unknown fields fuzzed

[asraa]

Hi,

I found an interesting crash on OSS-Fuzz after bumping libprotobuf-mutator to the latest commit:
https://github.com/envoyproxy/envoy/blob/011945dcf92b8a461ab4ba309fa2bebeffc15895/bazel/repository_locations.bzl#L166

https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=23823
Opening the testcase, we have

fkidd:[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[ [....]
}

Which is not a valid protobuf for the message https://github.com/envoyproxy/envoy/blob/master/test/common/http/header_map_impl_fuzz.proto

The stack trace looks something like:

#246 0x3eb856c in google::protobuf::TextFormat::Parser::ParserImpl::SkipFieldValue() /proc/self/cwd/external/com_google_protobuf/src/google/protobuf/text_format.cc:830:11
--
  | #247 0x3eb856c in google::protobuf::TextFormat::Parser::ParserImpl::SkipFieldValue() /proc/self/cwd/external/com_google_protobuf/src/google/protobuf/text_format.cc:830:11
  | #248 0x3eb856c in google::protobuf::TextFormat::Parser::ParserImpl::SkipFieldValue() /proc/self/cwd/external/com_google_protobuf/src/google/protobuf/text_format.cc:830:11
  |  
  | SUMMARY: AddressSanitizer: stack-overflow /src/llvm-project/compiler-rt/lib/asan/../sanitizer_common/sanitizer_common_interceptors.inc in strlen
  | ==1==ABORTING

I can reproduce the testcase locally, but what I'm curious about is why the testcase was generated in the first place.

[vitalybuka]

It looks like as an input from a different fuzzer. Maybe something in OSS-Fuzz tries to mix them?

[asraa]

Yes!! You're right. OSS-Fuzz does cross pollination of corpora.

Hmmm. I see. So this is not an issue of LPM generating unknown fields, but because unknown fields were passed in to the fuzzer.

[vitalybuka]

LPM does not generate unknown fields
However it would be nice to fix libprotobuf to not crash here. It has buffer overflow protection counter but it's probably not checked for this case.

[nareddyt]

Hi, I saw this issue pop up in OSS Fuzz and also google3 (example: b/160321599).

Root cause is that protobuf text format does not have proper stack overflow protection. This was initially noticed in #172. I added this code to fix it: https://github.com/protocolbuffers/protobuf/blob/6935eae45c99926a000ecbef0be20dfd3d159e71/src/google/protobuf/text_format.cc#L675

But it looks like there is one edge case where the text format library can recurse on unknown fields without hitting the recursion protection: https://github.com/protocolbuffers/protobuf/blob/6935eae45c99926a000ecbef0be20dfd3d159e71/src/google/protobuf/text_format.cc#L844

Which is triggered by the input @asraa posted above, deeply nested arrays.

I will make a PR to protobuf to fix this edge case...

[asraa]

Ah!! I see where it is. Thanks Teju, let me know if you need help.