[FUZZ] Nimbus unhandled exception IndexError

[Daft-Wullie]

I've identified a fuzzer crash and am contributing to the security of Ethereum 2!

I've done and provided the following:

• Checked to see if any other [FUZZ] issue already refers to that crasher
• Attached the crashing input (either attached to the issue as a .zip or .gz, or as a link to a file sharing service)
• Noted the beacon-fuzz version or commit used.
• Provided crash output
• Noted the command or fuzzer used to generate the crash
• Name of the original crash file
• (Optional but optimal) Checked if the crash can be consistently replicated by re-running the input.

Info to Reproduce

• Command run: e.g. make nimbus docker run -it -v `pwd`/workspace:/eth2fuzz/workspace eth2fuzz_nimbus continuously --filter nimbus

• Crasher file name: crash-b5e4385dd9d05ab097113e6313d22827c7590347
  crash-b5e4385dd9d05ab097113e6313d22827c7590347.zip

• Client exercised: nimbus

• Fuzzing engine used : nimlibfuzzer

Crash output and stacktrace

#91     NEW    cov: 1029 ft: 1819 corp: 25/15674b exec/s: 0 rss: 43Mb L: 301/4096 MS: 2 PersAutoDict-EraseBytes- DE: "\x00\x00\x00\x00\x00\x00\x00\x01"-
fatal.nim(49)            sysFatal
Error: unhandled exception: index -4703124616608923521 not in 0 .. 255 [IndexError]
==7042== ERROR: libFuzzer: fuzz target exited
    #0 0x4612f3  (/eth2fuzz/workspace/nimlibfuzzer/nimbus_proposer_slashing+0x4612f3)
    #1 0x406836  (/eth2fuzz/workspace/nimlibfuzzer/nimbus_proposer_slashing+0x406836)
    #2 0x418227  (/eth2fuzz/workspace/nimlibfuzzer/nimbus_proposer_slashing+0x418227)
    #3 0x7fbb5be740f0  (/lib/x86_64-linux-gnu/libc.so.6+0x430f0)
    #4 0x7fbb5be741e9  (/lib/x86_64-linux-gnu/libc.so.6+0x431e9)
    #5 0x56291f  (/eth2fuzz/workspace/nimlibfuzzer/nimbus_proposer_slashing+0x56291f)
    #6 0x5bf777  (/eth2fuzz/workspace/nimlibfuzzer/nimbus_proposer_slashing+0x5bf777)
    #7 0x5c04e2  (/eth2fuzz/workspace/nimlibfuzzer/nimbus_proposer_slashing+0x5c04e2)
    #8 0x4188d7  (/eth2fuzz/workspace/nimlibfuzzer/nimbus_proposer_slashing+0x4188d7)
    #9 0x423144  (/eth2fuzz/workspace/nimlibfuzzer/nimbus_proposer_slashing+0x423144)
    #10 0x4247af  (/eth2fuzz/workspace/nimlibfuzzer/nimbus_proposer_slashing+0x4247af)
    #11 0x413b6c  (/eth2fuzz/workspace/nimlibfuzzer/nimbus_proposer_slashing+0x413b6c)
    #12 0x406a52  (/eth2fuzz/workspace/nimlibfuzzer/nimbus_proposer_slashing+0x406a52)
    #13 0x7fbb5be52b96  (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
    #14 0x406aa9  (/eth2fuzz/workspace/nimlibfuzzer/nimbus_proposer_slashing+0x406aa9)

SUMMARY: libFuzzer: fuzz target exited
MS: 5 EraseBytes-CrossOver-ChangeByte-EraseBytes-InsertRepeatedBytes-; base unit: 153eb0b6669de022db041ff122b05a4c70c48010
artifact_prefix='./'; Test unit written to ./crash-b5e4385dd9d05ab097113e6313d22827c7590347

Your Environment

• Fuzzer ran: eth2fuzz
• Version/Commit used:
• Operating System and version: Ubuntu 20.04

[pventuzelo]

Congratz, look valid to me.
Reported here: status-im/nimbus-eth2#1323

[pventuzelo]

Fixed