Index out of bounds when printing JSON of ProcessState

I made the minidump_processor fuzzer look more like

let val: Result<_, _> = minidump_processor_fuzz::fuzzing_block_on(
    minidump_processor::process_minidump(&dump, &provider),
);
                                                                   
if let Ok(v) = val {
    v.print_json(&mut std::io::sink(), true);
}

And then found this:

thread '<unnamed>' panicked at 'index out of bounds: the len is 0 but the index is 0', /home/jess/src/rust-minidump/minidump-processor/src/process_state.rs:806:45
stack backtrace:
   0: rust_begin_unwind
             at /rustc/88fb06a1f331926bccb448acdb52966fd1ec8a92/library/std/src/panicking.rs:584:5
   1: core::panicking::panic_fmt
             at /rustc/88fb06a1f331926bccb448acdb52966fd1ec8a92/library/core/src/panicking.rs:135:14
   2: core::panicking::panic_bounds_check
             at /rustc/88fb06a1f331926bccb448acdb52966fd1ec8a92/library/core/src/panicking.rs:77:5
   3: minidump_processor::process_state::ProcessState::print_json
   4: rust_fuzzer_test_input
   5: LLVMFuzzerTestOneInput
   6: _ZN6fuzzer6Fuzzer15ExecuteCallbackEPKhm
   7: _ZN6fuzzer10RunOneTestEPNS_6FuzzerEPKcm
   8: _ZN6fuzzer12FuzzerDriverEPiPPPcPFiPKhmE
   9: main
  10: __libc_start_main
  11: _start
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
==3765619== ERROR: libFuzzer: deadly signal
NOTE: libFuzzer has rudimentary signal handlers.
      Combine libFuzzer with AddressSanitizer or similar for better crash reports.
SUMMARY: libFuzzer: deadly signal

json-crash.zip

[Gankra]

Ah yeah, we do some raw indexing with requesting_thread here:

https://github.com/luser/rust-minidump/blob/8e1f9a8f9fb67d25a817b48fdee7b9870e1cb321/minidump-processor/src/process_state.rs#L806

I'd need to think about the testcase and code more to have a strong opinion on whether this code should just be more careful or if the processor should be producing more reasonable output.

IMO the processor should be generating output in a such a way that will never cause a print to fail like this

we also have integer overflows in the printer, and if we don't know ahead of time which are valid/invalid, we'll need to deal with "oh we wrote half a dump and then failed.... what now?" Unless there's a mechanism in the format to say "this value is invalid but we continued on" or whatever. This was the human readable printer, but there also looks to be one in the json printer, see:

https://github.com/luser/rust-minidump/blob/8e1f9a8f9fb67d25a817b48fdee7b9870e1cb321/minidump-processor/src/process_state.rs#L785