Apache bRPC: Stack Exhaustion via Unbounded Recursion in JSON Parser

Uncontrolled recursion in the json2pb component in Apache bRPC (version < 1.15.0) on all platforms allows remote attackers to make the server crash via sending deep recursive json data.

Root Cause:
The bRPC json2pb component uses rapidjson to parse json data from the network. The rapidjson parser uses a recursive parsing method by default. If the input json has a large depth of recursive structure, the parser function may run into stack overflow.

Affected Scenarios:
Use bRPC server with protobuf message to serve http+json requests from untrusted network. Or directly use JsonToProtoMessage to convert json from untrusted input.

How to Fix:
(Choose one of the following options) 
1. Upgrade bRPC to version 1.15.0, which fixes this issue.
2. Apply this patch: https://github.com/apache/brpc/pull/3099

Note:
No matter which option

you choose, you should know that the fix introduces a recursion depth limit with default value 100. It affects these functions: 

ProtoMessageToJson, ProtoMessageToProtoJson, JsonToProtoMessage, and ProtoJsonToProtoMessage.

If your requests contain json or protobuf messages that have a depth exceeding the limit, the request will be failed after applying the fix. You can modify the gflag json2pb_max_recursion_depth to change the limit.