From f82abf7047392a2e73f0979b0bfa7217d3d1f055 Mon Sep 17 00:00:00 2001
From: Shawn <506895667@qq.com>
Date: Fri, 12 Mar 2021 11:33:11 +0800
Subject: [PATCH] fix(emqx): validate mqtt malformed variable byte integer

---
 src/emqx_frame.erl        | 3 +++
 test/emqx_frame_SUITE.erl | 9 ++++++++-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/emqx_frame.erl b/src/emqx_frame.erl
index 9e5f85dfc..bc9a9272f 100644
--- a/src/emqx_frame.erl
+++ b/src/emqx_frame.erl
@@ -123,6 +123,9 @@ parse_remaining_len(<<0:8, Rest/binary>>, Header, 1, 0, Options) ->
 %% Match PUBACK, PUBREC, PUBREL, PUBCOMP, UNSUBACK...
 parse_remaining_len(<<0:1, 2:7, Rest/binary>>, Header, 1, 0, Options) ->
     parse_frame(Rest, Header, 2, Options);
+parse_remaining_len(<<1:1, _Len:7, _Rest/binary>>, _Header, Multiplier, _Value, _Options)
+        when Multiplier > 2097152 ->
+    error(malformed_variable_byte_integer);
 parse_remaining_len(<<1:1, Len:7, Rest/binary>>, Header, Multiplier, Value, Options) ->
     parse_remaining_len(Rest, Header, Multiplier * ?HIGHBIT, Value + Len * Multiplier, Options);
 parse_remaining_len(<<0:1, Len:7, Rest/binary>>, Header, Multiplier, Value,
diff --git a/test/emqx_frame_SUITE.erl b/test/emqx_frame_SUITE.erl
index 96e744a5d..ec8717129 100644
--- a/test/emqx_frame_SUITE.erl
+++ b/test/emqx_frame_SUITE.erl
@@ -46,7 +46,8 @@ all() ->
 groups() ->
     [{parse, [parallel],
       [t_parse_cont,
-       t_parse_frame_too_large
+       t_parse_frame_too_large,
+       t_parse_frame_malformed_variable_byte_integer
       ]},
      {connect, [parallel],
       [t_serialize_parse_connect,
@@ -134,6 +135,12 @@ t_parse_frame_too_large(_) ->
     ?catch_error(frame_too_large, parse_serialize(Packet, #{max_size => 512})),
     ?assertEqual(Packet, parse_serialize(Packet, #{max_size => 2048, version => ?MQTT_PROTO_V4})).
 
+t_parse_frame_malformed_variable_byte_integer(_) ->
+    MalformedPayload = << <<16#80>> || _ <- lists:seq(1, 4) >>,
+    ParseState = emqx_frame:initial_parse_state(#{}),
+    ?catch_error(malformed_variable_byte_integer,
+        emqx_frame:parse(MalformedPayload, ParseState)).
+
 t_serialize_parse_connect(_) ->
     ?PROPTEST(prop_serialize_parse_connect).