5.0-[MQTT-3.1.2-12]
+- MQTT-v3.1.1-[MQTT-3.1.2-15], MQTT-v5.0-[MQTT-3.1.2-13]